| Title |
14: Develop near-balanced NBI for use in intrinsic rotation scaling experiments. |
| Name: | John Degrassie ( ) |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics (2009) |
Presentation time: |
Requested |
Co-Author(s): | J.Rice, W. Solomon, J. Ferron |
| Description: | We want to develop an understanding of how to use near-balanced NBI to raise BetaN and still accurately measure the intrinsic rotation. For relevance, the discharges will be dominated by ELMing H-modes, or if we can achieve RMP ELM-suppression with near-balanced NBI, this would be extremely valuable for a target discharge. Scans will be taken with varying degrees of near-balanced NBI added to ECH. We will go from ECH only to NBI only. We want the greatest range in BetaN attainable. Density scans will be needed because it is anticipated that the local torque density in near-balanced NBI will depend upon the NBI deposition profile. Scans in q95 should also be taken. It may facilitate the experiment to use Ferron's feedback of NBI torque on W/Ip, which we did not get to try in 2007. |
| Experimental Approach/Plan: | The majority of discharges will be H-modes. ELMing H-modes are desirable for more steady state conditions. If we can get RMP ELM stabilization in near-balanced conditions, this would provide an excellent target. The goal will be to show that we can follow Rice's scaling with a mixture of ECH and near-balanced NBI, going from essentially all ECH to much higher power NBI + ECH. We anticipate that detailed analysis will show that these intrinsic rotation values will be obtained with near zero NBI torque density inside of rho of about 0.8. Density scans will be very important since the torque density profile will depend somewhat on the NBI deposition profile. It is also important to do different Ip scans, that is, get more than one data path in the expected increase in intrinsic toroidal velocity with W. This experiment will be facilitated by using John Ferron's new capability to feed back torque on W, put into the pcs but not tried in 2007. |
| Background: | John Rice's scaling shows that intrinsic toroidal velocity increases with W/Ip, the plasma stored energy over the magnitude of the plasma current. The increase is in the co-Ip direction. This scaling has been found apply in many tokamaks, as described in Rice's 2006 IAEA paper. In DIII-D ECH H-modes, and Ohmic H-modes, we find this scaling near the outer ¾ region of the minor radius with the intrinsic velocity in the center apparently affected by something to do with ECH. This scaling can be recast as velocity increasing with BetaN, for a fixed machine size and fixed B. To date the points in the multi machine database barely exceed BetaN ~ 1 because they are from Ohmic discharges or RF-heated L- and H-mode discharges. We need NBI power to increase BetaN in order to have any confidence in an extrapolation toward ITER. But the large torques in the co- and counter-Ip NBI make this balance a sensitive one.
We have clear evidence of intrinisic rotation in the midst of near-balanced NBI, but moving to confidence that we can accurately measure the intrinsic rotation in such a case takes more work. For example, we need to develop a methodology wherein we can look at a case (with all the analysis codes) and say that we are seeing the remnant intrinsic rotation in the midst of 10 MW of near-balanced beam power, plus ECH, that has brought BetaN up to ~ 3! |
| Resource Requirements: | NBI: ideally all 7, minimally 21R/L, 30L, 33L/R
ECH: more is better, minimally 2 gyrotrons, enough to get H-mode in LSN in the good direction. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
15: Intrinsic rotation in helium H-mode discharges. |
| Name: | John Degrassie () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | W. Solomon, K. Burrell |
| Description: | *Obtain a set of intrinsic rotation measurements with helium as the bulk ion, so that we can measure the bulk ion intrinsic toroidal and poloidal velocities. ECH H-modes will be the starting point, but we need to add the near balanced NBI capability in order to increase BetaN (see proposal 14) . It is tbd whether or not the beams must be dominantly helium also (excluding some of the standard diagnostic beams). |
| Experimental Approach/Plan: | *We will use our developed experimental techniques to measure the bulk ion toroidal and poloidal velocities in helium discharges. The near balanced NBI extraction of intrinsic rotation (proposal 14) will be an important tool to increase BetaN and follow the change in intrinsic poloidal velocity with plasma energy. Matched discharges will be taken to measure the carbon intrinsic velocities as we did in the past. |
| Background: | *We have made intrinsic velocity measurements in ELMing H-mode discharges with helium as the bulk ion. This 2004 one day experiment has been most important in giving confidence that the carbon velocity typically measured is not misleading us in inferring intrinsic rotation of the plasma as a whole.
*The standard methodology to go from carbon velocity to bulk deuterium velocity utilizes the neoclassical theory for the bulk ion poloidal rotation, since it is not measured. However, the experiments of Solomon et al have shown that the carbon poloidal velocities do not agree with this neoclassical theory, throwing into confusion any attempt to compute the bulk ion toroidal velocity from the carbon impurity toroidal velocity. This affects any comparisons of intrinsic rotation experiments with theory.
*We must measure the bulk ion intrinsic poloidal velocity as well as toroidal velocity to establish a known data set against which all proposed theories can be scrutinized. In companion matched discharges the carbon velocities will also be measured, as we did before.
*Near balanced NBI will be an important tool since we believe that the poloidal velocity will increase with plasma stored energy, bringing it well out of the error bars. |
| Resource Requirements: | NBI: all beams no doubt. It may be necessary to have 21R/L and 15L/R in helium.
ECH: max power. Entry level is probably 3 gyrotrons to make a LSN H-mode in the good direction. |
| Diagnostic Requirements: | Standard set for intrinsic rotation experiments |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
16: Expand the dimensionless similarity database on intrinsic rotation |
| Name: | John Degrassie () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | W. Solomon, K. Burrell, J. Rice |
| Description: | *A prioritized plan will be developed to explore the scaling of intrinsic rotation with beta, q95, nustar, and rhostar to see to what extent it can be described by the dimensionless variables. A first experiment should simply be redoing dimensionless parameters from previous LSN H-mode discharges in USN and DND shapes to see whether there is a significant effect on intrinsic rotation. The experiment will be greatly facilitated by having the near-balanced NBI tool operational (proposal 14). Accommodation of turbulence measurements should be given thought in this plan, since there are now theories that predict intrinsic rotation arising from turbulence, and the profile of turbulence activity. This is a multi-day effort. |
| Experimental Approach/Plan: | *Execute the experimental plan that is developed. A first priority should be to get some data on the effect of shape on intrinsic rotation; X-point up/down, DND and triangularity. Then the next priorities would seem to be scans in Beta and q95, followed by nustar and eventually rhostar. This is a multi-day experiment.
*The balanced-NBI (proposal 14) is an enabling capability here. |
| Background: | *Rice-s C-Mod scaling of intrinsic toroidal rotation increasing with W/Ip is seen in a number of tokamaks, as described in his 2006 IAEA paper. This is an engineering scaling. We see this same scaling in DIII-D in the outer ¾ region in minor radius, in ECH H-modes, while the interior velocity profile appears to be modified by ECH details.
We need to turn this into a dimensionless scaling in order to have an empirical extrapolation to ITER. There is clearly some size scaling in this Rice engineering scaling. The slope of the scaling in DIII-D is about a factor of 10 less in DIII-D than in C-Mod, smaller machines have greater intrinsic rotation velocities perhaps.
*Cross machine similarity experiments between DIII-D and C-Mod are underway. JET will hopefully join this effort in 2008.
*We need to push a search for a similarity law in many directions, beta, q95, nustar, rhostar, and investigate the effect of shape, for which we have little information. The near-balanced beam tool (proposal 14) will be important to facilitate these scans.
*The effect of shape is largely unknown. If there is a significant effect, it will greatly expand the data landscape, but would then provide another knob and more opportunity to narrow down explanations. |
| Resource Requirements: | NBI: 21R/L, 30L, 33L/R needed. 15L/R desired.
ECH: more is better |
| Diagnostic Requirements: | standard for intrinsic rotation experiments |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
17: Mixed Gas MGI |
| Name: | John C. Wesley ( ) |
Affiliation: | General Atomics |
| Research Area: | Disruptions |
Presentation time: |
Requested |
Co-Author(s): | Team MGI |
| Description: | Conduct systematic study of mixed gas massive gas injection (MGI) using the six-valve MEDUSA injector. eg H2 + 1% to 20% Ar, at Q_in = 2000 torr-l. Quantify effects of variation in low-Z carrier gases (H2, D2 or He) and Ne and/or Ar admixtures. Provide data for integrated model validations of species, impurity radiation and impurity delivery (impurity entrainment) attributes |
| Experimental Approach/Plan: | Injection into \'standard\' ca 1 MJ NBI heated target plasma; with a range of mixed gas make-ups. Possible injection quantity or pulse length scans to find optimal or saturation onset levels. Longer-term objective is to determine \'optimal\' carrier and admixture species and concentration. Choice of a limited set of test mixtures TBD before starting campaign(s). Also need pure D2 baseline data if eg D2 + Ar mixtures are used. |
| Background: | Two existing DIII-D mixed gas shots show a combination of promising and puzzling results. Lack of systematic data makes comparison with the corresponding pure gas analogs very speculative. Examples we have show significant \'disproportionate\' plasma response effects. Data will support identification of optimal and/or \'tunable\' MGI concepts for eg ITER. |
| Resource Requirements: | Standard MGI target plasma (2 beams), MEDUSA injector, supplies of candidate gas mixtures, between shot gas change capability. |
| Diagnostic Requirements: | Standard + MGI/disruption-specific diagnostics, fast camera, etc. CO2 interferometer is critical (high n*l) |
| Analysis Requirements: | -- |
| Other Requirements: | H2 experiments may impact subsequent IC or other species sensitive experiments. Need end of week or H campaign scheduling. |
| Title |
18: Measure intrinsic rotation in the JET shape |
| Name: | John Degrassie () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | L.-G. Eriksson (EFDA) |
| Description: | Operate ELMing ECH H-mode discharges in the JET identity shape in DIII-D and measure the intrinsic velocity profiles. |
| Experimental Approach/Plan: | Run the JET shape with high BT and modest BetaN and make the standard intrinsic rotation measurements. The back end of the discharges can be used for near-balanced NBI intrinsic rotation studies also (proposal #14). When taking the dimensionless parameters to JET-size, BT invariably turns out to be in the 1T range. It seems possible to make an RF H-mode in JET at such a low BT but power delivered may be limited. So it is important to have modest BetaN to match. |
| Background: | |
| Resource Requirements: | ECH: 3 or more gyrotrons.
NBI: a) For the ECH intrinsic measurements only the diagnostic beams are needed: 30L, 33L/R.
b) to utilize the remainder of the shot for balanced beam intrinsic rotation at higher Beta we need at least 21R/L, with 15L/R desirable. |
| Diagnostic Requirements: | standard for intrinsic rotation. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
19: Use DIII-D pumping capability to separate density and temperature in Rice's scaling |
| Name: | John Degrassie () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | W.Solomon, J.Rice, K. Burrell |
| Description: | *TBD is the best approach to obtaining companion discharges with and without pumping. Hopefully the straightforward approach of having shots with the pump on and then off will work. Previously we attempted moving the strike-point slightly but we still needed pump-off shots, and given the limited one-day time we never optimized the pumping location. Pump on/off should allow time to fix the best pumping location.
*We need companion discharges at the same stored energy (beta) but with different densities, at the same Ip with the intrinsic velocity profiles measured.
*We want the above set at a) At least two values of stored energy and b) At least two values of Ip. |
| Experimental Approach/Plan: | We will use a DIII-D shape that gives the best chance for density control in ELMing H-modes with pumping, presumably an appropriate Single Null shape. We need velocity measurements at several density values, with nT constant. This will no doubt involve slight repositioning of the strike point. We will also need companion shots in the same x-point configuration with the pump off. |
| Background: | Rice's engineering scaling for intrinsic rotation shows that the toroidal velocity scales as W/Ip. The scatter in the international database does not allow one to surmise whether or not density and temperature enter W, the stored energy, on an equal footing. We can use the DIII-D pumping capability to vary the density in ELMing H-mode, adjust the mix of ECH and potentially near-balanced NBI to keep the stored energy constant and measure the intrinsic velocity. A definitive experiment will go along way in limiting potential theoretical explanations. |
| Resource Requirements: | Same as proposal 14. Want to do near-balanced beam intrinsic rotation measurements in the back of these discharges. |
| Diagnostic Requirements: | standard for intrinsic rotation |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
20: RMP penetration vs rotation |
| Name: | John Degrassie () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | T.Evans |
| Description: | *The key hypothesis is that at high q95 the plasma will be resilient against RMP-induced locking at low toroidal velocity. We will run the I-coils in n=3 odd parity for which the ELM-suppression resonance occurs just above q95 = 7. Using admixtures of counter beam we will vary the toroidal velocity and measure the threshold for RMP ELM-suppression. We anticipate that the threshold I-coil current will depend upon rotation rate, due to the physics of error field screening, and perhaps other reasons. A plot of these data will be the primary product of this experiment, leading to a flurry of potential theoretical explanations. |
| Experimental Approach/Plan: | *Re-establish RMP ELM-suppression with n=3, odd parity at q95 ~ 7. Vary the toroidal rotation velocity with varying amounts of counter-beam substitution and measure the threshold I-coil current for ELM-stabilization at each velocity level. The typical reduction in toroidal velocity with I-coil turn-on must be accommodated as we see what happens in the experiment. It may be advantageous to use NBI torque feedback on a velocity channel, at fixed power, to select a velocity point. We need to obtain at least three distinctly different target velocities (at the suppression threshold) and measure the necessary I-coil current at each. |
| Background: | *Attempts to study the effect of toroidal rotation on RMP ELM-suppression with the standard q95 ~ 3.5, n=3 even parity scenario have been plagued by RMP-induced locking as the toroidal velocity is reduced. This is important to study because of the need to experimentally understand the effect of toroidal rotation on error field penetration, and the accompanying so-called plasma response.
*There has been demonstrated an RMP ELM-suppression resonance at q95 ~ 7 using n=3, odd parity. The plasma should be far more tolerant of RMPs at low rotation at this q95, allowing the possibility of getting data on penetration vs velocity. We will measure the I-coil current threshold as an indicator of field penetration, i.e. screening. |
| Resource Requirements: | NBI: 7 sources. |
| Diagnostic Requirements: | Standard for RMP experiments. |
| Analysis Requirements: | Standard for RMP experiments. |
| Other Requirements: | -- |
| Title |
21: Does Confinement Improvement Saturate with Increasing Rotation? |
| Name: | Mickey R. Wade ( ) |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Conduct Mach number scan in low density hybrid dischrages to determine whether the confinement improvement generally observed as rotational shear increases saturates at very high levels of rotational shear. |
| Experimental Approach/Plan: | -- |
| Background: | ExB shear has been consistently shown to be reduce turbulence-driven transport. Recent experiments using the co/counter NBI
capability on DIII-D have shown that confinement increases nearly linearly with increasing rotational shear. Theory suggests that at some point ExB shear should fully stabilize long-wavelength turbulent modes. In such a case, confinement should saturate rather than improve linearly with increasing rotational shear. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
22: Collisionality Dependence of RMP Suppression |
| Name: | Mickey R. Wade () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Utilize two separate non-dimensional scans to assess collisionality dependence of ELM suppression using RMPs: 1) collisionality scan at fixed rho*, beta, and delta_br/Bt to determine collisionality threshold for RMP suppression; 2) rho* scan at fixed beta, collisionality, and delta_br/Bt to determine if ELM suppression can be obtained at fixed collisionality over range of conditions. |
| Experimental Approach/Plan: | 1) Starting with a successful case that has demonstrated ELM control using RMPS, conduct a collisionality scan at fixed rho*, beta, and delta_br/BT. This will require the following variations: density = constant, temperature as B^2, Ip as B, and delta_br as B. Higher field will mean lower collisionality so majority of scan will likely be done at lower field than successful case. 2) Starting with successful case, increase toroidal field at constant rho*. Will require varying density ~ B^4/3, temperature as B^2/3, Ip as B, and delta_br as B. |
| Background: | A still outstanding question for ELM suppression via RMPs is whether the density or collisionality (or some combination) is the key parameter in achieving ELM suppression. This is a key question in extrapolating this to ITER and future burning plasma devices as low density is unfavorable in a burning plasma device while low collisionalitly is expected in such a device. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
26: Commonality of Density Threshold for RMP ELM Suppression and QH-mode |
| Name: | Mickey R. Wade () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Compare the density threshold at which QH-mode and RMP ELM suppression is achieved in same plasma shape |
| Experimental Approach/Plan: | Establish q95 ~ 3.7 QH-mode plasma in a plasma shape amenable to RMP ELM suppression. Determine density threshold for ELM suppression. Establish q95 ~ 3.7 ELM suppressed plasma in same plasma shape. Determine density threshold for ELM suppression. |
| Background: | Both QH-mode and RMP ELM suppressed discharges are obtained at very low density (or collisionality) with particle transport drastically affected by the non-axiymettric fields in the edge, suggesting a commonality in the physics involved. Theory suggests that the density plays a role in determining the operating point on the peeling-ballooning diagram, pushing the most unstable mode to be more kink-like. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
27: Disruption Statistics and Prediction |
| Name: | John C. Wesley () |
Affiliation: | General Atomics |
| Research Area: | Disruptions |
Presentation time: |
Requested |
Co-Author(s): | Al Hyatt, Pete Taylor and Sean Flanagan |
| Description: | Effect automated search and analysis of disruption-related plasma and tokamak data. Compile 'statistics' re disruption causes, correlation of disruptivity with operation mode, proximity to operation limits, nature of experimental activity. Identify disruption pending indicators. |
| Experimental Approach/Plan: | Background data analysis methods development and validation on past and daily tokamak and plasma operations data. Intent is to minimize eventual staff monitoring and assessment of data. May eventually result in coupling to disruption avoidance methods and test of benefits in reducing disruptivity. |
| Background: | -- |
| Resource Requirements: | Staff time and participation for method development, daily review and refinement. Interaction with scenario development and exploration campaigns; perhaps eventually runtime to test avoidance strategies and results. |
| Diagnostic Requirements: | May require specific setting, gains, time base, etc. to detect and record data on precursor sihgnals, plasma and machine fault logic. |
| Analysis Requirements: | Automated methods development and reporting. |
| Other Requirements: | -- |
| Title |
28: Small-sized LSN to test off axis NBCD |
| Name: | John Degrassie () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | M. Murakami, W. Heidbrink |
| Description: | |
| Experimental Approach/Plan: | *Run this shape with NBI comparing left and right co-souces, and counter-sources, with, at minimum, blips from 30L (or 21R if validated) for MSE. L- or H-mode, beam modulation, using ECH to raise Te and lengthen the beam slowing down time will all be details to be determined in an actual run plan should time be allocated.
*After day 1 (with normal BT) selected discharges will be matched on day 2 in reversed BT. NBCD from detailed analyses will be compared.
*Reversing Ip instead of BT and using the 210 sources for co-NBCD is an option that will be considered also. This will keep BxGradB downward if it is deemed necessary to match H-mode characteristics in the same shape.
*With 3 days allocated for this important experiment, both reversed BT and reversed Ip can be used. |
| Background: | DIII-D is proposing to modify a beam-line to shoot off of the midplane in order to obtain off-axis NBCD. Off-axis NBCD in ASDEX-U has produced a result that falls below theory. Modeling by Murakami et al indicates that the problem may be the alignment of the prompt NBI orbit and the total B field, leading to more trapped fast ions in the misaligned situation. We can experimentally test this for ourselves before spending the megabucks to tilt the beamline. |
| Resource Requirements: | All beams
ECH: Possibly at least 2 gyrotrons if Te control becomes part of the plan. |
| Diagnostic Requirements: | standard. MSE. |
| Analysis Requirements: | "NVLoop" (or the modern equivalent) with MSE for toroidal current density. |
| Other Requirements: | -- |
| Title |
29: ITER-AT demonstration discharge |
| Name: | Holger Reimerdes ( ) |
Affiliation: | Columbia University |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The goal of this experiment is to develop a scale model of the proposed ITER-AT discharge (scenario 4 in Polevoi et al, IAEA 2002) with the same shape (SND) and the same safety factor profile in DIII-D. This scenario should be used to verify predicted stability limits. |
| Experimental Approach/Plan: | The main novelty of this experiment is the use of the ITER plasma shape (SND, kappa=1.76, delta=0.4) as an AT target. The q-profile is characterized by qmin>2 and q95 ranging from 4.1 to 5.1 (corresponds to ITER with Ip=9 to 12MA). The q-profiles have weak negative central shear and a large rho(qmin), which is expected to lead to an ITB at large radius. We plan to use ECCD to tailor the current profile and increase the fraction of non-inductive current. Since the main objective is the creation of a reference, steady-state operation is not a requirement. The ideal MHD no-wall limit is measured using active MHD spectroscopy. Tearing mode limits are evaluated as a function of beta and plasma rotation. |
| Background: | One of the ITER objectives is to aim at demonstrating steady-state operation using non-inductive current drive at Q>5 [Shimomura et al, Plasma Phys, Control. Fusion 43 (2001) A385]. The main candidate is a weak negative central shear plasma with a transport barrier at rho=0.75. Recent DIII-D experiments have demonstrated that a transport barrier can be compatible with operation well above the no-wall stability limit [A.M. Garofalo et al, Phys. Plasmas 13 (2006) 056110]. |
| Resource Requirements: | 7 NBI sources, AMAP gyrotrons |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
30: High beta error field threshold |
| Name: | Holger Reimerdes () |
Affiliation: | Columbia University |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The goal of this experiment is to develop an estimate of the high beta n=1 error field threshold and corresponding torque requirement and use it for an empirically or model-based extrapolation to ITER. The n=1 error field threshold is measured as a function of input torque and helicity (resonant component). |
| Experimental Approach/Plan: | The error field threshold is measured in quasi-stationary n=1 error field ramps in plasmas, where beta exceeds the no-wall stability limit. In addition to the error field threshold, we plan to measure the plasma response at the threshold. The measurement of the perturbed poloidal and radial magnetic field (and its toroidal phase) at the wall directly yields an independent estimate of the electro-magnetic torque, which can then be compared to transport calculations based on beam torque models and empirical momentum diffusion. The measurements are repeated at several values of input torque and with various poloidal spectra using C- and I-coils. |
| Background: | Experiments with balanced beams have shown that the rotation required for operation above the no-wall stability limit in the presence of error fields is significantly higher than in an axisymmetric configuration. This increase of the rotation threshold with applied n=1 fields implies a limit on tolerable error fields, which supposedly can be traded off against an increased momentum input. The effect of resonant field amplification at values of beta above the ideal MHD no-wall stability limit significantly reduces the error field tolerance with respect to low-beta error field thresholds. |
| Resource Requirements: | 5 co + 2 counter NBI beams |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
31: Parametric dependencies of RWM damping in rotating plasmas |
| Name: | Holger Reimerdes () |
Affiliation: | Columbia University |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | S.A. Sabbagh |
| Description: | Compare RWM damping under varying plasma conditions (e.g. ion collisionality, plasma rotation) for a test of RWM theory (joint experiment with NSTX). |
| Experimental Approach/Plan: | Measure RWM damping in high beta plasmas using active MHD spectroscopy under changing plasma conditions. We can vary the electron density to confirm NSTX observations of increased RWM damping (lower critical rotation) with increasing ion collisionality. Furthermore, we plan to vary the plasma rotation using simultaneous co- and counter-NBI to test predictions of decreasing RWM damping with increasing plasma rotation. |
| Background: | NSTX magnetic braking experiments showed a variation of the rotation threshold with ion collisionality, nu_ii. Increasing nu_ii by almost an order of magnitude resulted in a significantly lower (about 30%) critical rotation [Sontag, Sabbagh, Zhu et al. Nucl. Fusion 47 (2007) 1005]. Kinetic theory including trapped particle precession can predict less stability at intermediate rotation values. |
| Resource Requirements: | 5 co- and 2 counter-NBI |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
32: Multiple n dynamic error field correction |
| Name: | Holger Reimerdes () |
Affiliation: | Columbia University |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Attempt to improve error field correction in high beta plasmas using dynamic error field correction with independently controlled I-coils. |
| Experimental Approach/Plan: | The target plasma must be a high beta plasma where beta exceeds the n=2 no wall stability limit. In order to be able to control multiple n modes the I-coil must be independently controlled. A maximum current of up to 1.7 kA can be achieved by using a sub-SPA on each I-coil. The current will be chosen to cancel the radial field (total or plasma response) at the corresponding radial field sensor. The correction will be evaluated by observing changes to the plasma rotation assuming that an axisymmetric configuration results in the least drag. |
| Background: | RWM feedback control and simultaneous error field correction of multiple n is expected to lead to the most stringent requirements on the DIII-D RWM feedback system and will, possibly, require a further upgrade of the amplifier system (as described in the DIII-D 5-year plan). This experiment examines the required magnitude of DC error field correction currents. |
| Resource Requirements: | Sub-SPAs on individual I-coils. Minor modifications of PCS input channels. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
33: Real-time stability measurement using active MHD spectroscopy |
| Name: | Holger Reimerdes () |
Affiliation: | Columbia University |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Use spatial and temporal Fourier analysis of (integrated) magnetic measurements to extract the plasma response to externally applied rotating n=1 fields. |
| Experimental Approach/Plan: | This proposal will require some PCS development. While the sensors signals are already available in the PCS, several channels will be required for the results of the real-time calculations. |
| Background: | Early detection of imminent stability limits can prompt action to avoid the limit and return the discharge to a stable operating point. Low-frequency active RWM spectroscopy can be used to detect the ideal MHD no-wall stability limit as well as the damping rate of the stable RWM in the wall-stabilized regime. |
| Resource Requirements: | Piggy-back on high beta experiments. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
34: Cross-machine comparison of n=2 (non-resonant) magnetic braking |
| Name: | Holger Reimerdes () |
Affiliation: | Columbia University |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | J. Callen, A. Cole, A. Garofalo, C. Hegna, T. Hender, D. Howell, S. Wolfe |
| Description: | Test theory models such as neoclassical theory of toroidal viscosity against measurements in C-Mod, DIII-D and JET. Carrying out n=2 braking experiments in DIII-D will allow to compare the observed torque to observations in previous (and planned) n=2 braking experiments in C-Mod and JET and previous as well as proposed n=3 braking experiments in DIII-D. |
| Experimental Approach/Plan: | We plan to apply n=2 magnetic field pulses with the C-coil in NBI heated, fast rotating plasmas and measure deceleration and new equilibrium rotation. Both measurements should give independent estimates of the torque resulting from the externally applied non-axisymmetric magnetic fields. The C-coil currents are optimized to match the toroidal spectrum (n = 0, 2 and 4) in C-Mod and JET and the toroidal phase is chosen to minimize the interference with the plasma shape control. Alternatively, rotating n=2 fields could be applied. The experiment is repeated in similar plasmas with varying NBI-torque in an attempt to connect the observations in C-Mod plasmas without momentum input to the braking in JET plasmas with uni-directional NBI torque and gather further information on a possible rotation offset as predicted by neoclassical theory. The experiment should benefit form the results of ROF proposal 308 by A.M. Garofalo, which aims at separating resonant and non-resonant braking effects. |
| Background: | NTV theory has been successfully applied to explain n=3 magnetic braking experiments on NSTX [Zhu , Sabbagh, et al, Phys. Rev. Lett. 96 (2006) 225002]. The model has since been used to evaluate proposed non-axisymmetric coils for ITER. There is an extensive database of n=3 braking experiments in DIII-D. Further n=2 braking experiments were recently carried out on C-Mod (using the A-coil) and JET (using the error field correction coils (EFCCs) as part of an ITPA experiment on non-resonant braking. While the NBI heated JET experiments showed significant braking, the (intrinsic) rotation in ICRH heated C-Mod plasmas was not affected by the externally applied fields of comparable magnitude (i.e. same delta B(n=2)/B_0). |
| Resource Requirements: | C-coil in n=2 configuration. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
35: High central fast wave current drive efficiency at high electon beta with 110 GHz EC preheating |
| Name: | Robert I. Pinsker ( ) |
Affiliation: | General Atomics |
| Research Area: | Fully Noninductive High Beta Operation |
Presentation time: |
Not requested |
Co-Author(s): | F.W. Baity, J.C. Hosea, M. Porkolab, E. Fredd, J.M Lohr, A. Horton,R. Prater |
| Description: | Combine 6 gyrotrons-worth of central 110 GHz ECH (all launchers aimed at or near the center of the discharge without driving toroidal current) with the combined 60 MHz and ~90 MHz fast wave power. We would use the minimum neutral beam power necessary to create the sawtooth-free discharge in which the driven currents can be accurately measured, and to make the (MSE) measurement. Both L-mode and H-mode target discharges would be tried, although at full rf power, one would expect difficulty in keeping the discharge in L-mode. The basic scan would be a density scan, at each case obtaining at least a matching pair of discharges with co- and counter-current FW phasing. The object of the exercise would be to extend the range of central electon beta values, and hence of single-pass absorption of the FW power, considerably beyond what was possible without high power ECH. If time permits, comparison of the current drive efficiency of the 60 MHz and ~90 MHz systems could be performed - as the single-pass absorption increases, we expect at some point to observe more efficient current drive at higher launched parallel phase velocity (the higher frequency case). The experiment would seem to be the logical precursor to full utilization of the combined rf systems for AT work involving tailoring of the current profile. |
| Experimental Approach/Plan: | See description. |
| Background: | This experiment was tried on two days in the 2004-2005 campaign. However, technical problems prevented any useful data from being obtained. The DIII-D FWCD system was designed to be most efficient in a plasma with central electron temperature of about 10 keV, but the maximum electron temperature at which we have measured the FWCD efficiency to date is about 6 keV. The theoretical prediction is that the FWCD efficiency scales roughly linearly with central electron temperature, and all experiments to date have confirmed this prediction. |
| Resource Requirements: | Machine Time:
1 day Experiment
Number of gyrotrons: 5 Number of neutral beam sources: 4 |
| Diagnostic Requirements: | MSE, all standard profile diagnostics. FIDE to check for evidence of interaction between FW and beam ions. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
36: FW-only H-mode studies |
| Name: | Robert I. Pinsker () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | F.W. Baity, J.C. Hosea, M. Porkolab, E. Fredd |
| Description: | The fact that H-mode transitions were observed with fast wave power as the only auxiliary heating source, under conditions of rather low single-pass absorption was an important piece of evidence that multiple-pass absorption can be efficient. By expanding the range of rf frequencies, densities (and hence target electron temperatures), and using 3rd harmonic ECH, we can get a more quantitive measurement of the edge losses by determining the L-H transition threshold power under varying single-pass absorption conditions. |
| Experimental Approach/Plan: | The experiment consists of scans of target density, rf power (at two different frequencies: 60 MHz and ~90 MHz), toroidal field, and whether 3rd harmonic ECH is added (at the appropriate toroidal field), and comparison of co-, counter-current, and push-pull phasing. A beam is used for comparison, later in the shot. Minimal beam blips are used for CER, MSE diagnostics. At each condition, the power threshold for L-H transition is observed for both the rf and for the comparison beam. |
| Background: | H-modes with fast wave heating by direct electron absorption as the only form of auxiliary heating were discovered at DIII-D in July 1991, and have not been studied since. In particular, the fast waves in that experiment were launched with the shortest available parallel wavelength ("Pi phasing") at 60 MHz at around 1 T, and we have never studied H-modes with current drive phasing, either co- or counter-current, or at higher frequency than 60 MHz. |
| Resource Requirements: | Machine Time:
1 day Experiment
Number of gyrotrons: 4 Number of neutral beam sources: 4 |
| Diagnostic Requirements: | Profile diagnostics, edge reflectometry. Addition of high time-resolution antenna loading diagnostics would be a plus. |
| Analysis Requirements: | -- |
| Other Requirements: | Three FW systems, one at 60 MHz and the other two at ~90 MHz. |
| Title |
37: FW coupling and electron heating in ELM-stabilized H-modes with RMPs - continued |
| Name: | Robert I. Pinsker () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | C.C. Petty, T.E. Evans, M. Porkolab, F.W. Baity, E. Fredd, J.C. Hosea |
| Description: | It is arguable that since uncontrolled large ELMs are probably not acceptable for ITER and beyond and therefore ELM control is an absolute requirement, the most relevant regime for FW coupling is one in which ELMs have been suppressed with Resonant Magnetic Perturbations (RMPs). In this experiment, we would continue the study of high-power FW coupling and central electron heating in ELM-stabilized discharges with RMPs that we began in FY07. In a single day's exploratory experiment, we showed that ~2 MW of FW power could be coupled to an ELM-stabilized discharge, and obtained the first signs of central electron heating due to the FW. Much of the day was occupied with establishing an ELM-suppressed case with much smaller outer gap than had previously been used. Poor B-supply regulation led to significant difficulty in staying in the narrow q-resonant window. We did not get a good no-rf comparison shot in either of the two cases which we studied (different outer gaps). No significant power was coupled at 60 MHz from the 285/300 antenna, due to a problem in the antenna which has been remedied (we hope) in the present vent (Fall 2007). We need to continue this experiment, which is the world's first such attempt to couple fast wave power to an RMP-stabilized edge, with all of these issues addressed to obtain a publishable result on this important topic. |
| Experimental Approach/Plan: | Continuation of the experiment on this topic from 2007, in which the beam power (=programmed beta) and outer gap are minimized while maintaining the ELM suppression with RMPs and acceptable outer wall heating, the FW power added and documenting the resulting electron heating. Comparison of different antenna phasings (both co-, both counter, push-pull), measurement of electron heating profile with modulation of the FW power. |
| Background: | See description. |
| Resource Requirements: | Machine time: one day experiment, Number of beam sources: 6, three FW systems, one at 60 MHz and two at ~90 MHz, 7 kA operation of the I-coil in the configuration used for RMP experiments. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
38: Heat transport profiles and poloidal asymmetries |
| Name: | Jose A. Boedo ( ) |
Affiliation: | University of California, San Diego |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Requested |
Co-Author(s): | D. Rudakov, J. watkins, C. Holland, G. Tynan |
| Description: | -- |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
39: Rotation and ELMs |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | D. Rudakov, J. Watkins, C. Holland, G. Tynan |
| Description: | Use co and counter injection to vary rotation during ELMing discharges while keeping the input power constant. Find out if boundary rotation can be used to control ELM rotation |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
40: Heat Footprint active control using applied magnetic fields |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Requested |
Co-Author(s): | D. Rudakov, T. Evans, M. Schaffer, I. Joseph, J. Watkins, C. Holland, E. Hollmann, G. Tynan |
| Description: | Use static or dynamic magnetic fields to control heat flux at divertor floor. One way is to make the homoclinic tangles rotate, another is to try to create an ergodic footprint at the fllor to spread heat flux |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
41: ELM heat deposition characterization and control |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Requested |
Co-Author(s): | D. Rudakov, J. watkins E. hollmann, G. Tynan, C. Holland |
| Description: | Study in detail the heat deposition mediated by ELMs, so far it is known heat deposition seems to have a short decay length no matter what |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
42: ELM Heat deposition control using detachment |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | D. Rudakov, E. hollmann, J. Watkins, C. Holland, J. Yu, G. Tynan |
| Description: | -- |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
43: Rotation transfer across LCFS |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary |
Presentation time: |
Requested |
Co-Author(s): | D. Rudakov, C. Holland, S. Mueller, J. Watkins, G. Tynan |
| Description: | How momentum is transported across the boundary is not clearry known. It can be a classical or an anomalous process. We aim to determine which |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
44: Ploidal asymmetries of flows in the boundary/SOL |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary |
Presentation time: |
Requested |
Co-Author(s): | D. Rudakov, E. hollmann, J. Yu, J. Watkins, C. holland, G. Tynan |
| Description: | Measure and characterize the flow of plasma in the boundary/SOL and how it varies poloidally. ALso connection with midplane radial transport |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
45: Poloidal asymmetries of turbulence and heat/particle transport |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary |
Presentation time: |
Requested |
Co-Author(s): | D Rudakov, E. Hollmann, J. Yu, C. Holland, G. Tynan, |
| Description: | Measure the polidal distribution of particle and heat transport. Also profiles. Compare both profiles and poloidal variation to BOUT computations |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
46: Penetration of magnetic perturbations in plasma |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | D. Rudakov, T. Evans, I. Joseph, J. Watkins, E. Hollmann, J. Yu, C. Holland, G. Tynan |
| Description: | It is not clear why RMPs work and why some expected results are not obtained (heat and particle footprints). One posibility is that the perturbations do not penetrate in the core plasma. We need to measure the perturbations in the plasma using probes and BES and see if there is shielding. |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
47: Effect of RMPs on fluctuations and transport in edge/SOL |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | It is known RMPs affect the fluctuations in the boundary. Lots of details are unknown. Need to do massive transport diagnostic charaterization. Use turbulence diagnostics and porbes. |
| Description: | -- |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
48: Multi-field Measurements of NTMs and Fast Ion redistribution in Hybrid Plasmas |
| Name: | Raffi Nazikian ( ) |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Requested |
Co-Author(s): | M. Chu, G. McKee, M. VanZeeland, W.W. Heidbrink, R.B. White |
| Description: | This proposal will generate Hybrid discharges over a wide range of q-95 and net beam torque. The 3/2 NTM will be monitored using the newly upgraded BES linear array. The radial structure and amplitude of the NTM will be measured along with the fast ion redistribution using the FIDA diagnostic. The advantage of the radial BES array over the ECE system is that the NTM can be measured in the initial overdense phase of the discharge where ECE is inaccessible. By this method, the relation between the FIDA signal, the NTM amplitude and the fast ion redistribution can be determined early in the evolution of the Hybrid discharge and the rresults can be modeled using TRANSP and ORBIT. |
| Experimental Approach/Plan: | Operate machine at maximum toroidal field. Scan flattop current from shot to shot to obtain hybrid plasmas over a range of q-95 from 3.0 to 6.0. Monitor central q(0), NTM amplitude and FIDA signal in the early phase of the discharge as q(0) approaches unity. In later phase of discharge, monitor density and temperature components of the mode and confirm consistency of the two measurements relative to the inferred island width. Change neutral beam balance to more balanced and monitor the mode amplitude and structure. |
| Background: | There is still no smoking gun identifying the key physics responsible for the relationship betweeen the NTM and q(0) in Hybrid plasmas. This experiment will definitively identify the role of the NTM in the redistribution of fast ions, which is one of the key open issues in understanding this regime. |
| Resource Requirements: | 210 beams should be available for torque scan later in discharge. |
| Diagnostic Requirements: | Upgraded BES, ECE, MSE, etc. |
| Analysis Requirements: | TRANSP, kinetic EFIT, ORBIT, ... |
| Other Requirements: | -- |
| Title |
49: Multifield Measurement of Low-n Alfven Eigenmodes in the Core of DIII-D Plasmas |
| Name: | Raffi Nazikian () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Energetic Particles |
Presentation time: |
Requested |
Co-Author(s): | G. McKee, M. VanZeeland, W.W. Heidbrink, N.N. Gorelenkov, G.J. Kramer |
| Description: | Simultaneous measurements of the radial ECE and BES profile of low-n Alfvenic modes will be performed in order to distringuish the role of plasma compressibility vs radial displacement in the multifield structure and amplitude of AEs. The experiment will focus on beam driven RSAEs and TAEs in coinjection plasmas. In counter injection plasmas the study will focus on the n=0 mode and the high-n RSAEs. The objective of this study is to determine the applicability and limitation of the ideal MHD closure relation in the description of the observed mode activity. A key goal is to determine whether electron compressibility is relevant to the description of AEs in DIII-D over a wide range of frequencies from 10-200 kHz. A second goal is to determine if the mode polarization in the plasma core can be reliably determined from BES/ECE simultaneous measurements by comparing the inferred polarization against the polarization of external magnetic measurements. |
| Experimental Approach/Plan: | Establish equivalent discharge to 128556, co injection, normal current direction. Scan the BES array across the plasma (some limited scanning is needed). Add co/counter beam blips to identify and document the counter beam driven modes. |
| Background: | Experiments in 2006 proved that the electron response is inconsistent with ideal MHD for some modes. The extended radial BES array will allow the definitive identification of the breakdown of ideal MHD closure in the description of low and high frequency AEs. The work will ultimately impact on the interpretation of mode amplitudes and in the computation of fast ion transport associated with these modes. |
| Resource Requirements: | 210 beams are necessary. |
| Diagnostic Requirements: | BES, ECE, FIDA,... |
| Analysis Requirements: | NOVAK, TRANSP, ... |
| Other Requirements: | -- |
| Title |
50: Test of a theoretical model for the irreducible minimal pedestal width scaling |
| Name: | Richard Groebner ( ) |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Measure the width of the density pedestal while performing variations of pedestal ion temperature, toroidal magnetic field and plasma current to test a theory of the pedestal width. This theory predicts that the width of the density pedestal is proportional to sqrt (Ti Mi) / Bt, which implies a toroidal gyroradius scaling. Although the aim of this experiment is to test a specific model for pedestal width, it would also provide information for a wider class of models, based on ExB shear suppression ideas, which predict that pedestal width should scale with the toroidal gyroradius. |
| Experimental Approach/Plan: | Vary the toroidal magnetic field Bt over as wide a range as possible, while keeping the pedestal ion temperature and density as constant as possible. Perform measurements during ELM-free phase. Then, vary the pedestal ion temperature over as wide a range as possible with Bt fixed and density held as constant as possible. After this scan is completed, perform Ip scan at fixed Bt. Use breathing to obtain improved pedestal profiles for ions and electrons. Measure the electron density profile and its width in the pedestal. Compare the width to the theoretical formula. |
| Background: | C.S. Chang and colleagues have developed a theoretical expression for the width of the H-mode density pedestal under the assumption that the ion thermal and particle transport are entirely caused by collisions, orbit loss and banana squeezing/expansion (due to ExB shearing) (IAEA 2004). This theory predicts that the width of the density pedestal, as obtained from a tanhfit, is proportional to sqrt (Mi Ti) / Bt, where Mi is the ion mass, Ti is the pedestal ion temperature and Bt is the toroidal magnetic field. DIII-D pedestal data, obtained under ELM-free conditions, have been used for initial testing of this prediction. A best fit to these data showed the measured width going as (Ti)^0.4 and (Bt)^-0.6; these dependences are close to those predicted by the theory. The comparison with theory can be improved significantly by obtaining single parameter scans of ion temperature and toroidal field with other parameters held as constant as possible. A variation of current with fixed Bt is also proposed in order that the variation of pedestal width with ion poloidal gyroradius can be examined. |
| Resource Requirements: | 6 NBI sources
Cryopumps |
| Diagnostic Requirements: | Thomson
CER
CO2 interferometer |
| Analysis Requirements: | Select averaging times during the discharges; these time ranges must be ELM-free or inter-ELM. Use Osborne's python codes to fit pedestal profiles for Ti and ne. Obtain tiped and newid for available discharges and examine scaling relationship between tiped, newid and bt. |
| Other Requirements: | -- |
| Title |
51: Runaway electon diagnosis by impurity pellet injection |
| Name: | Alex James
( ) |
Affiliation: | University of California, San Diego |
| Research Area: | Disruptions |
Presentation time: |
Requested |
Co-Author(s): | E. M. Hollmann, G. R. Tynan, G. Jackson |
| Description: | Study runaway electron generation and transport by injecting impurity pellets into plasmas disrupted by MGI or killer pellet injection, and observing the interaction with runaway electrons using the UCSD fast framing camera and scintillation detectors. Resulting data will reveal clues about runaway electron spatial distributions and energy distributions in mitigated plasmas. Diagnosis of naturally disrupting plasmas may also be possible. Successful experiments will contribute to A. James' advancement to PhD candidacy. |
| Experimental Approach/Plan: | H-mode plasma disruption will be initiated with MGI or killer pellets. Theory predicts generation of runaway electrons coincident with the thermal quench, with runaway beam termination indicated by a radiation spike (probably due to photoneutrons) in proximal scintillators ~10ms later. Injecting impurity pellets into the runaway beam for bombardment generates a narrow, strongly directional, cone of radiation which will be observed with a scintillator array. Visible radiation will also be observed by the UCSD fast framing camera. |
| Background: | Many disruption mitigation schemes appear to generate the same runaway electron phenomena which they set out to prevent. Observing the radiation emitted by runaway electrons bombarding an impurity pellet will reveal information about the energy distribution of said electrons. Also, theory postulates a braiding like transport phenomena of runaway electrons which will manifest a particular temporal signature in the emitted radiation. While we can study runaway electrons in DIII-D, larger machines such as JET and eventually ITER may suffer critical damage preventing further operations due to runaway electron interaction with wall materials. |
| Resource Requirements: | Engineering and technician support will be required for reinstalling the old lithium pellet injector (LPI) hereforth know as the impurity pellet injector (IPI). |
| Diagnostic Requirements: | Experiments will require H-mode plasmas terminated by MGI or killer pellets. The disrupting plasmas will then be probed by the impurity pellet injector, which needs to be reinstalled pending bench tests. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
52: Determination of ITER LH Threshold power |
| Name: | Punit Gohil ( ) |
Affiliation: | General Atomics |
| Research Area: | General IP |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | To Determine the threshold power requirements for obtaining H-mode plasmas in ITER. Vary the input power for ITER-like conditions (density, shape, low toroidal rotation, etc.) using a mix of auxiliary heating relevant to ITER (ECH and NBI). |
| Experimental Approach/Plan: | Set up the discharges at conditions relevant to ITER (i.e. low toroidal rotation, density and collisionality, shape, etc.). Vary the input power using auxiliary heating systems relevant to ITER (i.e. mostly ECH with NBI to maintain the relevant toroidal rotation conditions). Perform power scans at these ITER-like heating conditions for different plasma parameters in order to determine a scaling relationship that can be used to accurately predict the ITER LH threshold power requirements. |
| Background: | Recent experiments on DIII-D have showed that the LH threshold power is dependent on the edge toroidal rotation. This has strong implications for ITER, which is expected to operate with low toroidal rotation. However, most of the scaling studies for the LH threshold power (and their extrapolation to ITER) have been performed with discharges with mostly co-driven NBI with significant toroidal rotation, which could lead to an inaccurate prediction for ITER. This experiment is aimed at determining the LH threshold power for ITER by using heating methods relevant to ITER and at ITER relevant conditions in order to reduce the uncertainty in the prediction for ITER. |
| Resource Requirements: | 4 co beams, 2 counter beams, 4-5 gyrotrons |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
53: Test of Paleoclassical Model for Pedestal Electron Temperature Profile |
| Name: | Richard Groebner () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | J. Callen |
| Description: | Test the paleoclassical theory for electron heat transport (effective chi_e) in the H-mode pedestal. Do this by attempting to make a plasma which has pedestal chi_e which is a factor ~5 less than the effective chi_e predicted by the theory. Perform plasma current scan to vary pedestal chi_e. |
| Experimental Approach/Plan: | Vary plasma current (and bt to maintain constant q) from about 0.5 - 1.5 MA (and higher if possible). Perform this in conditions which allow for a long ELM-free period - use moderately high triangularity and low beam power. Obtain good pedestal measurements at each value of current so that good profiles of te, ne and ti can be obtained. Use breathing to improve spatial resolution of pedestal profiles. Enhance the documentation of these discharges by obtaining density fluctuation levels and correlation lengths in the pedestal. |
| Background: | The paleoclassical transport model predicts a lower limit for electron thermal transport in a tokamak. In current H-mode tokamaks, this model has been proposed to explain te profiles in the pedestal. There are experimental features which are in rough agreement with the model. These include observations that eta_e is in the vicinity of two, as predicted, that the model can predict the upturn of chi_e that is observed at the very periphery of the pedestal and that some chi_e values from interpretive transport analysis are close to the predictions of the theory. At this time, it is not possible to test the underlying physics mechanism of this model which is that poloidal magnetic field lines diffuse radially and carry electrons with them. The most stringent test that can be made of the model is to attempt to make a pedestal with a low chi_e in an effort to obtain a chi_e value that is well below the predictions of the theory. At this time, we do not have good knowledge of how chi_e values scale in the pedestal. However, the pedestal gradients steepen as the plasma current is increased and it seems likely that chi_e can be varied significantly by varying current. Thus, we propose to vary the current over as wide a range as possible so that the pedestal chi_e can be varied by a large factor. |
| Resource Requirements: | 4-5 NBI sources
Cryopumps |
| Diagnostic Requirements: | Thomson
CER
CO2 interferometer
Quadrature reflectometer (desired)
BES (desired) |
| Analysis Requirements: | Use Osborne python codes to fit profiles to pedestal te, ti and ne. Perform interpretive transport analysis to obtain chi_e values in the pedestal. Evaluate paleoclassical model chi_e. Compare experimental and theoretical values for the effective chi_e. If some experimental values are significantly lower than theoretical values, perform sensitivity analysis to test our confidence in the experimental results. |
| Other Requirements: | Some software work may be needed to properly evaluate the best version of paleoclassical theory. This could be done in ONETWO. Alternatively, some of the calculation might be doable in an IDL code. |
| Title |
54: Steady State FDF Based on Hybrid Scenario |
| Name: | C. Craig Petty ( ) |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Demonstrate the existence of a fully noninductive hybrid plasma that satisfies the requirements for FDF. This will be achieved by adding central current drive from EC and FW to a previously obtained high beta hybrid discharge (129323) to eliminate the residual ohmic current and to slighly raise the normalized beta to 4.0. This demonstration will quickly put the physics basis for FDF on a firm foundation.
The starting point for this proposal is shot 129323, which was a hybrid scenario discharge that obtained normalized beta > 3.5 with co-NBI. This beta value is well above the ideal no-wall stability limit. Presumably the rapidly rotating plasma is wall stabilized. The confinement factor is good, H_89P=2.4, and the fusion gain factor of G=0.38 at q_95=4.9 is suitable for modest fusion gain on FDF (Q<10).
The parameters given below are from a self-consistent 0-D calculation using shot 129323 as the starting point. Typical values of the achieved current drive efficiencies for EC, FW, and NB on DIII-D are used. These parameters could be scaled up to full field if desired.
Parameter 129323 Goal
Ip (MA) 1.06 1.06
Bt (T) 1.54 1.54
q_95 4.9 5
n (10^19 m^-3) 3.9 3.9
beta_N 3.7 4.0
H_89P 2.4 2.4
G 0.38 0.38
P_tot (MW) 9 11
P_NB (MW) 9 7
P_EC (MW) 0 3
P_FW (MW) 0 1
I_BS (MA) 0.47 0.56
I_NB (MA) 0.31 0.24
I_EC (MA) 0 0.19
I_FW (MA) 0 0.07 |
| Experimental Approach/Plan: | - Start with shot 129323. Modify NBI program to use mainly left (co) beams.
- Inject maximum amount of EC and FW power available in co-current drive phasing. The EC should be deposited as close to the center as possible.
- Increase PCS feedback target for stored energy to obtain beta_N=4.
- The plasma current and toroidal magnetic field strength can be scaled up or down (at fixed q_95) to fine tune the noninductive fraction and eliminate the residual ohmic current. |
| Background: | The current proposal for FDF envisions a high q_min advanced tokamak scenario with 70% bootstrap current fraction. While this is compatible with the US view of DEMO, the physics of the high q_min AT scenario is still being developed. There is also an issue regarding the high off-axis current drive efficiency needed for FDF in this proposal.
Here I propose that the low q_min hybrid scenario is compatible with the requirements of FDF, and it has several advantages. First, the physics basis is well advanced. Long duration hybrid discharge with high beta and high confinement are routinely achieved. Second, because q_min=1 in the hybrid scenario, all of the external current drive can be deposited near the plasma center where the current drive efficiency is the highest (because of the lack of trapped particles and the high electron temperature). While the bootstrap current fraction will be lower in this low q_min hybrid scenario (50% rather than 70%), the increase in the current drive efficiency for central deposition more than makes up for this.
Experiments on DIII-D have shown that the current profile in hybrids is insensitive to the external current drive profile. The internal MHD appears to regulate the current profile shape so that sawteeth are eliminated in hybrids regardless of the ohmic current fraction. Therefore, I anticipate no adverse changes to the beneficial characteristics of hybrid plasmas as the ohmic current is reduced to zero. |
| Resource Requirements: | Neutral beams: 3 co left sources critical, 3 co right sources desired.
EC: Minimum 5 gyrotrons.
FW: Demonstrate ability to couple >1 MW into ELMy H-modes. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | Will analyze discharges using TRANSP. Various programs will be used to analyze the MSE data to verify the noninductive current fraction. |
| Other Requirements: | -- |
| Title |
55: non-VFI Operations with RTEFIT |
| Name: | Alan Hyatt ( ) |
Affiliation: | General Atomics |
| Research Area: | Model based Control |
Presentation time: |
Not requested |
Co-Author(s): | D. Humphreys, M. Walker, J.Leuer |
| Description: | Run a standard DIII-D DND or SND plasma without using the VFI bus constraint. |
| Experimental Approach/Plan: | Choose and interesting plasma that would benefit from non-VFI ops. Devise, implement and test an appropriate reference flux control algorithm for the PCS using the standard RTEFIT environment. Two half-day experiments requested, separated by at least one week. |
| Background: | non-VFI operations has been done successfully in the FLUXRATIO environment but the only attempt in the RTEFIT environment performed poorly due to an unsophisticated reference flux algorithm and unrelated operations issues. |
| Resource Requirements: | No special hardware resources required. Control software will need development. |
| Diagnostic Requirements: | Standard diagnostics only. |
| Analysis Requirements: | Standard EFITs OK. No special analysis requirements. |
| Other Requirements: | Will use a non-VFI patch panel, so hand-off to any other experiment will use 30-45 min before experiment resume. |
| Title |
56: Sustaining Low q(0) With Monster Sawtooth Control |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Not requested |
Co-Author(s): | W. W. Heidbrink, R. I. Pinsker, J. Lohr |
| Description: | For the high li scenario, postpone or suppress the monster sawtooth crash for q(0)<<1 by using off-axis current drive to keep the current profile from becoming too peaked. The concept of q(0) control could also be tested transiently by using BT ramps. |
| Experimental Approach/Plan: | Create H-mode plasmas with "strongly" monotonic q profiles with co-NBI. Cryopumping should be used to control the density. Create a large population of fast ions to give monster sawteeth. Inject maximum co-ECCD off-axis around rho=0.35 to broaden the current profile and present q(0) from dropping to ~0.8. If that doesn't work, try adding some counter FWCD power. |
| Background: | To achieve a high internal inductance (which gives a high no-wall beta limit), the central safety factor needs to be less than unity. That can be achieved by stabilizing the m/n=1/1 mode using a sufficiently peaked fast ion pressure profile. However, if the ohmic current is significant then the current profile will continue to peak in time until a monster sawtooth crash occurs. Using off-axis current drive from ECCD, and perhaps counter on-axis current drive from FWCD, it is intended to halt the decrease in q(0) above the monster sawtooth crash limit. (Counter NBCD will not help because the counter current drive profile needs to be more peaked than the ohmic current profile.) It is expected that this experiment is contingent on the success of similar low-beta, low-density, monster-sawtooth stabilization experiments in the "Stability and Control" topical science area. |
| Resource Requirements: | NBI: At least 5 co sources.
EC: Minimum 5 gyrotrons.
FW: Couple > 1 MW at 60 MHz. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
57: Gyroradius Scaling in Hybrid Plasmas |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | D. C. McDonald, T. C. Luce |
| Description: | This is a placeholder for Darren McDonald's proposal on rho* scaling of high beta plasmas using the hybrid scenario. |
| Experimental Approach/Plan: | Should coordinate with JET to extend rho* scan over a larger range than can be accomplished on any one machine. Keep beta, collisionality, and safety factor fixed. |
| Background: | This proposal is related to ITPA Joint Experiment CDB-8 and SSO-2.3. |
| Resource Requirements: | NBI: At least 6 sources.
EC: At least 4 gyrotrons. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
58: ECCD in High Beta Poloidal Plasmas |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | P. A. Politzer, R. Prater, M. Choi |
| Description: | Use off-axis ECCD for current profile control in high beta poloidal plasmas with large bootstrap current fraction. Also test the effect of beta poloidal on the ECCD efficiency. |
| Experimental Approach/Plan: | (1) Establish high beta poloidal plasmas with high bootstrap current using two gyrotrons for central heating. (2) Inject ECCD off-axis (4 gyrotrons) and measure the effect on the current profile evolution. Scan the resonance location radially, and scan the toroidal injection angle to compare the effects of co and counter ECCD. (3) Use an open loop method of adjusting the ECCD power and location to give the optimal current profile for the high bootstrap current experiments. (4) Keeping ne and Te fixed, raise the plasma current to lower beta poloidal. Measure the effect on the ECCD efficiency at various radial locations. |
| Background: | Demonstrating current profile control is an important next step for showing the utility of the ECCD system on DIII-D. High beta poloidal plasmas are a good candidate for this since they have little ohmic current (thus the back EMF effects are small). Current profile control may be a benefit to optimizing the high bootstrap current experiments. Furthermore, we can use these plasmas to extend our ECCD database by comparing the ECCD efficiency in plasmas with the same ne*Te but different Ip. This will be an important test of the effect of beta poloidal on the ECCD efficiency (high beta poloidal is expected to reduce trapping effects and increase the current drive efficiency). |
| Resource Requirements: | NBI: At least 4 sources.
EC: Minimum 5 gyrotrons. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
59: ECCD at High Electron Temperature |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | R. Prater, M. E. Austin |
| Description: | Measure the linear and quasi-linear ECCD efficiencies at high electron temperatures (>10 keV) for central deposition to test the CQL3D model in this extreme limit. |
| Experimental Approach/Plan: | The flexible ECH steering system on DIII-D allows us to study ECCD at different power densities while keeping the electron temperature approximately constant. The "linear" regime will be studied using one co gyrotron and four radial gyrotrons, while the "quasi-linear" regime will be studied using five co gyrotrons.(1) Make low density target discharges that have the potential for high central electron temperatures for at least 0.5 s. Most likely L-mode edge. Sawteeth should be avoided by either raising q(0)>1 using early NBI or increasing the error field to cause a non-disruptive locked mode. (2) Inject 5 gyrotrons radially and 1 in current drive phasing with B tuned for central deposition. Scan the parallel index of refraction for the current drive gyrotron from counter to co. Modulate the ECCD power at 5-10 Hz for a few cases if the high electron temperature can be maintained for at least 1 s. (3) Obtain fiducial discharge with all gyrotron in radial launch. (4) Set all gyrotrons to current drive phasing. Repeat scan of parallel index of refraction from couner to co. (5) If time permits, raise density to lower electron temperature and repeat some of the injection angle scans. |
| Background: | Previous ECCD experiments on DIII-D have focussed on measuring the effect of electron trapping. Analysis of the resulting database showed that parallel electric field effects were significant, but quasi-linear effects were not as clear. Meanwhile. experiments on JT-60U have measured the ECCD for central electron temperatures as high as 23 keV. Modeling these discharges using CQL3D showed that the parallel electric field effects were significant and the quasi-linear effect was smaller, similar to DIII-D. This was somewhat surprising since the RF power density was much larger on JT-60U than on DIII-D. Furthermore, CQL3D predicted a factor of 2 larger ECCD than TORAY-GA even for the linear regime, which is much different for typical DIII-D discharges. To help resolve some of these mysteries, it would be good for DIII-D to also study the ECCD efficiency in plasmas with high electron temperatures. |
| Resource Requirements: | NBI: co and counter MSE beams.
EC: Minimum 5 gyrotrons. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
60: Dependence of Stiffness on Elongation |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Scan the temperature gradient at fixed density using a power scan to determine the stiffness of transport. Repeat this at various values of plasma elongation. Compare results with GYRO, TGLF, GLF23, and MM theory-based models. |
| Experimental Approach/Plan: | (1) Establish H-mode plasmas with density control. (2) Scan NBI power to vary the ion temperature gradient. (3) Try to maintain constant ExB shear and Ti/Te ratio. (4) Repeat NBI power scan at elongations between 1.5 and 2.0. |
| Background: | Confinement databases have not been able to clearly distingush between the GLF23 and Multimode theory-based models, probably because the most sensitive parameters are not clearly varied. Perhaps the largest difference between GLF23 and MM is the level of transport stiffness, especially in the outer regions of the plasma. In addition, these models have a very different elongation scaling of the stiffness value. Studying this experimentally should help us to validate (or disprove) these two theory-based models. |
| Resource Requirements: | NBI: At least 5 sources.
EC: Minimum 4 gyrotrons. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
61: Direct Measurement of ECCD Width from Modulated ECCD |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Directly measure the ECCD profile width using the MSE diagnostic by modulating the ECCD power at a low frequency (10 Hz) and observing the back EMF effect. |
| Experimental Approach/Plan: | For off-axis ECCD, modulate the gyrotron power at 5-10 Hz with the beams on continuously to obtain MSE data. Stationary plasma conditions are preferred so that the time dependence of the MSE signals are dominated by the effects of the modulated back EMF. Unwanted electron temperature oscillations can be avoided by operating the ECCD in a push-pull manner, that is, alternating between co and counter ECCD at the same location. However, in this case an accurate determination of the ECCD profile width requires that the co and counter ECCD be well aligned at the same location. The MSE data can be analyzed between shots using HPA (Heat Pulse Analysis) to determine the amplitude and phase of the pitch angle response. |
| Background: | The modulation in the current density and back EMF effect can be detected on the MSE diagnostic by applying FFT to the measured pitch angles. The phase difference between the ECCD power modulation and the measured change in the pitch angle allows one to separate the back EMF effect from changes in the current profile. Despite the simplicity of this technique, we have never attempted it on DIII-D before 2003 since we have always been more concerned about the magnitude of the current drive rather than the profile width. However, recently the issue of ECCD profile broadening has gained importance, so the time is opportune to attempt to directly measure the ECCD profile width using the modulation technique. The optimal modulation frequency is as slow as possible, but one needs on order ~10 pulses to do FFT analysis. |
| Resource Requirements: | NBI: Co and counter MSE beams are needed, and one additional source.
EC: Minimum 5 gyrotrons. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
62: Measurement of Inductive Poloidal Current |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | P. A. Politzer |
| Description: | Measure the poloidal current density profile induced by ramping the toroidal field coil. Compare with the poloidal current expected from the parallel Ohm's law to determine if the perpendicular conductivity is large enough to give a significant contribution. |
| Experimental Approach/Plan: | Study H-mode plasmas with beta_pol near unity so that the "natural" poloidal current is negligible. Compare discharges with positive and negative ramps of the toroidal field to cases with no BT ramping. Keep the plasma current, density, and temperature constant during these ramps. Study two cases, a low electron temperature plasma with NBI heating only, and a high electron temperature plasma using ECH in addition to the diagnostic beams. |
| Background: | The magnitude of the perpendicular conductivity has not been measured to my knowledge in tokamaks. In this experiment, ramping the toroidal field will induce a poloidal electric field that can be exactly computed using Faraday's law. Multiplying this E_pol by the parallel conductivity gives the parallel contribution to Ohm's law, while multiplying E_pol by the perpendicular conductivity gives the perpendicular Ohmic current density. Using the MSE data (although not necessarily equilibrium reconstruction), both the poloidal current density and the parallel current density can be measured. By comparing plasmas with and without a BT ramp, it will be possible to determine if the measured change in the parallel current density is enough to explain the total measured poloidal current (i.e., the perpendicular conductivity is negligible). |
| Resource Requirements: | NBI: Co and counter MSE beams, and at least 2 other sources.
EC: Minimum 5 gyrotrons. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
63: Extreme Off-Axis ECCD |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | R. Prater, J. Lohr, M. Choi |
| Description: | Use the higher ECH power available this year and MSE system to test the physics of ECCD in the outer regions of the plasma, 0.5< rho_ec < 0.9, especially for cases where large trapping effects are expected. The current drive determined from MSE signals will be compared to theoretical models. |
| Experimental Approach/Plan: | These experiments can be done in either L-mode or H-mode plasmas, but H-mode is preferred since it is the standard operating mode for DIII-D. Co/counter current drive comparisons should be done. (1) Scan the ECCD location across the midplane radius on the high magnetic field side of the plasma from 0.5 < rho_ec < 0.9 by varying the toroidal magnetic field. (2) Scan the poloidal angle of the ECCD location at fixed rho by varying BT and the antenna steering for rho=0.5 and rho=0.8. (3) Scan the ECCD location vertically at a poloidal angle of 90 deg from 0.5 < rho_ec < 0.9 by varying the antenna steering. |
| Background: | Previous experiments on DIII-D have studied the effects of electron trapping and beta for ECH locations between 0.0 < rho_ec < 0.4 owing to limited power. However, many important applications of ECCD (such as NTM stabilization and AT sustainment) require current drive locations that are further off-axis. It is important to test the physics of ECCD in this situation so that predictive theoretical models can be used to guide the application of ECCD in future experiments. Furthermore, it is expected that the Ohkawa current drive mechanism (reverse ECCD from electron trapping) may dominate the Fisch-Boozer current drive mechanism (forward ECCD from reduced collisionality) far off axis, especially when the power deposition is on the low field side. It is important to test our theoretical models in this limit. |
| Resource Requirements: | NBI: Co and counter MSE beams, and at least 2 other sources.
EC: Minimum 5 gyrotrons. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
64: Sustained Monster Sawteeth |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Energetic Particles |
Presentation time: |
Not requested |
Co-Author(s): | R. I. Pinsker, W. W. Heidbrink |
| Description: | Sustain monster sawteeth for > 2 s by using a combination of ICRF for sawtooth stabilization and off-axis ECCD for q(0) control. |
| Experimental Approach/Plan: | (1) Create monster sawteeth using fast wave absorption on beam ions. This could be done at 60 MHz in low density plasmas. (2) Apply off-axis co ECCD outside the q=1 surface (around r/a=0.3-0.4) to prevent q(0) from dropping to 0.8. Try a few different locations and power scans. (3) If any fast wave power is not being used for beam ion heating, try counter FWCD to observe effect on q(0) (not expected to work as well as off-axis ECCD). |
| Background: | Monster sawteeth crash when q(0) drops to a critical value. Using off-axis ECCD to halt the decreasing evolution of q(0) should allow monster sawteeth to be sustained indefinitely. |
| Resource Requirements: | NBI: At least two sources.
EC: Mimimum 5 gyrotrons.
FW: Need >1 MW at 60 MHz. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
65: Simulation of Alpha Channeling Current Drive |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | K. L. Wong, W. W. Heidbrink |
| Description: | Demonstrate the practicality of using TAE's to selectively sweep co-moving energetic particles to larger radius, resulting in localized current drive to reduce or reverse the central magnetic shear even if the initial fast particle population is isotropic. Use the fast D-alpha diagnostic to verify the redistribution of energetic ions. |
| Experimental Approach/Plan: | (1) Inject balanced beams into low current L-mode plasma. Optimize the beam sources for the collection of MSE data. (2) Decrease the plasma density until the TAE's become unstable. Document the change in the current profile. (3) Compare with different NBI power levels and different mix of left and right sources. (4) Compare with co-only NBI and counter-only NBI. |
| Background: | Previous experiments on DIII-D with co-NBI showed that TAE modes can displace the energetic particles to larger radius, broadening the noninductuve current drive profile. This can be thought of as a simulation of the alpha channeling effect in a burning plasma. Since only co-moving fast ions can resonate with the TAE's and get ejected from the core towards the edge, this process allows local noninductive current drive to be obtained from an initially isotropic alpha particle distribution. To better simulate this alpha channeling effect on DIII-D, we will inject balanced beams and then use the TAE's to spatially separate the co-moving and counter-moving fast ions. While this may not result in much net current drive, it should dramatically change the magnetic shear profile. The spatial redistribution of the energetic ions can also be verified by the total pressure profile determined by the MSE diagnostic, and the fast D-alpha diagnostic. |
| Resource Requirements: | NBI: Co and counter MSE beamlines (4 sources total). |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
66: Separating Rotational Shear and rho* Scaling Effects on Transport |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | T. C. Luce, R. E. Waltz |
| Description: | Measure the rho* scaling of transport and fluctuations for both L-mode and H-mode plasmas as a function of the toroidal Mach number to ascertain the importance of the rotational shear on question of Bohm vs. gyro-Bohm scaling. |
| Experimental Approach/Plan: | Study both limiter L-mode and divertor H-mode plasmas on separate days. (1) Start at BT=2 T and q95=4. Scan the beams from all co to all counter in 5 steps (including a balanced case). (2) Go to BT=1 T at the same q95 and same plasma shape. Reduce density by factor of 2.5. NBI power should be adjusted to match beta values of first step. (3) Repeat scan of beams from all co to all counter in 5 steps. (4) Fine tune the mix of co and counter NBI to precisely match the Mach numbers between the low and high rho* cases. |
| Background: | Transport modeling of rho* scaling experiments, using either theory based modeling or turbulence simulation codes, have predicted that changing rotational shear during a rho* scan can make intrinsic gyro-Bohm transport appear to be Bohm-like. Experiments were begun (but not finished) on TFTR to separate the two effects by measuring the rho* scaling at different toroidal Mach numbers. It is proposed to use the balanced NBI capabilities on DIII-D to measure the rho* scaling of transport and turbulent fluctuations for both L-mode and H-mode plasmas as the Mach number is scanned for co-rotating to counter-rotating. This should allow multiple pairs of rho* scans at fixed rotational shear to be obtained. |
| Resource Requirements: | NBI: All seven sources required (not simultaneously). |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
67: High Performance Operation With Te=Ti |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Demonstrate high performance operation with Te=Ti to help establish the physics basis for AT operation in ITER. |
| Experimental Approach/Plan: | (1) Re-establish AT plasmas with qmin = 1.5 and beta_N > 3.5 using NBI. (2) Using NBI power feedback of the diamagnetic flux, inject as much ECH and FW power as possible in these plasmas. The ECH should be off-axis (rho=0.2-0.3) to prevent the electron temperature profile from becoming too peaked. Simulation works needs to be done before hand to determine whether current drive phasing is desirable. (3) Vary the inductive ramp up phase to vary the amount of NCS to determine the optimal safety factor profile for these plasmas. (4) Determine if early electron heating is better than applying the electron heating after the hot ion mode has formed. |
| Background: | In many if not most of the AT modes developed around the world, hot ion mode plasmas are used to suppress the linear growth rates of the turbulence (Burrell, IAEA, 1990). There have been some instances of strong ITB formation with Te=Ti, most notably in JT-60U, but strong ITB's usually lead to low beta limits and so this line of research has not been strongly pursued on DIII-D. This experiment proposes to utilize high beta AT plasmas with qmin=1.5, and replace as much NBI power with ECH and FW power as possible. Current drive phasing of the RF may be used if it leads to a desirable safety factor profile, but this is not the emphasis of this experiment. This proposal is related to ITPA Joint Experiment TP-3. |
| Resource Requirements: | NBI: At least 5 sources.
EC: Mimimum 5 gyrotrons.
FW: Desired to couple >1 MW. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
68: Modulation of Bootstrap Current |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | B. Hudson |
| Description: | Directly measure the bootstrap current profile near the H-mode pedestal by modulating either (1) the edge ECH heating power, or (2) the I-coil current, and observing the oscillating MSE/LIB response. |
| Experimental Approach/Plan: | (1) Establish QBD discharge using 210 beamline with good MSE and Lithium Beam diagnostics at relatively high field. (2) Aim ECH for power deposition near the top of the H-mode pedestal. Modulate all gyrotrons using several different frequencies (2-10 Hz). (3) Vary some parameter that should effect the magnitude if the bootstrap current (such as q95) and repeat. (4) Try modulating the H-mode pedestal pressure by modulating the I-coil current. |
| Background: | The bootstrap current profile near the H-mode pedestal strongly effects the plasma stability. If the bootstrap current density can be modulated, then the flux surface average value of the oscillating component can be determined by Fourier analyzing the pitch angles measured by MSE/LIB via the poloidal flux diffusion equation. The best method of modulating the bootstrap current is to apply modulated ECH near the H-mode pedestal [core ECH is not as desirable owing to (a) pulse pile up and (b) electron-ion collisional exchange]. QBD plasmas make good target discharges since the modulation effects of the ELMs are not present and the discharges last a long time. |
| Resource Requirements: | NBI: Co and counter MSE beams, and at least 2 more sources.
EC: Mimimum 5 gyrotrons. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | -- |
| Other Requirements: | Modulated I-coil current. |
| Title |
69: Electron Heat Pinch |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | T. C. Luce |
| Description: | (1) Demonstrate the existence of an electron heat pinch with convincingly small error bars. (2) Determine if the electron heat pinch is dependent upon the sign of the magnetic shear as predicted by some theories. |
| Experimental Approach/Plan: | (1) Reproduce the previous best cases of the heat pinch using the maximum ECH power available this year (up to 6 gyrotrons). The poloidal steering of the ECH antenna will allow variation of the heating location at constant target parameters. (2) Modulate the ECH power to obtain direct evidence on inward heat transport. (3) Use early off-axis ECH in low density plasmas to form negative shear discharges with rho_qmin > rho_ech. Measure the behavior of the Te profile as the q profile relaxes to a low shear state. (4) Repeat at several different densities (different Te) to vary the amount of shear reversal. |
| Background: | Understanding electron transport requires that the effects of diffusion and convection be distinguished, and the heat pinch issue falls squarely into this area. The inward transport effect seen with off-axis ECH remains a severe challenge to the theoretical community. Previous experiments using low field side, second harmonic launch found a negative electron heat flux near the plasma center, in support of the old 60 GHz ECH data from 1989-1990. However, due to higher ion temperatures, even in the ohmic phase, than 1989-1990, the error bars include positive (although small) values for the electron thermal diffusivity. This experiment will use the higher ECH power available this year to increase the separation betweem Te and Ti and thus reduce the error bars. Furthermore, the theoretical heat pinch model of coupled transport between Grad-J and Grad-T can be tested by comparing the non-diffusive electron transport for positive and negative shear plasmas. |
| Resource Requirements: | NBI: At least 2 sources.
EC: Mimimum of 5 gyrotrons. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
70: Neutral Beam Current Drive Profile |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Requested |
Co-Author(s): | W. W. Heidbrink |
| Description: | Measure the NBCD profile by measuring the changes in the profiles of parallel current density and parallel electric field for co and counter injection. |
| Experimental Approach/Plan: | Compare co and counter injection at the same plasma density and electron temperature using repeat shots. Comparisons should be done for (1) all left sources, (2) all right sources, (3) high power (two sources), (4) low and high electron temperature using ECH, (5) low and high density using L-mode or H-mode edge. |
| Background: | The profile and scaling of NBCD has not been as well documented experimentally as ECCD or FWCD, mainly because it has not been possible previously to compare co and counter injection on the same day. Limited data from DIII-D has found cases where the measured NBCD profile was broader than theoretically predicted. Since the NBCD profile plays an important role in our AT scenarios, it is important to validate our theoretical models. |
| Resource Requirements: | NBI: Require 2 counter sources, and at least 3 co sources.
EC: Minimum of 5 gyrotrons. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
71: Well Aligned Current Drive for Sustaining High qmin |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Sustain the high qmin target profile produced by combined Ip and BT ramps by better aligning the sources of noninductive current drive and reducing the plasma density. The central current over-drive will be eliminated by using a more balanced beam injection. To increase the effectiveness of off-axis ECCD, the lower divertor cryopump will be used for density control in this high triangularity plasma shape. (The higher electron temperature resulting from the lower density should also slow the undesired current evolution.) The off-axis location of the ECCD will be determined by code analysis to give a flat loop voltage profile with the desired high qmin current profile. With the current profile better decoupled from the heating profile, high beta value can be possible obtained because the q profile will not be adversely affected by increasing the NBI power. |
| Experimental Approach/Plan: | Two days are required for this experiment, with high power ECCD only being required on the second day. The first day will concentrate on density control in the "flat shear" scenario with combined Ip and BT ramps. The mix of co and counter NBI will also be adjusted to eliminate the central current over-drive. Between shot analysis of the loop voltage profile will guide the experiment. After the first experimental day, off-line analysis of the current profile evolution will determine the optimal location for the ECCD to achieve a flap loop voltage profile which will be close to zero for 100% noninductive current drive. The choice of which BT value to end the toroidal field ramping is part of this consideration. On the second experimental day, the off-axis ECCD will be added to sustain the desired current profile with high qmin. Again between shot loop voltage analysis will help guide the experiment. High beta will help increase the bootstrap current for more off-axis current drive. Since the tayloring of the noninductive current profile will better decouple the heating profile from the q profile, a push to high beta values in the second day of this experiment will probably be more successful than previous attempts. |
| Background: | Recent analysis of the "flat shear" experiments in Thrust 8, which include the effect of ramping the toroidal field on Ohm's law, showed that the sources of noninductive current drive were not well aligned with the target current profile. The loop voltage profile was negative near the axis and positive near the edge, which indicates that there was too much central current drive and not enough off-axis current drive. As a result, even though the integrated noninductive current fraction was close to 100%, the current profile continued to evolve until a q=2 surface appeared in the plasma which lowered the beta limit. If a better aligned noninductive current profile is utilized, then the targer high qmin profile can be sustained. The central NBCD overdrive can be easily corrected in 2006 by substituting some counter NBI. To increase the off-axis current drive, it will first be necessary to lower the plasma density. The previous experiments were essentially unpumped because of the high triangularity plasma shape; however, the modification to the lower divertor will now make it possible pump on these plasmas. (The optimal direction of BT for optimal pumping will need to be determined in separate experiments.) Using six long-pulse gyrotrons will then allow increased off-axis current drive to be obtained. This proposal is related to ITPA Joint Experiment SSO-1.1. |
| Resource Requirements: | NBI: At least 5 sources.
EC: For 2nd day of experiment, need 5 gyrotrons. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
72: Measuring the Structure of Tearing Modes |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Stability |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Measure the localized structure of slowly rotating tearing modes to determine the helical perturbations in density, temperature, and magnetic field. Compare these with theoretical predictions from codes such as NIMROD. This should be done for 2/1 tearing modes and possibly for 3/2 tearing modes as well. The key is to reduce the tearing mode rotation frequency to less than ~500 Hz using a mix of co and counter NBI. |
| Experimental Approach/Plan: | Use plasmas in the hybrid regime to produce long lasting discharges with a large saturated 2/1 tearing mode (and 3/2 tearing mode as well). Trade off counter-injection beams for co-injection beams to bring the 2/1 mode rotation frequency to ~500 Hz. Use feedback control of the 2/1 mode frequency if the PCS has been upgraded to that feature. Use continuous 30LT and 330 beams to collect MSE and CER data at high time resolution. May need repeat shots to collect all of the CER data, and also may need repeat shots for the BES data. |
| Background: | Previously the co-injection of beams into DIII-D resulted in a rotation frequency of ~10 kHz for the 2/1 tearing mode. At this high frequency, only localized data from ECE and BES has been found to be useful in measuring the tearing mode structure. (Attempts have been made to collect fast MSE data, but to date no quantitative information has resulted from this.) If the tearing mode rotation frequency can be reduced to ~500 Hz using a more balanced beam injection, then localized data also can be collected by the CER diagnostic (~4 kHz rate) and MSE diagnostic (2 kHz rate, perhaps this could be increased to 4 kHz). This would allow the helical perturbations in electron density, electron temperature, ion temperature, ion toroidal and poloidal velocities, and local magnetic fields to be obtained. Possibly other diagnostic could be added to this mix. This experiment should result in an excellent dataset for which to compare with theoretical predictions to improve (or verify) our understanding of tearing modes. |
| Resource Requirements: | NBI: All 7 sources needed (not simultaneously). |
| Diagnostic Requirements: | MSE, BES, CER, ECE. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
73: Mach Number Scan With Similar Parameters as JT-60U |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | E. J. Doyle, Yoshihiko Koide, Yoshiteru Sakamoto, Hajime Urano |
| Description: | The goal of this joint experiment is to determine the effect of Mach number on H-mode transport over a large range of rho* and a small range of aspect ratio. New machine capabilities allow us to perform a similarity experiment between JT-60U and DIII-D where the Mach No. (rotation) is varied from positive to negative values using co-/counter-/balanced-NBI. |
| Experimental Approach/Plan: | Perform three step comparison, as follows: (1) Both tokamak should scan the Mach number from positive to negative values using co-/counter-NBI at constant density, temperature, current, and magnetic field in H-mode plasmas. Keeping the plasma parameters fixed rather than the NBI power fixed will simplify the interpretation of the data because we will not have to worry about the effects of beta, collisionality, or relative gyroradius scaling on transport. (2) To help project the effect of rotation scaling of transport to ITER, each tokamak should make a second Mach number scan at a different rho* value. The plasma beta, collisionality, safety factor, and range of Mach numbers studied should be the same for the two different rho* values. This will allow us to determine whether the effect of Mach number on transport becomes stronger or weaker for larger devices like ITER. (3) The experiments on JT-60U and DIII-D should be joined together by matching the important dimensionless parameters. Since JT-60U has a higher aspect ratio than DIII-D, it is better to match the poloidal parameters rather than the toroidal parameters. Thus the two machines can match beta_poloidal in addition to collisionality and safety factor. The difference in the rho*_poloidal values should be made as small as possible by comparing a high field case on DIII-D to a low field case on JT-60U. The poloidal cross-section of the two devices should also be matched as well as possible. |
| Background: | Similarity experiments provide a powerful tool with which to investigate transport physics. Here, we propose to utilize this tool to investigate the effect of plasma rotation (Mach no.) on transport. This is ITPA Joint Proposal TP-6.2. |
| Resource Requirements: | NBI: At least 5 sources. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
74: Is the 3/2 NTM Worth Suppressing in Hybrid Discharges? |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | T. C. Luce, P. A. Politzer, M. Murakami |
| Description: | Use co-ECCD near the q=3/2 surface to (1) suppress the 3/2 NTM, and (2) drive enough off-axis current to keep q(0) above unity. Compare the plasma performance to the normal passive hybrid cases with the 3/2 NTM with the same amount of electron heating. |
| Experimental Approach/Plan: | Study hybrid plasmas with q95=4.4. (1) Use enough co-ECCD at q=3/2 location to suppress the 3/2 NTM. Use the remaining co-ECCD at a radius best suited for driving enough off-axis current to raise q(0) above unity. (2) Compare these plasmas with ECH (heating only - no current drive) at the same density and beta_n. |
| Background: | The 3/2 NTM in hybrid discharges is not completely benign because it decreases the confinement time by ~15% (compared to 4/3 NTM hybrids) and it slows the plasma rotation. However, the ECCD required to suppress the 3/2 mode is not free. The question is whether the hybrid scenario on ITER would achieve a higher Q by using the ECCD to suppress the 3/2 NTM, or live with the lower confinement time (but less auxiliary heating power). Since the ECCD also changes the Ti/Te ratio in a direction unfavorable to transport in DIII-D, it is important to include that effect in the "passive" 3/2 NTM hybrid cases. |
| Resource Requirements: | NBI: All 7 sources are required.
EC: Minimum 5 gyrotrons. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
75: Simultaneous Suppression of 3/2 and 4/3 NTM with ECCD |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Use co-ECCD at both the q=1.33 and q=1.5 surfaces to simultaneous suppress both the 4/3 and 3/2 tearing modes. Determine if an improved confinement state can be obtained, relative to plasmas with EC heating but no current drive (or NTM suppression). Determine if the beta limit is significantly affected. If sufficient gyrotron power exists, this idea can be extended to the simultaneous suppression of the 3/2 and 2/1 modes. |
| Experimental Approach/Plan: | (1) Divide the gyrotrons into two groups. The smaller group is aimed at the q=1.33 surface near the inner midplane. Its location is controlled by varying either R or BT. The larger group is aimed at the q=1.5 surface by poloidally steering the antennae upwards. Its location is controlled by either real-time steering or by shifting the plasma vertically. (2) Prepare target hybrid plasmas with beta_N=3 at either q95=4.4 or q95=3.1. (3) First suppress only the 3/2 NTM to determine the minimum amount of ECCD power required. Compare these cases with fiducial discharges with EC heating only. (4) With the 3/2 NTM suppressed, use remaining gyrotrons (but no more than necessary) to also suppress the 4/3 NTM that becomes dominant after the 3/2 mode is gone. Compare this with a fiducial case where the gyrotrons aimed at the q=1.33 surface are changed to radial injection. (5) Compare the plasmas with simultaneous 3/2 and 4/3 suppression to fiducial plasmas with no NTM suppression but same amount of EC heating. (6) For plasmas with both 3/2 and 4/3 suppression, determine beta limit for 2/1 NTM. |
| Background: | When the 3/2 NTM is suppressed by ECCD, the 4/3 NTM becomes unstable. While the 4/3 mode is likely more benevolent than the 3/2 mode (not proven for the case of ECCD suppression because of the deleterious effects of electron heating on confinement), the 4/3 mode is still expected to have some negative consequences. Therefore, it would be interesting to suppress both the 3/2 and 4/3 modes using ECCD. Since it only requires 3-4 gyrotrons to stabilize the 3/2 NTM, it is expected that the remaining gyrotrons can stabilize the 4/3 NTM which is at smaller radius. This may result in higher confinement, but to prove this fiducial discharges with the same electron heating but no current drive need to be studied. |
| Resource Requirements: | NBI: All 5 co sources are required.
EC: Minimum of 5 gyrotrons. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
76: Voltage controlled VFI bus operations |
| Name: | Alan Hyatt () |
Affiliation: | General Atomics |
| Research Area: | General PCO |
Presentation time: |
Not requested |
Co-Author(s): | D. Humphreys, M. Walker, J. Leuer |
| Description: | Test the feasibility of using a slow DC supply, like a T or C supply, to actively control the VFI bus voltage. Success will allow us to remove one of the main problems of VFI bus operations - command saturation. |
| Experimental Approach/Plan: | Use a C- ot T-supply to actively control the VFI bus voltage in a simple LSN plasma. Requires fairly simple modifications to the patch panel, probably using special cables, and develop the control software for the PCS. Prefer two half days separated by at least one week. |
| Background: | The VFI constraint has three different problems: Command saturation (inherent in the VFI), shape control impacted by too many return coils (too few power supplies), and shape control impacted by return coil - neighbor positive feedback (unsophisticated control algorithms). Controlling the VFI bus voltage directly removes the first problem and may affect the third problem positively. Advanced control algorithms would be much easier to generate if the VFI bus voltage was held near zero. Chopper command saturation occurs regularly in DIII-D whenever the VFI bus voltage exceeds 200 V or so. A feasibility test of this concept could be done with existing power supplies and some simple temporary modifications to the patch panel and protection circuitry. |
| Resource Requirements: | Simple patch panel mods, probably consisting of special cabling and a protective diode across the supply. A voltage control algorithm for the PCS neeeds to be developed. |
| Diagnostic Requirements: | No special measurements required. |
| Analysis Requirements: | No special analysis required. |
| Other Requirements: | This is a very special patch panel. Reverting to a standard patch will probably take 45-60 min before the next experiment begins. |
| Title |
77: Dependence of the H-L transition on toroidal rotation |
| Name: | Punit Gohil () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The LH transition has been determined to be sensitive to the edge toroidal rotation.The objective of this experiment is to determine the dependence of the back transition (H-L) to the edge toroidal rotation. This can be resolved by determining the power threshold for the back transition at various edge toroidal rotation values and plasma parameters, whilst examining the turbulence dynamics. |
| Experimental Approach/Plan: | Produce and maintain H-mode plasmas at different edge toroidal rotation values. Then decrease the input power at constant torque and observe the conditions at which the back transition to L-mode occurs. Focus all availabale turbulence dagnostics at the edge during these measurements. Repeat these scans for different plasma parameters and configurations to map out the operatinal space for the back transition. |
| Background: | Given the sensitivity of the H-mode transition to the edge toroidal rotation, an important issue for H-mode physics then becomes the dependence of the back transition (H-L) to the edge rotation and the determination of new key physics by observing the turbulnce dynamics across the back transition as a function of rotation. This is an especially important issue for ITER for which the conditions in which H-mode plasmas can be maintained at low toroidal rotation is now an open question. |
| Resource Requirements: | 4-5 co and 2 counter beams |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
78: High Collisionless NBI Torque Drive for GAMs, aka the VH-mode path? |
| Name: | John Degrassie () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | G.Mckee, L. Schmitz |
| Description: | *Use high power NBI co-torque to transiently drive Geodesic Acoustic Modes and measure the plasma response and mode properties with BES. The model requires that �??enough�?� prompt NBI radial current be injected to raise the E field �??fast enough�?� so that the plasma �??rings�?� in this fashion (see Background below). Actually, the proposed target plasma and suddenly switched-on NBI level are reminiscent of the VH-mode recipe. |
| Experimental Approach/Plan: | *Select a target plasma with low collisionality, with q95 ~ 6. We probably want a DND biased up with normal BT to stave off the H-mode transition as long as possible. 3 NBI co-sources are turned on simultaneously and BES is deployed to look for a GAM response. Other turbulence diagnostics will be useful. If struck, perhaps the GAM response can be followed with only the one (150) beam for some time. Perhaps we will be able to do a number of measurements with various beam mixtures after the thump and ideally see if there is any correlation between the GAM response and any subsequent H-mode transition. If we have something to measure, ECH may be a useful tool. |
| Background: | *NBI torque injected by ions into promptly trapped orbits results in a radial fast ion current that delivers this torque via Jfast X B. The low collisionality plasma responds as a dielectric for times much shorter than the momentum transport timescale, that is, a return polarization current is generated in the bulk ions. This polarization is calculable for collisionless orbits, and depends upon the details of the orbit topology for an ion. For timescales much shorter than the thermal ion bounce time the gyro-orbits shift, giving the so-called classical polarizability. For timescales longer than a bounce time the banana orbits shift giving the neoclassical polarizability, about 100 times larger than the classical value. Passing-trapped ion collisions bring the plasma response to a common neoclassical value.
*So, the plasma dielectric in this regime is a function of frequency (timescale). Striking the plasma �??fast enough�?� with a radial current source results in GAM generation as described in Hinton and Rosenbluth, PPCF vol 41, A653 (1999). These GAM oscillations are then collisionally damped.
*We need to get the E-field to rise fast enough in a thermal ion bounce time in order to modify the orbit. An estimate shows that the prompt radial fast ion current scales with the local plasma beta, and Ip^2. So we want a low beta target (and low collisionality is important for longer GAM damping time), and low Ip, i.e. higher q95, say 5-6. The estimate indicates 3 co-sources would be enough. Hopefully, less will work to give a range to study. |
| Resource Requirements: | NBI
ECH - maybe |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
79: Re-optimize the Breakdown process |
| Name: | Alan Hyatt () |
Affiliation: | General Atomics |
| Research Area: | Model based Control |
Presentation time: |
Not requested |
Co-Author(s): | D. Humphreys, M. Walker, J. Leuer, E. Lazarus |
| Description: | Re-optimize the Breakdown process in DIII-D. It has been >10 years since this has been systematically done, and there have been many hardware changes to the tokamak and the power supplies since then. There is ample anecdotal and some systematic evidence that the details of the breakdown significantly affect the plasma trajectory. Reoptimizing the initial breakdown and first 100 msec of rampup should improve reliability and repeatability for all experiments. In addition, sensitivity experiments of gas puff levels, null quality, initial Ip rampup, etc effects on flattop parameters in selected operations scenarios, such as hybrid or AT could be undertaken. |
| Experimental Approach/Plan: | Much of the work of reoptimization can be done in 'piggyfront' mode and in the system startup phase before physics operations begins. Sensitivity studies would require dedicated experiments. For these studies systematic variation of gas puff, null quality, etc would undertaken with effects on j(r), li, n(r), p(r), etc measured during rampup and into flattop for a chosen, fixed scenario. |
| Background: | The breakdown and first 100 msec of rampup haven't been systematically optimized since 1997. SInce then there have been many changes to the internal hardware of teh device, and many changes to the PF power supplies, including their response to cammands. The effects of these changes have accumulated to the point where breakdown is no longer close to the optimized point help in 1997. A systematic reoptimization of the breakdown and initial rampup process would likely result in better reliability and repeatability of experiments, and could be done in enough detail to begin to quantify the effects of variations in breakdown aspects on the plasma trajectory to flattop. This information could be very useful to thise involved in scenario development, as much of that work involves initial tweaking of the breakdown and rampup. |
| Resource Requirements: | Need access to change breakdown aspects if in piggyfront mode. |
| Diagnostic Requirements: | MSE is required for physics investigations of breakdown variations' effects on trajectories. |
| Analysis Requirements: | No special analysis required. |
| Other Requirements: | -- |
| Title |
80: Core transport barriers in EC-heated discharges |
| Name: | Max Austin ( ) |
Affiliation: | University of Texas |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | K. Gentle
K. Burrell |
| Description: | We want to investigate unusual transport properties observed in recent DIII-D discharges with off-axis electron cyclotron heating. In experiments this past year employing ECH, steady-state hollow Te profiles with sharp changes in gradients were seen in low density, low current discharges. These profiles are reminiscent of those on the RTP tokamak which were indicative of core electron transport barriers. We propose to investigate the thermal electron transport in these shots with modulated ECH, looking at heat pulse propagation across the implied barrier region. Preliminary analysis indicates the discharges are developing negative central shear and the radii with the sharp gradient changes are possibly located near low order rational q_min surfaces. |
| Experimental Approach/Plan: | Establish a low density, high q discharge like 129534 and apply heating with four gyrotrons to produce hollow Te profiles. Modulate one of the four gyrotrons, or add modulated power from a 5th gyrotron at a different radius to create heat pulses for transport analysis. Add neutral beam blips to some discharges to measure q profile with MSE data. Increase the plasma current to change the target q profile. Vary ECH deposition radius either during a shot with Bt ramp or shot-to-shot with launchers and look for step-wise changes in transport. Collect ne and Te fluctuation data for radii near the apparent transport barriers. |
| Background: | Discharges with strong ECH exhibiting steady-state hollow Te profiles and step-wise changes in transport were first seen it the RTP tokamak. The observed electron transport behaviour was attributed to good surfaces near low order rational q values in a reverse shear profile. This ties in with recent DIII-D experiments on changes in transport seen near integer q_min traversals. With the excellent diagnostic set on DIII-D including ECE, MSE, and fluctuation diagnostics, it should be possible to attain improved understanding of the role of special values of the safety factor in electron transport. Observation of zonal flow structures and changes in turbulent fluctuations would lead to validation of the rational-q transport model. |
| Resource Requirements: | Three neutral beam sources, including 30L.
At least four gyrotrons, nom. 2.4 MW total power and 1 sec pulse length. |
| Diagnostic Requirements: | ECE radiometer, FIR scattering, Correlation ECE, BES |
| Analysis Requirements: | Toray, possibly GYRO. |
| Other Requirements: | -- |
| Title |
81: ECH assisted breakdown and startup for DIII-D and ITER |
| Name: | Gary Jackson ( ) |
Affiliation: | General Atomics |
| Research Area: | ITER Startup, Shutdown, Vertical Stability |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Use the DIII-D ECH capabilities to explore breakdown and burnthrough for ITER. In DIII-D, potentially produce a more reliable startup and possibly modify of early sawteeth and li |
| Experimental Approach/Plan: | 1. For ITER: Using large bore OWL startup (X2 resonance inside LCFS), demonstrate improvements in burnthrough with ECH. Most important data:
a. Vloop scan
b. Bvf scan
2. For DIII-D optimize prefill, early gas, and Bvf and show effect on early MHD, including sawteeth, impurities, and current profile evolution. |
| Background: | DIII-D 2nd harmonic preionization experiments in 2006 and 2007 showed very interesting and sometimes counterintuitive results. For example best preionization was observed with the largest vertical field error and shortest connection length. In addition, after formation of the current channel, a large gas puff was required (0 to 50 ms) to keep dIp/dt positive.
In 2008 we propose experiments to validate the use of startup ECH for ITER, to further understand the breakdown and startup ECH physics, and to explore the use of ECH to improve DIII-D startup. |
| Resource Requirements: | 2 gyrotrons starting at t=-40 ms
Vloop feedback control (hasn't been used in many years) |
| Diagnostic Requirements: | Nothing new. Possibly configure visible camera to view tangentially beginning at t=-40 ms |
| Analysis Requirements: | Usual tools. Resurrecting MFIT, or possibly using JFIT, is desireable but not essential |
| Other Requirements: | -- |
| Title |
82: Optimize DIII-D startup, i.e. stop initiating on the outer wall |
| Name: | Gary Jackson () |
Affiliation: | General Atomics |
| Research Area: | General PCO |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Improve the DIII-D startup scenario to obtain more prompt ohmic breakdown and improve initial shape |
| Experimental Approach/Plan: | 1. Optimize the PCS breakdown algorithm and test on actual plasma shots. This can be done piggyback during the startup campaign. Minimize the value of Vloop where Dalpha light is first observed.
2. Calibrate our Ip diagnostics so that they don't pick up vessel current (this hasn't been done in years, if not decades) |
| Background: | More than a decade ago, breakdown in DIII-D was optimized (see Lazarus, Nuc Fus, 1998). Field line tracing showed connection lengths of ~4km and well defined field nulls. A random sampling of recent shots show breakdown has deteriorated. This probably affects most, if not all, discharges. Furthermore, the discharge now starts on the outer wall, probably from <10ms to ~30 ms (early EFITs are hard to come by). This MAY contribute to impurity influx, irreproducibility, and early MHD.
A second problem in understanding the breakdown phase is that pointname Ip no longer completely compensates for the vessel current. Both "Ip" and pseudopointname "Ip_probes" should be calibrated. |
| Resource Requirements: | Vacuum shots and piggyback time to adjust PCS breakdown phase. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
83: Is the Reduced L-H Threshold With Counter Beams Due to Lost Ions, or Velocity per se? |
| Name: | John Degrassie () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | G.McKee |
| Description: | *Measure the threshold power reduction as a function of target density. Fast ion loss from the counter beams is not dominated by prompt, first orbit loss, but rather by fast ions being lost before thermalization within the plasma. This loss tends to create a negative radial E field in the edge region. Reducing the fast ion slowing time in the target plasma, most readily with higher density, will reduce the number of counter flowing ions lost before thermalization.
*When the density is changed there will presumably be a different power threshold. If the toroidal velocity at the transition is the same, then we may not have separated the importance of fast ion loss versus the target velocity profile. If the velocity is different at the transition, then we have made the separation. |
| Experimental Approach/Plan: | *Start with the scan done in 2007 on L-H transition power with counter beams mixed in. Take a full co-beam case and one with added counter beams for a two point torque scan. Then raise the target density and repeat the two point torque scan for threshold power. Given the result, either raise, or lower the target density from the first level for a third density target.
*If it is clear that either lost fast ions, or the velocity per se is the controlling parameter, then devise a scan to reinforce this conclusion. |
| Background: | *Adding counter-Ip beams to the NBI mix results in a lower L-H transition power level. This could be due to the larger fraction of fast ions lost in the edge with counter injection as compared with co-injection, thereby promoting an edge negative E field and getting a head start on the H-mode negative E-well. Or there could be some reason that the lower target co-toroidal velocity itself is the driving factor in reducing the H-mode threshold. |
| Resource Requirements: | Same as for last years L-H power threshold scans. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
84: Physics of n=3 nonresonant braking. Is there an unknown n=3 error field? |
| Name: | Gary Jackson () |
Affiliation: | General Atomics |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | A. Garofalo, E. Strait,A. Cole, J. Callen, C. Hegna |
| Description: | Examine n=3 non resonant braking and its relation to NTV theory in discharges above and below the limit for rotational stabilization of RWMs. Quantify effect of varying n=3 phasing and examine the possibility of an n=3 error field. |
| Experimental Approach/Plan: | Starting with a high beta discharge, ramp an n=3 Icoil current. Do this for all parity and phases (4 discharges total). Repeat at low betaN.
Finally use a low betaN discharge (to avoid TM) and repeat with CTR beams and low rotation. |
| Background: | Recent results have shown that changing the PHASE, i.e. the current direction, in an n=3 Icoil configuration can have a dramatic effect on the toroidal plasma rotation. This can provide a tool to explore NTV theory for rotational braking and also to examine the possibility of an n=3 error field. The existence of the latter was suggested by analysis of two discharges, 127741 and 127846 where a best fit to the data required the addition of such a field. |
| Resource Requirements: | 0.5 day run time |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
85: Current driven RWM target discharges for feedback stabilization experiments |
| Name: | Gary Jackson () |
Affiliation: | General Atomics |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | A. Garofalo, E. Strait, M. Okabayashi, Y. In |
| Description: | Develop a reproducible current driven RWM target discharge and then apply Icoil feedback stabilization. |
| Experimental Approach/Plan: | Scan dIp/dt, density, and possibly NB power to obtain a robust RWM target discharge. Apply feedback to stabilize the m/n=4/1 RWM and continue ramping current to obtain a 3/1 RWM |
| Background: | For several years, an important goal of DIII-D RWM research has been to obtain a reproducible RWM discharge to use in feedback stabilization studies. For various reasons this has proved to be a difficult task. In 2007, current driven RWMs were obtained during the current ramp phase of DIII-D. However there was no experimental time to assess how reliable these targets were, or to explore feedback stabilization. |
| Resource Requirements: | 0.5 day run time to develop the RWM target, then 0.5 day to evaluate RWM feedback stabilization |
| Diagnostic Requirements: | SXR profiles to differentiate between the current driven RWM and tearing modes. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
86: Characterization of Turbulence Associated with TEMs |
| Name: | Jim C. DeBoo ( ) |
Affiliation: | General Atomics |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | E. Doyle, T. Rhodes, A. White |
| Description: | The goal of the experiment is to create a plasma where TEMs dominate the turbulent spectrum and then turn TEMs off by reducing the electron temperature gradient scale length, a/LTe, locally. This will allow a clear correlation of measured turbulent spectra associated with TEMs and create a simplified dataset with just one dominant drift wave mode to compare with GYRO and TGLF calculations. |
| Experimental Approach/Plan: | As has been done previously, set up an inside wall limited L-mode discharge at low collisionality. This has been calculated to result in a TEM dominated discharge over much of the plasma. Use the ECH swing technique, where ECH power is alternately deposited at two closely spaced spatial locations in the plasma, to swing the local value of a/LTe above and below the TEM threshold. The experiment must be done at sufficiently low a/Lne in order to increase the TEM growth rate sensitivity to variations in a/LTe. Lower values of a/Lne, may be found toward the plasma center, where smaller gradients exist. Thus a scan in r/a from the plasma midradius to about r/a ~ 0.2 should be done. Other methods to reduce a/Lne should also be explored. |
| Background: | The ECH swing technique was used in an experiment in 2007 in an attempt to turn off TEMs in the plasma at r/a =0.5. While the technique resulted in a factor of 1.8 variation in a/LTe, no clear changes in the measured spectra in the TEM wavenumber range was observed on any of our turbulent diagnostics. Recent calculations using the TGLF code have shown that for the experimental conditions TEMs dominated the drift wave spectra at r/a = 0.5, but reducing a/LTe by a factor of 2 in the code did not change the calculated growth rate significantly, consistant with experimental observations. Additional calculations show that a much greater sensitivity of the growth rate to variations in a/LTe can be obtained at lower values of a/Lne. |
| Resource Requirements: | At least 4 gyrotrons and 2 MW of ECH power |
| Diagnostic Requirements: | Full suite of fluctuation diagnostics |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
87: Impact of Rotation on Incremental Diffusivity in Hybrid Discharges |
| Name: | Jim C. DeBoo () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Study the impact of rotation on the incremental thermal electron diffusivity in Hybrid discharges. |
| Experimental Approach/Plan: | Apply electron heat pulses with modulated ECH to the outer region of the plasma and monitor the heat pulse propagation to the plasma core. Vary the plasma rotation with co/ctr NBI and characterize the impact on the heat pulse propagation. |
| Background: | Past experiments have shown that increased plasma rotation in hybrid plasmas increases the global confinement time and decreases the thermal diffusivity across the whole profile. Studying the impact of rotation on the incremental diffusivity, the change in diffusivity for a given change in temperature gradient, may help in the development of models and will certainly help further constrain any models developed to explain the key physics responsible for the improved transport. |
| Resource Requirements: | At least 2 gyrotrons |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | Will need to develop the capability to simulate the time dependent response of the plasma with say the TGLF transport code or other transport model in order to compare the simulations with measurements. |
| Other Requirements: | -- |
| Title |
88: Plasma rotation with Icoil rotating fields |
| Name: | Gary Jackson () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | F. Volpe |
| Description: | Use rotating magnetic field perturbations (up to 1kHz) to increase toroidal plasma rotation in low NB torque discharges |
| Experimental Approach/Plan: | Using a low NB torque high BetaN discharge with n=1 TM, apply a rotating n=1 field from the Icoils. Vary frequency from 0.2 to 1kHz and observe changes in rotation using CER. Repeat with a low betaN, low torque discharge with no TM |
| Background: | In principle a torque can be applied to a plasma using a rotating magnetic field, analagous to an induction motor. This has been discussed by Garofalo, et. al as the induction motor model. This concept was first applied by Jackson in 2003, but the large neutral beam torque hid any possible effects from the rotating fields produced by the Icoil. More recently, Volpe has had some success by applying rotating Icoil fields to mitigate NTMs. With the advent of the DIII-D counter beams, a plasma with no applied neutral beam torque can be produced and the smaller induced Icoil torque can be evaluated. Since the islands from NTMs can drive current and produce higher torque, both high betaN plasmas (with n=1 TMs) and low betaN plasmas will be evaluated. The former discharges shouldn't be a problem to produce as they plague the RWM discharges at low rotation.
Demonstration of such rotation control could be important for ITER, where methods to increase toroidal rotation for stabilization are being pursued. |
| Resource Requirements: | Need 0.5 run days |
| Diagnostic Requirements: | SXR cameras and ECE to characterize tearing modes. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
89: Higher Beta ELM-Suppressed Hybrids |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Continue RMP ELM control experiments in the ITER shape by controlling the 3/2 NTM amplitude to allow higher normalized beta to be achieved without rotational slowing and mode locking. The 3/2 NTM amplitude can be decreased by either (1) optimizing the error field correction to obtain higher rotation rates, (2) using ECCD at the q=1.5 surface, or (3) trying higher q95 (>4) if a RMP resonant window exists. The goal is to obtain RMP ELM-suppressed hybrids with beta_N~3 (close to the ideal no-wall limit). If naturally dominant 4/3 NTM hybrids can be produced, then the ECCD suppression of the 3/2 NTM is not necessary. The higher q95 cases should work because the coupling between the 3/2 NTM and the wall is weakened as the resonant layer is moved closer to the plasma center. This ELM suppression experiment should first use only co-NBI, but once optimized results are obtained then lower rotation plasmas should be studied using balanced NBI. |
| Experimental Approach/Plan: | (1) Repeat previous best ELM-suppressed hybrid case 129958. (2) Optimize error field correction to obtain highest rotation rates. (3) Use ECCD at q=1.5 surface to reduce and/or eliminate the 3/2 NTM. (4) Determine new beta limit during RMP ELM suppression. (5) Add counter NBI to slow rotation rate such that M<0.1. (6) Steer gyrotrons not needed for NTM control to core deposition to obtain Te=Ti. |
| Background: | Experiments in August 2007 used the I-coil to completely suppress ELMs in high beta hybrids for q95=3.7. If a dominant 4/3 NTM was present, then beta_N up to at least 2.5 could be achieved during the I-coil phase (actual beta limit not known). However, if a 3/2 NTM was present, then for beta_N>2.2 the plasma rotation slowed down rapidly during the I-coil phase and a locked mode terminated the hybrid discharge. |
| Resource Requirements: | NBI: All 7 sources are required.
EC: Minimum of 3 gyrotrons, prefer to have 5 gyrotrons. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | I-coil required. |
| Title |
90: RMP ELM-Suppression With Higher Confinement |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Increase the H-mode confinement factor to H_89P>2 during RMP ELM-suppression by adopting a standard AT plasma shape with a high pedestal stability limit. Use only the minimum amount of I-coil current to decrease the pedestal pressure below the peeling-ballooning stability limit. Use a PCS feedback-controlled hybrid scenario as the target plasma with q95=3.7 and beta_N>2.5. |
| Experimental Approach/Plan: | Similar experimental plan as 2007-02-04, but use the standard hybrid shape and the standard hybrid ramp up. May need to use ECCD at the q=1.5 surface to control the size of the 3/2 NTM at high beta (beta_N>2.2). |
| Background: | Revisit RMP ELM control in the standard AT shape to obtain higher pedestal height, and therefore higher H-mode confinement factors. Want to demonstrate ELM suppression with H_89P>2 at high beta. |
| Resource Requirements: | NBI: Require all 5 co sources.
ECH: Minimum 3 gyrotrons. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
91: Hybrid Beta Limit at Low Rotation |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine the beta limit (most likely due to the onset of a 2/1 mode) for low rotation hybrid plasmas. Compare the beta limit to the ideal no-wall limit, and to the limit in rapidly rotating plasmas. First study q95=4.2, and if time permits study q95=3 and q95=5 as well. |
| Experimental Approach/Plan: | (1) Establish hybrid plasma with q95=4.2 using PCS feedback control of beta_N and rotation. (2) Use counter NBI to reduce rotation rate to minimal value. (3) Program a slow ramp up in beta_N to determine the stability limit (likely limit is onset of 2/1 mode). (4) Repeat beta_N ramp using only co-NBI. (5) If time permits, repeat at q95=3 and q95=5. |
| Background: | The bulk of hybrid study on DIII-D has been with co-NBI, producing rapid plasma rotation. For q95~4, the beta limit appears to coincide with the ideal no-wall stability limit. At q95~3, the beta limit is about 80% of the ideal no-wall limit. At q95~5, some hybrid plasmas have exceeded the ideal no-wall limit (probably owing to rotational stabilization). However, it is expect that in future larger devices like ITER the normalized rotation rates will be much smaller. Experiments in standard H-mode plasmas indicate that the beta limit decreases at lower rotation. Therefore, we need to measure the beta limits for low rotation hybrid plasmas at different q95 as part of our validation of this scenario for ITER. |
| Resource Requirements: | NBI: All 7 sources are required. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
92: External n=3 RMP for ITER ELM Control Tests |
| Name: | Max E. Fenstermacher ( ) |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | M.E. Fenstermacher |
| Description: | Use the C-coil configured for n=3 up to the maximum current capability to explore whether an external, single midplane row coil can suppress ELMs. |
| Experimental Approach/Plan: | Apply a high current, n=3 RMP from the C-coil to the same ITER Similar Shape plasma at the ITER collisionality and resonant q95=3.6 used for n=3 I-coil RMP ELM suppression experiments. Use the Icoil for optimum error field correction. If ELM suppression obtained, do C-Coil current scan to determine minimum required C-coil current for suppression. If suppression not obtained, do q95 scan at maximum C-coil current to look for resonance window. Include a power scan to determine if the C-coil perturbation changes the L-H power threshold. |
| Background: | The current decision by the ITER team is to explore the possibility of installing coils for ELM suppression in up to 14 of the 18 ITER port plugs on the outer midplane. Calculations have been done to estimate the required current to achieve Chirikov parameter greater than 1 into the same location (PsiN=0.85) as in successful DIII-D ELM suppression experiments with the n=3 I-coil. But no single row RMP experiment has obtained ELM suppression to date. When a combination of n=1 and n=3 was use with the C-coil previously (experiments by Evans) ELM suppression was not obtained and the L-H power threshold increased by a large factor (like 3 or more). We now have more current capability in the C-coil and we need to try one more time for ELM suppression with an external, single midplane row RMP coil. |
| Resource Requirements: | Same resources as used for 2007 ISS ELM control experiments, see for example shot 128374 etc. C-coil maximum current, I-coil for optimum error field correction, 5 co-beams. |
| Diagnostic Requirements: | All pedestal and lower divertor diagnostics, fast lower divertor IRTV would be highly desirable. |
| Analysis Requirements: | Control room island overlap analysis with SURFMN. If ELM suppression seen, post experiment field line trajectory analysis with TRIP3D and other 3D modeling. |
| Other Requirements: | -- |
| Title |
93: Single Internal Row n=3 RMP for ELM Control |
| Name: | Max E. Fenstermacher () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | M.E. Fenstermacher |
| Description: | Use single toroidal rows of the I-coil (upper and lower separately) configured for n=3 up to the maximum current capability to explore whether a nearby internal, single row coil can suppress ELMs. |
| Experimental Approach/Plan: | Apply a high current, n=3 RMP from the I-coil to the same ITER Similar Shape plasma at the ITER collisionality and resonant q95=3.6 used for dual row n=3 I-coil RMP ELM suppression experiments. Use the C-coil for optimum error field correction and possibly additional n=1 fields to fill-in the island spectrum. If ELM suppression obtained, do I-Coil current scan to determine minimum required I-coil current for suppression using a single row. If suppression not obtained, do q95 scan at maximum I-coil current to look for resonance window. |
| Background: | The current decision by the ITER team is to explore the possibility of installing coils for ELM suppression in up to 14 of the 18 ITER port plugs on the outer midplane. Calculations have been done to estimate the required current to achieve Chirikov parameter greater than 1 into the same location (PsiN=0.85) as in successful DIII-D ELM suppression experiments with the n=3 I-coil. But no single row RMP experiment has obtained ELM suppression to date. Duing the dual row I-coil RMP ELM control experiments there were a few instances in which one of the rows did not come on (eg. 123300). The ELMs in these cases were changed but not suppressed. These cases were not in the ISS, nor at the maximum I-coil current capability or optimum plasma conditions. |
| Resource Requirements: | Same resources as used for 2007 ISS ELM control experiments, see for example shot 128374 etc. I-coil maximum current with C_suplies, C-coil for optimum error field correction, 5 co-beams. |
| Diagnostic Requirements: | All pedestal and lower divertor diagnostics. Fast divertor IRTV would be highly desireable. |
| Analysis Requirements: | Control room island overlap analysis with SURFMN. If ELM suppression seen, post experiment field line trajectory analysis with TRIP3D and other 3D modeling. |
| Other Requirements: | -- |
| Title |
94: Physics of Safety Factor Resonance for n=3 RMP ELM Suppression |
| Name: | Max E. Fenstermacher () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | M.E. Fenstermacher |
| Description: | Expand scope of physics studies of the safety factor resonance window for ELM suppression with the n=3 I-coils. |
| Experimental Approach/Plan: | Perform a very systematic study of the physics determining the resonance window for n=3 ELM suppression with the I-coils. Scan plasma current up at fixed BT to produce a q95 down ramp from 4.2 to 3.2. Also scan Ip down to produce a q95 up ramp from 3.2 to 4.2 to look for differences due to build-up of edge current due to the Ip ramps. Change Ip ramp rate to look for differences in build-up of edge current. Do shot to shot fine q95 scan at edge of resonance window to eliminate the possibility of Ip ramps affecting the edge current. Carefully monitor edge plasma profiles (small wags and jogs for high resolution profiles) to determine if profiles remain the same during q ramps, ie. if window for suppression is due to something besides changes in pressure profile, vis. current transport (Snyder idea). |
| Background: | There is evidence from previous RMP ELM control experiments (see 128470, 472, 473, 474) that the physics that controls the density pumpout and therefore the significant changes to the edge pressure profile when the RMP is applied, may be less sensitive to a resonance window in edge safety factor than ELM suppression itself. Density pumpout is seen even for q95 far outside (q95=4.2) the resonance window for ELM suppression (q95=3.6 +- 0.1). Physics understanding here should go a long way toward ideas to expand the safety factor window for ELM suppression with new coil designs. |
| Resource Requirements: | Same resources as used for 2007 ISS ELM control experiments, see for example shot 128374 etc. I-coil maximum current with C_suplies, C-coil for optimum error field correction, 5 co-beams. |
| Diagnostic Requirements: | All pedestal and lower divertor diagnostics. Edge current measurements (especially simultaneously) with the Li-beam and co- plus counter-beam MSE would be highly desirable as would fast divertor IRTV. |
| Analysis Requirements: | All pedestal and lower divertor diagnostics. Edge current measurements (especially simultaneously) with the Li-beam and co- plus counter-beam MSE would be highly desirable as would fast divertor IRTV. |
| Other Requirements: | -- |
| Title |
95: RMP Effect on Location of P-B Stability Boundary |
| Name: | Max E. Fenstermacher () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | M.E. Fenstermacher |
| Description: | Test possibility that n=3 RMP from I-coil can change the location of the stability boundary in P-B alpha-J space without affecting any change on the edge pedestal plasma profiles (Leonard idea). |
| Experimental Approach/Plan: | Use slowly oscillating I-coil current (as suggested by Wade - vis 50 Hz, +- 1 kA about centroid of 4 kA, ala shot 129208 in Moyer experiment in 2007) to vary the RMP within a plasma with fixed pedestal profiles. Apply this technique to the ELM suppressed phase of a standard ISS ELM suppression scenario. Since the effective particle confinement time in the ELM suppressed pedestal is about 250 ms, this oscillation should not produce any variation in the pedestal density or pressure, but will produce a variation in perturbed magnetic field strength in the pedestal. If there is an effect on the ELM suppression then this will suggest that the RMP changes the location of the stability boundary in P-B space. If changes seen in edge plasma profiles, try different oscillation frequencies (ie. probably higher up to allowable hardware limit). |
| Background: | This is a reminder to follow-up on the one interesting shot run in 2007 using this technique. Whether or not the RMP affects the location of the stability boundary in P-B alpha-J space is a critical question for our interpretation of the mechanism for RMP ELM suppression. Understanding in this are might geneate ideas for RMP ELM suppression at higher pedestal parameters than currently obtained. |
| Resource Requirements: | Same resources as used for 2007 ISS ELM control experiments, see for example shot 128374 etc. I-coil maximum current with C_supplies with capability for slow oscillation at intermediate currents, C-coil for optimum error field correction, 5 co-beams. |
| Diagnostic Requirements: | All pedestal and lower divertor diagnostics. Edge current measurements (especially simultaneously) with the Li-beam and co- plus counter-beam MSE would be highly desirable as would fast divertor IRTV. |
| Analysis Requirements: | Control room island overlap analysis with SURFMN. Post experiment kinetic EFIT analysis including edge current measurements, field line trajectory analysis with TRIP3D and other 3D modeling. |
| Other Requirements: | -- |
| Title |
96: Determine Adiabatic Electron Response for High-n Modes in QH Plasmas |
| Name: | Raffi Nazikian () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Energetic Particles |
Presentation time: |
Requested |
Co-Author(s): | G.J. Kramer, N.N. Gorelenkov, M. VanZeeland, G. Fu, W.W. Heidbrink |
| Description: | Long Pulse QH mode plasmas will be produced (ref. 128530) in order to obtain a long time evolution of the central safety factor. High-n RSAEs will be generated with a large range of poloidal wavenumbers over the range of qmin obtained. Radial scans of the upgraded BES radial array with ECE measurements will be obtained. The radial eigenmode structure of the high-n modes and the ratio of electron temperature to density fluctuations will be determined across the mode radial width. |
| Experimental Approach/Plan: | Current in the reverse Ip direction will be generated to obtain the conventional QH mode at high toroidal field (2.0T). Low density will be obtained for ECE measurements. BES radial array measurements will be taken in a scan from the edge to the core. |
| Background: | A PRL was published by Nazikian in 2006 on the thermal excitation of high-n RSAEs in DIII-D. Even at this time it was evident that the mode structure may not conform to ideal MHD expectations. More recent studies indicate that there is a major discrepancy between ideal MHD and the measured mode structure. The observations on DIII-D for both Te and ne can contribute fundamental new information on the adiabatic nature of the electrons in these high-n modes and on the role of compression over displacement in the mode characterization. |
| Resource Requirements: | QH mode plasma needed. One reproducible discharge required. |
| Diagnostic Requirements: | BES, ECE, ... |
| Analysis Requirements: | NOVAK, M3D, TRANSP, |
| Other Requirements: | -- |
| Title |
97: Operational implementation of model-based shape control (MIMO) |
| Name: | Michael Walker ( ) |
Affiliation: | General Atomics |
| Research Area: | Model based Control |
Presentation time: |
Requested |
Co-Author(s): | D.A.Humphreys, J.A.Leuer |
| Description: | The purpose of this experiment is to test revised versions of multivariable shape controllers on DIII-D, test algorithms that support the use of such controllers, and study the resulting effects of such controllers on shape and stability control. This work is a continuation of the testing of implementation of components of the combined inner loop, outer loop, and feedforward control approach which was begun following the first implementation of a MIMO (multiple-input-multiple-output, but here used to also refer to model-based design) controller in 1999. The long term objectives of this work are to provide integrated control capability for AT operation, to ensure robust stability (including reducing plasma oscillations), obtain more precise shape control, deal effectively and systematically with control limitation problems such as coil current sharing/fighting, coil current limits in high performance discharges, and VFI bus voltage limitations on control, and to provide methods for reducing shape development time. |
| Experimental Approach/Plan: | We propose to use a small number of dedicated 2-hour experiments, plus several piggyback experiments to complete the implementation and test the multivariable controllers that support all patch panels for LSN, USN, and DND plasmas. A final half-day experiment would be used to perform a systematic evaluation of the capabilities of such controllers. |
| Background: | Design of multivariable linear controllers requires a sufficiently good model of the plant response. Over the last several years, detailed models of DIII-D coils, vessel, power supplies, and plasma response have been developed and validated. These models have been used both in designing linear controllers and constructing simulation tools for testing of the controllers. A controller developed using these tools was first successfully tested experimentally in 1999. A more sophisticated version, which dealt with nonlinear limitations such as coil current limits and the conflict between vertical and shape control algorithms, was successfully tested experimentally in 2005 and 2006 on LSN and USN plasmas respectively. The extension of this algorithm to DND plasmas and to one particular DND configuration (nearly complete), which was known to be difficult to control, was performed during 2007. The two-hour blocks used to test the multiple required algorithm upgrades were essential to debug hardware and software problems; many problems appeared only during operational use, not in simulation. A new PCS test bed, which duplicates a portion of the PCS hardware for testing purposes, is expected to substantially reduce the number of problems discovered only during operation, which should significantly reduce the requirement for dedicated experimental testing time and remove much of the risk of hosting a piggyback experimental test. |
| Resource Requirements: | |
| Diagnostic Requirements: | Fast magnetics data acquisition desirable for piggybacks, necessary for dedicated exp.
Essential diagnostics 2 kHz magnetics desirable during piggyback test intervals, 5 kHz magnetics required during dedicated experimental time; voltage (fault system) diagnostics;
Power supply fault data, PCS data acquired at maximum rate for a portion of discharge.
Highly desirable diagnostics Thomson (multipulse core, divertor), tile current array, SPRED, MDS, MSE, fast SXR, vessel motion diagnostic, Vert./Horiz. ECE, CER, Zeff, Bolometers, interferometry. |
| Analysis Requirements: | -- |
| Other Requirements: | The PCS test bed system needs to remain working and representative of the DIII-D PCS during all of operations. |
| Title |
98: Ion response to Te heat pulses |
| Name: | Jim C. DeBoo () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Improve understanding of ion thermal transport by studying the parametric dependence of the Ti response to Te heat pulses from modulated ECH power in L-mode discharges. |
| Experimental Approach/Plan: | Apply modulated ECH power to an MHD-quiet, sawtooth-free, L-mode discharge with the ECH resonant off axis, rho ~ 0.7. Monitor the perturbed ion response to the electron heat pulses with CER. Vary the source strength and coupling conditions to gain insight on the key physics responsible for the ion response. Is the ion response stiff and thus independent of the drive amplitude? Scans could include ECH power to see if the ion response is linear in that driving term, collisionality (density scan to where TEMs are stable) to test if response is tied to TEM activity, and L_Ti (P_nbi scan) and Te/Ti (vary ratio of P_ech to P_nbi)to vary ITG stability. Discussions should be held to determine the best set of parameters to vary in a systematic way to achieve the goal. |
| Background: | Many previous modulated ECH experiments have displayed an ion response to electron heat pulses that can not be explained by simple ion-electron collisional coupling. In the past the electron behavior was always the focus of the experiments. This experiment is meant to focus on the ion response and the key physics responsible for the ion response. |
| Resource Requirements: | at least 4 gyrotrons |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
99: Establishment of a database for EMC3/EIRENE benchmark and direct comparison to TEXTOR (1) |
| Name: | Oliver Schmitz ( ) |
Affiliation: | FZ Juelich |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Heinke Frerichs (FZ Juelich), Marcin Jakubowski (MPI Greifswald), Bernhard Unterberg (FZ Juelich), Todd Evans (GA), Max Fenstermacher (LLNL), Ilon Joseph (UCSD), Rick Moyer (UCSD), Detlev Reiter (FZ Juelich) |
| Description: | For the analysis of energy and particle transport the fully 3D Monte-Carlo code EMC3/EIRENE is under adaptation to work for poloidally diverted tokamak geometries. The aim is to resolve the role of open, perturbed magnetic field lines for the transport changes and the pedestal pressure drop in RMP ELM control experiments. Hereto, since November 2006, a consistent experimental and theoretical approach is under execution in the frame of an IAE collaborative agreement between DIII-D and TEXTOR and an accompanying ITPA task (PEP-19) on collaborative experiments. The EMC3/EIRENE code is together with magnetic modelling tools the binding element between the experiments and it plays a key role for the comparison of the results. As so far this code was applied only in stellarator symmetry and in circular TEXTOR plasmas with non- axis symmetric perturbation, the code need to be adapted and improved for proper transport analysis at DIII-D in a poloidally diverted configuration. The aim of this experimental proposal is to establish a coherent data base to benchmark the code on the one hand and to tackle simultaneously generic physical questions during this benchmark shots on the other hand. This proposal is part of a coherent benchmark and analysis plan. Another proposal is submitted under TF ELM control. Both contain the complete list of shots to be performed creating a good benchmark data base on the one hand and simultaneously tackling basic physical issues. |
| Experimental Approach/Plan: | We intend to go from L-mode and H-mode plasmas in the limiter configuration - which will be compared to accompanying discharges at TEXTOR-DED - to the poloidally diverted configuration. Here also L-mode discharges will be the start point to be able finally tackling the poloidally diverted ELM suppressed H-mode discharges as ultimate target of analysis.
For best understanding we would like to do these different discharges each with toroidal mode number (in order of priority) n=3, n=2 and n=1. The n=2 configuration is also available at TEXTOR-DED and a prominent example for comparison to the JET results. Also to gain information on the collisionality on the transport and the description by the code (e.g. fluid limits in the conductive heat transport) we will do each discharge for low and for high collisionality.
We will rely for the design of each discharge on the best settings from the RMP experience at DIII-D. For those discharges not done for longer time (limiter L-mode, but with tiny beam for CER) we need some development.
In summary we will need the following set of discharges for both, low and high collisionality:
- limiter L-mode (n=3,2,1 each with reference as different error field (EF) situation)
- limiter H-mode (n=3,2,1 each with reference as different EF situation)
- divertor L-mode (n=3,2,1 each with reference as different EF situation)
- divertor L-mode, repeat shots with different filter settings on cameras -> get electron parameters from line ratios and impurity behaviour
- sweeps in divertor L-mode for enhancement of diagnostic coverage (e.g. LP on target) (n=3,2,1 each with reference as different EF situation)
- divertor H-mode (samples as good data base is existing, we intend to have corresponding samples to shots defined above for L-mode)
This would be the ideal set of discharges. However, the base mode numbers are mentioned in order of priority and it is more important to have one complete scan for one base mode than having single shots for different base modes.
For this task force especially the no-RMP discharges will contribute from the experimental point and also the shots with good diagnostic coverage can shed light to the particle and heat flux redistribution in the divertor. The EMC3/EIRENE modell is capabel to describe and study that. |
| Background: | The proposal described here is embedded in the ITPA inter machine experiments for investigation on the impact on RMP on particle and heat transport and the extrapolation towards ITER. It has three major topics which are combined in the establishment of a comprehensive database for the EMC3/EIRENE code benchmark after the adaptation is finished. The set of discharges described enables us to check the adapted version for general consistency (properly implemented poloidally diverted field aligned grid) and also to resolve the adaptations needed for the transport description. So far the anomalous perpendicular transport is described in EMC3/EIRENE as one input parameter in the whole radial modelling domain. There shall be the need to improve this and replace this radial constant by a radial function. In addition the discharges suggested allow analysis not done so far in particular in comparison to TEXTOR-DED. The role of the open, perturbed field lines in the magnetic flux loss region was elaborated here and it was shown that short field lines connecting to the wall are of dominant impact for the static and turbulent transport processes. This shall be resolved for DIII-D with these experiments as we will perform discharges in limiter configuration comparable to TEXTOR-DED and do a correspondent analysis on this topic for L-mode and H-mode discharges with RMP of different base modes. The experimental data will be compared to the magnetic topology modelled with the TRIP-3D code and eventually the transport is analyzed with the adapted EMC3/EIRENE code. During this procedure and based on this comprehensive database, the code shall be improved for a detailed analysis of the ELM suppression mechanism on both machines and for prediction to ITER. |
| Resource Requirements: | Limiter L- and H-mode plasmas, both with CER beam box, else are standard RMP requirements |
| Diagnostic Requirements: | standard RMP, in particular good CCD camera coverage (DiMES TV and tangential divertor TV systems), good IR camera coverage, fast probe operation, CER beam box, target Langmuir probes, pressure gauges, full Thomson scattering availability
In the frame of this proposal the mounting of a nozzle for parasitic He injection for beam emission spectroscopy (BES) is suggested. A low and non-disturbing flux of about 0.5e18 He atom s-1, is needed to obtain the line emission of three He lines. They are compared to a collisional radiative model of the related transitions and the electron density and temperature can be obtained with high radial and depending on the DAQ with high time resolution also. The technique itself was developed in FZ Juelich and is at TEXTOR-DED a reliable method to get these electron parameters in most of all TEXTOR discharges. The hardware equipment as well as the CRM needed for the evaluation and the experienced manpower to perform this task would be provided. |
| Analysis Requirements: | standard RMP requirements, kinetic EFIT runs for good equilibrium data for magnetic modelling and field aligned grid production, 2D transport analysis with the [onetwo code] or results from the [SOLPS5/EIRENE] effort started recently to get good input for the anomalous diffusion coefficients and ideas about the radial function of these input parameters |
| Other Requirements: | -- |
| Title |
100: Establishment of a database for EMC3/EIRENE benchmark and direct comparison to TEXTOR (2) |
| Name: | Oliver Schmitz () |
Affiliation: | FZ Juelich |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | Heinke Frerichs (FZ Juelich), Marcin Jakubowski (MPI Greifswald), Bernhard Unterberg (FZ Juelich), Todd Evans (GA), Max Fenstermacher (LLNL), Ilon Joseph (UCSD), Rick Moyer (UCSD), Detlev Reiter (FZ Juelich) |
| Description: | For the analysis of energy and particle transport the fully 3D Monte-Carlo code EMC3/EIRENE is under adaptation to work for poloidally diverted tokamak geometries. The aim is to resolve the role of open, perturbed magnetic field lines for the transport changes and the pedestal pressure drop in RMP ELM control experiments. Hereto, since November 2006, a consistent experimental and theoretical approach is under execution in the frame of an IAE collaborative agreement between DIII-D and TEXTOR and an accompanying ITPA task (PEP-19) on collaborative experiments. The EMC3/EIRENE code is together with magnetic modelling tools the binding element between the experiments and it plays a key role for the comparison of the results. As so far this code was applied only in stellarator symmetry and in circular TEXTOR plasmas with non- axis symmetric perturbation, the code need to be adapted and improved for proper transport analysis at DIII-D in a poloidally diverted configuration. The aim of this experimental proposal is to establish a coherent data base to benchmark the code on the one hand and to tackle simultaneously generic physical questions during this benchmark shots on the other hand.
This proposal was also submitted to the Thermal transport working group (ID 99). It is a coherent plan tackling basic physical question and simultaneously collecting well documented shots for EMC3/EIRENE benachmark. |
| Experimental Approach/Plan: | We intend to go from L-mode and H-mode plasmas in the limiter configuration - which will be compared to accompanying discharges at TEXTOR-DED - to the poloidally diverted configuration. Here also L-mode discharges will be the start point to be able finally tackling the poloidally diverted ELM suppressed H-mode discharges as ultimate target of analysis.
For best understanding we would like to do these different discharges each with toroidal mode number (in order of priority) n=3, n=2 and n=1. The latter ones are also available at TEXTOR-DED and a prominent example for comparison to the JET results. Also to gain information on the collisionality on the transport and the description by the code (e.g. fluid limits in the conductive heat transport) we will do each discharge for low and for high collisionality.
We will rely for the design of each discharge on the best settings from the RMP experience at DIII-D. For those discharges not done for longer time (limiter L-mode, but with tiny beam for CER) we need some development.
In summary we will need the following set of discharges for both, low and high collisionality:
- limiter L-mode (n=2,3,1 each with reference as different EF situation)
- limiter H-mode (n=2,3,1 each with reference as different EF situation)
- divertor L-mode (n=2,3,1 each with reference as different EF situation)
- divertor L-mode, repeat shots with different filter settings on cameras -> get electron parameters from line ratios and impurity behaviour
- sweeps in divertor L-mode for enhancement of diagnostic coverage (e.g. LP on target) (n=2,3,1 each with reference as different EF situation)
- divertor H-mode (samples as good data base is existing, we intend to have corresponding samples to shots defined above for L-mode)
All RMP shots, in particular the ones optimized for good diagnostic coverage belong to part (2) of the complete proposal. Please see proposal ID 294 by R. Moyer also. |
| Background: | The proposal described here is embedded in the ITPA inter machine experiments for investigation on the impact on RMP on particle and heat transport and the extrapolation towards ITER. It has three major topics which are combined in the establishment of a comprehensive database for the EMC3/EIRENE code benchmark after the adaptation is finished. The set of discharges described enables us to check the adapted version for general consistency (properly implemented poloidally diverted field aligned grid) and also to resolve the adaptations needed for the transport description. So far the anomalous perpendicular transport is described in EMC3/EIRENE as one input parameter in the whole radial modelling domain. There shall be the need to improve this and replace this radial constant by a radial function. In addition the discharges suggested allow analysis not done so far in particular in comparison to TEXTOR-DED. The role of the open, perturbed field lines in the magnetic flux loss region was elaborated here and it was shown that short field lines connecting to the wall are of dominant impact for the static and turbulent transport processes. This shall be resolved for DIII-D with these experiments as we will perform discharges in limiter configuration comparable to TEXTOR-DED and do a correspondent analysis on this topic for L-mode and H-mode discharges with RMP of different base modes. The experimental data will be compared to the magnetic topology modelled with the TRIP-3D code and eventually the transport is analyzed with the adapted EMC3/EIRENE code. During this procedure and based on this comprehensive database, the code shall be improved for a detailed analysis of the ELM suppression mechanism on both machines and for prediction to ITER. |
| Resource Requirements: | Limiter L- and H-mode plasmas, both with CER beam box, else are standard RMP requirements |
| Diagnostic Requirements: | standard RMP, in particular good CCD camera coverage (DiMES TV and tangential divertor TV systems), good IR camera coverage, fast probe operation, CER beam box, target Langmuir probes, pressure gauges, full Thomson scattering availability
In the frame of this proposal the mounting of a nozzle for parasitic He injection for beam emission spectroscopy (BES) is suggested. A low and non-disturbing flux of about 0.5e18 He atom s-1, is needed to obtain the line emission of three He lines. They are compared to a collisional radiative model of the related transitions and the electron density and temperature can be obtained with high radial and depending on the DAQ with high time resolution also. The technique itself was developed in FZ Juelich and is at TEXTOR-DED a reliable method to get these electron parameters in most of all TEXTOR discharges. The hardware equipment as well as the CRM needed for the evaluation and the experienced manpower to perform this task would be provided. |
| Analysis Requirements: | standard RMP requirements, kinetic EFIT runs for good equilibrium data for magnetic modelling and field aligned grid production, 2D transport analysis with the [onetwo code] or results from the [SOLPS5/EIRENE] effort started recently to get good input for the anomalous diffusion coefficients and ideas about the radial function of these input parameters |
| Other Requirements: | -- |
| Title |
101: Measurements of Neutral Beam Excited State Lifetime |
| Name: | George R. McKee ( ) |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | M. Shafer, D. Schlossberg |
| Description: | Indirectly measure the effective lifetime in plasma of the n=3 excited state of beam atoms as a function of density. This is to provide necessary atomic physics information to assist with calculations of the spatial spot size for beam emission spectroscopy measurements. This information will feed into calculations of measured turbulence characteristics (wavenumber spectra, amplitudes) and point-spread-functions/spatial transfer functions for use in synthetic diagnostics for simulation comparisons. |
| Experimental Approach/Plan: | Run low power, high field, low-temperature L-mode plasmas and measure the turbulence eddy structure with the 2D configuration of BES. Locate the BES array at the radial position with best optical resolution (near r/a=0.75), and at a safety factor profile that most closely aligns the local pitch angle with the sightline angle. Minimize the turbulence structure size, which has been shown to be proportional to ion gyroradius size, requiring low ion temperature and high field. Vary the 150L neutral beam acceleration voltage over as wide a range as feasible (e.g, 45-85 keV) and then separately vary the density over as wide a range as feasible, while maintaining the ion temperature (and gyroradius) nearly constant (power/density scan), staying in L-mode throughout. The goal is to minimize the turbulence structure size and optimize spatial resolution so that these so-called "beam smearing" effects will be most accute.
Measure turbulence radial (and poloidal) correlation lengths as a function of beam voltage (velocity) and density. Radial correlation length is of key importance here. The excited state lifetime will affect the measured radial correlation and variation should be discernible over the range tested. Basically, the variation of the radial correlations will be related to a spatial smearing that arises from the finite lifetime effects of the beam atoms. |
| Background: | The spatial resolution of BES plays an important role in the wavenumber sensitivity of the diagnostic and for discerning spatial characteristics of turbulence. This resolution is calculated from viewing optics, neutral beam geometry, magnetic field pitch angle as well as on the finite lifetime of the excited state atoms in the n=3 state (BES views emission from the n=3-2 D-alpha transition). This natural (in vacuum) excited state lifetime is about tau_l=10 ns, but this is significantly reduced to an effective lifetime of tau = 2-5 ns in a plasma as a result of collisional excitation/ionization processes [I. Hutchinson, PPCF (2002), fig. 2(c)]. This lifetime is calculated from theoretical atomic physics excitation rate calculations and therefore subject to uncertainties in those calculations. An 80 keV Deuterium beam atom has a line-of-sight velocity of v_b=2.8x10^6 m/s, so the spatial spread from from this finite lifetime is about L=v_b * tau=1 cm., comparable to the optical resolution and turbulence correlation lengths, so has a non-negligible impact on the effective spatial resolution of the diagnostic.
There is a sense from the turbulence imaging measurements obtained with BES that the actual spatial resolution is better than that calculated using these theoretical rates. One possible explanation is that the effective lifetimes are shorter than calculated. Given the importance of these lifetime for calculating the effective point spread function (spatial transfer function), for use in unfolding the turbulence characteristics and performing experimental validation of simulation codes via synthetic diagnostics, an experimental test is warranted. |
| Resource Requirements: | 150LT neutral beam and the 30/330L neutral beams; USN or IWL plasma |
| Diagnostic Requirements: | BES, CER, correlation reflectometry |
| Analysis Requirements: | BES and CR spatial correlation turbulence analysis |
| Other Requirements: | -- |
| Title |
102: Collisional damping of zonal flows/GAMs |
| Name: | George R. McKee () |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | D. Schlossberg, M. Shafer, K. Burrell, C. Holland, G. Tynan, L. Schmitz, A. White |
| Description: | Vary collisionality while examining zonal flow/GAM characteristics (amplitude, structure, etc.) to test expectations for ZF/GAM damping physics. |
| Experimental Approach/Plan: | Run plasmas were zonal flow/GAM (geodesic acoustic mode) features have been observed (moderate power, USN L-mode conditions) and vary the collisionality by adjusting the density and temperature, while maintaining profiles of other relevant dimensionless parameters approximately constant. The upper divertor pumps will be used to control density as much as possible. A combination of gas puffing, pumping, neutral beam power and ECH will be used to adjust density-temperature to vary the collisionality.
BES is being expanded and reconfigured during this coming 2008 run-period to allow for wider field and greater poloidal-extent measurements. This new capability will be especially valuable for these studies of zonal flows, which are predicted to be m=0 structures. It will allow for greater confidence in identifying the poloidal structure of these flows. |
| Background: | Zonal flows (including GAMs) are expected to be collisionally damped by ion-ion collisions. This is founded in the theoretical understanding of zonal flows and has been borne out in simulations. Damping of zonal flows can in turn reduce zonal flow shearing, resulting in higher turbulence and associated transport levels. GAMs have been robustly observed near the outer regions of L-mode discharges on DIII-D using the multipoint BES system, and recent measurements with the upgraded, high-sensitivity BES show features of the lower-frequency residual, or Zero-Mean-Frequency zonal flow deeper in the core. Thus we have the diagnostic capability to examine zonal flows and their characteristics. Experimental determination of the role of collisionality on zonal flows will help validate turbulence models and thereby increase our overall physics understanding as well as predictive capability.
This data set would allow simultaneous measurement of zonal flows/GAMs as well as the ambient turbulence as a function of collisionality. Simulations of these plasmas with GYRO and a comparison of the resulting turbulence/zonal flow characteristics with measurements will help challenge and validate the code.
An added benefit to this experiment will be to obtain measurements of general turbulence characteristics as a function of collisionality, thus continuing a program of nondimensional scaling of turbulence characteristics. |
| Resource Requirements: | Most NB sources |
| Diagnostic Requirements: | All fluctuation and profile diagnostics,esp. BES, Doppler reflectometer, CECE |
| Analysis Requirements: | Fluctuation/TDE analysis |
| Other Requirements: | -- |
| Title |
103: Turbulence and Transport dependence on Mach number in Hybrid discharges |
| Name: | George R. McKee () |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | C. Petty, T. Rhodes, D. Schlossberg. L. Schmitz, M. Shafer |
| Description: | Perform a Mach number scan (M=v_tor/c_s) in hybrid discharges using the co/counter neutral beam capability and measure turbulence characteristics along with transport variation. BES turbulence measurements, of particular interest for this experiment, could not be obtained during a previous similar experiment due to a shutter problem. |
| Experimental Approach/Plan: | Hybrid discharges very similar to those already developed by C. Petty et al. would be used, with the exception that the neutral beams used for beta feedback will need to be changed to allow for the BES measurements (which require the 150 left beam on steady). Other co and counter beams will be used in feedback to maintain beta and rotation. Similar discharges with modulated 30/330 beams required CER/MSE data will also be performed (150 likely in feedback mode). |
| Background: | Transport in Hybrid scenario discharges has been shown to depend sensitively on the toroidal Mach number (M = v_tor /c_s). By varying the injected neutral beam torque into hybrid plasmas and simultaneously maintaining beta constant via feedback control, it has been demonstrated that the "H-factor" decreases by approximately 20% as the Mach number is reduced from about M=0.5 to M=0.1 (Luce, IAEA-2006). This has been shown to be consistent with a reduction in ExB shearing at lower Mach number from GLF23 modeling. Previous measurements of turbulence characteristics in hybrid discharges with the upgraded BES diagnostic, showed that turbulent eddies exhibit a strongly tilted structure in these plasmas. This is in sharp contrast to the more radially-poloidally symmetric eddy structure typically observed in the core of L-mode discharges. The direction of this tilted eddy structure is consistent with the ExB shear flow in these plasmas, although it was questionable as to whether the shear magnitude could bring about such a strong tilt or shear.
An experiment to systematically study turbulent eddy structure as a function of Mach number in hybrid discharges could help address these issues by directly measuring eddy structure, magnitude, decorrelation rates, and radial & poloidal correlation lengths, in these hybrid discharges with the recently expanded upgraded BES system and the Doppler reflectometer system. The long-duration, stationary hybrid discharges make these an excellent platform in which to study the turbulence characteristics. The low-amplitude of fluctuations in the core of hybrid plasmas makes their study more difficult, but the stationary discharges (several seconds) allow for ensemble-averaging of the characteristics with good resulting signal-to-noise. This will allow us to examine the improved transport in hybrid discharges, and specifically the Mach number dependence, as well as to more broadly and generally examine the ExB shear effects on turbulence and transport. |
| Resource Requirements: | All 7 neutral beam sources |
| Diagnostic Requirements: | BES, Doppler Reflectometry, FIR |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
104: Excitation of the Geodesic Acoustic Mode via Radial Field Oscillation |
| Name: | George R. McKee () |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | G. McKee, A. Garofalo, C. Holland, G. Jackson, M. Shafer, D. Schlossberg |
| Description: | Attempt to perturb, excite and amplify the Geodesic Acoustic Mode, a coherent electrostatic zonal flow oscillation, using the high-frequency capability of the I-Coils. Measure the turbulence and GAM response to this radial field perturbation. |
| Experimental Approach/Plan: | Establish plasma conditions were the GAM has been observed: USN plasmas at moderate power (1-2 sources, co-injected, including 150L (steady) and 30L and 330L modulated out of phase). q-scaling experiments indicate that the GAM oscillation is stronger in higher q-discharges, so pick a higher q95 condition, e.g., Ip=1.0 MA, B_t=2.0 MA (119526). The I-Coil would be setup in an n=0, m=1 configuration (upper and lower coils 180 out of phase) and run near 15 kHz (SPAs operate at up to 40-100 kHz, so this should is feasible). The SPAs/I-Coils can operate at up to 250A (estimated by Gary Jackson) at 15 kHz. Radial field estimates can be made in the future.
Establish basic plasma condition and benchmark GAM parameters with radial scan of BES. Turn on I-Coil in above configuration at near 15 kHz, the known GAM frequency. Repeat this at several different frequencies in the expected GAM range (14-18 kHz). |
| Background: | The Geodesic Acoustic Mode (GAM), a class of high frequency zonal flows, has been observed at DIII-D in the outer regions of L-mode discharges. It has been measured via high-frequency poloidal velocity analysis of the turbulence obtained with BES. It is predicted to be radially localized, but is poloidally and azimuthally symmetric (m=0, n=0), consistent with the flow measurements obtained at the outboard midplane. Theoretically, it is predicted to have an m=1, n=0 pressure sideband as a result of the non-uniform ExB flow on a flux surface. The pressure buildup, nominally at the "top" and "bottom" of the plasma, relaxes via a radial drift current which gives rise to the very coherent GAM oscillation under some plasma conditions.
Typically, the GAM is observed near 15 kHz, peaking near r/a = 0.85-0.95, consistent with its predicted frequency of omega=c_s/R. The GAM is in principle capable of shearing turbulent eddies, and thus controlling and mitigating the saturated level of turbulence and resulting transport. It has also been shown to interact nonlinearly with the turbulence, driving a forward transfer of internal energy [C. Holland, PoP (2007)]. Estimates of GAM shearing rates suggest that its shearing rate is comparable to the turbulence decorrelation rate and thus might be playing a role in turbulence saturation.
If it were possible to amplify the GAM, it might be feasible to control and perhaps further reduce turbulence and resulting transport. The question is whether there is a feasible method of tweaking/perturbing/amplifying the the GAM. The new high frequency I-Coil and audio amplifiers implemented at DIII-D potentially offers such a mechanism. The concept would be to generate an n=0, m=~1 radial magnetic field perturbation at or near the GAM frequency with the I-Coil. The I-Coils produce a radial magnetic field. This might interact with the GAM in one of two (or more?) ways: 1) by producing a radial field that amplifies the radial drift current and thus the pressure relaxation, and 2) by creating a small pressure perturbation through small but finite equilibrium shape modification that enhances the pressure sideband.
Quantitative estimates of the radial magnetic field should be performed to assess the feasibility of this. |
| Resource Requirements: | Neutral beams: 150L, 330L, 30L, I-Coils, SPAs configured for n=0, m=1,10-20 kHz operation |
| Diagnostic Requirements: | BES, Doppler Reflectometer, CECE |
| Analysis Requirements: | TDE analysis of BES data for GAM studies |
| Other Requirements: | -- |
| Title |
105: Comparison of EC and NBI H-mode Thresholds |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Clarify the role of rotation by comparing the H-mode threshold power for co/balanced NBI and EC heating. CER data will be obtained in "pure" ECH plasma using the normal techniques developed by John deGrassie. This experiment proposes to first measure the ECH H-mode threshold (plasma conditions adjusted to place this in the range of 2-3 MW), and then fix the NBI power to the same level and conduct a torque scan to find the NBI H-mode threshold case. In addition, the H-mode power threshold for pure co NBI and balanced NBI (or even counter NBI) discharges will be documented. A comparison of the rotation profiles for all of these cases should shed light on the critical physics governing the H-mode threshold power, and allow us to make better predictions regarding the H-mode threshold power for slowly rotating plasmas on ITER. |
| Experimental Approach/Plan: | (1) For normal Ip and Bt direction, document the H-mode threshold power with pure ECH for LSN plasma shape. The density and bottom X-point height should be adjusted to place the ECH threshold power between 2-3 MW. (2) Keeping the plasma shape and density fixed, document the H-mode threshold powers for co NBI, balanced NBI, and counter NBI (if possible). (3) Assuming that the ECH threshold power falls in between the NBI extremes, fix the NBI power to the ECH threshold power and scan the torque to find the H-mode threshold. Document this situation. |
| Background: | It has been shown on DIII-D that the H-mode threshold power is lower for balanced NBI than for co NBI. However, it is not clear how this result extrapolates to slowly rotating plasmas on ITER, especially given the robust RF heating. The rotation profiles are not the same for balanced NBI and RF heating, even if the integrated torque is close to zero in both cases. This is because the balanced NBI actually induces a positive torque in the core and a negative torque in the edge, whereas the RF induced torque is negligible at all radii. One may wonder if the key to low H-mode threshold power on DIII-D with balanced NBI is the overall slow rotation rate, or some feature of the edge rotation profile where the local torque deposition from NBI is not negligible. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
106: Isolating particle sources and sinks in RMP H-modes with core pellet fueling |
| Name: | Todd E. Evans ( ) |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | tbd |
| Description: | The goal of this experiment is to establish a quantitative connection between core fueling with deuterium pellets, particle confinement, wall recycling and particle exhaust via the cryopumps. |
| Experimental Approach/Plan: | In this experiment we will attempt to separate the effects of pumping and recycling from changes in core transport by reproducing discharges with the same pellet and I-coil parameters while moving the OSP away from the cryopump entrance during the stationary ELM suppressed phase of the discharge. This will be done with several I-coil currents and q95 values to establish a clear dependence between the particle loss rate and changes in the recycling/pumping. during a separate scan we will increase the upper gap and reduce the upper triangularity to reduce the coupling to the upper cryopump and to recycling surfaces in the upper divertor. If time permits we would also like to vary the pellet velocity and deposition profile as well as use the LFS pellet injector to determine how these affect the particle loss rate and wall recycling/pumping. Finally a 3 point NBI power scan will be done using one of the configurations from earlier in the run day. Theree will also be time at the end of these disgharges for RMP related piggybacks. |
| Background: | Preliminary experiments last year with HFS pellets demonstrated that the decay rate of the core density due to an individual fueling pellet is controlled by the amplitude of the applied n=3 I-coil RMP. It was found that the pressure in both the upper and lower cryopumps was altered by changing the amplitude of the RMP during HFS pellets In additon, the D_alpha recycling following each pellet and the evolution of the pedestal pressure profile were controlled by increasing the level of the I-coil current. A key issue for understanding issue for understanding RMP ELM and pedestal control is what causes the density pump out effect. |
| Resource Requirements: | 7 kA I-coil, 5 co-NBI sources, upper and lower cryopumps with HFS and LFS pellet injectors. |
| Diagnostic Requirements: | Full RMP H-mode diagnostic set including upper and lower ASDEX gauges, upper and lower divertor Langmuir probes, upper and lower filterscopes, pellet diagnostics, tangential TVs, IR cameras, UCSD fast camera, UCLA profile reflectometer. |
| Analysis Requirements: | TRIP3D, SOLPS5/EIRENE and EMC3/EIRENE, python pedestal tools and kinetic EFITs. |
| Other Requirements: | -- |
| Title |
107: neutral beam injection for MSE calibration and comparison of NBCD with code calculations |
| Name: | Jay Jayakumar ( ) |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | Mike Makowsi, Chris Holcomb |
| Description: | MSE Calibration- Both in-vessel and beam-in-gas calibration techniques have less than the required correlation with MSE calibration under plasma conditions. In the past discharges with Ip ramp and pulsed beams have been used in conjunction with kinetic fits to calculate current profile and calibrate MSE offsets, in turn. However, since the beam power and energy are high compared to the background plasma, beam injection causes non-steady state conditions, where thermal and current profiles are evolving during and between pulses. It is likely that the plasma is also moving during these pulses. Therefore, Ip ramp discharges with beam pulses will be obtained and time dependent TRANSP will be carried out with the results coupled to free boundary equilibrium evolution in CORSICA. In addition, discharges with one steady beam and one pulsed beam will be obtained so that the pulsed beam is not a major perturbation compared to the background energy and power. Since changes in current profile are more accurately obtained by MSE compared to absolute current density profile, change in MSE angles would give NBCD profiles accurately as in ECCD experiments. Careful free boundary effects need to be included through TRANSP and CORSICA analysis would be required. High quality temperature, density and radial electric field measurements with fast-ion diagnostics would be needed to carry out this experiment.
These experiments would be repeated for Hybrid plasmas where controlled beam pulses would be applied to compare calculated plasma response and observed change in electric field, current profile and neutron flux.
These experiments would be repeated for high beta shot start up conditions with high q conditions.
During the above, beam attenuation will also be monitored using MSE and BES intensities.
Additional experiments with a well defined ECCD would also be useful in consistency checks. |
| Experimental Approach/Plan: | Low impurity plasma is required to minimize systematic errors in MSE system.
Accurate diagnostic capabilities including BES and if possible, reflectometry would be used.
* Shots with Ip ramp with 30 left pulses over either no beam or selected steady beams.
* Shots with beam pulses during flat top conditions, low beta discharges.
* low rotation discharges.
All shots preferably with L-mode. |
| Background: | -- |
| Resource Requirements: | Up to 5 beams one of which has to be 30 left and the other 330 left, one of them a counter beam and another 210 beam. |
| Diagnostic Requirements: | MSE, Thomson with CO2, ECE, CER with required beams (pulsed), BES |
| Analysis Requirements: | Extensive TRANSP and CORSICA analysis |
| Other Requirements: | -- |
| Title |
108: Comparison of main ion and impurity rotation velocity |
| Name: | Richard Groebner () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Measure toroidal and poloidal rotation for main ions and impurities. Compare the profiles to determine what the differences are, particularly in the H-mode pedestal. |
| Experimental Approach/Plan: | Produce H-mode discharges in helium plasmas. Measure the toroidal and poloidal rotation profiles for main helium ions and for impurity carbon ions. Take particular care to measure in pedestal region. Perform density scan to vary collisionality and coupling between the two species. |
| Background: | Edge rotation may play an important role in a number of phenomena: L-H power threshold, RWM threshold, RMP physics and edge confinement. Edge rotation is also of interest in studies of the generation and transport of intrinsic rotation. At the present time, measurements of edge rotation are made from impurities. However, near the edge, it is likely that the impurity rotation is not always a good proxy for the main ion rotation. There were direct measurements showing this in DIII-D in the mid-90s (published by J. Kim). Thus, it is important that main ion and impurity rotation be compared near the plasma edge so that we can obtain ideas about the limits of usefulness of impurity rotation. |
| Resource Requirements: | 6 NB sources, including the counter beamline. |
| Diagnostic Requirements: | TS
CER
CO2 interferometer |
| Analysis Requirements: | Generate edge poloidal and toroidal rotation profiles for impurities and main ions. Compare any differences in rotation velocity to theoretical predictions, such as those from NCLASS. |
| Other Requirements: | -- |
| Title |
109: Daily Reference Shot Monitoring of Wall Conditions |
| Name: | Phil West ( ) |
Affiliation: | General Atomics |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | P. West, M. Groth, N. Brooks |
| Description: | |
| Experimental Approach/Plan: | Run DRS as first discharge of each operations day |
| Background: | The daily reference shot was initiated in 2006 as a long-term monitor of changes in wall conditioning. It is designed with 4 phases, L-mode during rampup and early flat top, a power ramp phase to induce an L-H transition, an ELM free H-mode period, and an ELMing H-mode period. During these four phases, impurity line emission and radiated power provide monitors of impurity content. Gas fueling, density rate of rise after the L-H transition, and the density during ELMing H-mode serve as monitors of the wall fueling source. Over the 2006 and 2007 campaigns, little or no secular trends are seen in the key wall conditioning indicators. This is consistent with the ability to repeat high performance shots on a routine basis. Based on these finding, the repetition rate of boronization events has been decreased substantially. |
| Resource Requirements: | At least 2 beams, preferably 30L, 330L & R
Interferometer for density feedback control |
| Diagnostic Requirements: | Essential:
CO2 Interferometry
SPRED
Highly Desired:
CER
Thomson
Bolometry
Visible Bremsstrahlung
Filterscopes
Multichord Divertor Spectrometer
Lower Tangential TV |
| Analysis Requirements: | Routine running of the DRS database program (P.West)
Reconstruction of Lower Tangential TV data (M. Groth)
MDS spectra analysis (N. Brooks) |
| Other Requirements: | -- |
| Title |
110: Role of coherent modes on edge pedestal and ELM behavior |
| Name: | Dmitry Rudakov ( ) |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Role of coherent modes on edge pedestal and ELM behavior |
| Description: | 1. Test models of coherent modes in H-mode pedestal regions, including esp. scaling with [1] rotation shear, [2] electric field shear, [3] pressure gradient, and [4] collisionality 2. Check effect of the I-coil induced erogodic fields on the coherent modes 3. Use inter-machine comparisions to help separate the contributions of the individual drives |
| Experimental Approach/Plan: | 1. Establish low power high density (ne/nG ~ 1) H-mode with quasi-coherent or coherent pedestal modes 2. vary momentum input-toroidal rotation (change balance of co and counter NBI) 3. density scan (puff and pump) 4. vary edge pressure gradient with edge localized ECH 5. use I-coils to test the effect of ergodic fields on the coherent modes 6. characterize edge profiles, fluctuations, and flows with boundary diagnostics, reciprocating probes, CER, ... |
| Background: | 1. Various types of quasi-coherent, coherent, or harmonic edge modes have been observed in the pedestal region of many devices (D3D, Asdex-Upgrade, C-Mod, H-1, etc.) and have been associated with increased levels of cross-field transport that permit steady-state H-mode operation without Type I ELMs 2. Theoretical models for pedestal coherent modes are based on [1] toroidal rotation shear, [2] Er shear, [3] pressure gradient drive, and/or [4] edge collisionality 3. DIII-D is an excellent facility for testing these theories because it can obtain edge coherent modes which can vary significantly in their character (electrostatic vs. electromagnetic; particle and heat transport vs. heat transport only, etc.) 4. DIII-D has a way to control (by using I-coils) ergodic magnetic fields that were shown to affect ELMs and are likely to affect the coherent modes as well. |
| Resource Requirements: | Machine Time: 1 day Experiment
Plasma Control System Development
Number of gyrotrons: 2
Number of neutral beam sources: 4 (including co and counter) |
| Diagnostic Requirements: | 1. CER for edge Er and toroidal rotation 2. X-point probe for parallel flow (separatrix must be reachable with probe from bottom of machine) 3. full profile and edge diagnostics 4. edge current profile diagnostic if available |
| Analysis Requirements: | -- |
| Other Requirements: | 1. I-coils 2. Edge ECH 2. Pumping for control of edge collisionality |
| Title |
111: H-mode operation near the threshold power |
| Name: | Guiding Wang ( ) |
Affiliation: | University of California, Los Angeles |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Requested |
Co-Author(s): | J.C. DeBoo |
| Description: | The purpose is to characterize the H-mode access in ITER-like L-mode target plasma in DIII-D (ne~0.4*n_GW, ITER shape, q_95 ~3-3.5, low rotation) at different input power levels (PLTH/P_th~1.1, 1.2, 1.3, 1.5, etc). This is an ITPA joint experiment (CDB-11). |
| Experimental Approach/Plan: | After establishing ITER-like L-mode Deuterium target plasma at ne~0.4*n_GW and H-mode threshold power being found with power ramp, vary input power shot-to-shot but at a fixed level during each shot (PLTH~1.1, 1.2, 1.3, 1.5 x P_th). Establish new equilibrium condition. If new ne level is below 0.8*n_GW, then gas puff to achieve 0.8*n_GW to see if H-L transition occurs. Characterize ELMs and confinement properties after the L-H transition. If good confinement in the H-mode phase is not achieved, raise input power further. Repeat above process at 2 or 3 collisionality levels. |
| Background: | Due to power limitations, ITER will likely need to access H-mode at a low density (0.5*10^20 m^-3, ~0.4*n_GW) with input power close to H-mode power threshold then achieve their target flattop density of 1*10^20 m^-3 without more input power. So it is important to have dedicated experiments to demonstrate/document this scenario. Recent relevant results in different machines provide mixed information. For example on ASDEX database analysis shows that at input power close to threshold power, good confinement can be achieved with Type-I ELMs at low enough collisionality (<1), but at high collisionality Type-III ELMs appear and confinement is ~ 20% worse. On JET, when input power is close to threshold power, Type-III ELMs always dominate and confinement is 10-20% worse than H~1 except at low densities. Typically PLTH~(1.3-2.5)*P_th is needed to achieve Type-I ELMs with good confinement depending on conditions. On DIII-D, when input power is close to threshold power, normally Type-III ELMs appear, and confinement is normally poor at low densities but could reach higher H if edge pressure gradient increases at high density. |
| Resource Requirements: | All co- and counter-beams. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
112: Marginally Limited High Performance Plasmas with Density Control |
| Name: | Phil West () |
Affiliation: | General Atomics |
| Research Area: | Core-Edge Integration |
Presentation time: |
Not requested |
Co-Author(s): | P. West, T. Petrie, G. Jackson |
| Description: | |
| Experimental Approach/Plan: | |
| Background: | |
| Resource Requirements: | required: Shape development
required: 5 beams, desired: 7 beams
desired:ECH, 2 gyrotrons |
| Diagnostic Requirements: | 1) Usual high performance diagnostics
2) Usual pumping diagnostics
3) Divertor and centerpost IRTV |
| Analysis Requirements: | Step 1: routine performance and pumping analysis
Step 2: With success, more exhauust, pedestal, current profile and transport analysis will follow. |
| Other Requirements: | -- |
| Title |
113: Understanding low density limit for L-H transition power threshold |
| Name: | Guiding Wang () |
Affiliation: | University of California, Los Angeles |
| Research Area: | General IP |
Presentation time: |
Not requested |
Co-Author(s): | J.C. DeBoo, K.H. Burrell, J. Snipes |
| Description: | The purpose is to understand the mechanism and explore the scaling of low density limit (namely the density at minimum power threshold) with Bt and Ip for L-H transition power threshold. This has been identified as a potential issue for ITER. This is an ITPA joint experiment (CDB-10). |
| Experimental Approach/Plan: | Perform density scan of the L-H power threshold at one set of plasma parameters until the density at minimum power threshold can be identified. Scan Bt and Ip and do the similar density scans to achieve the Bt and Ip dependence of this density limit. Collect full set of edge profile and fluctuation data. |
| Background: | ITER is planned to access H-mode in a low density (0.5*10^20 m^-3, ~0.4*n_GW) L-mode target. However, low density limit for L-H transition power threshold has been observed in major tokamaks including DIII-D, namely power threshold increases at densities lower than a certain density. So it is crucial to find out if this ITER L-mode target density is below or above the low density limit for ITER in order to predict required power for H-mode access (The scaling law of power threshold in the ITPA power threshold database is defined by excluding low densities). Previous experiments on several major tokamaks including DIII-D showed a low density limit ~0.2-0.3*10^20 m^-3 (except for C-mod at 1*10^20 m^-3), but ~0.2-0.3 if normalized to the Greenwald density limit. So it is desired to find out the scaling of low density limit with Bt and Ip. There is no theory available to understand low density limit for power threshold. Edge fluctuation data could be helpful to understanding the mechanism. Recent experiment on C-mod showed no dependence on Ip. |
| Resource Requirements: | All co- and counter-beams. |
| Diagnostic Requirements: | fluctuation diagnostics |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
114: Test of TGLF transport model in pedestal |
| Name: | Richard Groebner () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | P. Snyder |
| Description: | Produce H-mode discharges with long ELM-free period and with long inter-ELM periods. Characterize pedestal in great detail, both during the ELM-free phase and during the inter-ELM phase, for use in benchmarking the TGLF transport model in the pedestal. (These data will also be useful for testing other models.) |
| Experimental Approach/Plan: | Produce long ELM-free discharge (118897 would be good target). Use breathing and high time resolution CER to obtain profiles with high spatial resolution as a function of time in the ELM-free phase and early in the ELMing phase. Use edge MSE to obtain data for q profile. Obtain pedestal profiles of density fluctuation level and radial correlation length. Obtain this data set at different values of q95, achieved by changing Bt. |
| Background: | On June 16, 2004, an experiment was performed to characterize the pedestal for purposes of providing a dataset to be used in benchmarking the TGLF code. This dataset has been very useful for a number of edge modeling projects, including some initial testing of the TGLF code. However, this dataset is showing its age. We now know how to obtain improved data with the diagnostics used in 2004 but more importantly, we have new diagnostics which can be used to measure important quantities not available in 2004. These include the edge MSE to provide q (and magnetic shear) profiles, the quadrature reflectometer to obtain profiles of density fluctuations in the pedestal and the edge profile reflectometer to obtain highly resolved edge density profiles. In addition, the new Te fluctuations diagnostic could be used to obtain useful data at the inner edge of the pedestal. Thus, we can now obtain a much improved dataset for benchmarking TGLF (and other edge codes) and we propose to do so. |
| Resource Requirements: | All beams needed except 210 sources.
Lower cryopump. |
| Diagnostic Requirements: | TS, CER, CO2, edge MSE, BES, quadrature reflectometer, profile reflectometer, Te fluctuations diagnostic |
| Analysis Requirements: | Analyze diagnostic data to obtain best profiles at several different times during evolution of ELM-free pedestal. Use CER (and edge MSE, if possible) to obtain profiles of edge Er shearing rate. Compare these to maximum linear growth rates from TGLF to see if pedestal occurs where ExB shearing rate exceeds turbulence growth rate. When non-linear version of TGLF is available in a transport code, use the model to see if it can predict the observed build-up of the pedestal and evolution of density fluctuation level. |
| Other Requirements: | -- |
| Title |
115: Stable Impurity Enhanced Radiative Divertor Operation with Pellet Pacing |
| Name: | Richard A. Moyer ( ) |
Affiliation: | University of California, San Diego |
| Research Area: | Core-Edge Integration |
Presentation time: |
Requested |
Co-Author(s): | Todd Evans, Tom Petrie, Jon Watkins, Larry Baylor, Tom Jernigan |
| Description: | This goal of this proposal is to develop a steady-state operating scenario compatible with Radiative Divertor operation using impurity seeding as envisioned for ITER. Stable, high performance H-modes are obtained, impurity is puffed (neon, argon) to detach the divertor legs and reduce strike point erosion presumably. Repetitive pellets (1-10 Hz) are used from the HFS and LFS to generate ELM-like transport events (ELM pacing) in order to control the accumulation of the impurity in the plasma core and provide a stable RD discharge. |
| Experimental Approach/Plan: | Use lower single null, high performance, co-NBI H-modes (4-5 sources) to produce a reference ELMing H-mode with cryopumping. This plasma should have a detached inner strike point and attached outer strike point, but characterize these conditions. Then, use impurity puffing to detach the outer leg (partial or full) and develop a Radiative Divertor with reduced average peak heat flux to the divertor. Add repetitive pellets (1- 10 Hz as needed) from the HFS or LFS to trigger "ELMs" of smaller amplitude and controlled frequency to flush impurities from the plasma edge and prevent accumulation in the core, which leads to an X-point MARFE, radiative collapse, and/or disruption. Time permitting, try varying the input neutral beam torque to more ITER-like rotation while maintaining the steady state RD operation in a high performance H-mode. |
| Background: | Although most poloidal divertor tokamaks (all?) have demonstrated that the time average peak heat flux to the divertor targets can be reduced by enhancing the level of radiation in the boundary with impurity puffing, this Radiative divertor operation has proven difficult to maintain in steady-state. The impurities tend to accumulate in the core, leading to an x-point MARFE, a radiative collapse or a disruption.
Pellets have been demonstrated to produce "ELMs" when injected into the plasma; this feature is used in e.g. ASDEX-Upgrade to mitigate large ELM heat flux impulses to the divertor by triggering ELMs at narrower spacing, and hence with lower amplitude ("pellet pacing"). However, fast IRTV measurements by Jakobowski et al and particle flux measurements with divertor probes and/or TV (Groth, Watkins, et al) suggest that these "ELMs" in DIII-D are much more "convective" than intrinsic, naturally occurring ELMs. Consequently, rapid, shallow pellets can be used to enhance pedestal particle transport while having only a minimal effect on the pedestal thermal transport, and may be a good tool for preventing the accumulation of the puffed impurity, leading to unstable RD operation. |
| Resource Requirements: | 5 co and 2 counter NB sources
neon and argon impurity injection
HFS and LFS pellets at 1 �?? 10 Hz
1 full day of operations is envisioned
Possible extension to include implimentation of a feedback control on the pellet injection frequency might be desirable but this would have to follow this first day to establish the range of conditions needed. |
| Diagnostic Requirements: | core, tangential and divertor Thomson scattering
CER system tuned for core impurity profiles
Floor Langmuir probes
Fast IRTV (Juelich; if available) or LLNL IRTV
Full pedestal and divertor diagnostics
Fast framing camera (UCSD)
Fast and Mirnov magnetics
Fluctuation diagnostics |
| Analysis Requirements: | Although I envision no specialized analysis requirements, these data would provide an excellent opportunity for edge modeling with e.g. UEDGE, SOLPS, etc. and may provide useful information on the physics mechanisms for pellet induced ELMs and how they are or aren�??t �??normal�?� ELMs (e.g. ELITE stability analysis; NIMROD?)
This experiment makes a good companion to the Petrie proposed experiment to provide steady-state RD operation with the RMP, the other tool DIII-D has which can enhance particle transport while leaving thermal transport relatively unaffected. |
| Other Requirements: | Development of a stable radiative divertor operating scenario, in addition to being of direct interest to steady-state integrated operation, would develop a reference discharge for use with DiMES and MiMES material sample exposures. |
| Title |
116: Access to betaN = 5 in a high li scenario |
| Name: | John Ferron ( ) |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Build on the promising results (betaN = 4.5) achieved in 2007 that used a new high li discharge formation technique in order to improve the discharge operation, increase the value of li at the peak of betaN, reach betaN = 5, and extend the duration of the high li phase. |
| Experimental Approach/Plan: | Further analysis of the 2007 data is required in order to decide the best approach for new experiments. Since we quickly tried quite a number of variations on the details of the discharge evolution, there wasn't any opportunity to choose the approach giving the best results and pursue it further. The focus would be on achieving 4li above 5 at the time of the peak betaN. The issues are the relative time evolution of beta and li, the choice of time for the H-mode transition and whether the rate of decrease of li after the H-mode transition can be reduced such as by reducing the edge pedestal height. Also, it isn't clear that the optimum plasma current and toroidal field were used. There is a long list of ideas for changing details of the experiment including operating with type 3 ELMs at high-density, operating at extremely low squareness, and going back to a discharge closer to what was used in the ITER startup experiments which reached higher values of li. In addition, we need to get data with the counter-beam viewing mse channels in order to improve the q profile measurement. |
| Background: | During 2007, a new approach to formation of a high li discharge was tested based on the constant q95 ITER startup scenario. This discharge formation technique is much simpler and more versatile than the current ramp or kappa ramp techniques used previously; toroidal field and flattop plasma current can be varied over a significant range allowing tuning of the discharge to meet various constraints. BetaN = 4.5 was achieved with high normalized confinement. During this one-day experiment a number of methods for operating the discharge were tested rather quickly with varying results for the betaN achieved and the beta limiting phenomenon. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
117: Investigating the Limits of Pellet pacing for ELM control |
| Name: | Richard A. Moyer () |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | This goal of this proposal is to develop a physics understanding of the mechanisms for producing tolerable small, high frequency ELMs using repetitive pellet injection, and to explore the limits of this approach to ELM control in contrast to RMPs. |
| Experimental Approach/Plan: | |
| Background: | |
| Resource Requirements: | |
| Diagnostic Requirements: | core, tangential and divertor Thomson scattering
CER system tuned for core impurity profiles
Floor Langmuir probes
Fast IRTV (Juelich; if available) or LLNL IRTV
Full pedestal and divertor diagnostics
Fast framing camera (UCSD)
Fast and Mirnov magnetics
Fluctuation diagnostics |
| Analysis Requirements: | |
| Other Requirements: | -- |
| Title |
118: NTM stabilization and RMP in high li, high betaN discharges |
| Name: | John Ferron () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Apply ECCD stabilization of NTMs to help maximize the beta in high li discharges. Use RMP to reduce the pedestal height in order to reduce the edge bootstrap current. |
| Experimental Approach/Plan: | Off-axis ECCD was applied in the 2007 discharges in order to avoid sawteeth. This seemed to be effective. To stabilize NTMs, the toroidal field and aiming of the ECCD would be adjusted for preemptive stabilization. ECCD could be used effectively in discharges in which we attempt to maximize betaN. This use of the ECCD will also have a good likelihood of stabilizing sawteeth by slightly raising q(0) as was observed in 2007. The application of RMP fields is known to reduce the pedestal height, particularly when the edge q is at the most resonant value. The new method for forming a high li discharge allows the toroidal field and plasma current to be chosen in order to produce the resonance condition required for most effective use of the RMP. In order to develop the technique, RMP would probably first be applied in a discharge with a relatively steady value of betaN (about 4). Then the application could be extended to higher betaN, more transient discharges in order to attempt to extend the period of high betaN. |
| Background: | Some of the high betaN, high li discharges produced in 2007 were limited by NTMs. The NTMs provided a rather soft limit to beta. So, if the NTMs could be avoided then higher values of beta might be accessible. Another feature of the high li discharges is that after the H-mode transition the edge bootstrap current increases resulting in a decrease in li. It is desirable to reduce the edge bootstrap current. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
119: Study of moderate beta, high li transport and stability |
| Name: | John Ferron () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Produce a high li discharge that runs without beta collapse at significant betaN (for example, about 4). Use MHD spectroscopy to look for the no wall beta limit as li evolves, particularly as it decreases at constant betaN. Evaluate the confinement in the absence of large dW/dt and the dependence of confinement on rotation. Evaluate the effect of the toroidal rotation velocity on the measured stability limit. |
| Experimental Approach/Plan: | In 2007 it was relatively easy to make a discharge with betaN above 4. So, it seems reasonable that we could make a discharge that regulates at betaN = 4 while li evolves to lower values after the H-mode transition. If the no-wall stability limit is above 4 at the higher values of li, then it ought to be possible to observe the discharge passing through the no wall limit as li decreases (using MHD spectroscopy). In addition, a discharge with relatively constant betaN would facilitate the study of confinement and the dependence on rotation that could be obtained by using the counter beams. A change in the stability limit could be observed at lower rotation. |
| Background: | MHD spectroscopy is an excellent tool for diagnosis of the low-n no-wall stability limit. In 2007 experiments, it didn't appear that, even at betaN = 4.5, the no-wall stability limit was exceeded. The 2007 high li discharges that reached high betaN had H factor about 3, but there was also still a large dW/dt. It would be good to establish that the confinement is still high in conditions with more steady state stored energy. Also, the normalized confinement increases significantly as the beam power is increased suggesting that perhaps there is a strong dependence of confinement on rotation. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
120: H-mode power threshold in Hydrogen plasmas |
| Name: | Punit Gohil () |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine the power required to produce H-mode plasmas in hydrogen discharges for a range of plasma conditions and configurations. determine the behaviour with chaning input torque.Compare this with deureum discharges at same plasma conditions and configuration. |
| Experimental Approach/Plan: | Determine the threshold power for H-mode plasmas by performing power scans for different plasma conditions and configurations. Change the input torque for different conditions and evaluate how the threshold power varies. |
| Background: | The H-mode power threshold is expected to be higher for hydrogen discharges compared to deuterium discharges. However, detailed knowledge of the differences and the behaviour as a function of plasma conditions , configurations and input torque is severely lacking, especially for extrapolations to ITER conditions. This experiment will aim to resolve these issues. |
| Resource Requirements: | co and counter beams |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
121: Reliable, flexible formation of 100% noninductive discharges |
| Name: | John Ferron () |
Affiliation: | General Atomics |
| Research Area: | Fully Noninductive High Beta Operation |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Improve the startup of steady-state scenario discharges by implementing: 1) routine use of feedback control of the q evolution, 2) counter-injection beams and gyrotrons as the heat sources, 3) avoidance of tearing modes probably using ECCD for preemptive stabilization, and 4) access to higher q_min made possible by startup at higher betaN with preemptive NTM stabilization. |
| Experimental Approach/Plan: | 1) Start using the feedback control of q routinely during experiments with steady-state scenario discharges. Use this control to specify the target q_min value at the start of the high-performance phase and enable the timing of the high-performance phase and corresponding q_min value to be varied independently. Also use the q_min control to enable experiments with the target q_min >2. 2) Develop the capability to use counter beams and gyrotrons as the heat source during the discharge formation without the appearance of tearing modes or mode locking. This will require a robust method to avoid tearing modes. A possibility is to use the gyrotrons for ECCD stabilization of NTMs. The maximum gyrotron power could be applied for preemptive stabilization. Then, the necessary amount of counter beam power to maintain the desired q evolution would be added by the PCS. As the tearing modes are typically observed at rather low beta, they may be classical tearing rather than neoclassical tearing. In this case, a different approach to stabilization will be required. Either way, as tearing modes are observed on a large fraction of the discharges, it is important to find a way to avoid them. It may be necessary to dedicate the gyrotrons to use during the discharge formation in order to do this development. However, in the future when real-time steerable mirrors are installed, gyrotrons can be used for one purpose at the beginning of the shot and another purpose during the high-performance phase. Also, it may be possible to design the gyrotron aiming in combination with an evolution of the toroidal field or major radius that makes a particular fixed gyrotron aiming compatible with the needs during both the beginning of the discharge and the high-performance phase. 3) Access higher values of q_min at the start of the high-performance phase by using preemptive NTM stabilization to allow relatively high betaN values during the discharge formation. In order to maintain the q_min at high values, relatively high electron temperatures are required leading to higher beta because of the correspondingly higher input power. 4) Try varying the plasma current ramp rate to test whether improvements in q control and tearing mode avoidance are possible. |
| Background: | During 2004-2007 techniques for feedback control of the q evolution during discharge formation were developed. This capability is now ready for routine use and will improve capability to reliably specify the q profile at the start of the high-performance phase and will improve flexibility to vary this target q profile from shot to shot. Difficulties with the startup of steady-state scenario discharges remain, however. Tearing modes often appear, even at relatively low beta. Also, there is a need to avoid use of the co-injection beams for discharge formation in order to conserve their energy injection capability to maximize beta and pulse length in the high-performance phase. This means using the counter beams and the gyrotrons to provide the necessary electron heating during discharge formation. Initial tests using the counter beams indicated that tearing modes are more likely to occur. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
122: ECCD stabilization of NTMs to improve the high beta phase of steady-state scenario discharges |
| Name: | John Ferron () |
Affiliation: | General Atomics |
| Research Area: | Fully Noninductive High Beta Operation |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | NTMs commonly occur during the high-performance phase of discharges designed to achieve 100% noninductive current. This limits the maximum stable betaN (and thus the bootstrap current fraction) and, in the case of a 3/2 mode, reduces the confinement so that the limited total beam energy available is used up more quickly. The goal here is to test the use of ECCD for NTM stabilization and to develop a gyrotron aiming that will be effective for NTM stabilization and simultaneously provide sufficient off-axis current drive for maintenance of the current profile. With NTM stabilization, increase the betaN to the maximum achievable and determine the effect on the noninductive current fraction. |
| Experimental Approach/Plan: | 1) Dedicate the ECCD during the high-performance phase to NTM stabilization, preferably preemptive. While NTMs are stabilized, maximize the betaN. 2) If the previous step was successful, determine whether the gyrotron aiming for NTM stabilization is compatible with current drive to maintain the steady-state phase. If possible, broaden the deposition profile of the ECCD in order to satisfy both the NTM stabilization and the current profile maintenance requirements. Or, dedicate some gyrotrons to each task. |
| Background: | The phase of steady-state scenario discharges with high noninductive current fraction must be operated at high beta, above the no-wall stability limit, in order to achieve a large bootstrap current. In past experiments, NTMs are often observed. Prior to 2007 the number of discharges that ran for the full 2 second high-performance phase without a 2/1 mode occurring was small. During 2007, the 2/1 mode was not common during the high beta phase but a 3/2 mode was nearly always present. A 2/1 mode will eliminate the high-performance. A 3/2 reduces confinement requiring that higher beam power be injected in order to reach the programmed betaN value. This uses up the available beam pulse length and limits the duration available for the study of the high noninductive current fraction plasma. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
123: Pursue the q_min >2 path toward high noninductive fraction discharges |
| Name: | John Ferron () |
Affiliation: | General Atomics |
| Research Area: | Fully Noninductive High Beta Operation |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Continue the effort toward moving the high-performance phase earlier in the discharge when q_min is higher than the typical value near 1.5 that was the primary focus in 2006-2007. Use feedback control of the q_min evolution to reliably form the target q profile. Focus on achieving high betaN values in the time interval available before q_min drops below 2. If necessary, use ECCD stabilization of NTMs. |
| Experimental Approach/Plan: | Experiments in 2006-2007 suffered from a wide variety of problems preventing high q_min at high betaN to be achieved reliably. Experiments using the q feedback control have been reasonably successful at producing elevated values of q_min at the end of the current ramp. Using feedback eliminates the need to spend a lot of experiment time playing with the early beam timing. So the approach would be to focus on reliability with feedback control of q. The q control would be integrated with the betaN control to allow a smooth transition to high betaN values. In the past, even though q_min is above 2, NTMs have still been observed. So if necessary, ECCD stabilization would be used. |
| Background: | A couple of days were spent in 2006-2007 attempting to produce high bootstrap current fraction discharges with q_min >2. The amount of time devoted to this parameter range is a small fraction of what has been spent on the case with q_min near 1.5. However, the possible benefit of operating with higher values of q_min is higher bootstrap current at a given betaN. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
124: Optimize the 6 gyrotron, q_min near 1.5, high noninductive fraction scenario |
| Name: | John Ferron () |
Affiliation: | General Atomics |
| Research Area: | Fully Noninductive High Beta Operation |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Apply several changes to the way the standard high noninductive fraction scenario has been operated to improve its performance. These would be in addition to the big change that is needed which is additional gyrotron power. The assumption here is that a total of 6 gyrotrons will become available, motivating an additional attempt at optimizing the q_min near 1.5 scenario. |
| Experimental Approach/Plan: | Several changes to the operating method for these discharges are suggested. 1) Use of feedback control of the q evolution, NTM stabilization with ECCD and use of counter beams and gyrotrons for heating during the discharge formation (these are described in separate proposals). 2) The start of the high-performance phase should be moved earlier in the discharge. To keep to the target q_min the same, q feedback should be used. This would allow an increase in the duration of the high-performance phase by using less beam energy during the formation. 3) Even without moving the high-performance phase earlier, there were adjustments in the beam usage that could have been made in the 2007 shots to give a few hundred milliseconds longer high-performance duration. 4) According to the ELM experts, if the double null shape is biased away from the grad-B direction, the ELM frequency is increased. This would help keep the density low. 5) More effort is probably needed on the optimization of the shape and achievable beta versus the pumping capability. Density still is rather high when the shape is double null. |
| Background: | The high noninductive fraction scenario which has received a lot of experiment time has q_min near 1.5 and has been successful in approaching 100% noninductive current. However, the duration of the high-performance phase has been short (about two seconds) and to achieve 100% noninductive current reproducibly, additional gyrotron power is what is really needed. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
125: Discharges with complete 2nd stable regime access |
| Name: | John Ferron () |
Affiliation: | General Atomics |
| Research Area: | Stability |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The goal is to further investigate discharges with ballooning mode second stable access across the entire radial profile. The primary task would be to demonstrate that the stability code prediction of second stable access is correct by producing a continuous series of discharges with and without full second stable access. Also of interest would be the relatively unusual MHD observed previously. The previous discharge demonstrated onset of a 3/1 tearing mode at high beta and qmin > 2 instead of the more commonly observed 2/1 mode. |
| Experimental Approach/Plan: | Shot 114723 would be reproduced first. This shot had a large gas puff in order to broaden the density and pressure profile. The pressure gradient profile was approximately flat with fairly large values in the region of rho = 0.7 where normally a dip in pressure gradient is observed in H-mode discharges. The gas puff amplitude would be scanned in order to vary the pressure profile. We would look for a transition between cases with relatively large pressure gradient in the outer portion of the discharge and cases with a pressure gradient dip more like standard H-mode. This transition would be correlated with calculations of the ballooning stability. Shot 114723 also had relatively broad electron temperature profile. Off-axis ECH heating could be used as a second method of varying the pressure gradient profile. |
| Background: | Shot 114723, a qmin > 2 case with very broad pressure profile, had ballooning mode second stable access across the entire profile according to stability analysis of the reconstructed equilibrium. This resulted from a very broad bootstrap current profile. It has been suggested that this is the first time that this has been observed. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
126: Dependence of ELM characteristics on toroidal rotation in hydrogen plasmas |
| Name: | Punit Gohil () |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine the ELM behaviour and characteristics as a function of the toroidal rotation in hydrogen discharges. This is particularly important for ITER which is expected to operate at low toroidal rotation. Use different mixes of the co and counter beams to vary torque and document the ELM behaviour and characteristics. |
| Experimental Approach/Plan: | Produce H-mode plasmas in hydrogen discharges and then vary the toroidal rotation using different ratios of co to counter beams. Document the changes in the ELM characteristics and other plasma properties. |
| Background: | Knowledge of how the ELMs are affected by varying the toroidal rotation is an important issue in both deuterium and hydrogen plasmas. This experiment will aim to resolve this issue in hdrogen plasmas and us ethe knowledge gained to compare with deuterium plasmas to get a better understanding of the ELM properties. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
127: Intrinsic rotation vs NTV |
| Name: | John Degrassie () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | A. Garofalo, G. Jackson, W. Solomon, A. Cole, J. Callen, and C. Hegna |
| Description: | Study the interplay of intrinsic rotation and NTV-induced rotation from n=3 I-coil error fields. |
| Experimental Approach/Plan: | *Do an experiment to follow the temporal transition between intrinsic rotation in ELMing ECH H-modes (co-directed) and the toroidal rotation driven by I-coil n=3 Neoclassical Toroidal Viscosity (NTV) (counter-directed). The counter-Ip n=3 NTV rotation has apparently been observed in DIII-D (Garofalo, Jackson).
*Try very short NBI blips ( ~ < 4 msec ), or balanced blips ( ~ 5msec of 30L,33L,21R,21L ) to obtain a temporal record of the (slow) toroidal velocity evolution as the n=3 perturbation is turned on, and off etc.
*Use small amounts of added co/counter NBI to vary the target toroidal velocity from about twice the NTV counter value to twice the intrinsic co value and follow the temporal evolution of velocity with n=3 switched on and off. |
| Background: | Close scrutiny of past data indicates that n=3 NTV-induced toroidal rotation (counter directed) has been observed in DIII-D (Garofalo, Jackson). To draw this conclusion one must apparently postulate that the intrinsic rotation has been quenched, or possibly reduced, by the n=3 error field. This conclusion has some uncertainty because carbon and not the main ion are measured. We believe that these experimental scans will reveal what is going on. |
| Resource Requirements: | standard for intrinsic rotation
standard for n=3 braking experiments
ECH, Beams |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
128: RMP ELM-control in hydrogen plasmas |
| Name: | Punit Gohil () |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | T. Evans |
| Description: | Determine the effectiveness of Resonant magnetic perturbations for ELM control in hydrogen plasmas. Evaluate how effectiveness of ELM control when compared with deuterium plasmas. |
| Experimental Approach/Plan: | Use the Icoils to control the ELMs in hydrogen plasmas for a range of different plasma conditions and configurations. Compare the effectiveness of ELM control with that for deuterium plasmas. |
| Background: | RMP ELM-control in deuterium plasmas has been well documented. However, the effectiveness of this technique in hydrogen plasmas has not been determined and requires detailed studies. |
| Resource Requirements: | 7 beams, Icoils |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
129: Study of low-Z pellet shell ablation |
| Name: | Eric M. Hollmann ( ) |
Affiliation: | University of California, San Diego |
| Research Area: | Disruptions |
Presentation time: |
Requested |
Co-Author(s): | T. Evans, A. James, P. Parks, J. Yu |
| Description: | An interesting possible approach to disruption mitigation is the delivery of large quantities of radiating impurities to the core plasma using low-Z shell pellets. Variations on this concept include shells filled with pressurized gas (proposed by T. Evans), filled with dust (proposed by P. Parks), or filled with a high-Z radiating material. The main concept is to deliver/disperse a large quantity of impurities on the magnetic axis with minimal edge radiation and current contraction. Successful implementation of these schemes requires an understanding of low-Z pellet shell ablation and the resulting edge current contraction. |
| Experimental Approach/Plan: | The lithium pellet injector with vertical launch can be used to inject different custom solid pellets into target discharges. Injected pellets can be designed with different thickness low-Z (e.g. C) shells and different core materials (e.g. LiF) with clear spectroscopic signatures. Monitoring of the pellet emission with different fast-framing camera filters would allow study of the pellet shell ablation rate by monitoring the brightness of the ablation plume and the pellet depth at which the shell material emission turned off. |
| Background: | Disruption mitigation experiments with small cryogenic pellets have been performed at DIII-D and elsewhere. Large runaway electron signals were seen when Ne and, especially, Ar, were used. However, the ability of solid shell pellets to delivery impurities into the plasma core without launching large MHD and without generating runaway electrons has not been studied. |
| Resource Requirements: | Lithium pellet injector, high-power H-mode discharges. |
| Diagnostic Requirements: | Fast-framing midplane camera with appropriate interference filters. |
| Analysis Requirements: | -- |
| Other Requirements: | Custom shell pellets (to be made in cooperation with the GA inertial confinement group). |
| Title |
130: High BetaN, f_BS, ITB plasmas |
| Name: | Chris Holcomb ( ) |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Fully Noninductive High Beta Operation |
Presentation time: |
Requested |
Co-Author(s): | Andrea Garofalo |
| Description: | Demonstrate BetaN>4, f_BS~90%, scenario with ITB, qmin>2, rhoqmin>0.6 and moderate pressure peaking in reverse Ip using counter NBI and ECCD |
| Experimental Approach/Plan: | In reverse Ip, start-up with counter NBI sources to i) reduce on-axis NBCD and ii) maintain sufficient rotation to avoid locked modes. Scan the starting Bt down from 2.1 T to obtain high Beta with fewer beams, lower density, and higher ECCD efficiency. Use early ECH/ctr-ECCD to compensate for the expected lower temperature and faster current evolution. Ramp Bt and Ip to obtain broad current profiles. In the high Beta phase, apply 2 co-beams (210r,l) as needed for feedback and diagnostics, and apply ctr-ECCD near rhoqmin to compensate for bootstrap current overdrive that otherwise would decrease qmin. Scan the deposition location to find where it has the greatest effect sustaining high qmin. |
| Background: | Steady state high BetaN with f_BS > 90% requires qmin>2, rhoqmin ~ 0.7, and moderate pressure peaking. (Turnbull, NF, 1998). BetaN ~ 4 with qmin ~2 with an ITB has been achieved transiently (Garofalo, PoP 2006). However, the rhoqmin was smaller than desired due to too much on axis beam current drive, and non-inductive current overdrive near rhoqmin lead to current profile evolution and a smaller n=1 ideal wall limit. In 2006 an experiment was conducted that used reverse Ip and up to 5 counter NB sources to try to expand rhoqmin. Ip and Bt ramps (starting at 2.1 T) were used to broaden the current profile. Start-up with co-rotation and a transition to counter-rotation caused a locked mode that disrupted these shots. Various important components, such as the MSE diagnostic and the RWM control, were not optimized correctly in the control room, and density control was a problem. The above experimental approach takes advantage of what was learned in the 2006 run day. |
| Resource Requirements: | All seven NBI sources. Five or more gyrotrons. |
| Diagnostic Requirements: | |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
132: Momentum Transport Measurement Using Shape Modulation |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | W. Solomon |
| Description: | This experiment proposes to study momentum transport by modulating the plasma shape between upper/lower null (using a symmetric DND patch panel). The NBI power will be kept fixed so that the injected torque is not modulated, and the resulting changes in rotation can be fit using the "source free" form of the angular momentum transport equation. It would be interesting to perform this experiment in both ELMy and ELM-stabilized (either QH-mode or RMP) plasmas. In addition, this experiment may help to determine the effect of residual error fields on the apparent momentum diffusivity by varying the error field shot-to-shot. |
| Experimental Approach/Plan: | (1) Modulate dRsep at ~10 Hz from +1 cm to -1 cm in an otherwise stationary plasma with fixed NBI power. (2) Compare an ELMy H-mode plasma with a ELM-suppressed plasma. (3) If a hybrid discharge is used (as opposed to QH-mode), then compare the momentum transport modulation for a 3/2 NTM scenario vs. 4/3 NTM scenario since the resonant drag effects on error fields could be different. |
| Background: | It was noticed in 2006 that hybrid (H-mode) plasmas have higher toroidal rotation when the controlling X-point is away from the grad-B drift direction. This was verified for both signs of B. An initial attempt (2 shots) to measure the perturbed momentum transport by modulating dRsep positive/negative was not successful because NBI power feedback to keep beta_N fixed was utilized. This caused a problem because the link between rotation and confinement caused the NBI power (and therefore the injected torque) to modulate at the same frequency as the dRsep modulation. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
133: Net Deuterium Retention In Unpumped and Pumped Discharges on DIII-D and Alcator C-Mod |
| Name: | Phil West () |
Affiliation: | General Atomics |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Requested |
Co-Author(s): | P. West, B. Lipschultz(MIT), N. Brooks, R. Maingi(ORNL), T. Petrie, D. Rudakov(UCSD), V. Soukhanovskii(LLNL), J. Watkins(SNL), D. Whyte(MIT) |
| Description: | Goals: Compare gas uptake on the all graphite wall DIII-D to that on the all high-Z metal wall C-Mod. In 2008 the focus will be on L-mode discharges, both unpumped and pumped, at two densities, ne/nGW ~ 0.3 and ne/nGW ~ 0.5.
1)Net uptake rate, including between shot out-gassing, and uptake saturation in unpumped discharges
2)Net depletion rate and depletion saturation, including between shot pump-out, in pumped discharges
3)Compare low density (ne/nGW ~ 0.3) and high density (ne/nGW ~ 0.5) L-modes
4)H-mode experiments also possible, may wait to 2009
To achieve good precision in the net uptake, the beam TIV�??s will be closed to avoid beam fueling and cold gas fueling from the charge exchange cell. This will also avoid unmonitored exhaust of gas between shots by pumping of the beamline cryopanels. The turbo pump TIV�??s will also be closed throughout most of the shot cycle to assist in gas balance. |
| Experimental Approach/Plan: | Key features to achieve good precision:
6:00 AM, Cryopump LN2 shield and LHe tube both at room temperature
6:30 AM, run a 15 minute helium glow.
8:30 AM, LN2 shield 77 K, LHe tube at roughly 77 K.
Part 1: 0.5 day of unpumped discharges with no between shot helium glow
1)Close Beam TIVs (no beam heating/fueling during shot, no pumping after shot)
2)Turbos TIVs closed during shot and for several minutes after shot: allow pressure in vessel to come to equilibrium after shot. Get an accurate and precise measure of vessel pressure using the capacitance manometers. Then open turbo TIV�??s to exhaust vessel prior to next shot, close turbo TIV�??s and start shot cycle.
3)Source from gas puffing should be well calibrated. Consider calibrating to exact waveform used in shots. Consider using a preprogrammed waveform rather than feedback control of density.
4)Use RGA to get an estimate of hydrocarbon content of post shot vessel gas.
Part 2: 0.5 day of pumped discharges with no between shot helium glow. Cool helium tube to LHe temperature
1)Same procedure as above except add a post-shot cryopump regeneration between each shot. Measure vessel pressure after regeneration. The open turbo TIV�??s and exhaust vessel. Re-cool LHe tube and close turbo TIVs before next shot cycle.
Part 3: End of day, also warm the LN2 shield and measure pressure and content of evolved gas with capacitance manometer and RGA.
Day 1: Low density, attached divertors (ne/nGW ~0.3)
Day 2: High density, cold, detached divertors (ne/nGW ~0.6). |
| Background: | Motivation: Retention of T in a reactor or ITER has the potential to limit in operation (to remove the T) or even preclude operation. At present the capability to predict the rate of T retention is poor, leading to large uncertainties in the mitigation requirements. A better understanding of the retention processes involved, how these processes evolve with time, as well as the role of local plasma bombardment in retention/removal is needed.
The goal of this proposal is to utilize the same technique of fuel particle accounting in both a high-Z (C-Mod) and low-Z PFC tokamak to determine the retention rate and processes as a function of plasma and operational parameters. More specifically, by empirical observations of global fuel retention versus operating conditions, we would seek to determine the location and quantity of retained fuel, the relative importance of processes that lead to retention (e.g. codeposition , bulk permeation), how these process would evolve with long plasma pulses or steady operation and how plasma and operational parameters affect the uptake and removal of D from any such reservoir.
Because of the complexity of the physical and chemical processes leading to retention, we anticipate the effort to extend over a few years. For 2008 we propose initial comparisons of the discharge-integrated retention/removal rate between graphite and molybdenum plasma facing surfaces in a set of matched L-mode discharges just below and above the detachment threshold. This information will be compared to divertor and first-wall ion fluxes, PFC erosion rates (and thus related to co-deposition rates). The dependence on density for simple discharges will develop the technique for follow-on studies that will examine the dependence on other parameters such as magnetic geometry, H-mode, and pulse length. |
| Resource Requirements: | Single Null, grad B ion drift away from x-point (high L-H threshold) and shape suited to window-frame measurements of radial flux.
ECH heating (2 gyrotrons/4 seconds): Maintain attached OSP in low density case
Bt ~ 2.1 T, Ip ~ 1.1 MA (choose values in coordination with C-Mod and compatible with ECH heating). |
| Diagnostic Requirements: | Pressure gauges: Capacitance Manometers and ASDEX gauges
RGA
CO2 interferometer; Core density
Thomson: Core and Pedestal profiles
Langmuir Probes (ion flux, ne and Te at divertor plates and upper baffle knee)
MDS: Impurity generation
Filterscopes (recycling)
CER spectrometers used for C, CD fluxes at midplane.
Midplane and X-point Fast Stroke Probes: SOL fluxes and profiles |
| Analysis Requirements: | 1)P1=PCM(vessel after shot) with gasa program but no plasma. (For divertor cryopumping case, must also regenerate cryopump before PCMM measurement.)
2)P2= PCM(vessel after shot) with same gasa program for plasma ops.
3)Relative uptake= (P1-P2)/P1
4)Absolute uptake= (P1-P2)*vessel volume
5)Time dependent input-exhaust provides time behavior of wall uptake
One source of systematic error is conversion of D2 molecules to hydrocarbon molecules, e.g. CD4, which will result in an under-measurement of the D content in the post vessel gas from the capacitance manometer. RGA can help correct for this possible error. |
| Other Requirements: | -- |
| Title |
134: Characterization of QH-mode and EHO properties with edge toroidal rotation |
| Name: | Punit Gohil () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | K.H. Burrell, M. Fenstermacher |
| Description: | Determine the properties of QH-mode plasmas and the EHOs as a function of the edge toroidal rotation. Change the edge toroidal rotation over multiple cycles of decreasing and increasing edge rotation in Q-mode plasmas and evaluate how the QH-mode plasmas and the EHO characteristics change. This is an ITPA related joint experiment. |
| Experimental Approach/Plan: | Establish QH-mode plasmas and then vary the edge rotation by changing the raio of co to counter beams in which the edge rotation decreases and increases over multiple cycles. Determine how the QH-mode plasma properties and the EHO characteristics change over these cycles through documentation by multiple edge diagnostics, especially theedge turbulence diagnostics. |
| Background: | Our knowledge of QH-mode plasmas and the EHO properties can be improved significantly by gaining a large set of data related to their dependence on the edge toroidal rotation, which appears to strongly affect the characteristics of the QH-plasmas and the EHOs.This experiment aims to obtain a systmetic and comprehensive data set on these quantities as a function of the edge toroidal rotation for a large range of operating conditions. |
| Resource Requirements: | co and counter beams, icoil, cryopumps |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
135: Carbon wall tritium removal using massive hydrogen injection |
| Name: | Eric M. Hollmann () |
Affiliation: | University of California, San Diego |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Requested |
Co-Author(s): | A. Pigarov, D. Rudakov |
| Description: | Injection of massive quantities of H2 into a H-mode discharge is proposed as a possible method of rapidly replacing T bound in soft C layers in the vicinity of the divertor strike points. MGI shutdown/disruption heat loads and wall fluxes are known to be much broader than the normal discharge strike points. Also, massive H2 injection has been shown to cause a very high density plasma (20x density increase), with fairly significant divertor and wall plasma fluxes (thermal quench radiated power loss of ~20% or less). |
| Experimental Approach/Plan: | To test the efficiency of divertor isotope replacement during hydrogen injection, MGI of D2 would be performed near or at the end of of H2 run day, with a graphite DiMES sample exposed and saturated with D2. After H2 MGI, the DiMES sample could be retracted and then analyzed for D2 and H2 content. For consistency, the reverse experiment could also be performed (H2 MGI into a D2 saturated DiMES sample). The intial target discharge could be biased downward slightly to ensure that the post-TQ VDE drifted downward and maximized divertor plasma flux. |
| Background: | Removal of co-deposited tritium from graphite divertor tiles is a challenging problem for which a wide variety of possible solutions have been proposed. The use of massive gas-injection shutdowns was proposed previously by D. Whyte. The present proposal is new in that instead of injecting a high-Z impurity like Ar and using the resulting radiation flash to thermally desorb T from the walls, H2 is injected and driven into the divertor in the resulting disruption, replacing T bound in the C surface. A preliminary piggyback experiment testing this idea (proposed by A. Pigarov) was performed in 2007, with encouraging initial results. |
| Resource Requirements: | A single high power shot during a H2 run day, as well as a single high power shot during a D2 run day. DiMES with graphite sample (and MiMES, if possible). |
| Diagnostic Requirements: | MDS and RGA could be used to monitor H/D ratios in subsequent discharges; this could provide some clue as to the global amount of H2/D2 swapped in a single MGI shot. |
| Analysis Requirements: | Thermal desorption spectroscopy of DiMES graphite samples can be done at UCSD. |
| Other Requirements: | -- |
| Title |
136: Completion of MP 2007-01-02: Dependence of Er, turbulence, and transport on RMP amplitude |
| Name: | Richard A. Moyer () |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | This goal of this proposal is to complete a scaling study of the effect of n = 3 RMPs on Er rotation, turbulence, and transport in ELM suppressed H-modes begun on June 24, 2007 as part of MP 2007-01-02. Successful RMP ELM suppression has been achieved at ITER-like pedestal collionalities by reducing the pedestal pressure gradient below the peeling-ballooning stability limit. This reduction results primarily from a reduction in pedestal density, rather than Te. A possible mechanism for this density pumpout is the observed increase in turbulence (density and magnetic fluctuaitions) which may play a similar role to the EHO which drives increased particle transport in QH modes [Moyer et al, IAEA; Snyder et al, IAEA]. Further, in high triangularity discharges, the pedestal pressure gradient in most strongly reduced at smaller minor radii than the peak value, suggesting that the transport changes might occur deeper in the discharge than the transport barrier. In this experiment, we will measure the changes in turbulence levels and properties versus radius, RMP dbr/Bt, and plasma rotation, and correlate these changes with profile changes, peeling-ballooning stability, and ELM behavior to assess whether or not increased fluctuation-driven transport in or near the top of the pedestal is the origin of the increased radial particle transport that leads to ELM suppression. |
| Experimental Approach/Plan: | Re-establish a robust, LSN H-mode with good ELM suppression: ITER-similar shape, ITER-like pedestal collisionality, co-NBI. Use multiple shots to characterize edge fluctuations with correlation reflectometry, BES, PCI, and probes (in SOL). Step I-coil current in each shot to obtain 3-point scan; repeat shots at interleaved currents to fill in scan. Repeat this approach for increasing levels of ctr NBI/lower target toroidal rotation. |
| Background: | To date, experimental results suggest that the density pumpout which reduces the pedestal pressure gradient enough to stabililze P-B modes might be due to an observed increase in edge fluctuation levels, in much the same way that the EHO produces Type I ELM-free H-modes by driving enhanced radial particle transport. However, we lack a conclusive correlation of the level and location of this increased fluctuation level with density pumpout.
In 2007, we undertook a 1 day experiment, of which this turbulence scan was a part. Unfortunately, various limitations to machine availability limited this study to a single I-coil current and rotation level. |
| Resource Requirements: | 5 co and 2 counter NB sources
I-coil with n = 3 operation up to 6.5 kA
Divertor cryopumps
1-2 full days of operation are envisioned |
| Diagnostic Requirements: | core, tangential and divertor Thomson scattering
CER system for ion profiles, rotation and Er
Floor Langmuir and reciprocating probes
Fast IRTV (Juelich; if available) or LLNL IRTV
Full pedestal and divertor diagnostics
Fast framing camera (UCSD)
Fast and Mirnov magnetics
Fluctuation diagnostics |
| Analysis Requirements: | these discharges will require extensive time commitment to analyze the turbulence data and build radial profiles of rms amplitudes, auto-correlation times, correlation lengths, etc. These data should provide an excellent dataset for turbulence modeling. |
| Other Requirements: | -- |
| Title |
138: Pellet induced H-mode at low toroidal rotation |
| Name: | Punit Gohil () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | L. Baylor, T. Jernigan |
| Description: | Produce pellet induced H-mode plasmas below the nominal threshold power for different sets of plasma conditions with low toroidal rotation. |
| Experimental Approach/Plan: | Inject inside and outside launched pellets in to L-mode plasmas at input powers well below the H-mode power threshold for a given set of conditions and at low toroidal rotation. Determine the power threshold with power scans using the pellets and document the plasma edge with edge turbulence diagnostics. |
| Background: | The ability to lower the H-mode power threshold using pellets has been proven from previous studies. However, the influence of the edge toroidal rotation has now to be determined for these plasmas and this experiment aims to resolve this issue. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
139: Direct Measurement of Momentum Drag from Error Fields |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | T. C. Luce |
| Description: | By modulating the error fields, and two comparing discharges where the phase of the error field has been changed by 180 deg, the profile of the error field drag can be determined. The toroidal rotation speed as measured by CER with ~5 ms resolution can be fit to a linearized (perturbative) momentum transport equation with two unknown profiles: the momentum diffusivity and the error field drag. Making a consisent fit of the data for both signs of error field perturbation helps to distinguish between the transport effect and the drag effect.
This modulation measurement can be used to determine the following effects: (1) the interaction between the error fields and magnetic islands, (2) resonant vs. non-resonant error field drag, and (3) rotational screening of the error field drag. |
| Experimental Approach/Plan: | (1) Establish stationary target plasma with high toroidal rotation rate. We should compare plasmas with and without tearing modes to document the interaction between magnetic islands and error fields. (2) Modulate the error field between 25-100 Hz. The stronger the plasma response, the higher the modulation frequency can be. Repeat with a 180 deg phase shift. (3) Vary q95 from <3 to >4 to help distinguish between resonant and non-resonant effects. (4) Repeat at lowest possible toroidal rotation rate. |
| Background: | This method is analogous to measuring the heating profile or the current drive profile by modulating the source, both of which have been done on DIII-D. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
140: Pellet pacing of ELMs in low toroidally rotating plasmas |
| Name: | Punit Gohil () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | L. Baylor, T. Jernigan |
| Description: | Determine the effectiveness of pellet pacing of ELMs as a function of the toroidal rotation by injecting pellets at varying frequencies into plasmas with different plasma rotation. |
| Experimental Approach/Plan: | Produce a set of standard ELMing H-mode plasmas with different toroidal rotations and inject pellets at relevant frequencies for ELM pacing and document the effectiveness at different rotation values. |
| Background: | The sensitivity of the ELM properties to toroidal rotation may be significantly affected by pellet injection since the the pellets will change the toroidal rotation through changes in the edge density. This experiment aims to resolve how the interplay between the pellets and the edge rotation affect the ELMs, especially at low toroidal rotation which is very ITER relevant. |
| Resource Requirements: | co and counter beams, pellet injector |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
141: Enhanced ohmic confinemnt using edge RMPs |
| Name: | Todd E. Evans () |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | tbd |
| Description: | The goal of this experiment is to obtain enhanced ohmic confinemnt discharges using I- and C-coil edge RMPs in order to study the basic physics of edge transport barriers. A stochastic transport barrier is attractive because its properties can be controlled using the current and mode spectrum of the external coils. This provides a tool that can be used to test transport barrier theories and to study the properties of plasmas (especially the physics of the pedestal formation, edge flows, Er profiles and changes in turbulence levels) with enhanced confinement over a range of parameters such as q_a, fueling rates, ohmic heating power levels and plasma shapes. |
| Experimental Approach/Plan: | Circular HFS wall limited ohimic plasmas will be used to minimize the level of cross field transport. Circualr plasmas are needed to minimize the area of contact with the HFS wall and the local recycling flux from the wall. The discharge will be initiated with the minimum amount of gas fueling needed to get stable operating conditions and the gas feed will be turned off as soon as possible after the plasma current has fully penetrated. The density will be allowed to deacy at the natural rate determined by the HFS recycling and the confinement. Once a stable density decay rate has been established various combinations of I- and C-coil currents and mode spectra will be used to induce the edge stochasic transport barrier (ESTB). After obtaining reproducible ESTBs q_a will be scanned by changing Bt while keeping Ip and the ohmic input power fixed. Then at fixed q_a we will scan the ohmic heating power by varying Ip/bt. If time permits we will increase the elongation of the plasma and the contact area of the plasma with the HFS wall. This will increase the wall fueling and reduce the rate of decay in the density after the intial gasa fueling is turned off. We will use hydrogen discharges for the first experiment of this type since this may help improve our understanding the physics of edge transport barrier formation in the hydrogen phase of ITER. |
| Background: | Signatures of an ESTB formation were first seen during ergodic magneic limiter (EML) experiments in TEXT (1985). Hints of improvements in the confinement were also seen in the helical island divertor experiment (HIDEX) in JIPP T-IIU (1987) and strong enhancement in the particle confinement were seen in circular HFS limited ergodic divertor (ED) experiments in Tore Supra with both ohmic (1988) and lower hybrid heated plasmas (1989). More recently TEXTOR (2006) has reproduced the Tore Supra results using NBI heating in circular HFS limited plasmas with the dynamic ergodic divertor (DED). Based on the accumulated experience gained in these earlier experiments we should be able to produce an ESTB in DIII-D using the C- and/or I-coils (assuming we have a reasonably good edge spectrum and sufficient coil currents which we believe is the case). Since DIII-D has significantly better edge diagnostics, pedestal profile and equilibrium reconstruction tools than these previous experiemnts we have a unique opportunity to develop a basic understanding of the edge transport, pedestal and barrier formation physics and to compare the properties of the ESTB to those of edge transport barriers in H-modes. This may result in a better understanding of the physics that controls the L-H power threshold. |
| Resource Requirements: | I- and C-coil. |
| Diagnostic Requirements: | The full set of edge turbulence and transport diagnostics (except BES and CER altough we may want to introduce short beam blips to obtain theis data if comaptable with the ESTB). |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
142: High Beta, Reactor Relevant Hybrid |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | This experiment will integrate a high beta hybrid plasma (similar to shot 129323) with the reactor relevance of Te~Ti and low rotation. Up to 3MW of ECH and 1 MW of fast wave direct electron heating can be used to raise Te. The counter beams will be used to reduce the toroidal rotation rate. |
| Experimental Approach/Plan: | (1) Repeat shot 129323 but with better feedback control of beta_N. Desire beta_N~3.5. (2) Add core electron heating with EC (3 MW) and FW (1 MW) to bring Te and Ti together. (3) Inject counter NBI to lower the toroidal rotation rate. Can use PCS feedback control of rotation rate. (4) If 2/1 mode becomes a problem, then redirect some gyrotrons to deposit ECCD at q=2 surface. |
| Background: | Shot 129323 achieved beta_N>3.5 with q95~5. This beta_N is above the ideal no-wall limit, so wall stabilization is probably playing a role. However, RWM experiments showed that only a very modest amount of rotation is needed for stabilization, so there may be room to lower the rotation rate while maintain the high beta_N value. If the 2/1 NTM becomes a problem at this high beta, then some ECCD at the q=2 surface should be able to suppress this mode. The rest of the RF power (EC and FW) should be deposited close to the magnetic axis to raise Te close to Ti. The NBI heating target shot had Ti(0)=7.1 keV and Te(0)=4.8 keV, with the temperatures nearly equated for rho>0.5. Therefore, a few MW of central electron heating should be able to bring Te and Ti together. |
| Resource Requirements: | NBI: All 7 sources required.
EC: Minimum of 5 gyrotrons.
FW: Desire >1 MW coupled to H-mode plasma. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
143: Particle confinement regimes with RMP in n=3 |
| Name: | Oliver Schmitz () |
Affiliation: | FZ Juelich |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | tbd |
| Description: | At TEXTOR-DED two particle confinement regimes were obtained under application of RMP fields from the DED - an improved particle confinement and a controlled degradation, the particle pump out. These experiments were done in m/n=6/2 and m/n=3/1 base mode configuration (m -> poloidal mode number, n-> toroidal mode number). Recently a transition between both regimes just by increasing the perturtbation field strength was found. With this proposal we suggest to reproduce these results with n=3 I-coil (unique for D3D) in HFS limited L-mode configuration and see how this setting affects the limiter H-mode transition. Furthermore the role of plasma elongation (islands will be deformed) and the transition towards the poloidally diverted topology should be studied. |
| Experimental Approach/Plan: | Do ohmic plasmas limited on HFS (see also ID 141 by T. Evans of this ROF) and produce both regimes with n=3, study transition behavior. Go to limiter H-mode and study the effect of the two settings obtained before on the limiter H-mode performance, elongate plasma and study impact, go to pol. div. settings and try to establish the improved confinement with RMP. See if here PO can be produced also (linked to TF ELM control). Check if with the improved confinement settings - if found - the H-mode performace can be affected. |
| Background: | At TEXTOR-DED two particle confinement regimes were found. On the one hand an improved particle confinement was obtained shifting the plasma towards the perturbation source (see also ID 141 by T. Evans, this ROF). The preliminary conclusion was that the equilibrium was optimzed such that just the next resonant island chain was destroyed when shifting the plasma. This leads to a short cut between these island's x-points and therefore for a change in the sheath potential and by that of the radial electric field. Accordingly an increase of the poloidal rotation was seen when the density steps up. These density steps are correlated to changes in the heat and particle flux on the DED target, indicating that the heteroclinic tangles of the next deeper island chain connect at this point. In contrast a controlled degradation of the particle confinement - the particle pump out - was found by shifting the plasma with constant edge q away from the perturbation source. A candidate for the mechanism is that the perturbed field lines don't reach the wall but lead to an ergodic domain with diffusive transport characteristics and enhanced radial transport. Fuelling the plasma with glas blow was hardly possible. Very recently we could resolve the transition between both regimes at fixed position just increasing the perturbation strength. Here a pronounced 4/1 island dissapears and we get immediately the transition from pump out to the improved confienemt. The characteristics of this transition should be studied with different base mode (n=3) and with the facility to elongate the plasma changing the steepness of the q profile. Here the resonant layers and accordingly the islands created come closer together and the resulting change in the transition shall be elevated. This will contribute to the understanding of the island overlapp criterium and might be also a method to check it comparing to the SURFM results. Going to the poloidally diverted configuration shall enhance the information if there is a smooth transition and how it evolves. The question if there can be an improved confinement produced by RMP in pol. div. L-mode plasmas is very interesting (see ID 141 of T. Evans again). |
| Resource Requirements: | L-mode plasmas limited on HFS, beam blips if possible for L-mode (CER), developement of this scenario and the limiter H-mode (beams accordingly), I-coils in n=3, EFC with C-coils
For this experiments the n=3 internal coils and the facility to elongate the plasma and go to pol. div. configuration is unique at DIII-D |
| Diagnostic Requirements: | fast probes, full TS capability, CER beam box, DiMES TV camera set to inner wall, possibly also IR camres with this view, any high resolution edge diagnostic (BES-Li beam) |
| Analysis Requirements: | SURFM and TRIP-3D post experiment, kinetic EFITS for improved magnetic reconstruction |
| Other Requirements: | -- |
| Title |
144: Resolve deviations between the measured and the EFIT predicted strike point position |
| Name: | Oliver Schmitz () |
Affiliation: | FZ Juelich |
| Research Area: | Model based Control |
Presentation time: |
Not requested |
Co-Author(s): | M. Jakubowski (MPI Greifswald) |
| Description: | Compare EFIT prediction for the SP position with measured data. |
| Experimental Approach/Plan: | Do pol. div. H-mode plasmas for different shapes (in particlular the ISS applied in ELM control experiments) and sweep the SP for continous comparison. Also do some of the sweep steps static to see if there is a difference. |
| Background: | During the application of the fast framing IR camrea from TEXTOR and the DiMES camera with view perpendicular to the 45 deg tile, a deviation of the strike point location seen in the camera pictures from the EFIT prediction was recognized. This deviation ranges between a few milimeters to 2-3 cm. Similar observations were made with LP data from the divertor during strike point sweeping. This has strong implications for the magnetic modelling and therefore for the code benchmark and deduced messages from the comparison of modeling/experiment. |
| Resource Requirements: | sweep of OSP and ISP, ISS H-mode requirements |
| Diagnostic Requirements: | LP target, DiMES TV observing ISP and OSP simultaneousely, tanTV lower divertor cameras, IR cameras and fast framing TEXTOR IR would be very desirable |
| Analysis Requirements: | EFIT team support, kinetic EFITs for higher accuracy, post experiment TRIP-3D to compare |
| Other Requirements: | -- |
| Title |
145: Resolve impact of mode spectrum on particle transport regimes with RMP |
| Name: | Oliver Schmitz () |
Affiliation: | FZ Juelich |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | tbd |
| Description: | If ID 141 and ID 143 will be succesfull it is desirable to analyze the impact of changing the toroidal base mode number to n=2,1 on the transport regimes. This is of particular interest as in these base modes the ELMs were not supressed in ELM control experiments of R. Buttery last year. |
| Experimental Approach/Plan: | Do the same scan/approach as described in ID 143 but with n=2 and n=1 and different EF mixture.
If here the tranbsport can be controlled successfully go back to the pol. div settings and apply findings for ELM control with n=1 external and n=2 fields. |
| Background: | see ID 141 and ID 143. DIII-D has the unique capability to study the internal n=3 and the externall/internal n=2 and n=1 mixtures of RMP and EF. This is used here. |
| Resource Requirements: | same as ID 143 |
| Diagnostic Requirements: | same as ID 143 |
| Analysis Requirements: | same as ID 143 |
| Other Requirements: | -- |
| Title |
146: Burst Disk Gas Jet for Disruption Mitigation on DIII-D |
| Name: | Larry R. Baylor ( ) |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Disruptions |
Presentation time: |
Requested |
Co-Author(s): | T. Jernigan, P. Parks, E. Hollman, S. Combs, C. Foust |
| Description: | A new multi-valve gas jet system that uses burst disks at the exit of the valve is proposed to enable high gas flow rates. This system is under development now at ORNL and if tested successfully in the lab it could be employed in 2008 for use on DIII-D. |
| Experimental Approach/Plan: | The experiments would be similar to the previous gas jet disruption mitigation experiments. Total flow would be limited to 2000 torr-L to minimize NBI interaction. |
| Background: | The use of gas jets for disruption mitigation was pioneered on DIII-D. A limitation of the technique is the conductance of the tube that the jet must flow in. A test of the highest possible gas jet flow rate is needed to compare with theory. The proposed burst disk system will enable that test. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | Clean vent for installation of gas jet assembly at exisiting R+1 DM port. |
| Title |
147: Burst Disk Gas Jet for Disruption Mitigation on DIII-D |
| Name: | Larry R. Baylor () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Disruptions |
Presentation time: |
Requested |
Co-Author(s): | T. Jernigan, P. Parks, E. Hollman, S. Combs, C. Foust |
| Description: | A new multi-valve gas jet system that uses burst disks at the exit of the valve is proposed to enable high gas flow rates. This system is under development now at ORNL and if tested successfully in the lab it could be employed in 2008 for use on DIII-D. |
| Experimental Approach/Plan: | The experiments would be similar to the previous gas jet disruption mitigation experiments. Total flow would be limited to 2000 torr-L to minimize NBI interaction. |
| Background: | The use of gas jets for disruption mitigation was pioneered on DIII-D. A limitation of the technique is the conductance of the tube that the jet must flow in. A test of the highest possible gas jet flow rate is needed to compare with theory. The proposed burst disk system will enable that test. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | Clean vent for installation of gas jet assembly at exisiting R+1 DM port. |
| Title |
148: electron transport in sawteeth |
| Name: | Ed Lazarus ( ) |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | Doyle, Rhodes, McKee, Luce |
| Description: | observe differences in fluctuation spectra seen in bean and oval sawteeth |
| Experimental Approach/Plan: | create plasmas we have run before
get reflectrometry, BES, doppler data
add short pulses of central ECH and look for
enhancement of fluctuations |
| Background: | In previous work we have discovered that we can create very large
changes in electron energy transport inside the sawtooth inversion
radius by changing the plasma shape. The differentiationn is perhaps the
maximum possible. In the bean shape in that the electron thermal
diffusivity is in agreement with Callen's paleoclassical calculation,
postulated to be the minimum possible. However in the oval, the electron
thermal diffusivity inside the sawtooth inversion radius is infinite: it
is not possible to create a local gradienet in eletron temperature. Lest
this be interpreted as some poor quality plasma dominated by MHD
activity, we point out that the ion confinement is excellent;
approximately neoclassical. In such a situation it would be advantageous
to search for fluctuations that correlate with these extreme differences
in electron transport. |
| Resource Requirements: | No unusual resources required.
A single gyrotron, possibly two. |
| Diagnostic Requirements: | all fluctuation diagnostics. The usual complement
of plasma diagnostics will be employed. |
| Analysis Requirements: | No abnormal requirements. |
| Other Requirements: | -- |
| Title |
149: Hybrid beta limit at lower rotation |
| Name: | Robert J. La Haye ( ) |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | R. Buttery, D. Brennan |
| Description: | q95=4.4 hybrid discharges at 2/3 of 4li go 2/1 unstable when rotation is greatly reduced with counter beams added. No systematic experiment of varying the rotation and then raising beta has been made to find the role of rotation on the limit. |
| Experimental Approach/Plan: | Reproduce hybrid discharges well below 4li,
vary the rotation, and then slowly raise beta,
from shot to shot. Similar was already done in 2006
for the sawteething H-mode. |
| Background: | The sawteething H-mode shows a considerable decrease in the 2/1 unstable beta as rotation is reduced from all co beams to as far on the counter side as was tried. |
| Resource Requirements: | At least 4 co and 2 counter beams.
Cryopumping etc as usual for hybrid. |
| Diagnostic Requirements: | Usual diagnostics. |
| Analysis Requirements: | PESTIII for tearing. |
| Other Requirements: | None. |
| Title |
151: Test of Pellet Fueling Fast Transport Theory |
| Name: | Larry R. Baylor () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | General IP |
Presentation time: |
Requested |
Co-Author(s): | P. Parks, T. Jernigan |
| Description: | An experiment is needed to better understand the physics mechanism for fast particle transport that occurs when pellets are injected. Much deeper particle deposition is observed with HFS pellet injection on DIII-D. This experiment will examine the scaling of this phenomenon with B,q,beta in order to compare with theory and extrapolate to ITER. |
| Experimental Approach/Plan: | Inject 1.8mm D2 pellets into otherwise steady L-mode and H-mode discharges with a scan of B,q while holding Beta and n relatively constant. Alternate the inner wall injection location (midplane and 45degree locations) and measure the density profile perturbations for the different pellets to determine the radial drift distance and the difference in deposition from the two inner wall locations. |
| Background: | Three theories or models have been proposed to explain this phenomenon based on ExB polarization drift and MHD pellet displacement. The MHD model proposed by Strauss has a local q dependence on the displacement that can be tested. Rational surfaces are also predicted to play a role in the Pegourie-Commaux model. This experiment should be done in concert with similar experiments in AUG and JET in order to maximize the scaling informatin obtained. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | Thompson Scattering
Fast Camera looking at inner wall
Pellet Filterscope for cloud measurements |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
152: 2D Velocimetry of edge turbulence structures at the LH-transition |
| Name: | Dave Schlossberg ( ) |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | G.R. McKee, M.W. Shafer, C. Holland, G. Tynan |
| Description: | Previous studies have revealed complex turbulence eddy structures at the time of the LH transition that reveal evidence of an increasing poloidal shear in the plasma edge. With the newly expanded BES array (to be implemented 2008), with up to 64 high-sensitivity channels, new explorations of turbulence physics will become accessible. By utilizing BES and other recently upgraded turbulence diagnostics, a more complete investigation of turbulence dynamics up to and at the time of the LH transition will be conducted. Possible H-mode trigger mechanisms (zonal flows/GAM), the role of turbulence flows and ExB shear in LH transition threshold power, comparison of flow shear and turbulence decorrelation rates, zonal flow behavior, nonlinear energy transfer, and spatial asymmetries in the eddy structures will all be investigated. |
| Experimental Approach/Plan: | Perform LH transition via neutral beam and possibly ECH. Obtain plasmas with fairly long ELM-free H-mode periods, and use the 64 upgraded high-sensitivity BES channels configured in an 8x8 array to examine turbulence behavior in the edge region (0.9 < r/a < 1.0) and also closer to the core (0.6 ~< r/a ~< 0.8). If necessary, alternate beam injection for CER/MSE measurements. Examine USN and LSN magnetic geometries for comparison of turbulence behavior at the transition time. |
| Background: | Perform LH transition via neutral beam and possibly ECH. Obtain plasmas with fairly long ELM-free H-mode periods, and use the 64 upgraded high-sensitivity BES channels configured in an 8x8 array to examine turbulence behavior in the edge region (0.9 < r/a < 1.0) and also closer to the core (0.6 ~< r/a ~< 0.8). If necessary, alternate beam injection for CER/MSE measurements. Examine USN and LSN magnetic geometries for comparison of turbulence behavior at the transition time. |
| Resource Requirements: | 150L&R, CER beams, other beams necessary for turbulence diagnostics, possibly ECH |
| Diagnostic Requirements: | BES, CER, other turbulence diagnostics |
| Analysis Requirements: | CERFIT for specific shots |
| Other Requirements: | -- |
| Title |
153: Simultaneous fluctuation amplitudes measured across the plasma radius in L- and H-mode |
| Name: | Dave Schlossberg () |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | G.R. McKee, M.W. Shafer, C. Holland, G. Tynan |
| Description: | Measure the density fluctuation amplitude across the radius of the plasma, both in L-mode and H-mode, and across the LH transition. With the recent upgrades to the BES system, it is possible to obtain fluctuation measurements at 64 spatially-resolved radial locations, spanning up to approximately 50 cm. By simultaneously measuring turbulence amplitudes along much of the plasma�??s entire radius, turbulence dynamics from the core to the edge can be quantified and spreading of turbulence can be measured. Shot-to-shot variation in turbulence behavior can be eliminated since comparisons will be done within a single shot. Radial correlation lengths can also be compared across the radius of the plasma. By investigating both L-mode and H-mode plasmas, a comparison of turbulence amplitudes can be made. Previous measurements show that turbulence is rapidly reduced at the LH transition even in the core region.
The diagnostic arrangement for BES is such that it would be difficult to change the array dimensions during an experiment. Therefore, the BES array would likely be configured as a 1x64 array for the duration of the experiment. |
| Experimental Approach/Plan: | Configure the BES array as a 1x64 radial array, spanning the radius of the plasma. Obtain stable L-mode, ELM-free H-mode, and LH-transitioning plasmas, and measure the turbulence amplitudes across the plasma radius. |
| Background: | Previous studies have found that turbulence amplitudes decrease at the time of the LH transition. However, it has yet to be determined whether these decreases in turbulence amplitudes propagate from, for example, the edge to the core region, or if they occur simultaneously across the plasma. By recording simultaneous measurements across the entire plasma radius, possible turbulence spreading and suppression front propagation will be measured. Furthermore, turbulence amplitudes in the core region will be compared to values in the edge region in L-mode, H-mode, and near the LH transition time. |
| Resource Requirements: | 150L neutral beam |
| Diagnostic Requirements: | BES, CER |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
154: Tearing Mode Beta Limits and Error Fields in Low Rotation Baseline Plasmas |
| Name: | Richard Buttery
( ) |
Affiliation: | UKAEA |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | R J La Haye, E Strait, D Brennan |
| Description: | A proposal is made to explore NTM thresholds at low rotation with error field ramps. In this way the sensitivity of ITER baseline plasmas to error fields can be determined to address: (i) whether error sensitivity is increased at low rotation and medium betan values; (ii) how broad the effect is in rotation value; (iii) what the scaling of the effect is for extrapolation to larger devices; and (iv) shed further light on NTM physics via the perturbative effects of the error field. These questions can be answered with a simple set of reliable shots taking about a day or so. Results will be used to determine error field correction and rotation requirements for mainstream scenarios in future large devices such as ITER. |
| Experimental Approach/Plan: | A simple and efficient scan is proposed: dial up specific torque and beta values, then apply error field ramps. Scan would explore a small grid in betan (1.5, 1.8) and torque (+/-50%, 25%, 12%, 0). At some chosen optimal point (low positive rotation, betan~1.8) 1d density and TF scans would then be performed to allow dimensional scaling to be obtained (using a dimensional constraint to infer machine size dependence, as previously used for Ohmic error field studies and confirmed by CMOD). Some additional shots with beta ramps at fixed error field and torque may augment the data set. A single phase scan would also checkout the intrinsic error role. Conditions: standard DIII-D single null ITER-like shape, q95=4.3 for good stability/disruption avoidance. Shots would be based on 2006 experiments where a robust shot design was arrived at. I coils would be used to correct intrinsic error or apply additional error, as these give cleanest and best understood error field spectra effects. |
| Background: | Recent DIII-D studies [Buttery EPS 2007] have shown that 2/1 tearing mode thresholds can fall significantly as net torque is removed, to betan values ~2. These studies also gave indications that beta thresholds were further lowered when error fields were applied, though data was limited to 3 points at medium (+~30%) torque. Certainly at high torque, an effect of error fields lowering NTM beta limits has been clearly observed [Buttery EPS05], while both experimentally and theoretically error field sensitivity is found/expected to be increased in low rotation plasmas [Buttery NF 2000, Fitzpatrick PP 1994].
Thus it is now time to systematically address this issue of error field sensitivity and impact for future devices such as ITER, with specific scans to assess the error field thresholds as a function of beta and rotation to determine the severity and breadth of the effect, and further scans in density and temperature, to infer scalings. The action of the error fields, in locally braking q=2 rotation is also a powerful tool to understand NTM physics, via the detailed observation of the chain of events involving plasma rotation profiles and mode onset (locked/rotating) behaviour. [ITPA MDC 3]. |
| Resource Requirements: | 2 co and 2 counter beams, plus 30L and 330L blips. I coils. ~1MA, 1.6T. Lower pump. |
| Diagnostic Requirements: | CER (all channels needed), ECE, magnetics, TS. |
| Analysis Requirements: | Results should be largely self evident, with some modest processing to obtain scalings, and standard DIII-D codes to obtain error field values. |
| Other Requirements: | None. |
| Title |
155: 2/1 NTM beta limits in modest to strong counter torque plasmas |
| Name: | Richard Buttery
() |
Affiliation: | UKAEA |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | R J La Haye, E Strait, D Brennan |
| Description: | A proposal is made to complete a previous torque scan exploring NTM beta threshold scaling with rotation. This will answer the critical question of how the threshold scales with increasing counter torque, which goes to the heart of understanding the physics of the behaviour, and therefore of extrapolations of NTM onset physics to future large devices. A simple scan in counter torque is proposed, which should take about half a day or so. |
| Experimental Approach/Plan: | Experiments would simply be an extension of the 2006 NTM rotation scan, with shots adapted for reverse field and current configuration. Points would be taken with up to 4 units of counter torque beams and down to balanced torque, to marry up with previous data. Shots would consist principally of beta ramps to access the 2/1 NTM, with some adjustment of net torque. Perhaps 7-8 data points are needed, though some work may be required to initially re-optimise shot in reverse field configuration, ensuring a robust front end (though a net counter start up to discharges was successfully devised in 2006). Conditions: standard DIII-D single null ITER-like shape, q95=4.3 for good stability/disruption avoidance. |
| Background: | Recent DIII-D studies [Buttery EPS 2007] have shown that 2/1 tearing mode thresholds can fall significantly as net torque is removed, to betan values ~2. However the studies revealed a subtle dependence on rotation, with thresholds falling as co- torque is removed but then remaining low as counter torque and counter rotation was increased. Tantalisingly, the highest counter torque shots gave a slightly lower threshold still. Unfortunately this scan was limited by having only 2 beams in counter configuration. Further shots are needed with increased counter torque (by operating in reverse field configuration) to determine if this is the start of a trend towards even lower thresholds with more counter injection. Also more rotation data is needed for the counter rotation shots from 2006, where operational reasons (need to have a strong net counter torque) prevented obtaining as much CER data as we would have liked.
This is an important physics study to perform because it goes to the heart of understanding the physics, which is required for a prediction of the effect in future large devices such as ITER. The DIII-D results indicate that high magnitudes of rotation or rotation shear are not simply stabilising - stability depends on the sign of rotation as well. This opens up a number of other models that need to be tested with wider data scans, such ion polarisation currents, or changes in delta prime. The resolution of the counter torque behaviour will provide a key constraint on such models. [ITPA MDC 3]. |
| Resource Requirements: | 4 co and 2 counter beams, including 30L and 330L blips. I coils for error correction only. ~1MA, 1.6T. Lower pump. |
| Diagnostic Requirements: | CER (all channels needed), ECE, magnetics, TS. |
| Analysis Requirements: | Results should be largely self evident, but extensive CER analysis after wards to reconcile with physics models. |
| Other Requirements: | None. |
| Title |
156: ECCD control of sawteeth and monster sawteeth to avoid NTMs |
| Name: | Richard Buttery
() |
Affiliation: | UKAEA |
| Research Area: | NTM Stabilization |
Presentation time: |
Requested |
Co-Author(s): | I Chapman, J Graves, R J La Haye, O Sauter |
| Description: | The goal of this experiment is to explore the effects of control and variation in sawtooth period on NTM thresholds in general, with particular emphasis on the most deleterious 2/1 NTM in particular. It is proposed to use ICRH to simulate fast particle effects, partially stabilising sawteeth to lengthen their periods. The impact of this on NTM thresholds should be tested in medium betan (~2) plasmas. ECCD q=1 control (destabilisation) of sawteeth should then be deployed to identify its benefits in raising NTM thresholds. In this way we hope to move towards the control schemes required in baseline and "advanced inductive" (or low q hybrid) scenarios that will be required in future fusion devices such as ITER. The experiments will also provide key insights and tests into the physics of sawteeth and NTM triggering. Extensions could also include the application of this technique on top of ECRH pre-emptive current drive at the NTM resonant surface to understand how this might ease the job for the system. [Note: The author is happy if these ideas are followed up as part of the ongoing and very interesting work being performed in 2006-7 programmes on fast particle sawtooth stabilisation and control, and does not necessarily seek/expect a leading role in these studies. ] |
| Experimental Approach/Plan: | These experiments will be quite challenging, but benefit from DIII-D's unique ECRH and control capabilities. The most challenging element will be to use real time system to keep ECCD targeted on q=1 (or just outside/inside). The approach at this stage is largely proof of principal, so does not require many successful shots, just a step-wise progression through the sequence: (i) establish H modes with beta ramps to trigger 3/2 and 2/1 NTMs; (ii) repeat, applying ICRH to stabilise sawteeth and observe NTM threshold changes; (iii) repeat, with ECCD at q=1 to reduce sawtooth size in presence of ICRH (and scan ECCD power levels needed). Additional shots at fixed betan values may be required to optimise coupling or deposition at various points. An alternative approach, which may prove fruitful should q=1 ECCD tracking be difficult, would be to operate each shot at fixed betan, and then apply ICRH power ramps to vary sawtooth period within a shot; pre-programmed levels/positions of ECCD could then be added in repeat shots to test the effectiveness of sawtooth control. Conditions: Any reliable baseline scenario, q95~4.3 would provide better disruption avoidance, but lower q95 may help access mode more easily. |
| Background: | The ITER Q=10 baseline scenario is expected to suffer from large, long period, fast particle stabilised sawteeth [Porcelli, F., et al., Plas. Phys. Con. Fus. 38 (1996) 2163]. Such events can readily trigger serious, performance terminating, 2/1 Neoclassical Tearing Modes (NTMs) with large amplitude at low betan values, which otherwise appear to be confined to higher beta plasmas [Buttery 20th IAEA 2004]. They also lead to much lower than expected beta thresholds for 3/2 NTMs [Sauter PRL 2002, Buttery NF 2004], which might be expected to reduce fusion power by ~30-40% if left unchecked.
Control of fast particle stabilised sawteeth was demonstrated on JET [Eriksson PRL 2004] using two "flavours" of ICRH: core heating to induce fast particles to stabilise the sawteeth; and q=1 current drive to destabilise them again. However the use of the ICRH for the current drive element may also have helped eject fast particles from the core. ICRH also provides a relatively imprecise control, with a broader deposition that might be desirable. For future devices, we need to demonstrate ECCD control of sawteeth (which can be much more localised and efficient) in realistic medium to high betan scenarios.
Thus this study will help specify requirements for sawtooth control in ITER, and the benefits in terms of requirements for pre-emptive / post-onset NTM control via current drive at the resonant surface. It will also provide key data on the underlying physics, including that of sawtooth stability, and NTM seeding physics. [ITPA MDC5 and MDC8]. |
| Resource Requirements: | 4-5 co beams. ICRH. As many gyrotrons as possible (2 min). I coils for error correction. |
| Diagnostic Requirements: | CER (all channels needed), ECE, magnetics, TS, MSE is key. |
| Analysis Requirements: | Results should be largely self evident, although provide an ongoing basis for more detailed physics investigation into sawtooth physics and NTM triggering. Detailed cutting edge sawtooth triggering MHD modelling will be performed as part of this project. |
| Other Requirements: | None. |
| Title |
157: ELM pacing with small pellets |
| Name: | Larry R. Baylor () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | T.Jernigan, M. Fenstermacher |
| Description: | This experiment is to use the pellet dropper installed on DIII-D to trigger rapid small ELMs in order to test this mode of operation for ITER. |
| Experimental Approach/Plan: | Drop pellets from the dropper into ELMing H-mode discharges at higher rates than the normal ELM rate and compare ELM characteristics with and without the pellets. |
| Background: | ITER needs ELM control to limit energy on first wall from ELMs to 1 MJ per event. Pellet ELM triggering is a possible technique to limit the ELM energy per event by forcing the ELMs to occur at a high frequency. Scenarios based on this technique have been demonstrated on AUG for short durations. Further testing and experiments with this technique are needed extrapolate to ITER. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | IR divertor camera
Fast Camera
Pellet photodiode |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
158: Marginal island for 2/1 NTMs |
| Name: | Robert J. La Haye () |
Affiliation: | General Atomics |
| Research Area: | Stability |
Presentation time: |
Requested |
Co-Author(s): | R. Buttery, M. Maraschek, S. Sabbagh, E. Strait |
| Description: | The marginal island is where the small island threshold physics kicks in, dominates, and rapid stabilization occurs below this size. It determines both how low a beta one has to operate at to remove the metastable space, or how much ECCD has to drive an island down to to remove it. |
| Experimental Approach/Plan: | Excite a 2/1 mode, reduce betap slowly, stay in H-mode, and look for spontaneous stabilization of the 2/1 mode. |
| Background: | 3/2 NTM marginal island widths in either betap ramp down or ECCD removal are about twice the ion banana width. This suggests that the wpol threshold is more important than the wd threshold. Collaboration between DIII-D, AUG, JET, and JT-60U on the 3/2 mode allowed a bigger range in ion banana width and has been published. This empirical scaling seems to work for 2/1 removal but no systematic study has been made. Recent 2/1 beta ramp down exps in NSTX also yield twice the ion banana width. NSTX experiments with 2/1 mode have recently been done and fitted and this is a good test of the aspect ratio effect.
Previous DIII-D experiments dropped out of H-mode before the 2/1 mode stabilized. |
| Resource Requirements: | Standard sawteething H-mode plasma but at high q95
to stay in H-mode as beam power is reduced. |
| Diagnostic Requirements: | Usual. |
| Analysis Requirements: | Code is written for fitting the time dependent MRE
with either the wpol or the wd threshold models. |
| Other Requirements: | -- |
| Title |
159: Turbulence dynamics of integer q surfaces in near-sationary NCS discharges w/ off-axis ECCD |
| Name: | Morgan Shafer ( ) |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | G. McKee, D. Schlossberg, M. Austin, K. Burrell |
| Description: | Develop stationary or slowly evolving NCS L-Mode discharges to examine zonal flows and turbulence dynamics in the vicinity of low-order rational q surfaces at zero magnetic shear to examine ITB formation. Use ECCD to drive off-axis current to slow evolution in near-stationary L-Mode NCS discharges. This will allow for far more detailed examination of the evolution and provide good statistics (long, stationary windows for averaging) for high frequency velocity measurements with BES. |
| Experimental Approach/Plan: | Necessary discharge conditions: L-Mode, NCS, low density. Various ECCD deposition locations will be utilized, ideally rho(qmin)>0.5., with qmin=2. Application of the ECCD will slow down the evolution of qmin to provide near-stationary q profiles. Two cases of toroidal rotation, 2 co- beams, 1 co- and 1 counter- beams. Previous experiments have shown RSAE modes are less excited at lower rotation, which improves velocity measurements from BES. Repeat scans of the BES array will be needed, given sufficient discharge conditions. MSE data is necessary. A specialized BES channel configuration with 4x12 to 4x16 poloidally offset channels maybe used for extended poloidal coverage for ZF studies. |
| Background: | Previous measurements with BES have shown rapid changes in turbulence and turbulence flows near low-order rational q surfaces in NCS discharges. There have similarly been clear simulation and theory predictions for zonal flows or zonal flow-like structures (convective cells) tied to integer q surfaces with weak or no magnetic shear. Higher frequency zonal flows were unresolvable given the rapidly evolving conditions and the long averaging windows required for the measurement. Previous attempts to trigger ITBs with integer values of qmin have used an early NBI to create a temporary off-axis current peak, which moves into the core as the discharge evolves. This resulted in non-stationary NCS q-profiles. |
| Resource Requirements: | Neutral Beams, ECCD |
| Diagnostic Requirements: | BES, MSE, CER, ECE |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
160: Dependence of turbulence and transport on the safety factor and magnetic shear |
| Name: | Morgan Shafer () |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | G. McKee, D. Schlossberg, C. Holland |
| Description: | Characterize core turbulence parameters (i.e. fluctuation levels, radial correlation lengths, flows) vs. q, while profiles of other relevant dimensionless parameters (rho*, Te/Ti, nu*, etc. ) are kept nearly constant. Transport measurements will likewise be obtained. This data will contribute to the testing and validation of nonlinear simulations. |
| Experimental Approach/Plan: | Use L-Mode discharges. Keep non-dimensional parameters constant, while varying q_95. Repeat discharges needed for spatial BES and other fluctuation diagnostic scan. The number of BES channels will be increased from 32 to 48 to increase spatial coverage for turbulence and turbulence flow measurements. |
| Background: | Confinement is generally found to decrease at higher q. Likewise, previous evidence suggests that turbulence changes with q, and in particular the GAM amplitude is a strong function of q. Theoretical work has similarly shown a dependence of turbulence and transport on magnetic shear. A systematic scan of turbulence parameters is needed to characterize the dependence of turbulence and transport on both safety factor and magnetic shear. This data also contribute to the testing and validation of nonlinear turbulence simulations codes, i.e GYRO. |
| Resource Requirements: | Neutral Beams |
| Diagnostic Requirements: | BES, MSE, CER |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
161: Multiple low-n RWM identification and feedback control |
| Name: | Yongkyoon In ( ) |
Affiliation: | FARTECH, Inc. |
| Research Area: | RWM Physics |
Presentation time: |
Requested |
Co-Author(s): | J. Kim, J.S. Kim, D. Humphreys, M. Okabayashi, A. Garofalo, H. Reimerdes, E. Strait |
| Description: | The proposal is first to investigate the presence of multiple low-n (up to n=3) RWMs, and then to provide the corresponding feedback control. Both rotational stabilization and active multiple mode feedback controls are to be mobilized. |
| Experimental Approach/Plan: | The first step will be to investigate the presence of the multiple low-n RWM modes. Quite often, ELM-induced RWMs in high beta plasma are accompanied by significant multiple low-n modes (at least for both n=1 and n=3 modes).
Once these modes are identified, the feedback control will be provided to suppress each mode simultaneously 1) using rotation control and/or 2) using independently controlled coils. |
| Background: | It is well known in theory that even after n=1 resistive wall mode (RWM) is suppressed, the other low-n modes, such as n=2 or 3, will appear sequentially, as beta increases. In recent experiments, we observed that while the n=1 mode was suppressed likely due to both rotational stabilization and n=1 RWM feedback, the n=3 mode appeared dominant, leading to beta collapse. Using FAR-TECH's expanded matched filter (in which n=1 and n=3 RWM basis vectors are simultaneously considered), we found that these ELM-induced modes are composed of not only n=1 mode but also other low-n mode (i.e. n=3). Considering that the n=2 mode identification is in steady progress, the multiple low-n mode identification for RWM would be feasible, once high beta plasma exceeds the corresponding ideal MHD no-wall limits. While PCS is already equipped with rotation control capability, the operational capability of fully independent I-coil control needs to be confirmed, prior to the experiments. |
| Resource Requirements: | 7 NBI sources, 4 gyrotrons for ECCD |
| Diagnostic Requirements: | n=2 magnetic sensors (e.g. N2QUAD) |
| Analysis Requirements: | -- |
| Other Requirements: | Rotation control would be used first to see if the n > 1 modes are rotationally stabilizable. Then, the active multiple mode control will be provided. |
| Title |
162: Can we prevent locked mode from being locked ? |
| Name: | Yongkyoon In () |
Affiliation: | FARTECH, Inc. |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | Jin Soo Kim, Michio Okabayashi, Holger Reimerdes |
| Description: | The proposal is to assess if a mode-locking is avoidable by taking a control action in pre-locked stage. |
| Experimental Approach/Plan: | In high beta, low torque plasmas, locked modes were frequently observed. However, to assess if locked modes are avoidable in pre-locked stage, low density plasmas below the ideal MHD no-wall stability limit would be primarily used, unless other plasma conditions (e.g. high beta, low torque plasmas) are identified to be more favorable to locked modes.
To avoid locked modes from being locked, the following attempts will be made in pre-locked stage using;
1) FAR-TECH's model-based dynamic Kalman filtered algorithm
2) Complex gains to provide toroidally advanced phase
3) Rotating field that would interact with a pre-locked mode.
Assuming that the attempts in Step 1) show positive progress in terms of plasma responses, we may need to do some gain scans to optimize the effectiveness of the applied field. If no satisfactory responses are obtained in Step 1), we will attempt other approaches to see if the locked mode can be diverted using complex gains or rotating fields. |
| Background: | During high beta, low torque experiments, locked modes frequently occurred, even after reasonably good error field correction was provided. Interestingly, the RWMID algorithm, which combines the matched and Kalman filters based on FAR-TECH's DIII-D/RWM model, showed that the growth of locked mode has remarkable similarity to that of typical n=1 RWM in pre-locked stage. Considering that locked modes cannot be easily unlocked and no control is taken to avoid them, we might be able to take advantage of the model-based RWM algorithm to suppress or divert the locked modes electromagnetically.
Regarding complex gains, recent RWM experiments showed that the coil current demands were significantly reduced at a toroidally shifted angle from the measured mode phase which is typically attributed to 'unknown' error field. Thus, using complex gains might tackle the 'unknown' error field that might be linked to locked modes more directly.
As for rotating fields, the pre-locked mode, which is not locked yet, would interact with the applied rotating field where the electromagnetically moving field would divert the locked stage. Compared with MHD spectroscopy, this approach of rotating field will be almost the same except the necessity that the applied magnetic field perturbations should affect the plasma motion. |
| Resource Requirements: | 4 co-beams and 2-counter beams, 4 gyrotrons for ECCD |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | FAR-TECH's model-based RWMID algorithm |
| Title |
163: How to maximize ELM control resources? |
| Name: | Yongkyoon In () |
Affiliation: | FARTECH, Inc. |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | M. Fenstermacher |
| Description: | The proposal is to investigate how to maximize the ELM control resources. First, we will investigate if ELM suppression is feasible with modulated n=3 field. If the ELM suppression is feasible without operating DC field, we will search for the optimized duty cycles of the pulses, and pulse shapes. However, if n=3 DC field is found to be absolutely needed for ELM control, we can find an operationally feasible way [e.g. only every other I-coils on, with the other I-coils idle]. As a result, the operational strategy to make the most of ELM control resources in ITER can be established. |
| Experimental Approach/Plan: | Establish the operational window of ELM suppression in ITER-like plasmas. Once an optimized condition for ELM control is found, modulate the I-coils with square pulses which would allow the I-coils to be running in various frequencies (e.g. tens of Hz, hundreds of Hz, up to thousand of Hz). If ELM suppression is feasible in modulated I-coils, test various types of pulse shapes (e.g. squares, triangle, sinusoidal) with an optimized frequency. If no ELM suppression is achieved using the pulse modulation, the I-coils would be running in DC manner with only every other coils on.
In this operational testing, both odd and even parities can be evaluated. |
| Background: | While ITER design review has not been finalized, the midplane ITER coils are expected to have multiple purposes; error field correction, RMP and RWM. Considering that the control resources of power supply and coils are limited, it is important to know the lower and upper limits necessary for each topical purpose. While the error field correction needs to be operated in DC-like manner and RWM would need to be running faster in the order of resistive wall time, it is not clear that the RMP would need n=3 DC field constantly. Once the necessity of DC field for ELM control can be relaxed, the limited resources of power supply and coils can be utilized in more effective way. If the RMP physics demands the steady demands of DC field, the operational strategy to maximize the limited resources needs to be established. |
| Resource Requirements: | 5 co-beams |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | fully independent I-coil control is desirable |
| Title |
164: Catastrophic MHD-affiliated non-axisymmetric fields |
| Name: | Yongkyoon In () |
Affiliation: | FARTECH, Inc. |
| Research Area: | Error Fields |
Presentation time: |
Requested |
Co-Author(s): | M. Okabayashi, E. Strait |
| Description: | The proposal is to investigate the 'unknown' inherent non-axisymmetric fields in DIII-D plasmas that would readily interact with other catastrophic MHD activity (e.g. RWM, ELMs, NTM or locked modes). If successful, we may be able to not only characterize these error fields but also help to establish the control algorithm to either mitigate or divert the catastrophic influences, though it would be ideal to eradicate catastrophic MHDs. |
| Experimental Approach/Plan: | Identify a set of plasma conditions that would be influenced by the non-axisymmetric error fields (n = 1, 2 and 3). For example, three plasma sets would be listed;
1) high beta, high torque plasmas (for ELM-induced RWM),
2) high beta, low torque plasmas (for NTM or RWM-prone plasmas),
3) low density plasmas near locked mode condition
Once the plasma conditions are repeatable, sweep the externally stimulated non-axisymmetric field (e.g. n= 1, 2, 3) toroidally to observe the plasma responses. Since the relevant waveforms might not be the same for different types of plasmas, it would be better to investigate each case (which is expected to require half a day) in separate run days. Regardless of the types of the runs, the 'unknown' field that is inherently combining the vacuum and plasma non-axisymmetric field would be measurable.
If a certain toroidal angle has stronger plasma responses for all the n spectra, the error field source might reside externally. If no preferable toroidal angle is found, it would suggest that no dominant non-axisymmetric fields are present. |
| Background: | Recent experiments showed that RWM could be triggered by ELMs in high torque plasmas, where the plasma rotation supposedly exceeded the RWM rotational thresholds. Although the mechanism needs to be thoroughly investigated, one could imagine that a wall stabilized RWM would interact with ELM-induced non-axisymmetric components and then the resonant field would be amplified enough to drag the plasma rotation below the effective rotation threshold, resulting in unstable RWM. Similar observations were made even with externally stimulated n=1 pulses, which are supposed to mimic the ELM-induced n=1 error fields. Interestingly, during a toroidal sweep of such external n=1 pulses, there was stronger plasma response in a certain toroidal angle than in the other toroidal angles. This indicates that even the 'unknown' error field, which is likely to be a sum of all the residual error fields from machine and plasmas, would have a certain preferred toroidal angle. Considering that the goal of the error field study is ultimately relevant to understand the plasma responses in various plasma conditions, it would be more relevant and practical to apply various waveforms of externally controlled non-axisymmetri fields (n=1, 2, and 3) and then investigate the 'unknown' fields. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | fully independent I-coil control is desirable |
| Title |
165: Dependence of Turbulence and Transport on Te/Ti in Low Rotation L & H Modes |
| Name: | George R. McKee () |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | C. Holland. T. Luce, C. Petty, T. Rhodes, D. Schlossberg, M. Shafer, G. Wang, A. White, L. Zeng |
| Description: | Examine the dependence of turbulence over a wide wavenumber range, spatial range and multiple fields, as well as particle, momentum and thermal transport on the electron to ion temperature ratio, Te/Ti, shown theoretically and experimentally to be a critical parameter for transport. The electron temperature profile will be self-similar as Te/Ti is varied, while other dimensionless parameters (rho*, nu*, q, beta) are kept nearly constant. |
| Experimental Approach/Plan: | Establish low power L-mode target plasma, with 2 balanced injection sources (minimize rotation), providing diagnosing beam for BES and CER, MSE (150R, 1/2-30L,330L), inner wall limited discharges to maintain L-mode conditions.
- Scan Te at constant Ti w/off-axis ECH heating, maintaining self-similar electron temperature profile shapes by varying ECH deposition location as necessary
-Maintain constant Ti temperature at low rotation through adjustment of co/counter beam sources and power (previously in co-rotation discharges, rotation dropped significantly as Te increased during previous experiment)
- Scan Ti at constant Te (via balanced NBI injection)
- Scan Te and Ti at constant Beta (trade off ECH and NBI) as feasible
- Increase density if necessary to further equilibrate temperatures
- Obtain fluctuation data with all fluctuation diagnostics (expanded high-sensitivity BES, multi-wavenumber FIR, ECE, microwave back-scattering, correlation reflectometry, PCI, probes)
-Examine particle diffusivity with helium puffs
- Repeat experiment in H-mode plasmas |
| Background: | Numerous experiments have demonstrated that as Te/Ti, which is typically less than one in modern experiments, increases towards unity or above, transport increases, in general agreement with ITG-based turbulent transport theory. This experiment will seek to quantify the underlying turbulence mechanism giving rise to this dependence. Previous experiments have shown there to be a modest increase in low-wavenumber turbulence as Te is increased at constant Ti, however the experiments were not conclusive because of uncontrolled variation in the rotation and resulting ExB shear. This experiment will seek to investigate this issue in low-rotation discharges, now feasible with the balanced beam-injection, and also to investigate behavior in both L-mode and H-mode plasmas, as well as to employ the wide array of new and upgraded diagnostics. Of special note will be the capability to examine not only density but also electron temperature fluctuations with the newly implemented CECE diagnostic (UCLA).
These experiments will be simulated with TGLF and GYRO as reasonable to contribute to the effort to compare and challenges the codes and ultimately validate turbulence and transport simulations. |
| Resource Requirements: | Co and Counter beams, maximum ECH power (5 gyros) |
| Diagnostic Requirements: | All fluctuation diagnostics: BES, CECE, FIR (multi-wavelengths), correlation reflectometry, PCI, CO2 interferometer, Langmuir probes |
| Analysis Requirements: | Lots of transport and turbuelnce analysis required... |
| Other Requirements: | After experiment, simulate with modeling and nonlinear simulation codes (TGLF, GYRO, etc.). |
| Title |
166: Test theory based models and empirical scaling for intrinsic rotation by changing turbulence modes |
| Name: | Edward Doyle ( ) |
Affiliation: | University of California, Los Angeles |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | A single experiment is proposed to directly test a key prediction of theoretical and empirical models for intrinsic plasma rotation, and simultaneously provide a key transport model validation test. Leading theories to explain intrinsic plasma rotation predict that the direction of the intrinsic plasma rotation should change sign depending on whether the turbulence mode is in the ion or electron drift direction (Hahm, Diamond, etc). Experiments with balanced NBI (zero net NBI torque) and with/without ECH should be able to directly test this prediction, by changing the plasma from ITG to TEM dominated turbulence. By performing this experiment at constant normalized beta, the current empirical "Rice scaling" can also be tested. In the Rice scaling, the intrinsic plasma rotation is proportional only to beta and q, i.e. at fixed beta (and q), the rotation should be fixed. Finally, this experiment would also provide another route to test the predicted ITG/TEM transition boundary, and thus also provides a transport model validation Performing the experiment with zero net NBI torque will maximize the contribution of the mode dispersion and intrinsic rotation contributions to the measured turbulence rotation, such that ITG/TEM mode transitions should be more easily discerned than in rotating, NBI-driven plasmas. |
| Experimental Approach/Plan: | Separately generate ITG and TEM dominated plasmas with zero net NBI torque, at fixed beta. ITG dominated plasma will be balanced NBI only, TEM dominated would add ECH (at fixed beta). The NBI-balance for zero net torque will have to be retuned in the ECH case, both because of ECH induced deposition changes, and also because the NBI power will have to change so as to maintain constant beta. The modulated source NBI technique would also be utilized to determine diffusive and pinch momentum transport terms. ECH could utilize the "swing" technique to modulate profile gradients dynamically. |
| Background: | "Rice Scaling" - J. Rice et al, IAEA 2006, and also ITPA talks.
Theoretical models; Hahm et al. POP 14, (2007), and H_mode WS and ITPA talks, Gurcan, et al., POP 14, (2007). |
| Resource Requirements: | Co- and counter-NBI. ECH |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
167: Intermittency scaling for ITER |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary |
Presentation time: |
Requested |
Co-Author(s): | D. Rudakov, J. Watkins, E. Hollmann, C. Holland, G. Tynan, J. Yu |
| Description: | Intermittency transports particles (mostly) and heat from the LCFS into the SOL and walls. A basic theoretical scaling of this transport with basic plasma parameters already exists and needs to be verified. |
| Experimental Approach/Plan: | Vary L_par, resistivity at plates/X-point and Bt and measure intermittency paramaters such as velocity and size. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
168: ELM supression at high density |
| Name: | Larry R. Baylor () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Requested |
Co-Author(s): | M. Fenstermacher, T. Evans, R. Moyer, T. Jernigan |
| Description: | This experiment is to demonstrate the viability of ELM supression with external magnetic field ergodization with high density operation using pellet fueling. |
| Experimental Approach/Plan: | Select an optimized discharge for ELM supression in ITER like plasma shape and add the injection of 1.8mm fueling pellets at the highest frequency available (~15 Hz). Determine operational window with ELM supression. If ELMs occur, determine the ELM energy loss using fast EFIT and compare to natural ELMs without I-coil operation. |
| Background: | The ITER plasma facing components have a limit on the energy that can be expelled from an ELM of 1 MJ. Methods to limit the ELM energy and eliminate ELMs all together are needed. Supression of ELMs with ergodic fields has been demonstrated on DIII-D and may be attempted on ITER. IT will be necessary for ITER to operate at high density in order to maximise fusion power. The combination of high density and ELM supression are needed and this experiment will attempt to achieve this scenario and to show a credible operational option for ITER. |
| Resource Requirements: | I coil
Pellet Injector inner wall locations |
| Diagnostic Requirements: | Full complement of ELM and pellet diagnostics |
| Analysis Requirements: | --Fast EFIT for energy loss determination from ELMs (if they occur). |
| Other Requirements: | -- |
| Title |
169: Can the RMP coils eliminate ELMs from SNs with B x gradB out of the divertor? |
| Name: | Thomas W. Petrie ( ) |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | T. Evans, M. Fenstermacher, and M. Schaffer |
| Description: | This experiment is the first necessary step for determining whether the ELM suppression method developed here at DIII-D is compatible with radiating divertor scenarios. Previous DIII-D studies focused on the effect that particle drifts in the SOL/divertor had on fueling, particle pumping, and radiating divertor behavior. We concluded that the most promising (only?) way to successfully employ a radiating divertor in order to reduce heat flux at the divertor targets with a minimal cost to plasma core H-mode properties was to use a SN plasma characterized by having the gradB ion drift directed OUT of the divertor. Presently, however, it is unclear whether ELM suppression in SNs using the RMP coils is attainable, if the gradB ion drift is directed out of the divertor. In this experiment, we investigate if it is possible to suppress ELMs of a SN plasma with the gradB drift direction out of the divertor. Once demonstrating the feasibility of eliminating ELMs under these conditions, we are then ready to move onto the next step in demonstrating the feasibility of RMP ELM suppression in a radiating divertor environment. |
| Experimental Approach/Plan: | The upper SN plasma is maintained in a standard ELMing H-mode regime (i.e., Ip =1.2 MA, Bt = -1.75 T, dRsep = +1.0 cm, q95=4.2, and Pinj = 6 MW). These parameters yielded the best of the radiating divertor results, but the resulting q95 may (or may not) be optimal for ELM suppression with the I-coil. To identify the range in q95 that yields the best prospects for ELM suppression, q95 is reduced during the shot by reducing Bt while the I-coil current is set to maximum. Once this q95 range is identified, choose value of q95 in the middle of that range and run successive shots with increasingly lower I-coil current. This is done to identify the minimum coil current, so as to minimize the perturbing effect of the RMP on the pedestal region. |
| Background: | Eliminating ELMs from H-mode plasmas using the I-coil approach presents an interesting possibility for resolving the ELM-issue in ITER and future highly powered tokamaks. Yet, even if the damage to the divertor structure from ELMs pulses were eliminated via the I-coil approach, steady peak power loading at the divertor targets could still be unacceptably high. A radiating divertor solution, whereby an impurity gas is injected into a pumped divertor with simultaneous deuterium gas puffing upstream of the divertor, has shown promise as a way to reduce peak power loading at the divertor targets without concomitant degradation of the ELMing H-mode plasma properties [IAEA 2006, PSI2006]. However, in combining the I-coil approach with such puff and pump scenarios while still maintaining favorable H-mode operation, the injected impurity must still be prevented from escaping the divertor and contaminating the main plasma.
The most promising radiating divertor scenario involves using a SN divertor with the gradB directed out of the divertor. However, it has not been demonstrated that a SN with the gradB out of the divertor is itself compatible to ELM suppression with the RMP coils. We suspect it is, because (1) SN plasmas run at typically lower density than corresponding plasmas with the gradB drift directed into the divertor and (2) SN plasmas with the gradB drift out of the divertor have a pumping rate on the outer separatrix that is about 50% greater than for a corresponding SN with the gradB drift into the divertor. Both these factors should result in lower collisionality in the pedestal in the gradB OUT case and thus better ELM suppression. Lower collisionality in the pedestal is helpful in ELM suppression with the RMP coils. As a result, the collisionality in the gradB out of the divertor cases will be lower than in the more standard gradB INTO cases, and the former would be expected to tolerate the higher gas puff rates needed to impede the escape of the impurities from the divertor. |
| Resource Requirements: | Machine time: 0.5 day (in forward Bt), I-coil, dome- and upper baffle cryo-pumps cold, minimum 6 beams. |
| Diagnostic Requirements: | Asdex gauges (in particular, dome and upper baffle locations), core Thomson scattering, upper divertor and centerpost fixed Langmuir probes, and CER. |
| Analysis Requirements: | UEDGE, with ONETWO |
| Other Requirements: | I-coil |
| Title |
170: Comparison of impurity screening between ELMing and ELM-suppressed plasmas? |
| Name: | Thomas W. Petrie () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | T. Evans, M. Fenstermacher, and M. Schaffer |
| Description: | This experiment presents the second step in determining whether the ELM suppression method developed here at DIII-D is compatible with radiating divertor scenarios. This experiment, which uses non-perturbing (trace) argon under puff-and-pump scenarios, provides a side-by-side comparison of how well the injected impurity is screened in ELMing H-mode plasmas and in ELM-free H-mode plasma (with I-coil). DIII-D IS UNIQUELY CONFIGURED TO DO THIS EXPERIMENT. We focus on addressing the following questions: (1) Is there a significant difference in the argon accumulation in the plasma core under I-coil operation? (2) How does the exhaust enrichment change between the ELMing- and the ELM-free (I-coil) cases? |
| Experimental Approach/Plan: | The plasma is maintained in a standard ELMing H-mode regime under the conditions established in the lead-in experiment (e.g., Ip =1.2 MA, Bt = -1.75 T, dRsep = +1.0 cm, and upper SN). A trace amount of argon is injected into the private flux region of the upper divertor, while deuterium plasma flow toward the divertor is enhanced by a combination of deuterium gas injected from the bottom of the vessel and active cryo-pumping from both upper divertor locations. Trace argon is injected at a steady but trace level from t = 3.0 s to 7.0 s. A standard ELMing H-mode regime is established previous to t = 4.5 s of the discharge. At t = 4.5 s, the I-coil is activated and the ELMs are eliminated. This provides a direct comparison of the trace argon behavior between ELMing H-mode and ELM-free H-mode (I-coil) under similar conditions. [Note that the q95 and the coil current selected have been determined from the lead-in experiment: Can the RMP coils eliminate ELMs from SNs with the gradB OUT of the divertor�]
The deuterium injection rate is scanned. The key measurables are the accumulation of argon in the core and divertor plasmas. |
| Background: | Eliminating ELMs from H-mode plasmas using the I-coil approach presents an interesting possibility for resolving the ELM-issue in ITER. Yet, even if the damage to the divertor structure from ELMs pulses were eliminated via the I-coil approach, steady peak power loading at the divertor targets could still be unacceptably high. A radiating divertor solution, whereby an impurity gas is injected into a pumped divertor with simultaneous deuterium gas puffing upstream of the divertor, has shown promise as a way to reduce peak power loading at the divertor targets without concomitant degradation of the ELMing H-mode plasma properties [IAEA 2006, PSI2006]. However, in combining the I-coil approach with such puff and pump scenarios while maintaining favorable H-mode operation, the injected impurity must still be prevented from contaminating the main plasma. This is by no means assured, due to the ergodic nature of the pedestal. In this experiment, we compare the dynamics of impurity screening between ELMing H-mode plasmas and ELM-free H-mode (plus I-coil) plasmas. |
| Resource Requirements: | Machine time: < 0.5 day (forward Bt), I-coil, dome- and upper baffle cryo-pumps cold, minimum 6 beams. |
| Diagnostic Requirements: | Asdex gauges (in particular, dome and upper baffle locations), Penning gauge, core Thomson scattering, upper divertor and centerpost fixed Langmuir probes, and CER. |
| Analysis Requirements: | UEDGE and ONETWO |
| Other Requirements: | I-coil |
| Title |
171: Completion of n=1 RMP ELM control studies |
| Name: | Richard Buttery
() |
Affiliation: | UKAEA |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | Max Fenstermacher, T Evans, D Howell, M Schaffer, O Schmidt, R Moyer, T Osbourne, G Jackson |
| Description: | This is a small half day proposal to complete a key element of the 2007 experiment exploring n=1 control of ELMs. Although these experiments did not complete a number the field configurations planned, this follow up proposal is targeted on a particular aspect using one further field configuration that should allow us to go further in addressing the key limiting issue and evaluating the technique.
The 2007 experiments revealed a more severe limitation than expected in the n=1 error field technique due to the inducing of 2/1 error field locked modes. However these experiments used C coils to correct intrinsic error in order to allow I coil operation with other configurations. The C coils are known to correct intrinsic error on DIII-D less effectively that I coils in 240 phasing, and to do so in a way that is not well understood theoretically, potentially even enhancing some non-resonant perturbations.
It is therefore proposed that, we explore use of the I coil in 240 degree phasing configurations. This will allow edge resonant I fields to be applied, while simultaneously phasing the coils for correction of core resonant intrinsic error fields. In this way better correction of intrinsic errors should be possible compared to 2007, enabling us to apply increased edge resonant fields without encountering error field locked mode limits. If successful the effects can be further explored with q95 and amplitude optimisation. |
| Experimental Approach/Plan: | As previously, experiments will apply maximum available fields within locked mode limits, and utilise q95 scans to determine the resonance spot and optimal effect. No RMP references will be taken. At optimal resonance repeats using RMP field ramps will be taken and compared with no-RMP cases. We would use a previously optimised plasma configuration and ramp-up in the ITER-like single null shape. I coils would be in the usual 240 phasing configuration (but key element is to phase them in the direction used for intrinsic error correction). C coils might be used to explore extension of I fields to higher amplitudes by using them to (ie use C coil to cancel core resonances generated by I fields as they go beyond intrinsic error correction levels). About half a day is needed. |
| Background: | Recent experiments on JET have shown that the application of broadly resonant n=1 perturbations can substantially (~x10) reduce ELM sizes, while increasing their frequency and having modest impact on confinement [Liang PRL 2007]. The DIII-D tokamak has unique capabilities to study the physics and design requirements of this process, through its configurable I coils, as well as its C coil systems. It ought to be able to improve on the results obtained at JET by applying more edge resonant fields.
Experiments were undertaken on DIII-D using n=1 RMP s to control ELMs in 2007. Significant change to ELM behaviour was observed with substantial rises in type I ELM frequencies. Thus the experiment was partially successful, but with locked mode difficulties and control system failures on the day, it did not complete most of the phase scans envisaged.
The 2007 experiments were limited by the occurrence of locked modes, even when the C coils were deployed to help cancel out core resonant 2/1 error fields. This is attributed to the uncertainties introduced by the C coil correction process, which is calculated to *enhance* fields, and hypothesised to act through non-resonant field effects on plasma viscosity. Therefore the C correction may not be the appropriate technique to use in experiments where additional fields are ramped up to control ELMs. |
| Resource Requirements: | I coils 240, C Coils, 4 beams |
| Diagnostic Requirements: | Usual ELM control diagnostics, with particular emphasis on pedestal measurement. Esp. CO2, TS, CER, magnetics, filterscopes. |
| Analysis Requirements: | Results should be self evident, but detailed diagnostic analysis will be required to quantify effects. |
| Other Requirements: | -- |
| Title |
172: Is the Radiating Divertor Scenario Compatible With ELM Suppression? |
| Name: | Thomas W. Petrie () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | T. Evans, M. Fenstermacher, and M. Schaffer |
| Description: | This experiment is the third in a series experiments for determining whether the I-coil method of ELM suppression is compatible with radiating divertor (i.e., puff and pump) scenarios. This experiment provides a side-by-side comparison of how a standard ELMing plasma and an ELM-free plasma (with I-coil) respond to a puff-and-pump scenario with a perturbing amount of argon as the injected impurity. DIII-D IS UNIQUELY CONFIGURED TO DO THIS EXPERIMENT. We focus on addressing the following questions:
(1) Is there a significant change in the argon accumulation in the plasma core under I-coil operation?
(2) How does argon entrainment in the divertor change when the I-coil is activated?
(3) How does the ratio of divertor-to-core radiated power change when the I-coil is activated? |
| Experimental Approach/Plan: | The plasma is maintained in a standard ELMing H-mode regime (e.g., Ip =1.2 MA, Bt = -1.7 T, dRsep = +1.0 cm, and upper SN). This setup is similar to the one that was shown previously (IAEA2006) to perform robustly under the puff and pump scenario. Significant deuterium gas puffing, which is needed to raise the SOL plasma flow into the divertor, will also raise the density. A previous experiment will have shown that ELMs are suppressed under these conditions by a pre-selected I-coil current: Comparison of impurity screening between ELMing and ELM suppressed plasmas�. Hence, it is possible that adjustments to the I-coil settings may be necessary if the D2 injection rate is changed, as it is in this experiment.
After this prep work is done, argon is injected into the private flux region of the upper divertor, while deuterium plasma flow toward the divertor is enhanced by a combination of deuterium gas injected from the bottom of the vessel and active cryo-pumping from both upper divertor locations. A radiating divertor plasma in an ELMing H-mode regime is established previous to t = 4,5 s of the discharge. At t = 4.5 s, the I-coil is activated and the ELMs are eliminated. This provides a direct comparison between ELMing H-mode and ELM-free H-mode under similar plasma conditions.
The argon injection rate with a fixed D2 injection rate is scanned; then the D2 injection rate with a fixed argon injection rate is scanned. Important measurables are the changes in the radiated power distribution and heat flux values, the accumulation of argon in the core and divertor plasmas, and the density and temperature conditions at both divertor targets. |
| Background: | Eliminating ELMs from H-mode plasmas using the I-coil approach presents an interesting possibility for resolving the ELM-issue in ITER. Yet, even if the damage to the divertor structure from ELMs pulses were eliminated via the I-coil approach, steady peak power loading at the divertor targets could still be unacceptably high. A radiating divertor solution, whereby an impurity gas is injected into a pumped divertor with simultaneous deuterium gas puffing upstream of the divertor, has shown promise as a way to reduce the peak power loading at the divertor targets without concomitant degradation of the ELMing H-mode plasma properties [IAEA2006 and PSI2006]. However, in combining the I-coil approach with such puff and pump scenarios, it is by no means clear that the injected impurities can be prevented from building up the main plasma as effectively as in the ELMing H-mode cases. |
| Resource Requirements: | Machine time: 0.5 day, I-coil, dome- and upper baffle cryo-pumps cold, minimum 6 beams. |
| Diagnostic Requirements: | Asdex gauges (in particular, in the dome and upper baffle locations), Penning gauge, core Thomson scattering, upper divertor and centerpost fixed Langmuir probes, and CER. |
| Analysis Requirements: | UEDGE, ONETWO. |
| Other Requirements: | I-coil |
| Title |
173: Compatibility of ELM suppression with the radiating divertor in the hybrids |
| Name: | Thomas W. Petrie () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | T. Evans, M. Fenstermacher, and M. Schaffer |
| Description: | This experiment is the fourth in a series of experiments for determining if the ELM suppression method using the I-coil is compatible with radiating divertor scenarios in the hybrid regime. This experiment provides a side-by-side comparison of how an ELMing hybrid plasma and an ELM-free hybrid plasma with I-coil perform under puff-and-pump scenarios with argon as the injected impurity. DIII-D WOULD BE UNIQUELY CONFIGURED TO DO THIS EXPERIMENT. We focus on addressing the following questions:
* Is there a significant change in the argon accumulation in the plasma core under I-coil operation?
* How does argon entrainment in the divertor change when the I-coil is activated?
* How does the ratio of divertor-to-core radiated power change when the I-coil is activated?
This experiment will be attempted only after it has been demonstrated that RMP ELM suppression has been demonstrated in the hybrid regime, where the gradB ion drift is directed OUT of the divertor. |
| Experimental Approach/Plan: | The plasma is maintained in a ELMing hybrid H-mode regime (e.g., Ip =1.2 MA, Bt = -1.7 T, dRsep = +1.0 cm). This setup was shown previously (EPS2005) to be robust under puff and pump operation (examples: 123265-123279). Argon is injected into the private flux region of the upper divertor, while deuterium plasma flow toward the divertor is enhanced by a combination of D2 gas injected from upstream of the upper divertor targets and active cryo-pumping from both upper divertor locations. A radiating divertor plasma in the ELMing hybrid regime is established previous to t = 4.5 s of the discharge. At t = 4.5 s, the I-coil is activated and the ELMs are eliminated. This provides a side-by-side comparison between ELMing hybrid and ELM-free hybrid.
The argon injection rate and the deuterium injection rate are separately scanned. Key measurables are the changes in the radiated power distribution and heat flux values, the accumulation of argon in the core and divertor plasmas, and the density and temperature conditions at both divertor targets. |
| Background: | Plasma operation in the hybrid regime has been put forward as a paradigm for ITER, and would become particularly attractive if ELMing could be eliminated. Suppressing ELMs from hybrid H-mode plasmas using the I-coil approach is an intriguing possibility for resolving the ELM-issue in ITER. However, even if the damage to the divertor structure from ELMs pulses were eliminated via the I-coil approach, steady peak power loading at the divertor targets could still be unacceptably high. A radiating divertor solution, in this case, puff and pump, has shown promise as effective way of reducing peak power loading in ELMing hybrid plasmas, while at the same time maintaining good hybrid properties, e.g., energy confinement time. Our experiment will address whether the puff and pump radiating divertor concept is also as effective for hybrid ELM-free plasmas during I-coil operation. At this juncture, the I-coil method has not been completely successful in eliminating ELMs for plasmas in the hybrid regime. Clearly, this experiment should be attempted after ELM suppression in hybrid is successfully demonstrated. |
| Resource Requirements: | Machine time: 0.5-1.0 day, I-coil, dome- and upper baffle cryo-pumps cold, minimum 6 beams. |
| Diagnostic Requirements: | Asdex gauges (in particular, dome and upper baffle locations), Penning gauge, core Thomson scattering, upper divertor and centerpost fixed Langmuir probes, and CER. |
| Analysis Requirements: | UEDGE, with some ONETWO |
| Other Requirements: | I-coil |
| Title |
174: What is the nature of the heat flux outside a slot divertor and are particle drifts important? |
| Name: | Thomas W. Petrie () |
Affiliation: | General Atomics |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | N. Brooks |
| Description: | Investigate the dependence of heating on the baffle top on particle drifts in the SOL and divertor. In the lower SN cases addressed in this experiment, we have found greater interaction of the plasma with the top of the lower baffle extension for the grad-Bt direction out of rather than into the lower divertor, if these particle drifts are important. We determine the differences in the scrapeoff widths in density, temperature, and heat flux for each Bt direction, in attached and detached cases. If the divertor scrape-off widths in ne, Te, and Qp are significantly different in the forward and reverse Bt cases, this will require two different divertor slot widths. This piece of information bears directly on an acceptable design of a slot divertor for ITER and beyond. |
| Experimental Approach/Plan: | The plasma is a high triangularity, lower SN, with dRsep = 3.0 cm. The toroidal field direction is forward, i.e., the direction of the gradB ion drift is downward. The outer lower cryopump is cold. (1) Use the D2 gas injector from locations upstream of the lower divertor (e.g., GasA). Scan the D2 gas injection rate up to and including the H-L back-transition. This range in density will include the partial detachment of the outer divertor separatrix. Reverse the Bt direction and repeat.
Important measurables from this experiment are the changes in the heat flux (IR) and particle flux (Langmuir probes) profiles in the slot and along the top of the lower baffle. Upstream electron density, electron temperature, and ion temperature measurements in the pedestal and near-scrapeoff layer (Thomson scattering and CER) are essential. Radial sweeps of the outer strike point inward are likely to be needed for a full radial profile in ne, Te, and Qp. |
| Background: | During the plasma shaping experiments from 2000 we noted that the heat flux on the horizontal section of the upper outer baffle shelf was NOT reduced during high density, radiating upper SN divertor operation, even though the heat flux inside the slot (i.e., between the dome and baffle pump opening) was reduced 3-5 times. Even under high density, detached conditions inside the slot, there was no reduction of heat flux outside the lip of the divertor "slot". Formation of a strong radiating region on the horizontal upper shelf with significant heating on the baffle top were observed. Energetic ions far out in the SOL, largely decoupled from the radiatively-cooled electrons, were thought to be responsible for this undiminished heating on the horizontal shelf of the upper outer baffle. Subsequent analysis with the UEDGE code has suggested that particle drifts (e.g., ExB and grad-Bt) may have been responsible for the spillover interaction the plasma with the baffle. Reversing the direction of the grad-Bt drift reduced this plasma-baffle interaction. The same kind of interaction was observed again during the summer�??s radiating divertor experiments. More recent UEDGE analysis indicates that drifts in the SOL and divertor are playing key roles.
Engineering implications of this are significant: If the electrons and ions are decoupled in the SOL outside the slot, then radiative divertor operation has little effect on heat flux outside the slot. Hence, the width of the slot must be widened when the grad-Bt drift direction is out of the divertor. If our supposition about drifts is correct, then a narrower slot can be used if the grad-Bt drift is into the divertor. Should the "slot" divertor concept be applied to future generation, high power tokamaks, our understanding of this result would be particularly important. |
| Resource Requirements: | Machine time: 0.2 day (forward Bt) + 0.2 day (reverse Bt), lower divertor cryo-pumps cold, minimum 6 beam sources. |
| Diagnostic Requirements: | Asdex gauges inside the lower outer baffle, IRTV monitoring the lower divertor, core Thomson scattering, all of the lower divertor fixed Langmuir probes, filterscopes, and CER. |
| Analysis Requirements: | UEDGE |
| Other Requirements: | -- |
| Title |
175: Turbulence & transport modifications in ECH plasmas and comparison to gyrokinetic simulation |
| Name: | Tony Peebles ( ) |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | Anne White, Lothar Schmitz, Terry Rhodes, Guiding Wang, Jon Hillesheim, Troy Carter, Chris Holland, Lei Zeng, E. J. Doyle |
| Description: | Perform local measurements of low and high-k density turbulence and low-k electron temperature turbulence in both Ohmic and ECH heated plasmas. ECH (deposited at r/a ~ 0.4) will be used to significantly modify electron temperature and normalized temperature gradient while keeping density and ion temperature gradients fixed. Resultant modifications in a range of local turbulence parameters at r/a ~0.6 will be used to assess their relative contributions to the increased electron thermal diffusivities. In addition, the phase relationship between low-k density and electron temperature fluctuations will be measured for the first time in the core of a tokamak plasma. The above measurements will be directly compared with predictions of relative fluctuation levels, phase relationships and resultant transport using nonlinear gyrokinetic simulations (e.g GYRO). |
| Experimental Approach/Plan: | Lower single null Target plasmas, similar to 120328, will be utilized using at least three gyrotrons (deposited at r/a 0.4) to modify the electron temperature profile. Multichannel reflectometry, microwave backscattering and correlation ECE will be employed to probe the local turbulence response at r/a~ 0.6. These systems will all operate using the same optical path and radial location. Reflectometry and correlation ECE will also be used to determine the phase relationship between density and electron temperature fluctuations. Doppler reflectometry together with CER (beam blips) will be used to determine modifications in ExB flow. Doppler reflectometry together with FIR scattering will also be used to monitor turbulence change at intermediate turbulence scales. Turbulence and transport measurements will be compared with predictions from flux tube gyrokinetic simulations. |
| Background: | A previous 2004 experiment in a similar plasma (minus CECE and Doppler reflectometry) indicated that low and intermediate -k density turbulence was only slightly perturbed, whereas high-k density turbulence was strongly modified. A separate 2007 experiment (White et al.), where ECH was applied to a beam heated L-mode plasma, indicated that low-k electron temperature fluctuations increased (~30%) whereas low-k density turbulence did not. Recent GYRO simulations (for the above beam-heated L-mode plasma) predicted density and potential fluctuations to be closely in-phase, whereas temperature and potential fluctuations were clearly out of phase. Since predicted (and measured) fluctuation levels were similar for both density and electron temperature fluctuations this strongly suggests that the turbulent driven electron heat flux, for those plasmas, was dominated by electron temperature fluctuations. Unfortunately no experimental measurement of the phase relationship was available for those plasmas.
In summary, the proposed experiment will
(1) Identify which turbulence parameters (low and intermediate-k density, high-k density, low-k electron temperature fluctuations) are modified by application of ECH and allow direct quantitative comparison with predictions from gyrokinetic simulations.
(2) Measure the phase relationship between density and electron temperature fluctuations and allow, for the first time, a stringent test of gyrokinetic predictions related to these important transport-related turbulence properties.
(3) Correlate measured local changes in turbulence properties with modifications in electron heat diffusivity and predictions from nonlinear gyrokinetic simulations |
| Resource Requirements: | Beam blips for Ti profile, Er, MSE, BES
Number of Gyrotrons: 3 to 5 |
| Diagnostic Requirements: | All core turbulence systems (correlation ECE, FIR scattering, microwave backscattering, BES, reflectometry, PCI), profile reflectometer, MSE, CER, etc. |
| Analysis Requirements: | Non linear gyrokinetic calculations and associated transport analysis, etc. |
| Other Requirements: | -- |
| Title |
176: Investigation of fast wave damping at 2nd and 3rd harmonics on injected hydrogen beams |
| Name: | Robert I. Pinsker () |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | W.W. Heidbrink, M. Porkolab, J.C. Hosea, F.W. Baity, E. Fredd, T. Scoville |
| Description: | DIII-D experiments have shown that 60 MHz fast waves can be damped on injected 80 keV deuterium beams at the 4th harmonic (2 T) quite strongly, to the point where the accelerated deuterons can partially stabilize sawteeth ('monsters'). Furthermore, 60 MHz fast waves have been shown to be damped strongly on thermal hydrogen at the 2nd harmonic if the hydrogen fraction exceeds around 25%. We therefore expected that 90 MHz fast waves could be strongly damped on injected hydrogen beams at 2 T and thereby produce a similar effect on sawteeth as the 4th harmonic at 60 MHz on deuterium beams had. However in a short (~1/3 of a day) experiment in FY07, no evidence was found of strong damping of 90 MHz fast waves on injected H beams. Instead, direct electron damping appeared to dominate. The FIHA diagnostic saw only a very weak H signal, suggesting the possibility that the two sources run in H were producing a significantly lower power full-energy component than expected.
We propose to revisit this experiment after careful tuning of the operation of the beams in hydrogen is carried out, and to add 60 MHz power (2nd harmonic) for comparison with the 90 MHz, 3rd harmonic case. (The latter had not been possible in the FY07 experiment due to poor 60 MHz antenna performance, which we hope to have remedied in the autumn 2007 vent.) |
| Experimental Approach/Plan: | Reproduce the L-mode discharges with hydrogen beam injection, perhaps operating a second beamline in H to allow greater H beam power, and emphasizing careful measurement of the injected H-beam power (modulation studies, etc.) Quantitative understanding of the FIHA signals in the absence of FW power as a function of injected H beam power is a prerequisite to understanding the effect of the FW power to the proton distribution function. Compare the effect of 60 MHz power and 90 MHz power in otherwise identical discharges with H beam injection. |
| Background: | This experiment should dovetail well with plans for a hydrogen campaign, in that presumably full H beam operation is needed for such experiments. Understanding the FIHA signals with H beams is also needed for such experiments, since we lose all of the neutron diagnostics and are thereby weak on other probes of the beam distribution functions in such discharges. |
| Resource Requirements: | At least one beamline (two sources) operated in H with sufficient time beforehand to have optimized the source operation in hydrogen. Prefer two beamlines (four sources) in hydrogen. The plasma can be either deuterium or hydrogen, though a purely hydrogen plasma is preferred for simplicity. All three FW sources, two at ~90 MHz and one at 60 MHz, at greater than 1 MW each, are needed. One full day experiment. |
| Diagnostic Requirements: | FIHA diagnostic is crucial. |
| Analysis Requirements: | Analysis of absorbed power from the H beams, via modulation analysis. FIHA data must be quantitatively analyzed. |
| Other Requirements: | -- |
| Title |
177: Compatibility of the radiative divertor with high performance plasma operation |
| Name: | Thomas W. Petrie () |
Affiliation: | General Atomics |
| Research Area: | Core-Edge Integration |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | This study will combine ALL the essential elements for making the first real test of a radiating divertor concept in an AT/hybrid DN (or near-DN) plasma, using realistic high triangular shape and particle exhaust configuration anticipated for high performance tokamaks. PRESENTLY, ONLY DIII-D HAS THE CAPABILITY TO MAKE THIS TEST. Argon is injected into the private flux region near the upper outer divertor separatrix target. Enhanced deuterium plasma flow toward the divertor in the low field SOL is enhanced by a combination of deuterium gas injected upstream of both outer divertor targets and active cryo-pumping from both outer divertor locations. Locating the optimum value of magnetic balance (dRsep) that results in a significant reduction in divertor heat flux while still maintaining good AT-properties is the focus of this experiment. |
| Experimental Approach/Plan: | The plasmas are DN and near-DN AT, and the upper inner- and both outer divertor cryo-pumps are at liquid helium temperature. The gradB-ion drift direction is downward. This experiment is probably best done in as follows:
* First establish the sensitivity of AT plasmas to deuterium gas injection at dRsep = +1.5 cm. Scan the deuterium gas puff rate, i.e., establish operational limit to how much D2 gas injection the AT plasma can accommodate before plasma degradation results; trace argon is injected into the private flux region of the upper divertor,
* Repeat for dRsep values closer to DN. Establish the minimum dRsep for which AT/hybrid conditions can be maintained during significant gas puffing, and
* Scan of the argon injection rate at a reasonable D2 injection rate at this minimum dRsep at the best D2 injection.
Important measurables from this experiment are the changes in the (poloidal) radiated power distribution and heat flux values, changes in the density and electron temperature at the divertor targets, and the accumulation of argon in the core and divertor plasmas. |
| Background: | High performance AT and hybrid plasmas in the double-null (DN) and near-DN configurations are attractive for future power reactor operation due to their high toroidal beta and energy confinement properties. However, for futuristic AT-machines (like ARIES-AT), there can be severe divertor power loading problems. A possible way of reducing excessive power loading at the divertor target(s) is to radiate significant power outside the main plasma, mainly in the divertor (hence, radiative divertor). But the resulting divertor cooling may also lead to a cooling of the upstream (core) plasma, which, in turn, may result in a marked degradation in AT-edge properties (e.g., bootstrap current). The expected increase in the argon presence in the pedestal can also be expected to affect the AT-pedestal adversely.
Previous work with radiating divertor H-mode DN plasmas has shown that the �??balanced�?� DN results in overly rapid accumulation of the seeded impurity (argon) in the core plasma. Two important reasons for this are (1) the relatively easy penetration of an impurity specie from the high field side into the core plasma of the DN and (2) the particle drifts in the scrape-off layer plasma in one of the divertors that always assist in the escape of injected impurities from the divertor region to the vulnerable high field side SOL [NF2007(submitted),APS2007]. On the other hand, the radiating divertor was shown to be effective in magnetically unbalanced DNs (dRsep=+1 cm) for reducing divertor heat flux while still maintaining good (hybrid) H-mode properties. Clearly, there is an optimal value of dRsep between 0 and +1 (with gradB drift down) for which the divertor heat flux reduction is attained with minimal loss of good H-mode properties. Since the heat flux scrape-off width for this class of H-mode is about 0.5-0.6 cm, the �??optimal�?� dRsep for heat flux reduction AND maintaining good H-mode plasmas would likely fall between +0.5 cm and +1.0 cm. This suggests the best chance for compatibility between good AT-class AND heat flux reduction would also fall in this range in magnetic balance. |
| Resource Requirements: | Machine time: 1 day, dome- and both outer baffle cryo-pumps cold, minimum 6 beam sources. |
| Diagnostic Requirements: | Asdex gauges inside the dome and inside both outer baffles, core Thomson scattering, upper divertor and centerpost fixed Langmuir probes, upper divertor IRTV, and CER. |
| Analysis Requirements: | UEDGE, MIST, ONETWO |
| Other Requirements: | -- |
| Title |
178: Optimal location for fueling pumped DN plasmas |
| Name: | Thomas W. Petrie () |
Affiliation: | General Atomics |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | N. Brooks |
| Description: | It is important to determine the most efficient way of fueling DN divertors in order to minimize the amount of deuterium (or tritium) needed to maintain a set density value. With simultaneous pumping on both outer divertor legs of a magnetically balanced high-triangularity DN now possible, DIII-D IS UNIQUELY CONFIGURED TO DETERMINE DEFINITIVELY whether it is more effective to fuel a DN plasma from the high field side or from a divertor versus from the standard low-field side location. Related to this question, it is also important to assess any positive or negative effects to fueling from these locations (e.g., how is tauE affected). This experiment should be done in both forward and reverse toroidal field. |
| Experimental Approach/Plan: | A high triangularity, symmetric DN shape is maintained throughout the shot. The upper- and lower outboard cryo-pumps are cold and the inboard (dome) cryo-pump is warm. Conceptually speaking, this approach is made up of four parts: (1) A steady gas puff is injected from the inboard centerpost location into a standard DN H-mode plasma. (2) On the subsequent shot, the same steady gas puff is injected directly into the private flux region of the divertor in the direction of the gradB ion drift. (3) In the third shot, the same steady gas puff is injected from an outboard location (e.g., GasA). We expect that gas injection from the first two locations to yield higher core densities than from GasA. (4) GasA is now programmed to reach the densities achieved in the centerpost puff and divertor puff cases. We expect that more gas will be required to reach these densities using GasA than was used by the gas injectors from the other two locations. It is best to do this experiment in both forward and reverse toroidal field directions in order to account for any effect that differences in the structure of the upper and lower divertors. |
| Background: | We have previously found that unpumped DN H-mode plasmas fuel much faster than comparable SN plasmas (PSI1998). In those experiments fueling was done from the outboard vessel side. When gas puffing was used to fuel DNs, an almost immediate detachment of the inboard divertor legs permitted recycled gas from the outboard legs to escape to the inboard side of the core plasma, suggesting after some analysis (UEDGE) that fueling from the inboard side would be more effective than fueling from the outboard side. Experimentally, IR camera and Langmuir probe data from DN cases indicate that both ne and Te may be significantly lower along the inner SOL than along the outboard SOL and that the scrapeoff widths are also narrower on the inboard SOL (PSI2002). We thus expect easier neutrals penetration of the core from the inboard side and thus more effective fueling. An absence of ELMs along the inboard SOL (NF2003) is another reason to expect effective fueling from the inboard side. More recent data from radiating divertor experiments (2007) indicated that injecting impurity (argon) directly into the divertor pointed to by the gradB ion drift direction results in a very rapid impurity ion buildup in the core plasma. Due to the very quick detachment of the inner divertor leg of that divertor, one might expect that deuterium gas injected into the private flux region would also fuel the core plasma just as effectively as from the high field side. |
| Resource Requirements: | Machine time: 0.3 (forward Bt) + 0.3 days (reverse-Bt), both upper and lower outer divertor baffle cryo-pumps cold, minimum 5 beam sources. |
| Diagnostic Requirements: | Asdex gauges inside both outer baffles, core Thomson scattering, upper divertor and centerpost fixed Langmuir probes, and CER. |
| Analysis Requirements: | UEDGE, ONETWO |
| Other Requirements: | -- |
| Title |
179: Effect of particle drifts on particle exhaust in an ITER-like configuration |
| Name: | Thomas W. Petrie () |
Affiliation: | General Atomics |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | N. Brooks |
| Description: | ITER has chosen the pumping of neutrals from the private flux region as its method of particle control. To-date, modeling of the effectiveness of this approach has been done but this modeling presently does not include the effect of particle drifts in the divertor, such as those involving ExB, might have on these results. It is the intention of this experiment to evaluate whether or not neglecting these drifts can an appreciable effect on particle exhaust and detachment, when particle control is based on pumping on the private flux region. Note that detachment is crucial to ITER in maintaining power loading to acceptable values and we know that it also would be affected divertor particle drifts. Hence, these are rather important issues that need to be resolved sooner rather than later. |
| Experimental Approach/Plan: | An upper SN plasma (dRsep > +3 cm) has its outer strike point on the side of the outer baffle just above the entrance to the outer baffle. Simulate the ITER plasma shape as much as practical. The inner strike point is tangent to the dome next to the entrance to the inner pump plenum. Only the upper outer pump is at liquid helium temperature. Hence, neither the inner nor the outer strike points are pumped directly; only neutrals from the private flux region are pumped. This configuration is similar to the pumping setup describe in the ITER Technical Basis [G A0 FDR 1 01-07-13 R1.0], except for absence of a semi-permeable dome located between the pump and the private flux region.
The experiment is straightforward. The main parameter scan is core density and pumping rate vs gas puff rate (from the bottom of the vessel). The range in core density for which the plasmas are attached and detached and the neutral pressure values in the private flux region and inside the upper outer plenum are determined in both forward and reverse Bt cases. |
| Background: | The geometry of the ITER divertor has been based on simulations obtained using the B2-EIRENE Monte Carlo code and by extrapolation from results of tokamak experiments. The reference configuration for the ITER divertor is a vertical target/baffle with an open private flux region and a dome below the Xpoint. Neutrals that have entered the dome (which is partially open to neutrals from the inner and outer divertor legs) can then be pumped out of the vessel. Also, the magnetic field lines intercept the vertical target at an acute angle for power spreading on a larger wetted area and for easier partial detachment.
The calculations used to evaluate pumping expectations were based on models that do not include the particle drifts that studies at DIII-D have indicated play a very large roles in particle behavior in the divertor. We can simulate the ITER pumping scenario well enough to determine whether or not neglecting drifts are important for ITER. In addition to experimental verification, the progress that UEDGE has made in modeling these types of plasmas with drifts, particularly the Etheta x B and the Er x B drifts, should provide a theoretical underpinning to our measurements. Etheta is the poloidal component of the electric field on an SOL flux surface, arises principally from the poloidal gradient in Te on that flux surface, and is directed toward the divertor target. |
| Resource Requirements: | Machine time: 0.25 (forward Bt) + 0.25 days (reverse-Bt), upper outer divertor baffle cryo-pump is at liquid helium temperature, minimum 6 beam sources. |
| Diagnostic Requirements: | Asdex gauges inside both outer baffles, core Thomson scattering, upper divertor and centerpost fixed Langmuir probes, upper divertor IRTV, and CER. |
| Analysis Requirements: | UEDGE, ONETWO |
| Other Requirements: | -- |
| Title |
180: Complete ELM suppression with n=2 RMPs |
| Name: | Richard Buttery
() |
Affiliation: | UKAEA |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | Max Fenstermacher, T Evans, D Howell, M Schaffer, O Schmidt, R Moyer, T Osbourne, G Jackson |
| Description: | It is proposed to extend the 4 shot proof-of-principal 2007 studies which demonstrated complete ELM suppression with n=2 fields. These shots identified a possible "sweet spot" in q95 ramps, at q95=3.4, where ELMs were completely suppressed for up to 500ms. Other narrower resonances were observed at other q95 values. The key goal of this follow up study is to confirm the location of the resonance, and test whether slower q ramps or freezing the q value, allows the ELM removal effect to be sustained longer or indefinitely. It should also explore how wide the resonance is in q95.
The initial proof of principal confirmation would take around half a day, but should be extended if a robust method is found. A range of follow up studies (vary harmonic mix with I phasing, explore several sweet spots, combine with n=3 fields could be envisaged if successful, explore collisionality dependence, and physics studies with pellets). Prioritisation committees are invited to consider also planning for an extension along these lines. |
| Experimental Approach/Plan: | This would pick up 2007 studies, using already optimised discharges (ITER-like shape single null), q95 ramps, and maximum possible I fields. I phasing of 120 would be used - calculated to be optimally aligned with field pitch. Error correction to be done by C coils. No RMP references will be needed of all key results. |
| Background: | Complete and robust suppression of ELMs is a requirement for fusion power plants and highly desirable for ITER. Present n=3 techniques have been somewhat limited in their range of applicability, although appear to demonstrate the best potential for the power plant goal. Use of other n values may establish a way of extending resonance windows, either inherent to the different harmonic (eg applying a broader resonance) alone, or by combining fields with different n.
In this proposal we are taking a first step by evaluating use of n=2 fields alone. A wide range of extensions can be envisaged, if this proved successful, and should include combining with n=3 fields if suitable wiring is possible.
This experiment utilise a unique capability worldwide, in terms of DIII-D capacity to apply high amplitude n=2 fields, which through I coils flexible phasing, can have poloidal spectrum tuned for optimal resonance with the plasma. Further experiments on JET will be bid for 2008, though we should note that these will be more limited with regard to spectrum and amplitude, and the coils tend to apply higher levels of core resonance than DIII-D's I coils. Nevertheless, preliminary first tests of n=2 at JET in 2007 showed a modest ELM frequency rise, indicating a potentially viable technique.
The complete suppression demonstrated in DIII-D also showed signs of strike splitting and redistribution, which may indicate edge ergodisation effects, although further studies (eg with pellets) are needed. |
| Resource Requirements: | I coils 240, C Coils, 4 beams, (possible use of pellets as a further diagnostic). |
| Diagnostic Requirements: | Usual ELM control diagnostics, with particular emphasis on pedestal measurement. Esp. CO2, TS, CER, magnetics, filterscopes, Dimes TV, IR. |
| Analysis Requirements: | Results should be self evident, but detailed diagnostic analysis will be required to quantify effects. |
| Other Requirements: | -- |
| Title |
181: Vertical Stability Control Physics for ITER |
| Name: | Dave Humphreys ( ) |
Affiliation: | General Atomics |
| Research Area: | ITER Startup, Shutdown, Vertical Stability |
Presentation time: |
Requested |
Co-Author(s): | T. Casper, M. Cavinato, J. Lister, A. Portone, M. Walker, A. Welander |
| Description: | The goals of this 2-day experiment are to study the fundamental limits of vertical controllability of DIII-D with two different control coil sets and in such a way as to experimentally quantify controllability metrics being used for ITER design. The key performance quantities to be determined are the maximum stabilizable growth rate and the maximum displacement that can be restored following an uncontrolled VDE drift. Certain key disturbances will also be triggered and characterized, and the control responses to these disturbances will be quantified. This falls under a new ITPA joint experiment topic being considered by the ITPA MHD, Disruptions, and Control Group. |
| Experimental Approach/Plan: | Using ITER similarity plasmas, increase elongation in steps, holding for periods > 10-20 growth times. Determine highest growth rate sustainable with no VDE onset, and growth rate beyond which VDE is guaranteed (or extremely likely). Using targets near maximum growth rate, freeze coil commands to disable vertical/shape control for varying lengths of time, allowing VDE. Apply explicit step command to control coils to determine maximum displacement beyond which instability cannot be suppressed. Perform with both ITER-like coilset (PF6,7 only) and with usual (including PF2) coilset. Perform in ohmic and H-mode plasmas. Produce disturbances near control limits by dropping beams, either staying in H-mode or dropping to L-mode. Possibly inject impurity gas to contract current channel to cause delta-li perturbation. |
| Background: | |
| Resource Requirements: | 3-4 beams (co), PCS modification |
| Diagnostic Requirements: | MSE, 5 kHz magnetics sampling |
| Analysis Requirements: | standard EFITs, TokSys, Corsica |
| Other Requirements: | -- |
| Title |
182: Measurement of the electrostatic Reynolds stress across the L-H transition |
| Name: | Richard A. Moyer () |
Affiliation: | University of California, San Diego |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | C. Holland, G. Tynan, S. Mueller, J. Watkins, G. McKee |
| Description: | The goals of this proposal are to 1) directly measure the turbulent electrostatic Reynolds stress in L and ELM-free H-mode, and across the L-H transition using the Reynolds stress head for the midplane probe that was commissioned in CY07. 2) benchmark TDE-based turbulent particle flux measurements against probe measurements in the plasma edge in L and H mode. 3) If possible, make measurements with both ion gradB drift directions (different L-H power threshold). 4) Use the results to test models for Reynolds stress driven sheared flows and turbulent transport regulation.
This proposal is an extension of the intrinsic rotation studies using the Reynolds stress head of the midplane probe proposed by S. Mueller et al. |
| Experimental Approach/Plan: | Use two separate run days to vary L-H power threshold; if only 1 day, use LSN with normal Ip, Bt direction and lowest possible L-H power threshold. Re-create previous low power L-H transition discharges from turbulent heat flux experiment (CY05) using 1-2 gyrotrons for ECH heating. This eliminates fast ion interaction with the probe, improving penetration depth and signal quality. Repeat with low power NBI (duplicate shots for 330L edge CER and 150L BES). If separatrix is optimally placed for the high density CER edge chords (sep = 2.30 m), then a high triangularity LSN that "fits" in the lower divertor will provide easy access inside the separatrix at the probe elevation (z = -0.188 m). Obtain CER and BES measurements on the same flux surfaces as the probe but time dwell of plunge between beam "blips". First, acquire data inside the separatrix in L-mode just before the transition; second, acquire data in ELM-free H-mode just after the transition (ECH H-modes have long ELM-free periods); third: time probe plunge to "catch" the transition. |
| Background: | Motivation: we still lack a direct experimental verification of the role of the turbulent electrostatic Reynolds stress in driving mean flows that regulate turbulent transport in spontaneous L-H transitions in tokamaks. There is also considerable uncertainty over the level of rotation in ITER (a low input torque machine) and the role of the diamagnetic rotation. that is, will ITER be a high rotation H-mode due to the high performance pedestal parameters, and is such a high performance regime accessible without high torque input (e.g. from neutral beams)? In CY07, UCSD and SNL demonstrated the capability ot exchange probe heads overnight using the MiMES airlock, and commisioned first measurements (in piggy back) with two new SOL flow and electrostatic Reynolds stress probe heads. Successful parallel flow measurements were made in piggy back up to 1 cm inside the separatrix, with the depth limited by the session leader's choice of shape for the primary experiment. Previous experiments to look at the change in Te fluctuations and turbulent particle flux across the L-H transition were successfully up to 1 cm inside the separatrix using ECH L and H mode target plasmas. If time permits, measurements with low power (de-rated 150L to preserve long beam on times for BES) can be used to validate TDE based estimates of the turbulent particle flux. |
| Resource Requirements: | Since this experiment requires detailed probe measurements inside the separatrix in the H-mode transport barrier, we require absolute control of the discharges: shaping, power, auxiliary heating method, etc. to ensure that the maximum amount of high quality probe data is acquired. this is envisioned to take 1 day for each ion gradB drift direction. We do anticipate availability of the "back end" of the flattop for piggy back measurments, provided it doesn't jeopardize the success of the probe measurements. |
| Diagnostic Requirements: | Probe operators must have complete control over discharge conditions to maximize the amount and quality of the probe data due to the invasive nature of the probe measurements inside the separatrix. In addition, we require edge CER and BES for supporting Er, Ti, rotation and fluctuation measurements. We would also request profile and Doppler reflectometry, FIR scattering, and correlation ECE (to match the Te fluctuation measurements in the pedestal with measurements deeper in the discharge. |
| Analysis Requirements: | This work will require extensive flluctuation analysis by all fluctuation diagnostics. the target should be to produce ntidle measurements on overlapping flux surfaces from the various diagnostics, to compare rms ampitudes, correlation lengths and times, etc. |
| Other Requirements: | -- |
| Title |
183: Improved Gas Jet Disruption Mitigation by I-coil-Enhanced Impurity Transport |
| Name: | Dave Humphreys () |
Affiliation: | General Atomics |
| Research Area: | Disruptions |
Presentation time: |
Requested |
Co-Author(s): | T. Evans, E. Hollman, T. Jernigan, J. Wesley |
| Description: | Explore possible improvements to disruption mitigation effects by massive gas injection using the I-coil to impose high Chirikov parameter fields on pre-disruption and plasmas and during injection. |
| Experimental Approach/Plan: | Move standard disruption target plasmas into close proximity of I-coil and gas jet (R+1) to increase penetration of I-coil field (high Chirikov parameter). Establish baseline jet injection pre-emptive disruption mitigation without I-coil field. Then test several different scenarios, including cases with I-coil at full current/field before firing gas jet, and ramping field as jet fires; high vs low frequency time-varying I-coil field; and using either Ar or D+Ar. |
| Background: | Recent experiments with impurity injection to mitigate disruption effects have shown severe limits to both impurity neutrals and ions producing electron assimilation fractions below 10% of the Rosenbluth density. While massive impurity injection appears to effectively mitigate many damaging disruption effects including divertor heat loads and halo current forces, mitigation of runaway electrons via thermal (free+bound) electron collisions will require much increased transport in order to place the necessary particle density deep in the core where runaways are expected to be born. RMP experiments have suggested that I-coil fields with high Chirikov parameter can enhance particle transport at the edge, helping to reduce the energy in the pedestal and suppress ELMs. Using the same principle in a pre-emptively mitigated disruption may serve to improve impurity particle transport in the same way. Varying the I-coil current slowly or rapidly may serve to further stochastize the edge field and further enhance particle transport. Even if the transport only serves to increase the impurity density to within the rho~0.90 surface, the ensuing global MHD events may transport a larger number of ions into the core than when the ion population is confined to the SOL or outside. |
| Resource Requirements: | Massive gas jet hardware (MEDUSA valve), Ar, D+Ar gases |
| Diagnostic Requirements: | Usual disruption diagnostics: 5 kHz magnetics, DISRAD, Thomson, new IR camera strongly desirable, fast cameras (LLNL and UCSD) |
| Analysis Requirements: | KPRAD, other impurity/radiation codes; |
| Other Requirements: | -- |
| Title |
184: Test of neoclassical toroidal viscosity (NTV) theory for magnetic braking |
| Name: | Ted Strait ( ) |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | J. Callen, C. Hegna, A. Cole |
| Description: | The goal of this experiment is to test the hypothesis that non-resonant magnetic braking is predicted by neoclassical toroidal viscosity theory (NTV). Several key predictions can be tested:
(1) The strong scaling of torque with ion temperature: Ti^(5/2), leading to a deceleration that scales as Ti^(7/2) at constant beta
(2) The scaling of torque with toroidal mode number: n^2
(3) The "offset frequency" to which rotation saturates with strong braking
Agreement with the theory in all of these features would constitute strong evidence of the validity of NTV theory. |
| Experimental Approach/Plan: | A square pulse of magnetic braking with n>1 is applied using the I-coil. (The C-coil provides optimized n=1 error field correction.) The transient response of the plasma to the braking pulse (initial dv/dt) yields the torque at the initial value of beta and rotation. The three features of the theory described above will be tested by:
(1) Density scan at fixed beta. Due to the strong scaling, only a small range of density is needed (20% change in density should yield a factor of 2 change in deceleration).
(2) Comparison of n=2 and n=3 braking.
(3) Variation of the initial rotation value using co/counter NBI. Determine whether the torque is proportional to V or (V-V0). |
| Background: | NTV theory is widely quoted as predicting the torque due to non-resonant braking. It was used as one figure of merit in assessing options for ELM control coils in ITER. However, a systematic experimental test of the theory has apparently not been performed.
This experiment should include a contribution to an ongoing joint experiment between JET and C-Mod on n=2 braking. |
| Resource Requirements: | I-coils and audio amps. |
| Diagnostic Requirements: | CER rotation profiles |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
185: Completion of MP 2007-01-02: test RMP effect on ELM stability and increase neped with pellets |
| Name: | Richard A. Moyer () |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | Evans, Fenstermacher, Baylor, Jernigan |
| Description: | On June 24th, 2007, we began an experiment (MP 2007-01-02 to investigate the mechanisms for density pumpout in RMP ELM suppressed discharges. As part of this experiment, we used rapid (10 Hz) HFS pellets to investigate 1) evidence for a direct effect of the applied RMP on the Peeling-Ballooning stability independent of the pedestal density, and 2) to attempt to raise the pedestal density during ELM suppression to widen the operating space and recover a portion of the lost pedestal pressure. Unfortunately, we ran out of liquid helium (and hence pellets) before we were able to inject successfully into the discharges. This proposal is to conclude this part of the MP. |
| Experimental Approach/Plan: | 1. Investigate the direct effect of the RMP on ELM stability, independent of the density pumpout: use repetitive pellets with inter-pellet spacing < density pumpout timescale (typically a few tens of ms in the pedestal; a few hundreds of ms in the core) in RMP ELM suppressed discharges to vary the pedestal conditions on a time scale too fast for transport to respond, but relatively slowly in terms of MHD stability. 2) Attempt to broaden the RMP ELM-suppressed operating window and recover some portion of the lost pedestal pressure by using core fueling with rapid HFS launch pellets. |
| Background: | At low collisionality and high triangularity, we stabilize ELMs by reducing the pedestal density. The operating window has consequently been rather narrow in neped when using gas puff fueling. Attempts to increase the neped level lead to onset of small ELM-like events (grassy or type II ELMs perhaps) coincident with the reduction in pedestal toroidal rotation below a critical value and increase in pedestal density above a critical value. Concomittent with these changes, the Er well broadens and flattens (Er shear decreases in the pedestal). Linear peeling-ballooning stability analysis indicates that these small ELMs onset when the pedestal becomes again unstable. Core fueling with pellets might avoid increased rotation damping/increased viscosity in the edge from gas puffing and enable the core and pedestal density to be raised while maintaining ELM suppression.
by selecting an inter-pellet spacing that is long compared to MHD timescales but short compared to the pedestal transport change timescales (50 ms in the pedestal for density pumpout), we will also be able to test whether or not the applied RMP directly effects the ELM stability without reducing the pedestal density. |
| Resource Requirements: | 5 co and 2 counter NB sources
cryopumping
HFS repetitive pellets
n = 3 I coil operation up to 6.5 kA |
| Diagnostic Requirements: | standard RMP ELM control diagnostics :
profiles: core, tangential, and divertor Thomson; CER, profile reflectometry
fast and slow magnetics
poloidal and toroidal SXR
filterscopes
fluctuation diagnostics
fast framing camera
IRTVs in the divertor |
| Analysis Requirements: | Requires extensive analysis: kinetic EFIT equilibrium reconstructions, fast stored energy loss from fast magnetics, profile and Er analysis, ELITE stability analysis. May provide good dataset for further NIMROD and/or IPEC modeling of RMP penetration. |
| Other Requirements: | -- |
| Title |
186: Role of error fields in resistive wall mode stability |
| Name: | Ted Strait () |
Affiliation: | General Atomics |
| Research Area: | RWM Physics |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | The goals of this experiment are to:
(1) demonstrate the tradeoff between torque and error field correction required for RWM stability
(2) test the hypothesis that the apparent critical velocity for RWM stability is in most cases a result of error field penetration
(3) if possible, determine the "true" critical velocity in the absence of error fields
-- This experiment could also be considered under the Rotation task force. |
| Experimental Approach/Plan: | In a plasma with beta above the no-wall stability limit, vary the error field shot by shot, and find the "critical rotation velocity"in each case.
(a) Use feedback to determine the optimal error field correction with combined C-coils and I-coils.
(b) Ramp the neutral beam torque downward at constant beta. Look for the error field amplitude where the rotation locks and/or the RWM becomes unstable. If necessary, reduce Bt slightly to permit reaching zero torque at constant beta.
(c) Program the C-coil and I-coil current to match the feedback output of the previous shot. Add a small n=1 error field at the beginning of the torque rampdown. Look for the critical torque and rotation as the error field is varied.
The anticipated results relative the three goals described above are:
(1) Critical neutral beam torque varies proportional to the error field.
(2) The rotation threshold for RWM instability is half of the initial velocity (as observed previously).
(3) If a non-zero critical velocity exists that does not depend on error field, the scaling of critical torque proportional to error field described in (1) should break down at small values of the error field. |
| Background: | This experiment will help to establish some key physics for ITER: the tolerance for error fields at high beta and low rotation, and the possible need for RWM feedback control coils. The decision on "port plug" coils for RWM control in ITER will be made in 1-2 years.
Some of the effects described above have been observed in a database covering multiple days and experimental configurations, and also in more systematic error field ramp experiments conducted early in 2007. This experiment is distinguished from the previous data in at least two ways: the error field is held constant in each discharge, as it would be in an ITER discharge, and the focus is on the behavior at small error field and torque. |
| Resource Requirements: | I-coils |
| Diagnostic Requirements: | All available diagnostics should be used to determine whether the observed non-rotating modes have an ideal kink or island structure: SXR toroidal array, ECE, Thomson scattering, CER (Ti profile), MSE.
CER rotation profiles are also critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
187: Stability control and disruption avoidance: initial demonstration of an integrated approach |
| Name: | Ted Strait () |
Affiliation: | General Atomics |
| Research Area: | Disruptions |
Presentation time: |
Requested |
Co-Author(s): | J. Wesley |
| Description: | The goal of this experiment is to use existing capabilities for a first, simple demonstration of an integrated, multi-layer approach to stability control and disruption avoidance:
- NTM suppression with ECCD
- remedial action if ECCD suppression fails
- mitigation of an impending disruption |
| Experimental Approach/Plan: | - Establish a plasma in which the NTM is avoided by pre-emptive ECCD at the q=2 surface.
- Use the dud detector to reduce the beam power if an n=1 rotating mode appears. Demonstrate this during programmed or unprogrammed reductions of ECCD power.
- Configure the dud detector to trigger massive gas injection if the rotating n=1 mode locks. If such events do not occur naturally, induce them by adjusting the NB power in the dud phase.
Much of this experiment could be done in combination with an experiment on ECCD stabilization of the 2/1 NTM. The final step of applying MGI might need some dedicated shots, though the gas species and quantity could be selected for minimum after-effects. |
| Background: | An integrated system for stability control and disruption avoidance is crucial for ITER, and is an important element of the next DIII-D five-year plan. This experiment combines several of the building blocks of such an integrated system, and should provide a foundation on which additional features can be added. |
| Resource Requirements: | PCS programming is needed before the experiment. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
188: ELM control with a single row of RMP coils |
| Name: | Ted Strait () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The goal of this experiment is to determine what degree of ELM control is possible with a single row of RMP coils. If ELMs are not completely suppressed, can their frequency be modified without adverse effects on plasma performance? What is the impact on plasma rotation and H-mode barrier? How do the results (impact on ELMs and rotation braking) depend on toroidal mode number? The effects of the C-coil and a single row of I-coils are to be compared, since each has similarities and differences from the proposed midplane port plug coils for ITER. |
| Experimental Approach/Plan: | In an ITER-like plasma shape, apply n=3 perturbations using the C-coil and (separately) a single row of I-coils. Use a slow sweep of q95 to look for ELM suppression or modification during resonances. Vary the amplitude of the perturbation.
As a second phase of the experiment, compare n=3 vs. n=2 perturbations.
The choice of upper vs. lower I-coils should be based on calculations of the RMP spectrum in the ITER-like plasma shape. If time permits, both upper and lower coils could be tried. |
| Background: | The current plan for RMP coils in ITER is a single row of port plug coils at the midplane. We need to learn whether such a configuration can be effective for ELM control, and whether there are prohibitive side effects. |
| Resource Requirements: | I-coils |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
189: Model Validation of Electron Transport Using Modulated ECH |
| Name: | Kenneth Gentle ( ) |
Affiliation: | University of Texas |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Many workers, for example Ross, Mikkelson, and Bravenec, have each noted that validation comparisons often prove inconclusive because uncertainties in the input parameters (density profiles, impurity profiles, etc.) can accommodate a rather broad range in predictions. One simple type of modulated ECH experiment might offer a better opportunity for testing predictions of electron thermal transport. The most rigorous test, comparing Te(r,t) over the profile and modulation period, is not yet practical. Instead, we can take advantage of the experimental observation that for square-wave modulation at typical periods, the discharge follows a nearly exponential relaxation to alternate baseline and heated states. A code like GYRO could be run for either an annulus or full plasma for the baseline (adjusted to fit within uncertainties) and heated states. The test is whether the difference in the model predictions for the two conditions matches the experimental difference. The advantage is that the poorly known inputs would be known not to change over the comparatively short modulation cycle. Experimentally, averaging over many modulation periods gives a precise determination of the differences, and the higher ECH power to be available on DII-D will greatly improve signal-to-noise in both data and model. The test can be done in whatever radial range is most appropriate for the model and for any conditions accessible from early beam heating to delay sawteeth. |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | Full set of standard diagnostics for transport analysis plus fluctuation diagnostics appropriate to model prediction. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
190: Assessment of ITER startup with DIII-D similarity shapes |
| Name: | Thomas A. Casper ( ) |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | ITER Startup, Shutdown, Vertical Stability |
Presentation time: |
Requested |
Co-Author(s): | T. Casper, G. Jackson, T. Luce, D. Humphreys, J. Leuer |
| Description: | |
| Experimental Approach/Plan: | Improve initial breakdown conditions and vary the plasma shape around the DIII-D ITER-similar shapes developed in previous experiments. Explore methods to minimize the PF coil current variations in achieving the shape evolution proposed for ITER startup. Benchmark simulations used for predictions for ITER. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
191: Accessibility to AT regimes with ITER-scaled DIII-D shapes |
| Name: | Thomas A. Casper () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | ITER Startup, Shutdown, Vertical Stability |
Presentation time: |
Not requested |
Co-Author(s): | T. Casper, T. Luce, G. Jackson |
| Description: | Reference scenarios for ITER startup exhibit a rapid drop in the qmin and early onset of sawteeth well before reaching current flattop. We will explore startup scenarios using different plasma shapes (e.g. large bore, perhaps found in other ITER-related experiments) in the early part of the current ramp to maintain elevated q profiles in the ITER-similar shapes. |
| Experimental Approach/Plan: | Use discharge shape variations to control parameters during startup and extend the time to sawtooth. Vary the time of X-point formation and explore its effect on q-profile evolution. Apply auxiliary heating to maintain the higher qmin using variations consistent with ITER-relevant capabilities. Use ECH and/or NBI to heat or drive current during the ramp to explore the possibility of high qmin in these ITER shaped discharges. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
192: ITER controller assessment |
| Name: | Thomas A. Casper () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | ITER Startup, Shutdown, Vertical Stability |
Presentation time: |
Not requested |
Co-Author(s): | T. Casper, D. Humphreys, J. Leuer |
| Description: | Stability during the current ramp is determined in part by the shape variation, current ramp and profiles determining the internal inductance and vertical stability growth rate. |
| Experimental Approach/Plan: | Vary the stability growth rate and internal inductance using different current ramp and/or shapes or auxiliary heating to change the current profile. Explore variations in time of X-point formation relevant to ITER scaled parameters. Study the controllability of the ITER-shape during the current ramp up using the variations obtained possibly in other experiments. Explore controllability in the flattop for both Ohmic and H-mode discharges using the ITER-relevant shape. Benchmark codes used to study the control of an ITER-like plasma. This data will be needed for DIII-D milestone #166. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
193: Transport Locality and ECH Deposition |
| Name: | Kenneth Gentle () |
Affiliation: | University of Texas |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The detailed analysis of the accurate Te(r,t) data now provided by the DIII-D ECE system for electron transport with modulated ECH [K.W. Gentle, et al, Phys. Plasmas 13, 012311 (2006)] produced some enigmatic results. If the full absorbed ECH is deposited in the expected resonance region, a nonlocal transport coefficient is required -- the transport coefficient cannot depend only on local parameters but must change directly with ECH power [cf. Stroth et al, Plasma Phys. Control. Fusion 38, 611 (1996).] However, if a modest fraction of the power is presumed to be deposited over a broader region (at very low power density) in a self-consistent manner, the analysis provides a determination of reasonable local transport coefficients. Resolving this question is critical to our understanding of electron thermal transport. If the transport were truly nonlocal, none of our theories or computational models would be correct. We would be missing some important new physics. On the other hand, if there is some subtle misunderstanding of our ECH configuration that is leading to a sort of tail on the deposition profile, we must understand and quantify the effect to interpret experimental results properly. These effects have been seen in modulated ECH for electron transport for several years, at least since 105663. (Our level of quantitative analysis has reached the level of being quite sensitive to such details.) |
| Experimental Approach/Plan: | The experiment would be to use several gyrotrons to deposit power at a resonance location near the center to give a large temperature rise but without nonlinear effects in the ECE temperature measurements. Each gyrotron would be applied separately to confirm its resonance location, which can be quite well determined from the signals from and single gyrotron, and then all would be used together to maximize the effect of lower power deposition at other radii. The search would include both Te(t) measurements to detect a break in slope coincident with ECH and modulation at high frequency, for which the signal, particularly the component in phase with ECH, represents local deposition rather than transport. |
| Background: | -- |
| Resource Requirements: | 2+ MW ECH |
| Diagnostic Requirements: | Fast ECE. Standard set for transport analysis. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
194: Current profile feedback controller verification for AT experiments |
| Name: | Thomas A. Casper () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Model based Control |
Presentation time: |
Not requested |
Co-Author(s): | T. Casper, Y. Ou, E. Schuster, D. Humphreys |
| Description: | Experimental verification of developing current profile controllers. Iterate designs of profile controllers and test their operation on DIII-D. Use the ECH/ECCD and NBI actuators to benchmark and verify the controller designs and performance. Apply results to optimizing current profiles for AT discharges. |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
195: ECCD control of 2/1 NTM in ITER q95=3.2 shape |
| Name: | Robert J. La Haye () |
Affiliation: | General Atomics |
| Research Area: | NTM Stabilization |
Presentation time: |
Not requested |
Co-Author(s): | C. Petty, R. Prater, E. Strait |
| Description: | Stabilize 2/1 NTM in low q95 plasma with large value
of rho21. |
| Experimental Approach/Plan: | Produce the ITER Scenario 2 with q95=3.2, increase beta until the 2/1 mode occurs and stabilize or keep stable with off-axis ECCD at rho21=0.77. |
| Background: | We have stabilized 2/1 in hybrid only and with q95=4.4 typically with rho21=0.66 or so.
Larger rho21 and lower rotation could make this more difficult in ITER. |
| Resource Requirements: | 6 gyrotrons aimed at q=2 as ECCD efficiency will be lower at larger rho21. |
| Diagnostic Requirements: | Standard. |
| Analysis Requirements: | TORAY-GA |
| Other Requirements: | -- |
| Title |
196: Density peaking at low collisionality |
| Name: | Thomas A. Casper () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | T. Casper |
| Description: | Run discharges, preferably with an ITER-relevant shape, which exhibit anomalous core density peaking at low collisionality, e.g. at low density. This is in response to ITPA request CDBM-9 |
| Experimental Approach/Plan: | Vary the collisionality with heating (ECH and NBI) and fueling to explore effect of collisionality on the anomalous particle transport responsible for density peaking. |
| Background: | |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
197: Simultaneous ECCD control of 3/2 and 2/1 NTMs |
| Name: | Robert J. La Haye () |
Affiliation: | General Atomics |
| Research Area: | NTM Stabilization |
Presentation time: |
Not requested |
Co-Author(s): | D. Humphreys, C. Petty, R. Prater, E. Strait |
| Description: | At least 2 gyrotrons of ECCD directed at q=3/2 and 4 more at q=2 for simultaneous control of both modes. |
| Experimental Approach/Plan: | Make an ITER Scenario plasma, perhaps at higher q95 than the 3.2 planned,
raise beta to as usual first get 3/2 and then 2/1 NTMs. Apply ECCD at q=3/2 with alignment by RSURF and ALSO at q=2 with alignment by ZSURF. If real-time mirror steering is available, this would be used as in ITER for one or better both modes. |
| Background: | ITER must remove both the 3/2 AND the 2/1 modes which are expected to prevent successful performance. This requires dual-mode control which has not been demonstrated anywhere. |
| Resource Requirements: | 6 gyrotrons minimum.
Desirable is at least one launcher with real-time steering or better three. But RSURF and ZSURF simultaneous control is in the PCS and launch can be done to make these nearly orthogonal for q=3/2 and 2/1. |
| Diagnostic Requirements: | None special. |
| Analysis Requirements: | TORAY-GA |
| Other Requirements: | -- |
| Title |
198: Tearing Mode locking avoidance with toroidal phase advance in the feedback |
| Name: | Michio Okabayashi ( ) |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Disruptions |
Presentation time: |
Requested |
Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait |
| Description: | The feedback experiment in last year has shown very interesting results on the tearing mode behavior. The feedback operated with toroidal phase shift can synchronize the I-coil currents to the tearing mode, and not only prevent the mode from locking, but also modify the mode characteristics. The scheme can be applied for successful maneuverability of tearing mode in ITER once RWM control coil is installed.
Observations were:
(1) The Feedback can shift freely the tearing mode direction and frequency without losing the stored energy.
The feedback fields accelerate/decelerate the mode and, interestingly, the mode frequency is lower by two-three times in the CTR direction (to the plasma rotation) compared to that in the CO direction.
(2) The synchronization transition from 0.5-1 kHz frequency to the feedback-controlled frequency (20-60 Hz) is smooth when the phasing is correctly adjusted.
The choice of +30 degrees (CTR-direction of the mode) is very favorable, but so far only one shot tried. On the other hand, the -30 degrees (CO- direction of the mode) causes mode locking and beta collapse, which was reproducibly observed more than several shots. The zero phase shift may be acceptable.
These results suggest that the tearing mode is quite maneuverable so that the mode can be slowed down to low frequency range, and then can be controlled. Although it is to be examined further whether the tearing mode can be quenched in time, it seems, at least, we can sustain as a forced rotation-tearing mode. However, caution is to be made that this can occur only when the error field correction is extremely well compensated and of course only with high bandwidth amplifier-coil system.
We conclude that it is worthwhile to pursue this subject further, considering the possibility of the ITER application with internal coils |
| Experimental Approach/Plan: | Proposed experiments
(1) To survey systematically the impact of feedback toroidal phase on tearing modes
(2) To explore possibilities of quenching by varying the phase/gain in time
(3) To explore the implication to ITER internal coil option. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
199: RWM: Mode non-rigidity in low/high rotation plasmas |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics |
Presentation time: |
Requested |
Co-Author(s): | M. Chance, M. Chu, A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | The Resistive Wall Mode (RWM) is usually modeled as a rigid mode in many feedback analyses. Various useful conclusions have been developed with this simple model. Here, a possible limitation due to the multi-branch coupling has been studied by using the NMA code. According to the recent NMA calculation, toroidal phase-mismatch between the mode and feedback field can induce the response of the stable branch to the feedback field. This response can be unfavorable and lead the RWM into the unstable region, since these stable branches are located in shallow stable region. The comparison between the observation and theory should provide some aspect of mode non-rigidity, which has not been clearly identified yet.
NMA code also provides a different view on the coupling between the RWM and feedback field compared to the rigid mode assumption. For example, in the ITER RWM feedback control, the coils located away from the mid-plane "off-midplane port coils" have been considered very ineffective according to the rigid mode assumption. However, the NMA code predicts these coils remain effective when the operation is combined with mid-plane coils.
It is urgently needed to verify the appropriateness of the NMA code, since the decision of the ITER off-midplane port coils will be determined soon. This experiment will contribute greatly to this objective. |
| Experimental Approach/Plan: | Approach
Coil arrangement:
(a) The non-rigid poloidal field pattern can be made in a self-regulated manner, by energizing upper / lower coil independently with two independent sets of upper/lower sensors.
(b) More flexible pattern is with "autonomous feedback" where a pair of coils (facing each other toroidally connected in anti-series) is to be energized each up to 0.5 kA.
Observation
(1) RFA produced with extra n=1 pulses
RFA will be produced by pulsed field added through I-coil and/or C-coil
(2) We apply the feedback onto the RFA or its decay period, while observing the transient process. We should observe the asymmetric characteristics relative to the phase shift.
The toroidal phase shift will be added through PCS system
(3) Documentation
The comparison of amplitude and toroidal phase between upper/lower MPID signal and at midplane, since they are least sensitive to the applied field |
| Background: | |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
200: Edge Current Control of ELMs |
| Name: | James D. Callen ( ) |
Affiliation: | University of Wisconsin |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | R.J. Groebner, who will present at ROF |
| Description: | OBJECTIVE: Control ELMs via reduction of the edge current density at rho ~ 0.85 using ECCD. |
| Experimental Approach/Plan: | PROPOSED EXPERIMENT: The basic idea would be to use (counter) ECCD just inside the top of the pedestal to arrest the recovery of the local current density there (from about 20 A/cm^2 to 40 A/cm^2) after an L-H transition and/or an ELM crash. That is, the objective would be to prevent the current density just inside of the pedestal top from becoming large enough and broad enough to add sufficient peeling drive to destabilize the peeling-ballooning mode and precipitate a Type I ELM. It would be desirable for the ECCD to be injected at about rho of 0.85 and be radially localized within about 10% of the plasma radius (FWHM ~ 7 cm?) about this point. The ECCD would hence be applied to a cross-sectional area of about 2500 cm^2. Thus, to achieve a desired local current density change of about 20 A/cm^2 at rho ~ 0.85 would apparently require about 50 kA of ECCD. But less than this might be sufficient to determine if Type I ELMs at low collisionality could be affected and/or controlled by ECCD at about rho of 0.85. The ECCD might also be able to arrest the slow radially inward propagation of the top of the density pedestal. |
| Background: | Recent analysis of DIII-D shots 118897 (Groebner) and 98889 (Osborne) have shown that after an L-H transition or an ELM, while the edge pedestal electron density and temperature profiles come into a "transport quasi-equilibrium" in less than about 10 ms, the pedestal density continues to evolve slowly -- the top of the density pedestal moves radially inward and increases in magnitude slowly (on 30 to 100 ms or longer time scales). The edge current density also continues to evolve slowly as the edge inductive electric field induced by the pedestal bootstrap current decays resistively on a commensurate local magnetic skin diffusion time scale. This slow current profile evolution may be the underlying cause of the continuing slow density pedestal evolution. A typical current profile evolution (from EFIT and ONETWO modeling) was presented in viewgraph 16 of Mickey Wade's 1999 Year End Review talk (http://fusion.gat.com/diii-d/ExpPlans00 ). Then, Type I ELMs apparently occur due to peeling-ballooning modes when the edge pressure gradient and current density are large enough AND broad enough (i.e., reach far enough into the plasma -- to rho < 0.85?). The experimental proposal would be to inject counter ECCD to arrest the increase of the current density at rho ~ 0.85 and thereby arrest the inward propagation of the density pedestal, prevent the increase of the current density just inside the edge pedestal, and thus prevent the plasma from evolving toward a peeling-ballooning instability that would precipitate an ELM. |
| Resource Requirements: | Shots similar to 118897 which had a long ELM-free period after an L-H transition, and/or 98889 which had a long period (~ 36 ms) between roughly equally spaced Type I ELMs. |
| Diagnostic Requirements: | Thomson, CER, CO2 Interferometer, edge MSE? |
| Analysis Requirements: | For developing a detailed scenario, revisit ONETWO analysis that was presented in viewgraph 16 of Mickey Wade's 1999 Year End Review talk including ECCD at rho ~ 0.85, and explore its possible effects on stability of peeling-ballooning modes. And after the experiments are performed redo such analysis for the particular shots with the specific ECCD that is feasible. |
| Other Requirements: | DIAGNOSTICS: Direct measurement of the temporal development around rho ~ 0.85 of the current density, q or poloidal magnetic field (via edge MSE?) would be highly desirable to see if the ECCD does produce the desired reduction in the local current density there.
ANALYSIS: The space-time development of such ECCD and edge pedestal bootstrap current effects which are radially localized to such a small region of the plasma (less than 15% of the plasma radius) would require either a large number of radial points in ONETWO (>~ 200?), or packing of the spatial grid near the edge. This would likely require some careful work and testing of the ONETWO code to efficiently handle such complications. |
| Title |
201: Improvement of Dynamic Error Filed Correction by Active MHD Spectroscopy approach in closed feedback |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | In the 2007 campaign, we have shown that a simple model of dynamic error field correction iteration process can describe the experimental observations in a satisfactory manner.
The Dynamic Error Filed Correction (DEFC) approach is a power tool to minimize the resonant error field component and to improve the macro MHD activity. It is very attractive if the approach is extended to C_beta ~ 0 regime where many AT discharges have to go though in time for achieving higher betan conditions. The RFA is expected to be weak at C_beta ~ 0, however, the lower rotation may enhance the amplification as if a singularity.
The challenging part is to evaluate the plasma response and to set the complex gain in PCS system.
Here, it is proposed to determine the plasma response by using the Active MHD spectroscopy approach in closed feednback system mode. |
| Experimental Approach/Plan: | Approach
(1) To prepare the Active MHD spectroscopy technique along with closed feedback option
(2) To document the closed loop performance at various frequencies.
(3) To predicts the maximum gain in the PCS system for DEFC, including the possibility of complex gain setting
(4) To verify the predicted performance and improve the process |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
202: Development of Model-based Current Profile Control at DIII-D |
| Name: | Eugenio Schuster
( ) |
Affiliation: | Lehigh University |
| Research Area: | Model based Control |
Presentation time: |
Requested |
Co-Author(s): | John Ferron, Tim Luce, Mike Walker, Dave Humphreys, Tom Casper, Bill Meyer, Yongsheng Ou |
| Description: | The objective of this experiment is to implement open-loop controllers developed for the regulation of the q profile evolution during the early phase of the discharge, including ramp-up and beginning of the flattop, with the ultimate goal of achieving a desired target profile at some time during the first part of the flattop phase. The experiment will allow not only to evaluate the performance of the proposed controllers but also to validate the simplified models for current profile evolution used for the control synthesis. The validation of these models is crucial to decide about the viability of using them for model-based closed-loop control design. The experiment will also contribute to evaluate the correctness of actuation constraints considered during the control synthesis. The evaluation of control feasibility through use of open loop trajectories and the validation of the control model are both key prerequisites for the next step, which is to implement a feedback controller to drive the q profile to the desired target. |
| Experimental Approach/Plan: | The open-loop control laws will be expressed as time trajectories for the actuators: total plasma current, average plasma density, and non-inductive current drive (NBI, ECH) power. Special care will be put in reproducing in the experiment those initial conditions for the poloidal magnetic flux considered for the synthesis of the open-loop control laws. Comparison between desired and achieved time trajectories for the actuators will enable the redefinition of actuation constraints and the redevelopment of new open-loop controllers that could be tested later in the date. The evolution of the poloidal magnetic flux, plasma density and plasma temperature will be used for model validation. Different initial and target profiles will be considered mainly in L-mode but we also intend to carry out part of the experiment in H-mode. We also plan to consider different initial conditions and evolutions for plasma density and temperature to determine how they affect our control-oriented model. The ultimate goal of these experiments is the validation of a simplified dynamic model that could be used for closed-loop control.
Note: A separate proposal is being submitted to test closed-loop model-based control strategies for current profile regulation. Our goal is to carry out these open-loop experiments early in the experimental campaign, before the closed-loop experiments. |
| Background: | Setting up a suitable current profile has been demonstrated to be a key condition for the achievement of advanced scenarios with improved confinement and possible steady-state operation. The current approach at DIII-D focuses on creating the desired current profile during the plasma current ramp-up and early flattop phases with the aim of maintaining this target profile during the subsequent phases of the discharge.
The development of model-based current profile controllers aims at saving long trial-and-error periods of time currently spent by fusion experimentalists trying to manually adjust the time evolutions of the actuators to achieve the desired current profile at some pre-specified time during the early flattop phase. A simplified dynamic model describing the evolution of the poloidal flux, and therefore the q profile, during the inductive phase of the discharge has been proposed. Since this simple model serves not only as a fast simulation test-bed but also as the mathematical model used for the design of both open-loop and closed-loop model-based controllers, its validation is simply crucial. An initial experiment in July 2007 showed promising results. However, further and more in-depth validation experiments are still necessary.
Open-loop controllers satisfying many constraints of the actuators have been designed using Extremum Seeking and Nonlinear Programming techniques, and successfully tested in simulations, to match a desired q profile within a predefined time window during the flattop phase of the tokamak discharge. Based on the promising results obtained in simulation studies, it is anticipated that the scheme can play an important role in fusion plasma physics experiments at the DIII-D tokamak. |
| Resource Requirements: | Machine time: 1 day
Note: Some coordination with the Steady-State Scenario group might allow use of piggybacks or individual shots on their experimental days.
Beams, ECH. |
| Diagnostic Requirements: | Core and tangential Thomson, CER, CO2, magnetics, MSE, ECH diagnostics, a reasonable set of fast ion instability diagnostics (UF interferometers, FIR scattering, ECE at 500 kHz, fast magnetics with fast delay set in the current ramp), FIDA. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
203: Characterization and optimization of H-mode plasmas |
| Name: | Pete Politzer ( ) |
Affiliation: | General Atomics |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine the beta limits and optimize the confinement of an H-mode plasma in both the ITER shape and in an optimized shape. Develop a modern reference H-mode plasma. |
| Experimental Approach/Plan: | |
| Background: | There has been little or no work on improving the performance of standard H-mode plasmas in DIII-D in recent years. This experiment will update the H-mode benchmark plasma. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
204: Model-based Closed-loop Current Profile Control at DIII-D |
| Name: | Eugenio Schuster
() |
Affiliation: | Lehigh University |
| Research Area: | Model based Control |
Presentation time: |
Requested |
Co-Author(s): | John Ferron, Tim Luce, Mike Walker, Dave Humphreys, Tom Casper, Bill Meyer, Yongsheng Ou |
| Description: | The objective of this experiment is to implement closed-loop controllers developed for the regulation of the q profile evolution during the early phase of the discharge, including ramp-up and beginning of the flattop, with the ultimate goal of achieving a desired target profile at some time during the first part of the flattop phase. It is expected that closed-loop controllers will add robustness to previously tested open-loop controllers. |
| Experimental Approach/Plan: | The closed-loop control will regulate in real-time three actuators (total plasma current, average plasma density, and non-inductive current drive (NBI, ECH) power) based on real-time measurements of poloidal flux or current. We will assess the ability of the closed-controller to drive the current profile from an initial condition different from (but close to) the nominal one to a specific target profile. Different initial and target profiles will be considered mainly in L-mode but we also intend to carry out part of the experiment in H-mode.
Note: A separate proposal is being submitted to validate simplified control-oriented models and to test open-loop model-based control strategies for current profile regulation. Our goal is to carry out these closed-loop experiments late in the experimental campaign, after the model validation and open-loop control testing experiments. |
| Background: | Setting up a suitable current profile has been demonstrated to be a key condition for the achievement of advanced scenarios with improved confinement and possible steady-state operation. The current approach at DIII-D focuses on creating the desired current profile during the plasma current ramp-up and early flattop phases with the aim of maintaining this target profile during the subsequent phases of the discharge.
The development of model-based current profile controllers aims at saving long trial-and-error periods of time currently spent by fusion experimentalists trying to manually adjust the time evolutions of the actuators to achieve the desired current profile at some pre-specified time during the early flattop phase. A simplified dynamic model describing the evolution of the poloidal flux, and therefore the q profile, during the inductive phase of the discharge has been proposed. This model will be validated early in the experimental campaign and used for the synthesis of closed-loop current profile controllers.
Closed-loop controllers have been and are being designed by obtaining a reduced order model from the original simplified control-oriented infinite-dimensional model through the Proper Orthogonal Decomposition (POD) technique. The reduced-order model is combined with Optimal Control theory for bilinear systems to synthesize closed-loop controllers. Based on initial results obtained in simulation studies, it is anticipated that the scheme can play an important role in fusion plasma physics experiments at the DIII-D tokamak. |
| Resource Requirements: | Machine time: 0.5 day
Note: Some coordination with the Steady-State Scenario group might allow use of piggybacks or individual shots on their experimental days.
Beams, ECH. |
| Diagnostic Requirements: | Core and tangential Thomson, CER, CO2, magnetics, MSE, ECH diagnostics, a reasonable set of fast ion instability diagnostics (UF interferometers, FIR scattering, ECE at 500 kHz, fast magnetics with fast delay set in the current ramp), FIDA. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
205: Characterization and optimization of advanced inductive and hybrid plasmas in the ITER configuration |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Assess the impact of ITER shape and other constraints on the performance of hybrid and AI plasmas. Determine the influence of ITER startup constraints and control constraints on the formation and maintenance of these plasmas. |
| Experimental Approach/Plan: | Using the usual hybrid/AI recipe, apply (initially) only the ITER shape constraint. As the startup scenario is developed, incorporate that into the assessment. Similarly, when the capability of simulating the ITER PF controls becomes available, assess its impact on hybrid and AI plasmas. |
| Background: | This is part of the development of a baseline set of ITER scenario demonstrations, to be used for evaluating the impact of ITER constraints and assessing future improvements. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
206: Intrinsic rotation and SOL flows |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine the influence of flows in the SOL on bulk plasma rotation. |
| Experimental Approach/Plan: | In a zero NB torque plasma, vary the magnitude and direction of the flow in the SOL to the divertor by changing plasma shape and SOL density. |
| Background: | |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
207: Perpendicular resistivity in Ohm's law |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | |
| Experimental Approach/Plan: | Using transient perturbations (e.g., a magnetic field ramp or an ECH heating pulse) obtain the perpendicular electric field and current from analysis of the evolving equilibrium. |
| Background: | Although the resistivity perpendicular to field lines is a key transport coefficient for establishment of plasma equilibrium, as well as for stability of electromagnetic modes, it is an unknown quantity. Dedicated time is needed to document the effect of Bt ramps on quiet plasmas. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
208: Measure the NBCD profile |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Using the capability provided by co+counter beams, determine the current profile driven by NBI. |
| Experimental Approach/Plan: | By modulating between co and counter beams, determine the NBCD profile. The base case should be done in a quiet, low beta discharge with no evidence of fast ion scattering or diffusion. The measurements should be extended to cases with tearing modes, AE modes, sawteeth, and other possible mechanisms for radial diffusion of fast ions. |
| Background: | At present the NBCD profile is determined only by modeling calculations, and experimental verification is needed. In many cases, ad hoc corrections must be made to account for nonclassical fast ion orbit effects. These also are now quantifiable. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
209: Intermediate/high-k turbulence in electron ITBs and tests of gyrokinetic code predictions |
| Name: | Lothar Schmitz ( ) |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | T.L Rhodes, G. Wang, W.A. Peebles, E.Doyle, A.E. White, T.A Carter, G. McKee |
| Description: | Electron heat transport is perhaps the least understood transport channel in tokamak plasmas. Initial experimental evidence exists (Rhodes EPS 2007) linking electron heat transport to increased high-k turbulence. In addition, internal electron transport improvements are thought to occur due to low-k turbulence suppression by sheared rotation. Internal transport barrier formation offers the opportunity to study the transition to regimes dominated by TEM and ETG turbulence. We propose to examine the evolution to this state over a broad range in wavenumber, using the full suite of DIII-D fluctuation diagnostics. The results will significantly constrain the predictions of non-linear simulations (e.g. GYRO) allowing a rigorous (or more stringent) test of their predictive capability. The effects of fluctuating shear flows (Zonal flows) on turbulence level will be measured by Doppler Reflectometry providing simultaneous flow and intermediate-k density fluctuation spectra. Mapping of the transport barrier evolution at different times will be attempted to map out the dependence of flows and fluctuation levels on magnetic shear. |
| Experimental Approach/Plan: | Intermediate and high-k turbulence is predicted to be dominant in electron transport barriers in strong negative central shear (NCS) , ECRH-produced, and quiescent double barrier (QDB) discharges. Transport barriers in all four transport channels at r/a ~ 0.5 have been previously seen in DIII-D NCS discharges with injected neutral beam power Pinj >8 MW. While NCS electron barriers tend to be transient, off-axis ECRH heating may be used to trigger/stabilize ITBs in the vicinity of the local minimum in safety factor. QDB discharges offer sustained (but less steep) barriers with improved MHD stability and diagnostic access. Two fields of low-k turbulence (density and electron temperature fluctuations) will be measured via BES, low-k scattering and CECE (correlation ECE) diagnostics. The density will be chosen such that intermediate and high-k density fluctuations can be probed at the same radial location by intermediate/high-k FIR scattering and Doppler Reflectometry. The high-k scattering diagnostic can obtain localized ETG turbulence spectra (k perp ~ 35-40 cm-1) within the transport barrier if the second harmonic cyclotron resonance, used as an internal beam dump, is translated across the barrier region. (this requires a small adjustment of the toroidal magnetic field). The transport barrier region will also be probed by a four channel O-Mode Doppler Reflectometer to obtain the poloidal ExB flow profile within the barrier region, as well as the profile of intermediate-k (6 cm-1 < k pol < 12 cm-1) fluctuation spectra characteristic of TEM and ETG regimes. The measured fluctuation spectra will be compared to gyrokinetic modeling results in these TEM and ETG dominated regimes. Profile reflectometry is crucial for density profile reconstruction. |
| Background: | -- |
| Resource Requirements: | 7 Beams f; ECH (4 gyrotrons) |
| Diagnostic Requirements: | All fluctuation diagnostics, in particular FIR scattering, Doppler reflectometry,CECE,and BES.
Fast ECE, CER, MSE, and profile reflectometry. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
210: Effect of loop voltage fluctuations on the pedestal |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine whether and to what extent the loop voltage (both DC and fluctuating) affects the density pedestal shape. |
| Experimental Approach/Plan: | Use a well-documented H-mode pedestal discharge. Apply low-pass filtering to the E-coil command to gradually reduce control fluctuations of the loop voltage. Reduce the fluctuations to zero (strictly constant voltage). Look at changes in the pedestal shape, particularly density. |
| Background: | The r.m.s. fluctuation amplitude of the loop voltage at the plasma surface is large (> 10 V). The effect of this on the pedestal is unknown. These has been some indication in noninductive discharges that transformer clamping broadens the density pedestal. A systematic search for such an effect is called for. If an effect exists it may help elucidate the dynamics of the pedestal profile. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
211: Dependence of Zonal Flows on magnetic shear in internal transport barriers |
| Name: | Lothar Schmitz () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | G. Wang, T.L. Rhodes, E. Doyle, W.A. Peebles, A.E. White. G. McKee, M. Austin |
| Description: | Magnetic shear (in addition to ExB flow shear) is thought to control the amplitude of Zonal Flows and the radial turbulence correlation length in internal transport barriers. This process of turbulence self-regulation is predicted to control the resulting transport fluxes. A reduced radial correlation length for low-k fluctuations has been observed in DIII-D (T.L. Rhodes, Phys. Plasmas 9,2141,2003). Localized core measurements of Zonal flow structures by Doppler Reflectometry can now be attempted in DIII-D. The measurements proposed here rely on Doppler reflectometry in addition to BES, ECE and correlation ECE (CECE), and FIR scattering, to map out the transition from low-k dominated turbulence to TEM and/or ETG dominated turbulence which may occur as the transport barrier forms. The goal of the experiment is to map the evolution of poloidal flow components, <v pol> and v~ pol, and their correlation to the medium-k density fluctuation amplitude vs. magnetic shear. Since turbulence evolution is also determined by the <ExB> flow shear, discrimination of both effects is important. |
| Experimental Approach/Plan: | The Quiescent Double Barrier (QDB) discharge is suitable as an initial target for this work. It is stationary and relatively free of MHD activity in the barrier region. The barrier cover regions of negative and positive magnetic shear. Four-channel O-Mode Doppler reflectometry will be employed combined with BES to cover low and intermediate-k fluctuation spectra. Polodal flow spectra are extracted from these data. Profile reflectometry of the barrier region is crucial for density profile reconstruction. |
| Background: | A reduction of turbulence correlation length has been previously observed by reflectometry in QDB plasmas in DIII-D (T. Rhodes), and in ITB plasmas in JT60 (Nazikian et al, Phys. Rev. Lett. 94, 135002-1 (2005). Transient Zonal flow structures in the electron temperature profile have previously been seen in Internal Ion Transport Barriers triggered at rational-q surfaces. (M. Austin et al., Phys. Plasmas 13 082502 (2006).
The dependence of zonal flows on magnetic shear has been predicted theoretically (R. Waltz, 2006, Miyata et al., IAEA 2006,Kishimoto, 2004) |
| Resource Requirements: | -- |
| Diagnostic Requirements: | 4-channel Doppler and Profile refectometry, BES,
FIR-scattering, ECE and CECE, CER, MSE |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
212: Burn control simulation |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | General PCO |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Study the evolution and stationary state of a plasma with power input dependent on plasma parameters (e.g., beta^2 to simulate an alpha source). Develop methods to control the operating point. |
| Experimental Approach/Plan: | Regulate a portion of the power input to the DIII-D plasma to be proportional to the equivalent fusion power, Palpha~n^2*f(Ti). The remainder of the power is used in part for steady auxiliary heating and in part for feedback control of beta and of the operating point (i.e., maintain constant Palpha) in the presence of perturbations such as ELMs, sawteeth, MHD instabilities, etc. Also examine burn control using fueling and pumping to modify the fuel ion mix, impurity radiation, and average density. |
| Background: | It may be desirable to operate a burning plasma at a sub-ignited operating point, which will probably be unstable to temperature and power excursions. DIII-D now has the capabilities to start work on the control of the operating point. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
213: QH-mode in hydrogen plasmas |
| Name: | Punit Gohil () |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Produce QH-mode plasmas in hydrogen discharges. Determine how the QH-mode and EHO properties compare with deuterium plasmas and also with standard ELMing H-mode plasmas in hydrogen. |
| Experimental Approach/Plan: | Use counter-injected beams to produce QH-mode plasmas. Determine if QH-mode can be produced by co-NBI by gradually increasing the mix of co to counter beams. Document all possible edge quantities. |
| Background: | The QH-mode plasmas in deuterium discharges have certain distinctive properties. How do these properties vary in hydrogen plasmas and can they provide an insight in to the physics of QH-mode plasmas? Resolving these issues is an important concern, especially for ITER in which the early operational phase will be with hydrogen plasmas. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
214: |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine whether the modulation of the NTM by ELMs is the driver for the central current profile modification. |
| Experimental Approach/Plan: | |
| Background: | Test the hypothesis that modulation of the NTM leads to flux pumping and elevation of the central q. There is evidence from analysis of MSE data that this effects is operating at some level; a more quantitative measure is needed. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
215: The n=3 RFA excitation in the ELM-induced RWM by applying the n=3 extra error field |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | In the RWM buildup period, we often observe the ELM-induced RWM followed by the RFA period before the final collapse takes place. Since the ELM event produces many n-components, it is quite possible that the n=3RFA also should be excited along with the n=1 component in the event of the ELM-induced RWM events.
Before 2005, we observed frequently the excitation of n=3 components along with n=1 component in ELM-induced RWMs. However, strangely in 2006-2007 campaign, we seldom observed the n=3 component until very late period of the discharge termination. At present, this weak n=3 component remains as a little mystery.
Here, it is hypothesized that the n=3 error field component was indeed reduced by the coil lead correction in 2005 major opening period.
If this hypothesis is reasonable, the n=3 RFA should reoccur in the ELM-induced RWM by applying n=3 error field. If the n=3 RFA reappears, we will attempt to excite the n=2 RFA by applying n=2 field from C-coils. |
| Experimental Approach/Plan: | Experiment
(1) We introduce the n=3 component from I- or C- coil and then we observe the ELM event
(2) The DEFC of n=1 should be kept applied to minimize the n=1 component for better noise ratio.
(3) if n=3 RFA is observed in ELM-induced RFA, n=2 RFA possibility will be explored |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
216: Measurement of Zonal Flows in the H-mode pedestal |
| Name: | Lothar Schmitz () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | G. Wang, G. McKee, T.L. Rhodes, W.A. Peebles, A.E. White, T. A. Carter |
| Description: | Zonal Flows, including low frequency ZFs and Geodesic Acoustic Modes (GAMs), are thought to regulate local turbulence levels. We propose simultaneous low and intermediate-k fluctuation measurements, along with poloidal flow measurements (<v pol> and v~ pol) in ELM-free H-mode in the transport barrier (pedestal) region. The observed increase of fluctuations after initial suppression at the L-H transition will be investigated with regard to changes in flow patterns. |
| Experimental Approach/Plan: | In DIII-D, the average and time dependent poloidal flow in the H-mode pedestal can be measured simultaneously with low-k and medium k density fluctuations spectra by Doppler reflectometry. (2cm-1< k pol < 5 cm-1), combined with BES (k pol < 3 cm-1). Doppler reflectometry can also measure the instantaneous correlation of the flow amplitude with the density fluctuation level. Four x-mode reflectometry channels (50-70 Ghz) can obtain a radial flow profile for pedestal densities n ped < 2.5x 10^13 cm^-3. The outer gap should be chosen to allow the edge CER chords to cover the pedestal region to obtain the mean flow profile with high spatial resolution. |
| Background: | There is experimental evidence of the interaction of low frequency ZF flows and broadband density fluctuations from the Compact Helical Device (CHS) and JFT-2M. These measurements were done with Heavy-Ion Beam Probes and edge Langmuir probes.
In DIII-D, GAMs and low frequency ZFs have been measured by BES and Doppler reflectometry, and signatures of low frequency ZFs in the H-mode pedestal have been recently detected by Doppler reflectometry. |
| Resource Requirements: | USN plasmas with outer gap adjusted to allow edge CER measurements, 150 Beam constant for BES |
| Diagnostic Requirements: | Four channel Doppler reflectometry, BES, FIR low/intermediate k, CECE, profile reflectometry |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
217: Is q profile modification the key element in hybrid and advanced inductive plasmas? |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Test whether the q profile (as modified by the NTM) is the key to good hybrid performance. |
| Experimental Approach/Plan: | |
| Background: | The hybrid mode can be more reliably scaled to ITER if the physics behind its improved performance is understood. It has been argued that the changes in the q profile due to the presence of the 3/2 NTM (in DIII-D) lead to better confinement and improved stability to the 2/1 mode. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
218: Minimum rotation for hybrid/AI plasmas |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine the minimum rotation for hybrid operation. |
| Experimental Approach/Plan: | Use co+counter NBI to control the toroidal torque and flow. Determine whether the rotation threshold for locking of plasma rotation can be reduced by improving the error field compensation. |
| Background: | Low torque and rotation will be inherent characteristics of ITER. The accessibility of the hybrid scenario in low rotation plasmas may be limited by the interaction between the NTM and the wall. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
219: Hybrid/AI plasmas rotating in the counter-Ip direction |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine the performance limits for counter-rotating hybrid and advanced inductive plasmas. |
| Experimental Approach/Plan: | Apply the standard hybrid startup sequence in a negative Ip discharge. Compare confinement and stability characteristics with previous co-Ip operation. |
| Background: | Determine whether behavior at low rotation depends on co- versus counter-rotation. Extend understanding of low rotation behavior of hybrids. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
220: Investigation of Alfvenic Activity and Resultant Fast Ion Transport with Low NBI Power |
| Name: | Michael Van Zeeland ( ) |
Affiliation: | General Atomics |
| Research Area: | Energetic Particles |
Presentation time: |
Requested |
Co-Author(s): | W. Heidbrink, R. Nazikian, W. Solomon |
| Description: | The primary goal of this experiment is to investigate the transition in which a well documented discharge used for Alfven eigenmode (AE) studies goes from the regime of classical fast ion transport with weak or no Alfvenic activity to that in which AEs are thought to dominate the fast ion transport. The same series of discharges will also determine typical fast ion betas at which various types of AEs are triggered in DIII-D, the changes in mode structure with drive, and provide data on a new type of Alfvenic fluctuation, the BAAE (Beta Induced Alfven Acoustic Mode). |
| Experimental Approach/Plan: | |
| Background: | |
| Resource Requirements: | Machine Time: 1 day
NBI = 2 sources |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
221: Investigate Impact of ECH on Alfvenic Activity |
| Name: | Michael Van Zeeland () |
Affiliation: | General Atomics |
| Research Area: | Energetic Particles |
Presentation time: |
Requested |
Co-Author(s): | W. Heidbrink, R. Nazikian, W. Solomon |
| Description: | The primary goal of this experiment is to further our understanding of the ECH suppression of RSAEs observed during the last run campaign. |
| Experimental Approach/Plan: | Begin with discharge 128560 as a reference in which RSAEs were stabilized by ECH deposition near qmin. All discharges thus far have begun with ECH and NBI starting simultaneously at t=300 ms. ECH injection will be delayed to successively later times in a series of discharges and the impact on the RSAE as well as TAE suppression documented. The time of initial ECH injection may alter the stabilization if the actual mechanism relies on some type of feedback process that can only be triggered early in the discharge when the relative change in Te possible with limited gyrotron power is largest. Also, delaying the ECH to much later in the discharge will test whether or not ECH stabilization of RSAE or TAE is possible in H-mode plasmas as opposed to the L-mode, current ramp phase studied so far. To investigate the dependence of ECH deposition radial width relative to RSAE mode width, the gyrotron deposition will then be spread out about qmin in a series of discharges. Next, to build on modulation experiments carried out in 2007, ECH modulation will be carried out at several different rates and deposition locations. The impact of modulation on RSAE suppression is convoluted by the fact that RSAEs have transient chirping frequencies. To make clear the impact on RSAEs, 50% duty cycle modulation will be carried out with two nominally similar discharges and the ECH modulation180 degrees out of phase on each. This results in essentially two spectra with ECH off and two with ECH on for comparison. Also, the impact of ECH on weakly driven AEs will be studied by lowering the injected NB power. |
| Background: | Alfven eigenmodes cause fast ion transport and as a result, their presence can range from detrimental to advantageous depending on the circumstances. A tool for targeting and altering the amplitude of specific AEs would thus be extremely beneficial.
Experimental results obtained in the 2007 run period showed ECH suppression of RSAEs and the concomitant reduction of fast ion transport. Currently, the mechanism for ECH induced RSAE suppression is not understood and further experiments aimed at understanding this interaction should be carried out to identify the underlying physics. In the process, these experiments will help to elucidate the roles electron temperature and finite plasma pressure play in AE physics, as well as the possibility for extending this method to impact other types of AEs. |
| Resource Requirements: | Machine Time: 1 day
4 gyrotrons, 2 neutral beam sources |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
222: Reduced beta hybrid/AI plasmas and the transition to ELM-free VH-mode-like operation |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Study the transition to ELM-free operation seen in hybrids as betaN is reduced. Determine whether the uncontrolled density increase due to excessive confinement (VH-mode) be avoided. |
| Experimental Approach/Plan: | By reducing beta in a hybrid discharge, the interval between ELMs becomes longer, until ELMs cease. Use various methods for spoiling confinement at the edge to avoid VH-mode like runaway and collapse. Possible methods using the I-coils are RMP stochasticization (may be less perturbing that ELM suppression) or n=0 oscillatory perturbation of the plasma surface. |
| Background: | This behavior was seen in beta scaling experiments. ELM-free hybrid operation, even at reduced beta, would be a very interesting regime. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
223: |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | Fully Noninductive High Beta Operation |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Expand the regime of high beta-p noninductive (HBPNI) plasmas to lower q95, primarily by reducing the magnetic field strength. |
| Experimental Approach/Plan: | Thus far, the HBPNI discharges have been run with a single value of magnetic field (1.9T). Reducing the magnetic field should make interesting values of G (beta_N*H/q^2) more accessible. |
| Background: | It has been pointed out that the magnetic field is less important in maintaining confinement and noninductive current than is the total plasma current. Also, one concern about the HBPNI plasmas has been the relatively high value of q95, leading to G ~ ¼ G_ITER. A downward magnetic field scan will expand the HBPNI operating regime and make these plasmas more interesting. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
224: |
| Name: | Pete Politzer () |
Affiliation: | General Atomics |
| Research Area: | Fully Noninductive High Beta Operation |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine the nature of the broadband MHD turbulence that occurs in high beta_p noninductive (HBPNI) plasmas and which limits confinement. |
| Experimental Approach/Plan: | Establish an optimized HBPNI discharge. During the early part of the NI phase, when the MHD is active, use the density and Te fluctuation diagnostics in conjunction with magnetics (Mirnov and MSE) to characterize the spatial location, mode structure, and spectral properties of these fluctuations. Correlate the modes with variations in current and pressure profile widths. |
| Background: | In HBPNI discharges, the plasma profile evolution in the first second or two of the NI phase is slow, and beta rises slowly as well. During this phase broadband MHD turbulence is seen (noticed after the experiment). After a period of evolution, the MHD turbulence disappears, the confinement improves noticeably, and the beta rises more rapidly. Understading this process will help to eliminate it and improve the ultimate performance of these plasmas. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
225: Edge Ti (rotation) disturbance with residual stable RWM activity |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | 2007 Observation
The high-N plasmas with error field correction applied show the existence of residual stable n=1 activity. Typically, the stable RWM amplitude reaches ~ 5gauss in the midplane MPID sensors. Since these weak fluctuation occurs in slow time scale ~ 100 Hz or less, we have not paid attention to these activities.
However, we found that the direct RWM feedback reduced the amplitude by more than a factor of two and simultaneously reduced the edge Ti (rotation) disturbance. Here, the terminology of disturbance is used since the samping rate of Ti(rotation) was 2 ms.
A hypothesis is that the n=1 activity was caused by the RFA due to the small but finite residual error field. The RFA process does capture the helical flux and then expel with the appearance of other MHD like ELMs.
The dynamic error field correction (DEFC)-only is not sufficient to reduce this weak n=1 activity.
This disturbance propagates into q=2 surface area. It is quite possible that these disturbances can impact the edge profile as well as the onset of other edge-related phenomena. |
| Experimental Approach/Plan: | Experiments
(1) Apply fast feedback above the no-wall limit in fast feedback mode in AT plasmas rather than the standard DEFC operation.
(2) The better feedback can be made with using upper/lower separated sensor signals and energizing independently upper/lower I- coils. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
226: Density, Bt, and Ip dependence of toroidal rotation effect on L-H transition power threshold |
| Name: | Guiding Wang () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | J.C. DeBoo |
| Description: | The purpose is to quantify density, Bt, and Ip dependence of toroidal rotation effect on L-H transition power threshold on DIII-D, so as to predict this rotation effect for ITER. |
| Experimental Approach/Plan: | Perform rotation scan with combination of co- and counter-beams of the L-H power threshold at one set of plasma parameters (Bt, Ip, ne, etc) in LSN plasma (ion grad-B drift toward null which ITER will run). Scan ne, Bt and Ip one at a time and do the rotation scans to achieve the ne, Bt and Ip dependence of this rotation effect. |
| Background: | Rotation effect on L-H transition power threshold has been found on DIII-D. To assess this effect for ITER, detailed information on the dependence of this effect on ne, Bt and Ip is needed. |
| Resource Requirements: | all co- and counter-beams |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
227: Inter-machine comparisons for heat flux scaling |
| Name: | Charles Lasnier ( ) |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Requested |
Co-Author(s): | Maingi, et al |
| Description: | Use a coordinated approach to compare heat flux scaling between machines. Form the basis for a scaling which explains results on several machines. |
| Experimental Approach/Plan: | |
| Background: | Many previous single machine scalings have been developed, as well as attempts to fit a multi-machine database. Different attempts gave different results, and there was no attempt to coordinate discharges between several machines. |
| Resource Requirements: | DIII-D and other machines. Rajesh Maingi at NSTX is interested. It would also be good to work with CMOD, JET, ASDEX, JT60-U, EAST, and physicists from TEXTOR. |
| Diagnostic Requirements: | SOL and divertor diagnostics, boundary fluctuation diagnostics. Not all machines have the same diagnostics-we need to work around this. |
| Analysis Requirements: | SOL and divertor diagnostics, boundary fluctuation diagnostics, intermachine comparisons |
| Other Requirements: | -- |
| Title |
228: Optimization of combined Dynamic Error Field Correction and Direct RWM Feedback at Low Rotation |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics |
Presentation time: |
Requested |
Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | In 2007 campaign best shots of long-duration low-rotation discharges have been frequently produced by applying DEFC through C-coil or I-coil. Near the termination in these discharges (like in 127941), the n=1 RWM mode amplitude was increased with the increase of C- or I-coil coil currents as if the system became unstable. There remains as an unanswered question whether this is due to the unstable RWM or DEFC difficulty
Proof of principle experiment of combined DEFC and RWM direct feedback has demonstrated that the combined control of the RFA by C-coil DEFC and I-coil direct feedback made it possible to reduce the ELM-driven RWM activity leading to discharge sustainment (1286312 / 128613).
The optimization of combined operation of DEFC and direct feedback is one of main issues in 2008
Subjects
(1) To examine whether limitation at low rotation is due to DEFC failure or unstable RWM
(2) To optimize the combined operation of DEFC and RWM direct feedback process above the limitation
- Including the I-coil 180 degree connection
- DEFC and direct Feedback parametric scan, mainly the gain balance between the two systems |
| Experimental Approach/Plan: | Approach
(1) Fundamental information is taken with additional n=1 pulses
- DEFC or Direct feedback will be examined in the middle of additional n=1 pulse
- Transient process: the major documentation
(2) The gain balance of dynamic / direct feedback (128313/312) without n=1 pulses
Extra information obtained
1. Sensitivity to residual error field
2. Possible formation of magnetic island and locking
3. Uniqueness of RFA (non-rigidity?) even with same statistic error field
4. Criticality of toroidal phase shift for avoiding locking (forced rotation)
Discharges
Approaching in time to the operational limit in low rotation (like 127941) |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
229: Beam Ion Excitation of Beta Induced Alfvenic Acoustic Eigenmodes |
| Name: | Nikolai Gorelenkov ( ) |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Energetic Particles |
Presentation time: |
Requested |
Co-Author(s): | M. Van Zeeland |
| Description: | The core of the proposed experiment is to investigate recently discovered instabilities, called Beta-induced Alfvén-acoustic eigenmodes, which appear due to coupling of two fundamental MHD branches, Alfvénic and acoustic. |
| Experimental Approach/Plan: | The evolution of the current profile will be measured with MSE and complete equilibrium diagnostic data as well as FIDA measurements of confined fast ions will be collected. The experiment will target plasma conditions with a strong NB fast ion component and high electron temperature such as D3D #128926 in which the BAAE has been observed. The main study will be focused on BAAE mode structure and frequency measurements. Te variation and its effect on the BAAE frequency when the mode is inside the Alfvénic and acoustic gap will be also studied. |
| Background: | Global BAAE modes were discovered on NSTX, and on JET in different regimes but in both cases with rather high fast ion to plasma beta ratio. These modes have low frequency, typically below RSAE/TAE frequency range and are due to the coupling of the Alfvénic and acoustic branches mediated by the geodesic acoustic curvature and the plasma pressure. On NSTX these modes were successfully identified with the internal structure measured by the SXR and reflectometer diagnostics. The frequency was in excellent agreement with the theory based on the MSE q-profile in NSTX. The frequency of BAAEs often is observed as chirping in time from the plasma rotation frequency as q relaxes. Agreement of the BAAE frequency evolution inferred q_min and MSE q_min validates BAAE based spectroscopy. In JET BAAE frequency was reaching the saturation level predicted by the theory due to the mode entering the Alfvén-acoustic continuum gap. The major problem in the comparison was that the having quantitative and qualitative agreement with the theory predicted BAAE frequency for the saturated values was well above the measured one in JET, by at least 70%. Part of the uncertainty comes from the undiagnosed safety factor profile and ICRH minority ion pressure in JET. A DIIID experiment would help to resolve this issue and investigate the correlation of the BAAE instabilities and possible fast ion transport with its powerfull fast ion diagnostics. One puzzle of the theory of BAAEs is that they are observed despite of the strong expected damping of acoustic component and strong expected Landau damping. |
| Resource Requirements: | Run-Time: 1 day
4 gyrotrons
2 NB sources |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
230: Modulated ECCD for 2/1 NTM suppression |
| Name: | Anders Welander ( ) |
Affiliation: | General Atomics |
| Research Area: | NTM Stabilization |
Presentation time: |
Requested |
Co-Author(s): | R.J. La Haye, F. Volpe |
| Description: | The purpose is to investigate the effectiveness of modulated electron cyclotron current drive (ECCD) for suppression of the m/n = 2/1 NTM and compare with continuous wave (cw) ECCD. The first goal is to suppress a 2/1 NTM using modulated ECCD with the best guess of phase for the modulation based. The phase detection of the island is done using Mirnov signals. The second goal is to obtain cw-ECCD data under the same target plasma conditions for comparison. Physics data on the dependence of suppression rate on modulation phase error will be collected by sweeping the phase of modulation. |
| Experimental Approach/Plan: | A combination of co- and counter beams will be used to trigger a 2/1 NTM and drop the frequency to a few kHz. Suppression of the 2/1 NTM will be attempted using modulation with best guess of correct phase difference between the deposition location and the outboard midplane where the island is detected using the Mirnov signals. After that a reference shot with cw-ECCD will be taken. After that the phase difference will be varied to study the suppression rate and to check whether the guess was correct. |
| Background: | Continuous wave ECCD has proven effective in completely suppressing NTMs. It can also prevent NTMs, when preemptively applied in the correct radial location. The cw-ECCD requires good alignment and a narrow deposition region with respect to the island width. In ITER the ECCD will have a relatively wide deposition region which will make cw-ECCD less effective since the destabilizing effect from current driven in the X-point will nearly cancel the stabilizing effect from the current driven in the O-point. This problem can be solved by switching the gyrotrons on when the O-point passes by their respective line-of-sight and off when the X-point passes by. Predictions made by F.W. Perkins suggest that a modulation scheme using a square pulse train with a 50% duty cycle will give close to maximum feasible suppression rate. Previous work on ASDEX-UG has demonstrated the efficacy of modulated ECCD. The present experiment seeks to study the suppression of the 2/1 NTM with modulated ECCD, and demonstrate the use of modulated ECCD with realtime frequency/phase detection along with sustained synchronization with the mode. The system to be demonstrated constitutes a general solution for mode frequency/phase detection that will be readily extendable to simultaneous suppression of multiple modes using launcher steering in future DIII-D upgrades. |
| Resource Requirements: | Lower pump (upper pumps desirable), He cooled.
All NB sources required including 30L and 330L for diagnostics (MSE, CER) and both 210 sources for counter injection and to control rotation.
I coils in I240 configuration, powered by the SPAs. |
| Diagnostic Requirements: | Magnetic (fast and slow)
CER on 30L and 330L.
MSE Thomson.
CO2 interferometers.
ECE radiometer |
| Analysis Requirements: | -- |
| Other Requirements: | Real-time Mirnov acquisition.
Control of gyrotron modulation. |
| Title |
231: Hydrogen Confinement at Low Rotation |
| Name: | Steve Allen ( ) |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | L-H transition physics in hydrogen. Assess affect of plasma rotation. Determine if the threshold can be reduced by plasma shaping, x-point height, direction of the grad-B drift, pumping. |
| Experimental Approach/Plan: | Operate DIII-D with close to the ITER shape and determine the L-H mode transition power and confinement properties. Vary the plasma rotation with the co-counter beam mix. |
| Background: | Initial ITER operation will be in hydrogen with limited power. |
| Resource Requirements: | Hydrogen operation with hydrogen beams - at least 2 beamlines, co and counter. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
232: Rho-star scan for transport validation studies |
| Name: | Christopher Holland ( ) |
Affiliation: | University of California, San Diego |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | G. R. Tynan, G. R. McKee, M. W. Shafer, A. E. White, T. Rhodes, J. DeBoo, R. Prater, G. Staebler, J. Kinsey,R. E. Waltz, J. Candy |
| Description: | The goal of this experiment would be to repeat previous rho-star scaling experiments (101381/101391) to obtain a comprehensive characterization of fluctuations across the plasma. The results would then be used to carry out detailed validation studies of transport codes such as GYRO. |
| Experimental Approach/Plan: | Follow run plan from original shots, but take multiple discharges at each condition to allow radial profiles of density and Te fluctuations to be obtained via BES and CECE. The main control would be a scan of toroidal field from 1 T to 2T, yielding a 1.6 rho-star variation with other dimensionless parameters held fixed. |
| Background: | The 101381/391 pair of rho-star scaling shots have proved to be one of the most fruitful experimental data sets for modeling with transport codes. Since those shots were taken, significant diagnostics upgrades and additions (esp. BES and CECE) now allow for a significantly increased characterization of the plasma turbulence, in both core and edge regions. With the recognition of code validation as a key priority for DIII-D, the shots represent a natural starting point for obtaining experimental data to serve as the basis for validation studies. As rho-star is also a key player in the amount of �??non-locality�?� in the plasma dynamics, obtaining detailed fluctuation measurements at different rho-star values would allow for testing of various �??turbulence spreading�?� theories. Furthermore, as analysis has revealed not all dimensionless parameters were as well-matched as hoped, and so a more successful overall matching is an additional goal of this experiment. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | complete profile and fluctuation measurements |
| Analysis Requirements: | TGLF/GYRO/fluctuation and transport analysis |
| Other Requirements: | -- |
| Title |
233: ELM control in hybrid discharges |
| Name: | Steve Allen () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | M. Fenstermacher, C. Petty |
| Description: | Continue experiments that were started last year to combine ELM control RMP discharges with hybrid discharges. One run day was attempted last year. |
| Experimental Approach/Plan: | Start with a successful RMP discharge and change the heating profile to obtain higher beta normalized. |
| Background: | This experiment was started last year, and one run day was attempted. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
234: Mach number scan for transport validation studies |
| Name: | Christopher Holland () |
Affiliation: | University of California, San Diego |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | G. R. Tynan, G. R. McKee, M. W. Shafer, A. E. White, T. Rhodes, J. DeBoo, R. Prater, G. Staebler, J. Kinsey,R. E. Waltz, J. Candy |
| Description: | The goal of this experiment would be to revisit previous Mach number scaling experiments (shots 126284-8, 126295-299) to obtain a comprehensive characterization of fluctuations across the plasma, as well as improved profile measurements. The results would then be used to carry out detailed validation studies of transport codes such as GYRO. |
| Experimental Approach/Plan: | Follow run plan from original shots, taking multiple discharges at each condition to allow radial profiles of density and Te fluctuations to be obtained via BES and CECE. Shots would be run in inner-wall limited plasmas, preferably up-down symmetric profiles. |
| Background: | Previous Mach number scan experiments were hampered by difficulty in matching profiles, and profile measurements were not sufficiently accurate for modeling with transport codes. However, validating these codes for both strongly and weakly rotating plasmas is essential for extrapolating to ITER. A significant limitation of the earlier experiments was the (unknown at the time) effect of low-rotation on power thresholds, which is better understood today. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | Complete profile and fluctuation measurements |
| Analysis Requirements: | TGLF/GYRO/fluctuation and transport analysis |
| Other Requirements: | -- |
| Title |
235: nu-star scan for transport validation studies |
| Name: | Christopher Holland () |
Affiliation: | University of California, San Diego |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | G. R. Tynan, G. R. McKee, M. W. Shafer, A. E. White, T. Rhodes, J. DeBoo, R. Prater, G. Staebler, J. Kinsey, R. E. Waltz, J. Candy |
| Description: | The goal of this experiment would be to carry out a nu-star scaling study, to validate gyrokinetic simulations of in plasmas with varying collisionality. In contrast from usual scaling studies, we would want to push nu_star down rather than up. |
| Experimental Approach/Plan: | TBD. Basic idea is to scan nu-star (using a reference point at r/a=0.5-0.6) downwards, while holding rest of plasma as constant as feasible. For each value of nu-star, carry out multiple repeat discharges to obtain radial profiles of ne and Te fluctuations. Up-down symmetric plasmas would be preferable |
| Background: | One of the largest challenges for current gyrokinetic transport simulations of L-mode plasmas (which provide the largest fluctuation levels to compare against) is the relatively large value of nu-star relative to linear growth rates, particularly at larger radii. In order to better accurately characterize the performance of the codes, carrying out a nu-star scan to facilitate validation studies would be extremely helpful. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | complete profile and fluctuation measurements |
| Analysis Requirements: | TGLF/GYRO/fluctuation and transport analysis |
| Other Requirements: | -- |
| Title |
236: Grad-Ti/Stiffness scan for transport validation studies |
| Name: | Christopher Holland () |
Affiliation: | University of California, San Diego |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | G. R. Tynan, G. R. McKee, M. W. Shafer, A. E. White, T. Rhodes, J. DeBoo, R. Prater, G. Staebler, J. Kinsey, R. E. Waltz, J. Candy |
| Description: | The goal of this experiment would be to carry out a deviation from criticality scaling study, to validate gyrokinetic simulations of �??deep core�?� ITG turbulence and its scaling |
| Experimental Approach/Plan: | TBD. Basic idea is to scan grad-Ti or some other parameter (using a reference point at r/a=0.5-0.6), while holding rest of plasma as constant as feasible. For each value of grad-Ti, carry out multiple repeat discharges to obtain radial profiles of ne and Te fluctuations. Up-down symmetric plasmas would be preferable. The real test here is to do a scan of deviation from critical gradient for ITG modes. If we cant push on grad-Ti, could try varying a parameter to push on what the critical gradient is, with grad-Ti fixed. |
| Background: | Gyrokinetic simulations of plasma turbulence are believed to be most successful in predicting the ion heat flux due to long-wavelength ion temperature gradient (ITG) transport. However, to the author�??s knowledge there has been no systematic validation study of this effect using modern gyrokinetic simulations and detailed fluctuation measurements. Because grad-Ti is the dominant parameter in setting ITG dynamics, a series of experiments in which it is systematically varied would provide extremely useful data in quantifying the success of these codes in predicting core ion heat flux. More generally, stiffness can be quantified by delta = grad-Ti - grad-Ti_crit, where grad-Ti_crit is the critical temperature gradient for ITG instability. Thus the essential parameter to scan is actually delta, rather than grad-Ti. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | complete profile and fluctuation measurements |
| Analysis Requirements: | TGLF/GYRO/fluctuation and transport analysis |
| Other Requirements: | -- |
| Title |
237: Feedback Controlled Radiative Divertor |
| Name: | Steve Allen () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | T. Petrie, J. Ogena |
| Description: | Develop a reliable input signal and feedback controller to attempt to control the radiation in the mantle and divertor during puff and pump discharges. |
| Experimental Approach/Plan: | 1. Evaluate and pick a diagnostic input signal - bolometer, spectroscopy, etc.
2. Develop a feedback control algorithm with the controls group to control the deuterium and impurity flow in puff and pump experiments. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
238: Search for long-range correlations and non-local behavior in turbulence dynamics |
| Name: | Christopher Holland () |
Affiliation: | University of California, San Diego |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | G. R. Tynan, G. R. McKee, P. H. Diamond |
| Description: | The goal of this experiment would be to take advantage of the latest upgrades to the BES system, which will cover a significantly larger radial range, and search for evidence of long range (�??mesoscale�?�) correlations in the turbulence. |
| Experimental Approach/Plan: | A steady discharge with significant transport and fluxes is desirable. An inner-wall limited L-mode discharge analogous to what was used in the 2006 Mach number scaling experiment would be suitable. If possible, varying rho-star to affect turbulent eddy size would be desirable |
| Background: | The question of nonlocal dynamics has a long history in the study of plasma turbulence, and remains an active area of theoretical investigation. The potential relevance of these mechanisms becomes particularly important in light of the limited success of local simulations in successfully predicting heat and particle fluxes in the outer core and edge region of magnetic confinement devices. The goal of this experiment would be to collaborate with members of theory community to identify potential signatures of these dynamics (such as long-range correlations in turbulent fields, including zonal flows, in a steady plasma), and then search for these signatures using the newly radially extend BES diagnostic. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | profile measurements, BES |
| Analysis Requirements: | transport and fluctuation analysis, TGLF/GYRO simulation |
| Other Requirements: | -- |
| Title |
239: Scaling of SOL heat flux |
| Name: | Charles Lasnier () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Boedo, Maingi |
| Description: | Make parameter variations to form a database of fluctuation and heat flux measurements. Use Bout to predict fluctuation-induced heat flux transport in the boundary under those conditions, and compare with measurements. Derive experimentally-determined and model-predicted scalings of heat flux, and reconcile them. |
| Experimental Approach/Plan: | Use the two plunging probes, reflectometers, other fluctuation diagnostics to measure Te~ & Ne~ and calculate heat flux across SOL flux surfaces. Measure divertor surface temperature with IRTV, particle temperature and density with fixed probes, to make calculations of divertor heat flux. Then reverse Bt and do it again. Scans of Bt, Ip, density, Pinj. Make measurements for SOL and divertor heat flux in as many poloidal and toroidal places as possible and compare with predictions of heat flux derived from BOUT. |
| Background: | Many previous single machine scalings have been developed, as well as attempts to fit a multi-machine database. Different attempts gave different results, and there was no attempt to coordinate discharges between several machines. We have new Te measurement capability on one of the plunging probes. |
| Resource Requirements: | ELMing H-mode, forward and reversed Bt, beams |
| Diagnostic Requirements: | SOL and divertor diagnostics, boundary fluctuation diagnostics. |
| Analysis Requirements: | SOL and divertor diagnostics, boundary fluctuation diagnostics. Calculate experimentally-derived and model-predicted heat flux scalings and reconcile those. |
| Other Requirements: | -- |
| Title |
240: B-Stark Validation Using Deuterium Beams |
| Name: | Novimir Pablant ( ) |
Affiliation: | University of California, San Diego |
| Research Area: | General IP |
Presentation time: |
Not requested |
Co-Author(s): | K. Burrell |
| Description: | In order to determine the effectiveness of the B-Stark diagnostic in measuring the magnetic field line pitch, detailed comparisons need to be made with MSE over a range of fields and currents. A diagnostic of similar design to B-Stark is being considered for ITER. So far no comparisons of this type of system have been made with MSE. The fitting model used for the B-Stark spectra uses the measured plasma density and temperature. Scans of these parameters will aid in validating the fitting model. |
| Experimental Approach/Plan: | Produce and maintain plasmas during which current, field, and density scan cans be performed. In addition to the scans we will also use current diffusion during the startup to obtain a q scan. Field to be scanned between 1.40 - 2.16 Tesla. Current scan to be performed over the maximum possible range consistent with q95 < 3, < 2.5 preferred. Density scan over the range 2x10^19 - 6x10^19. For these scans either L or H mode shots may be used. |
| Background: | A new diagnostic, B-Stark, has been developed for the DIII-D tokamak to measure the magnitude and direction of the internal magnetic field. This diagnostic relies on the relative line intensities and spacing of Stark split emission from the neutral beams. This technique may have advantages over a Motional Stark Effect (MSE) diagnostic in future devices, such as ITER. In ITER, films deposited on first surface mirrors are expected to cause changes in the polarization direction, interfering with the MSE diagnostic. The B-Stark diagnostic is not sensitive to changes in the polarization direction, only to polarization dependent transmission. As part of fitting the Stark spectrum we will be utilizing an atomic code to predict the population levels. Comparisons with MSE will aid in validating this code. |
| Resource Requirements: | Modulated 330L and 330R beams. |
| Diagnostic Requirements: | MSE, Thomson |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
241: Evaluation of effect of double-layer Faraday screen on rf voltage standoff in ELMing H-mode |
| Name: | Robert I. Pinsker () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Requested |
Co-Author(s): | F.W. Baity, M. Porkolab, E. Fredd, J.C. Hosea, J.-M. Noterdaeme, A. Horton, W.C. Martin |
| Description: | This experiment aims to evaluate the effect of a double-layer, nearly-optically-opaque Faraday shield on an ICRF antenna. In particular, if the density burst in the antenna structure induced by large ELMs is responsible for transient depression of the rf standoff voltage in the antenna structure, the nearly optically-opaque Faraday shield installed on the 285/300 FW antenna on DIII-D should reduce the size of the decrement in standoff voltage due to ELMs. |
| Experimental Approach/Plan: | This experiment primarily uses the 285/300 antenna at 60 MHz, since this is the one with a double-layer shield, but in all cases, we could also monitor the rf voltage standoff of one of the 0 deg or 180 deg antennas (with a single-layer tilted Faraday screen) for comparison. After establishing an antenna rf standoff voltage in vacuum of ~30 kV, then measure the reduction standoff voltage in 1) L-mode plasmas as a function of the outer gap, and 2) in H-mode plasmas using ECH (and 60 MHz FW) as the only heating sources, as a function of the outer gap and with different ELM types, controlled by shape changes (e.g. X-point height, etc.), and 3) substitute neutral beams for the EC power and repeat the scans of step 2, to investigate possible effects of fast ion losses on voltage standoff. |
| Background: | In the late 1970s and early 1980s, ICRF antennas typically had a ceramic (MACOR) cover, on which the Faraday screen was placed, usually with two layers. First the ceramic cover was removed, with no apparent deleterious effect, then the second layer of the Faraday screen was removed, again without apparent deleterious effect. Since it is easier to make a single-layer shield that is thinner, hence place the strap closer to the plasma surface and increase the resistive loading (and thereby lower the peak voltage per MW coupled), single-layer Faraday screens quickly became nearly universally used. However, when antenna feed circuits that were able to cope with the rapidly changing loading due to ELMs were introduced (first at DIII-D then at ASDEX-U), it became apparent that the density burst at the antenna due to each large ELM tended to momentarily reduce the dielectric strength of the 'vacuum' near and in the antenna structure. Hence the double-layer shield for the DIII-D 285/300 antenna, which had been used in 1990-1991, was reinstalled during the LTOA in order to investigate this. Unfortunately, the antenna standoff in vacuum since the LTOA has been very poor, thus not permitting this experiment. During the present vent period, we hope to have remedied this problem by making a minor modification to the antenna vacuum coax, and if the antenna now returns to ~30 kV standoff in vacuum, we should be ready to carry out this experiment. This is of great significance to the ITER community as well as being of practical importance for the use of FW in ELMing H-mode discharges on DIII-D. |
| Resource Requirements: | One day experiment. ~4 NB sources, at least 4 gyrotrons, the 285/300 antenna having been conditioned to ~30 kV in vacuum, and the 0 deg antenna similarly well conditioned. |
| Diagnostic Requirements: | If the 0 deg antenna is used, the UCSD fast camera should be optimized for its view of the 0 deg antenna. If available, high time resolution loading diagnostics (~1 MHz digitizing rate) should be used on 285/300, each burst of data being triggered by the arc detector, with 50% pre-trigger samples. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
242: Beta Scaling of turbulence and transport in low-rotation H-Mode Plasmas |
| Name: | George R. McKee () |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | C. Petty, C. Holland, T. Luce, D. Schlossberg, M. Shafer |
| Description: | The plasma pressure plays a key role in both driving and stabilizing turbulence. This experiments seeks to vary beta systematically in a set of dimensionally-matched H-mode discharges (similar to those run by C. Petty in 2003) and examine the turbulence characteristics to see if they scale in a manner consistent with theory/simulation and observed transport scaling. |
| Experimental Approach/Plan: | Develop low to moderate rotation H-mode discharges at the highest feasible beta_N, then step down beta_N (from perhaps near 3 to about 1) while maintaining other dimensionless parameter nearly constant. Toroidal field and current will be varied by perhaps 25% in this process as density and beam power are scaled more strongly so as to maintain dimensionless parameters roughly constant. At each condition, several repeat discharges will be required to acquire the necessary spatial scan with BES. Also, 150L should be run steady while 150R is off.
All fluctuation diagnostics will be utilized to obtain as comprehensive a set of turbulence characteristics as possible. |
| Background: | Experiments and simulations have shown the importance and impact of beta scaling on turbulence and transport. Generallly, as plasma pressure increases, one might expect the turbulence drive to likewise increase. At some beta, alpha-stabilization kicks in and begins to stabilize turbulence. At yet higher beta, electromagnetic instabilities such as kinetic ballooning modes might be driven unstable. For purely electrostatic ExB turbulence, beta does not play a direct role. H-mode beta scaling studies on D3D showed that transport and confinement time vary little with beta (Petty, PoP, 2004), consistent with transport dominated by electrostatic turbulence.
The upgraded BES system provides significantly enhanced sensitivity to small-amplitude fluctuations and has demonstrated capability to measure turbulence in the core of H-mode discharges. We will utilize this capability to monitor turbulence characteristics as beta is varied while other relevant dimensionless parameters are held nearly constant.
A similar experiment was performed in hybrid discharges in 2007, however the beta range was quite limited due to ELM-free operation at low beta, and NTMs at higher beta. Furthermore the discharges were not very reproducible which limited the ability to obtain comprehensive measurements with fluctuation diagnostics.
The goal will be to utilize the scaling of turbulence characteristics to compare with and help validate models and nonlinear simulations (TGLF, GYRO, etc.). |
| Resource Requirements: | All NB sources |
| Diagnostic Requirements: | Full Profile and fluctuation diagnostics |
| Analysis Requirements: | Lots... |
| Other Requirements: | -- |
| Title |
243: Assess sensitivity of ITER demonstration discharges to variations in key physics parameters |
| Name: | Edward Doyle () |
Affiliation: | University of California, Los Angeles |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | This experiment proposes to scan key physics parameters in the four different types of ITER demonstration discharge. Key parameters to vary include shaping (e.g. squareness, X-point location), as well as average input NBI torque (ExB shearing rate), Te/Ti ratio, etc. Such a sensitivity study is essential as part of the projection to ITER, and is also required in justifying any potential change to the ITER detailed design, i.e. the ITER demonstration discharges should not be run so as to only determine performance at a "single point", which is difficult to interpret. |
| Experimental Approach/Plan: | Utilize DIII-D control tools to scan key physics parameters in ITER demonstration discharges. As a starting point, it is assumed that demonstration discharges have already been developed and stationary high performance obtained for each of the four ITER regimes (baseline, advanced inductive, hybrid and steady-state). Specific scans which can be performed include shaping (i.e. squareness and X-point location), as well as momentum input (via NBI co-/counter beam mix), and Te/Ti (using ECH). |
| Background: | -- |
| Resource Requirements: | 7 NBI sources, ECH |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
244: B-Stark Validation Using Hydrogen Beams |
| Name: | Novimir Pablant () |
Affiliation: | University of California, San Diego |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Requested |
Co-Author(s): | K. Burrell |
| Description: | In order to determine the effectiveness of the B-Stark diagnostic in measuring the magnetic field line pitch, detailed comparisons need to be made with MSE over a range of fields and currents. These comparisons would be improved by taking measurements using a hydrogen neutral beam. A hydrogen beam will have sqrt(2) the wavelength separation of the Stark components as compared to deuterium, potentially improving our spectral fits. Characterization done with hydrogen will also be relevant to ITER, where a greater Stark separation will be seen as compared with DIII-D. The fitting model used for the B-Stark spectra uses the measured plasma density and temperature. Scans of these parameters will aid in validating the fitting model. |
| Experimental Approach/Plan: | Produce and maintain plasmas during which current, field, and density scan cans be performed. In addition to the scans we will also use current diffusion during the startup to obtain a q scan. Field to be scanned between 1.40 - 2.16 Tesla. Current scan to be performed over the maximum possible range consistent with q95 < 3, < 2.5 preferred. Density scan over the range 2x10^19 - 6x10^19. For these scans either L or H mode shots may be used. While dedicated shots duplicating scans taken with deuterium beams are desired, these measurements can likely be done piggyback. |
| Background: | A new diagnostic, B-Stark, has been developed for the DIII-D tokamak to measure the magnitude and direction of the internal magnetic field. This diagnostic relies on the relative line intensities and spacing of Stark split emission from the neutral beams. This technique may have advantages over a Motional Stark Effect (MSE) diagnostic in future devices, such as ITER. In ITER, films deposited on first surface mirrors are expected to cause changes in the polarization direction, interfering with the MSE diagnostic. The B-Stark diagnostic is not sensitive to changes in the polarization direction, only to polarization dependent transmission. As part of fitting the Stark spectrum we will be utilizing an atomic code to predict the population levels. Comparisons with MSE will aid in validating this code. |
| Resource Requirements: | 330 Beams using hydrogen. |
| Diagnostic Requirements: | MSE, Thomson |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
245: Real time disruption detection/mitigation |
| Name: | Michael Walker () |
Affiliation: | General Atomics |
| Research Area: | Disruptions |
Presentation time: |
Not requested |
Co-Author(s): | Al Hyatt, Dave Humphreys, Eric Hollmann, Phil West |
| Description: | Begin implementation of basic disruption detectors. Then integrate with a disruption mitigation trigger (for massive gas puff or other mitigation scheme). Eventual target is to demonstrate routine detection and mitigation of all disruptions, but build this capability in a stepwise manner over several operational campaigns. Begin this year concentrating on disruptions in Ip rampdown. Develop rampdown scenarios relevant to ITER operations. |
| Experimental Approach/Plan: | Begin with implementation of some basic disruption detection algorithms in the PCS for real time use. First, execute in real-time code in a non-interfering manner. Next, phase in disruption mitigation, but trigger only if disruption occurs during the Ip ramp-down. If this type of operation will be accepted as a piggyback on sufficiently many experiments, no dedicated time is needed. If not, then request a half day to either demonstrate no adverse effects on experiments or develop methods to prevent adverse effects. Incorporate additional and improved detection logic as understanding of disruption precursors improves. Enable triggering of alternative mitigation methods to support experimental testing of these methods.
Experiment with control scenarios relevant to ITER that incorporate various combinations of reductions in heating, shape modification, and disruption detection and mitigation.
Coordinate with work on disruption data base for development of disruption detectors and with people working on disruption mitigation physics to obtain good data for physics studies.
Develop database of effects on early phase of subsequent discharge after mitigated and unmitigated disruptions. Monitor impurity line emission and radiated power during breakdown and burn-through, gas fueling to reach target density, volt-second consumption, and early MHD activity. |
| Background: | The problem of disruption detection and mitigation is critical for ITER, and especially relevant in rampdown since there presently appears to be no viable rampdown scenario for ITER operation. Many of the causes of disruptions are well known and, in some cases, real-time capable detection algorithms already exist. Studies of disruption mitigation have been ongoing at DIII-D for several years, so the mitigation actuators are in place and mature. It has been possible �??in principle�?� for some time to do routine disruption and mitigation for DIII-D plasmas, but the ability to do this routine process has never actually been demonstrated. In addition, the relevance of the mitigation scenarios to ITER has not yet been demonstrated. |
| Resource Requirements: | Machine Time: 4 hour experiment + piggybacks
Number of neutral beam sources: >=4
PCS programming support for implementation of detection and triggering logic. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
246: Improve empirical error correction for right-handed plasmas |
| Name: | Michael J. Schaffer ( ) |
Affiliation: | General Atomics |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | LaHaye, Strait, Scoville (expected) |
| Description: | Develop improved empirical error correction for right-handed plasmas. Preferably, I-coil and C-coil -based corrections would both be developed, to give experimenters more flexibility. The new correction(s) are expected to be better than the presently used (but poorly performing) right-handed corrections. |
| Experimental Approach/Plan: | Use the previously developed Ohmic, low-density, locked-mode error field test plasma and technique. Choice of the I-coil configuration is still open; present correction uses quartets with 180 deg phasing, but J-K Park's new theory suggests 120 deg phasing will be best. |
| Background: | Empirical error field corrections improve operational space for many affected experiments. Right handed plasmas (either Bt or Iplas reversed from normal) are less commonly run than the "normal" or "standard" left handed plasmas. Error correction for right handed plasmas is not as well developed as for left handed. The qualitative consensus of "right handed plasma users" is that the present error correction is inadequate and limits experiments.
New theory by J-K Park et al, PRL (accepted 2007) explains previous DIII-D empirical error correction semiquantitatively, via the coupling between the external error and correction fields with the least stable ideal MHD plasma mode, whose non axisymmetric currents strongly dominate inside the plasma. The theory will help to choose the I-coil configuration (phasing) to begin with. |
| Resource Requirements: | I-coil and C-coil systems essential.
Ohmic plasmas --- no NBI. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
247: BetaN=5 for 2 seconds |
| Name: | Andrea M. Garofalo ( ) |
Affiliation: | Columbia University |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Not requested |
Co-Author(s): | C. Holcomb, E. Doyle |
| Description: | Demonstrate sustained betaN~5 for at least ~2 seconds. Use Ip and Bt ramps if necessary to maintain NTM stability by driving current at large minor radius, as in discharge 122004. Use counter-current drive to compensate bootstrap current overdrive as betaN is pushed above 4. |
| Experimental Approach/Plan: | A key requirement to sustain betan >4 is the sustainment of qmin>2. - This requires counter-current drive just inside the radius of qmin, possibly combined with co-current drive outside the radius of qmin.
For efficient ECCD current drive, we will need to develop better density control than in discharge 122004. This will require tweaking the plasma shape to take advantage of the lower divertor high-triangularity pump, not available at the time of shot 122004.
With the energy confinement of shot 122004, 5 NBI co-Ip sources should allow reaching betan=4.5. We propose to investigate reducing the Ip ramp rate to both help reducing the density rise, and make available more NBI power to push betan toward 5. Lowering the toroidal field may also be a viable way to make more co-Ip NBI power available. |
| Background: | The target for the DIII-D 5 year plan is to achieve betaN~5 in steady state. An intermediate step would be the long pulse demonstration of betan=5, i.e. sustained but not necessarily steady-state. Experiments in 2005 have demonstrated betan~4 for 2 seconds, and have shown the possibility for stable betaN=5, if qmin is above 2. |
| Resource Requirements: | All 5 co-Ip NBI sources. 4 or more gyrotrons for ECCD. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
248: Internal Structure of n=1 MHD Activity in Low Rotation Plasma |
| Name: | Ioan N. Bogatu ( ) |
Affiliation: | FAR-TECH, Inc. |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | Yongkyoon In (FAR-TECH, Inc.), Jin-Soo Kim (FAR-TECH, Inc.), Matthew Lanctot (Columbia University), K. Burrell (GA), W. Solomon (PPPL), E.J. Strait (GA) |
| Description: | To investigate the multi-faceted physics of the interaction of the internal structure of n=1 component of MHD activity (RWM ) with toroidal rotation and current density profile evolution in low rotation plasma. |
| Experimental Approach/Plan: | |
| Background: | |
| Resource Requirements: | Piggy-back on low-rotation plasmas |
| Diagnostic Requirements: | SXR three toroidal arrays (TAs), CER (CERFIT), MSE, and ECE |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
249: Determination of intrinsic rotation using torque ramps |
| Name: | Wayne M. Solomon ( ) |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | J. deGrassie, K.H. Burrell |
| Description: | The goal of this experiment is to establish a more efficient way of estimating the intrinsic rotation using our beam-based CER diagnostic. |
| Experimental Approach/Plan: | Nominally balanced neutral beam injection will be used as a rough baseline for intrinsic rotation measurements. Unfortunately, balanced NBI does not imply a zero torque profile across the plasma, and so the plasma rotatino profile can be influenced relative to 'intrinsic' level. By using occasional torque ramps from slightly co to counter, it should be possible to refine the crude estimate of the intrinsic rotation profile from balanced injection. This correction can then be applied for the time history. The intrinsic rotation inferred in this way can be compared with the traditional method, where the NBI power is replaced with ECH (probably can only match one effective NBI source with ECH). |
| Background: | Historically, the intrinsic rotation has been measured using short beam blips in combination with fast CER timing. In this way, the unperturbed rotation profile can be deduced by extrapolating the measurement back to prior to the NB pulse. Sufficient time must elapse between these blips to allow the rotation to return to the 'intrinsic' level. This approach, while accurate, is not very efficient (especially for measuring time histories), since typically acquiring one or a few points per shot. |
| Resource Requirements: | Machine Time: 1 day Experiment
Number of neutral beam sources: 5
AMAP gyrotrons + co/counter NBI |
| Diagnostic Requirements: | CER, Mach probe measurement of SOL flows if possible |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
250: H-mode transition assisted by edge ECH |
| Name: | Ron Prater ( ) |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Apply ECH near but inside the edge of an L-mode plasma to see if that can reduce the total heating power needed to achieve the H-mode transition. |
| Experimental Approach/Plan: | Apply ECH to the edge of an L-mode plasma while ramping up the NBI power from zero to above the H-mode transition. Repeat with the ECH central instead, and find whether the power needed to effect the transition is different. |
| Background: | Methods to reduce the power needed to achieve H-mode are needed for ITER, especially during the hydrogen campaign. In the 1990's it was found in some tokamaks that edge ECH was effective in making the H-mode more accessible, but this was not followed up. |
| Resource Requirements: | 2.5 MW ECH, 10 MW NBI. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
251: Dependence of intrinsic rotation on applied error field |
| Name: | Wayne M. Solomon () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | J. deGrassie, K.H. Burrell |
| Description: | The aim of this experiment is to investigate whether the intrinsic rotation level is influenced by the error field. |
| Experimental Approach/Plan: | The I-coil will be used to apply n=3 non-resonant braking (increasing the error field over the optimal correction) and the intrinsic rotation will be measured, either using the traditional blip technique, or if the technique from proposal #249 is successful, this may be used also. The question will be whether the rotation is altered (either slowed or accelerated). Care is required to make sure that any change is not just a result of the non-resonant field altering the pedestal pressure/beta, which would change the intrinsic rotation according to the Rice scaling. |
| Background: | Theoretical predictions suggest that the level intrinsic rotation is at least in part influenced by the level of error field and associated torque to the plasma. This experiment will try to address the degree to which the error field sets the intrinsic rotation level. |
| Resource Requirements: | Machine Time: 1 day Experiment
Number of neutral beam sources: 5
AMAP gyrotrons |
| Diagnostic Requirements: | CER, Mach probe measurement of SOL flows if possible |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
252: Test of toroidal momentum pinch model |
| Name: | Wayne M. Solomon () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | T.S. Hahm, P.H. Diamond, K.H. Burrell |
| Description: | Some experimental evidence has been produced to show that simple diffusion of momentum is not sufficient to explain momentum transport. Theoretical models exists to describe sources of momentum pinch. This experiment aims to test the recent theory of Hahm (PoP 2007), which predicts that the momentum pinch velocity should scale as chi_phi/R, where chi_phi is the momentum diffusivity. |
| Experimental Approach/Plan: | Study a range of plasmas, from L-mode (where chi_phi tends to be particularly large, to H-mode and ITBs (where chi_phi tends to be reduced). Looking at high and low rotation cases will also be useful, since measurements have indicated that chi_phi ~ chi_i at large rotation, but this coupling appears to be lost at low rotation. |
| Background: | Preliminary momentum perturbation experiments on DIII-D and NSTX have shown the existence of a momentum pinch. The exact form of this pinch needs to be experimentally verified. |
| Resource Requirements: | Machine Time: 1 day Experiment
Number of neutral beam sources: 6 |
| Diagnostic Requirements: | CER |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
253: Main ion rotation studies |
| Name: | Wayne M. Solomon () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | K.H. Burrell |
| Description: | Typically, the plasma rotation is determined indirectly through measurements of an impurity species such as carbon. Although neoclassical calculations exist to compute the main ion rotation based on impurity measurements by imposing radial force balance, there have been several indications that this approach may not always be applicable. |
| Experimental Approach/Plan: | This experiment requires helium plasmas, so that main ion CER measurements can be made. Repeat shots will be taken, with the CER set to impurity carbon and main ion He for comparison. Both toroidal and poloidal rotation measurements will be useful as independent checks. Scans of the ion temperature and density gradients should be made (since these are the neoclassically relevant quantities for converting rotation between different species). It would also be worthwhile to do this at several basline rotation/torque values (so as to isolate potential systematic charge exchange cross-section effects). |
| Background: | Measurements of the impurity poloidal rotation has been found to differ from neoclassical predictions under some circumstances. Likewise, there have been cases of disagreement between the toroidal rotation observed between the main ion (He) and impurity different than the correction supplied by neoclassical theory. Establishing the conditions for which we may rely on neoclassical theory to tell us about the main ion rotation is clearly an important issue. |
| Resource Requirements: | Machine Time: 1 day Experiment
Number of neutral beam sources: 6 |
| Diagnostic Requirements: | CER |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
254: Rotation studies in the absence of Alfven Eigenmodes |
| Name: | Wayne M. Solomon () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | M.A. VanZeeland |
| Description: | Alfven eigenmode (AE) activity is believed to be capable of redistributing fast ion profiles through enhanced fast ion transport. This deviation from classical fast ion transport makes it more difficult to accurately compute the torque profile deposited by the neutral beams. Therefore, the goal is to study the rotation and associated momentum transport properties in plasmas with different levels of AE activity. |
| Experimental Approach/Plan: | Start with a plasma like #122116, with 1 net source where the AE activity is weak (can lower beam power if needed). Measure the rotation and momentum transport properties. Begin to introduce ECH power on axis, which should destablize AE's (probably RSAE's). Observe the change in rotation and deduce the altered NB torque profile through analysis. |
| Background: | Previous studies of the stabilization of RSAE's using ECH showed evidence of a redistribution of the fast ion by looking at the momentum channel. In particular, the total stored angular momentum was not changed (indicative of a redistibution as opposed to an outright loss), but the local rotation profile and associated inferred momentum diffusivity was changed. This could be attributed to a change in the torque source profile. |
| Resource Requirements: | Machine Time: 1/2 day Experiment
Number of neutral beam sources: 2
AMAP gyrotrons |
| Diagnostic Requirements: | CER, MSE |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
255: Role of turbulent momentum transport for intrinsic rotation |
| Name: | Stefan Muller ( ) |
Affiliation: | University of California, San Diego |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | J. Boedo, C. Holland, R. Moyer, D. Rudakov, G. R. Tynan, J. H. Yu |
| Description: | The goal of this experiment is to investigate the role of turbulent momentum transport for intrinsic rotation, with the emphasis on the role of the SOL (Is the SOL spinning up the core? Are there indications of a recoil action from SOL ejection events?). Measurements of the vr-vpar Reynolds stress (= radial transport of parallel momentum) and SOL flows are performed with the reciprocating Langmuir probes and CER. A scan of nu* over a wide range allows to influence the relative importance of neoclassical and anomalous terms in the parallel-momentum transport equation. Both terms are inferred independently from the measurements, allowing to search for possible "source-like" contributions ("residual stresses"). The question of boundary conditions for rotation at the separatrix is addressed by measuring the sign and gradient of stresses across the separatrix. A second goal consists of the investigation of the relation between minority-ion and bulk-ion rotation by comparing CER and Mach-probe measurements on the same flux surface. |
| Experimental Approach/Plan: | Use LSN divertor discharges with ion gradB drift toward the X-point to produce a low L-H power threshold (about 250 kW). Use the Reynolds-stress head of the midplane probe to measure turbulent momentum flux and parallel flows in low-power L-mode discharges. Select outer gap to optimize high spatial density chords of CER (separatrix = 2.30 m), which, for LSN discharges that "fit" into the lower divertor, allows probe access to the same flux surfaces for Mach probe measurements. Use lower divertor cryopump to perform pedestal collisionality scan by varying the pumping. Time permitting, increase NB power to cross L-H threshold into H-mode and repeat measurements in H-mode. |
| Background: | As ITER will be a low-torque input machine, it is of crucial importance whether the intrinsic plasma rotation will be sufficiently fast to stabilize Resistive Wall Modes. It arises the need to understand and predict the magnitude of intrinsic rotation in tokamaks. Experiments have shown that the intrinsic toroidal rotation typically exceeds neoclassical levels significantly, suggesting an important role of turbulent fluctuations, analogously to their well established importance for particle and heat transport. Emerging theories include variations of neoclassical theory, the existence of "source-like" contributions to momentum transport ("residual stresses"), and core rotation as a recoil action of SOL ejection events. A parameter scan of nu* is an excellent way to achieve contrast between these mechanisms. In order to quantitatively predict the magnitude of core rotation, theories need boundary conditions at the separatrix, which are presently under debate. CER and Mach probe measurements across the separatrix could contribute significantly to clarify this question. Finally, most available data on toroidal velocities is obtained by using CER on carbon impurities, and it is not clear whether the velocities of the bulk ion species can be reliably inferred. Simultaneous measurements with CER and Mach probes at the same flux surface could clarify this point. |
| Resource Requirements: | Optimized error field correction with i-coil; balanced NBI; lower divertor cryopump at liquid helium temperature |
| Diagnostic Requirements: | CER: ion temperature, rotation and Er; Thomson scattering: core, tangential and divertor; BES; PCI; Doppler reflectometry; FIR scattering (if possible); Correlation ECE (Te fluctuations) |
| Analysis Requirements: | -- |
| Other Requirements: | Due to the limited flexibility and high vulnerability of the reciprocating Langmuir probes, the success of the proposed experiments depends crucially on the possibility to fine tune the power input and the plasma shape. For these reasons, the session leadership for at least one day of operation is requested. |
| Title |
256: Turbulence characteristics in edge pedestal and its correlation with pedestal structure evolution from L-H transition to the first ELM |
| Name: | Guiding Wang () |
Affiliation: | University of California, Los Angeles |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | UCLA group |
| Description: | The purpose is to obtain turbulence characteristics (fluctuation level and radial correlation length) in edge pedestal and its correlation with pedestal structure evolution from L-H transition to the first ELM utilizing multi-channel correlation/Doppler reflectometer, addressing issues like how turbulent transport in the pedestal is related to the pedestal structure (height/width). |
| Experimental Approach/Plan: | Make clean L-H transition and a fairly long ELM-free H-mode (~ several hundred milliseconds) before a first ELM occurs. During the phase from L-H transition to the first ELM, try to avoid MHD activities, keep density pedestal height controlled at given magnetic field so that multi-channel correlation/Doppler reflectometer can access the whole pedestal region. Perform collisionality or power scan to change ELM types. |
| Background: | Underlying physics that sets the H-mode edge pedestal width, height, stability, transport, etc is yet to be explored. Multi-channel correlation/Doppler reflectometer is providing a new capability for measuring turbulence characteristics (fluctuation level and radial correlation length) in the pedestal, potentially addressing some important issues like how turbulent transport in the pedestal is related to the pedestal structure. Due to the limited accessible density range of the reflectometer system, dedicated experiments are required for a full coverage of the edge pedestal. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
257: Poloidal rotation as a function of toroidal rotation |
| Name: | Wayne M. Solomon () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | K.H. Burrell |
| Description: | Recent theoretical work by S.K. Wong suggests that signficant corrections over standard neoclassical theory are required at large toroidal rotation. Hence we would like to establish whether the discrepancy between the measured and neoclassical poloidal rotation (from NCLASS) scales with the toroidal rotation. |
| Experimental Approach/Plan: | A plasma where the anomalous poloidal rotation has previously been observed should be used as a reference (probably a QH-mode plasma). The poloidal rotation should be measured during a systematic scan of the toroidal rotation. Some data probably exists on this already, however, if QH-mode can be pushed further to balanced or co-direction as is planned, then this would provide a better data set. |
| Background: | Poloidal rotation discrepancies between measurement and NCLASS have been observed, but typically exists in rapidly rotating (toroidally) plasmas. |
| Resource Requirements: | Machine Time: 1 day Experiment, probably piggyback...
Number of neutral beam sources: |
| Diagnostic Requirements: | CER |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
258: Measurement of radial profile and radial propagation of density perturbations due to EHO in QH plasmas |
| Name: | Guiding Wang () |
Affiliation: | University of California, Los Angeles |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | UCLA group |
| Description: | To measure radial profile and radial propagation of density perturbations due to EHO in QH plasmas utilizing correlation reflectometer. |
| Experimental Approach/Plan: | Make QH plasmas at desired combination of magnetic field and pedestal density so that correlation reflectometer can access the whole pedestal region. |
| Background: | The upgraded UCLA correlation reflectometer is providing a new capability of detecting radial profile and radial propagation of density perturbations due to EHO in QH plasmas. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
259: Effect of aspect ratio on momentum confinement |
| Name: | Wayne M. Solomon () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | S.M. Kaye, C.C. Petty |
| Description: | The goal of the experiment is to obtain the first comparison of momentum confinement between NSTX and DIII-D, using perturbative techniques in order to separate out the roles of diffusion versus convection of momentum transport. |
| Experimental Approach/Plan: | A short perturbation to the rotation can be applied using n=3 non-resonant braking on both DIII-D and NSTX. DIII-D also has the option of using co/counter NBI blips for comparison. By performing the experiments on the two machines at fixed dimensionless parameters, the dependence of momentum confinement on aspect ratio can also be determined. Note that because beta between the machines is so inherently different, it cannot be held constant. Similar to the energy confinement similarity experiments in 2005 between NSTX and DIII-D, a more accessible dimensionless quantity is beta_p. Therefore, the dimensionless parameters to hold fixed would be the poloidal gyroradius, poloidal beta, nu* and the safety factor. |
| Background: | Similarity experiments on energy confinement were run between DIII-D and NSTX in 05. These shots should be investigated to see what refinements are necessary to make suitable candidates for these experiments (eg low n=1 MHD etc). |
| Resource Requirements: | Machine Time: 1 day Experiment
Number of neutral beam sources: 7 |
| Diagnostic Requirements: | CER and all profile diagnostics |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
260: Poloidal spin up of plasma using off-axis neutral beam injection |
| Name: | Wayne M. Solomon () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | K.H. Burrell |
| Description: | The idea is to displace the plasma vertically to significant z values (ideally up to +/-20 cm), such that the neutral beams can impart a poloidal torque to the plasma, and drive poloidal rotation. Such a displaced plasma might also be used to investigate off-axis current drive. |
| Experimental Approach/Plan: | The measurement must first be performed with the plasma centered on the midplane. This is necessary to utilize vertical chords viewing the magnetic axis. Such chords are important for determining the effective lifetime of the charge exchange state, which is needed for proper treatment of the atomic physics corrections to the measurements. The plasma can then be incrementally displaced vertically to introduce poloidal torque. Since we will lose the on-axis vertical chords, the previously determined lifetime will be used throughout the experiment. By shifting both upwards and downwards, we can evaluate whether the poloidal rotation flips sign as might be expected. Although poloidal rotation is in general heavily damped, driving poloidal rotation of the order of 10-20 km/s would be a significant source of Er even under typical conditions. Furthermore, if we run balanced type injection such that the toroidal rotation is small, then the Er can be dominated by the poloidal rotation contribution. A key question will be whether the resulting ExB shearing rate is sufficient in these conditions to achieve turbulence suppression. |
| Background: | Anomalously large poloidal rotation of order 5-10 km/s has been observed in QH-mode and ELM-suppressed H-mode plasmas. Adding direct neutral beam drive may allow us to access larger poloidal rotation regimes. |
| Resource Requirements: | Machine Time: 1 day Experiment
Number of neutral beam sources: 5 |
| Diagnostic Requirements: | CER |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
261: Poloidal rotation comparison between forward & reverse Bt |
| Name: | Wayne M. Solomon () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | K.H. Burrell, M. Zarnstorff, W. Houlberg |
| Description: | The purpose of this experiment is to compare the inferred poloidal rotation profiles with forward and reverse Bt in otherwise matched discharges. From a symmetry point of view, the radial electric field may be expected to be unchanged. As such, the poloidal rotation must flip signs (to keep the Vpol*Btor contribution to Er the same). |
| Experimental Approach/Plan: | A target discharge (probably standard ELMing H-mode) will be established in the usual Bt direction. For these experiments, the toroidal rotation should be kept low by use of balanced beam injection, to minimize the toroidal rotation contribution to Er (as well as reducing toroidal pickup on the vertical chords). MSE will be used as an independent check on the Er profile, and BES and reflectometer measurements will allow indirect evaluation of Er by looking at the poloidal propagation velocity of the turbulence. Power scans at fixed torque and density scans will be performed. The experiments will then be repeated in reverse Bt conditions. The MSE, reflectometer and BES will provide checks that the Er is indeed unchanged in the reverse Bt conditions. |
| Background: | Inference of poloidal rotation from CER measurements is complicated by various atomic physics effects. While tests have been made to check the validity of the analysis techniques, further tests are highly desirable. |
| Resource Requirements: | Machine Time: 2 half-day experiments
Number of neutral beam sources: 6 |
| Diagnostic Requirements: | CER, MSE, reflectometer, BES |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
262: Validation of GYRO |
| Name: | Ron Prater () |
Affiliation: | General Atomics |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | Chris Holland, Anne White, George McKee |
| Description: | Recent work by Chris Holland and Anne White have shown that GYRO can predict accurately the heat transport at the mid-radius of an L-mode discharge. It would be a good step in the validation of GYRO to see whether the transport trends can be predicted as well. |
| Experimental Approach/Plan: | Starting from the well-studied discharge already studied, vary parameters that are known to affect the confinement time. For example, vary the plasma current up and down by 50% and change the heating power by 50% (but staying in L-mode). See if the experimentally observed trends in diffusivity and fluctuation parameters can be understood in subsequent GYRO calculations. |
| Background: | Build on success in modeling a simple case. Take small steps from an understood case before moving to discharges which are much more complicated. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | CECE, BES |
| Analysis Requirements: | Lots of GYRO calculations. |
| Other Requirements: | -- |
| Title |
263: Direct Measurement of E_rad Corrugation at Rational Surfaces |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | M. E. Austin |
| Description: | Use the combination of co and counter MSE views to directly measure the corrugation in the radial electric field at rational q surfaces that is responsible for transport barriers. The target plasmas are balanced-NBI L-modes with early heating so that q>2. The analysis will focus on MSE channels that view the radius where a rational surface, such as the q=2 surface, first enters the plasma. In the absence of E_rad effects, the co and counter viewing MSE channels will measure the same magnetic field pitch angle. Thus, a separation between the co/counter MSE signals at the time a rational q surface enters the plasma is a direct measurement of the E_rad corrugation effect. |
| Experimental Approach/Plan: | (1) Establish L-mode plasma with early beam heating to slow the evolution of the current profile. (2) Use 30LT and 210RT beams without modulation to collect continuous MSE and CER data. (3) May need to move the plasma location around to make sure the MSE channels are looking exactly at the location where the rational q surface (especially q=2) first enters the plasma. |
| Background: | Previous experiments by Max Austin found corregations in the electron temperature profile when a rational q surface entered the L-mode plasma. These corrugations were observed for both co-NBI and balanced-NBI (although only the co-NBI cases resulted in long lasting transport barriers). The GYRO turbulence simulation code predicted the existence of these corrugations by means of a equilibrium ExB shear flow driven by the zonal flows. This experimental proposal will look for direct evidence of this ExB shear flow by means of the E_rad sensitivity of the MSE diagnostic. |
| Resource Requirements: | NBI: 30LT and 210RT essential. |
| Diagnostic Requirements: | MSE is critical. |
| Analysis Requirements: | Need GYRO simulations. |
| Other Requirements: | -- |
| Title |
264: Simultaneous measurement of density and temperature fluctuation level and radial correlation length in both low and high field side of L-mode plasmas |
| Name: | Guiding Wang () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | UCLA group |
| Description: | The purpose is to make simultaneous measurement of density and temperature fluctuation level and radial correlation length in both low and high field side of an L-mode plasma, and compare with TGLF, GYRO predictions. |
| Experimental Approach/Plan: | Develop an L-mode plasma with appropriate Bt and density so that correlation reflectometer and CECE system can take measurements in both low and high field side. Take data together with BES in the low field side in repeat shots. Fluctuation data will also be collected with Doppler reflectometer, FIR scattering, PCI, and Langmuir probes, etc. |
| Background: | In the last run period for the first time simultaneous density and temperature fluctuation measurement using CECE and BES in the low field side was very successful. Expand this effort to high field side for the first time, which is achievable with CECE and correlation reflectometer will provide further test of predictions of modeling and simulations. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
265: Poloidal rotation comparison between forward & reverse Ip |
| Name: | Wayne M. Solomon () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | K.H. Burrell, M. Zarnstorff, W. Houlberg |
| Description: | The purpose of this experiment is to compare the inferred poloidal rotation profiles in forward and reverse Ip conditions. One of the suggestions for the observed anomalous poloidal rotation is that it is caused by friction between the thermal ions and the fast beam driven ions, which follow the field line. |
| Experimental Approach/Plan: | A target discharge (probably standard ELMing H-mode) will be established in the usual Ip direction. For these experiments, balanced beams should be used, so that when Ip is reversed it does not alter the plasma rotation effects. A density scan should be performed since this is a key parameter for neoclassical poloidal rotation. The experiments will then be repeated in reverse Bt conditions, with matched shape and plasma profles. |
| Background: | A large discrepancy is observed between the experimentally observed poloidal rotation and the neoclassical prediction from NCLASS. This experiment allows testing one particular source for the anomaly. Some experimental data already exists that hints that this is not the dominant mechanism for the anomalous poloidal rotation, but a systematic comparison of co vs counter Ip is needed to definitively claim this. |
| Resource Requirements: | Machine Time: 2 half-day experiments
Number of neutral beam sources: 4 |
| Diagnostic Requirements: | CER, MSE |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
266: "burning plasma" control |
| Name: | Phil Snyder ( ) |
Affiliation: | General Atomics |
| Research Area: | General PCO |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Plasma control in DIII-D commonly operates in a beta feedback mode, where beam power is reduced as beta increases to avoid tearing mode and disruption beta limits. In a burning plasma, the opposite type of feedback will exist, with alpha heating power increasing strongly as beta increases. Control of such plasmas, particularly at Q>5, may be a substantial challenge, and at very high Q, some sort of "soft beta limit" may be essential to avoid a disruption. |
| Experimental Approach/Plan: | Use first one pair of co and counter beams, and then two pairs of co/counter beams to simulate alpha heating (attempt to balance torque of the beam pairs). Program control system to have 'alpha power' proportional to beta^2 (or more precise fusion power algorithm). Attempt control via remaining beam power, ECH etc, first at Q~5, and then at Q~10. Assess importance of operating in a regime with soft beta limits, as well as ability to tweak confinement via profile control in order to stay below beta limits. Perhaps extend by attempting control using an approximation of ITER's available control tools. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
267: Eigenmode model-based n=1 RWM feedback control |
| Name: | Yongkyoon In () |
Affiliation: | FARTECH, Inc. |
| Research Area: | Model based Control |
Presentation time: |
Requested |
Co-Author(s): | Jin Soo Kim, Dave Humphreys, Mike Walker, Eugenio Schuster, RWM physics working group |
| Description: | The goals of this proposal are to
(1) demonstrate the superior performance of the dynamic Kalman filter based on wall surface current eigenmodes, compared to the counterpart based on picture-frame wall model
(2) evaluate the performance of the eigenmode model-based PD controllers, compared with the off-line predictions
(3) assess the robustness of model-based controllers |
| Experimental Approach/Plan: | Establish high beta, high torque RWM plasmas, where ELM-noises are dominant. It is expected that ELM-induced RWMs would readily occur. When RWM cannot be obtained in high torque plasmas, lower the plasma rotation by injecting counter beams with no magnetic braking.
Once RWM is obtained in high torque plasmas, the dominant non-RWM noise will be likely to be ELMs. Thus, the performance of the eigenmode model-based Kalman filter will be tested in comparison with picture frame model-based counterpart with respect to ELM-noise discrimination quality (related to Goal 1). Simultaneously, the closed-loop performance will be evaluated with respect to RWM suppression (related to Goal 2), which may necessitate gain scans. As the RWM experiments have been plagued by a reproducibility issue, careful comparison needs to be made even when RWM is believed to be actively stabilized. Thus, a successful RWM-free shot will be followed by an open-loop testing, which will also provide the measured open-loop RWM growth rate. Since RWM open-loop growth rate is the key parameter to relate experimental observation to eigenmode model-based modeling, it will be a good indicator how appropriately the model has been established for a given growth rate.
If RWM is obtained in low torque plasmas, the non-RWM noise might not be ELMs, but fishbones or tearing modes. This will require the Kalman gain changes, so a set of the Kalman filters (e.g. based on a variety of process noise covariance magnitudes) will be prepared. The rest of the procedures will be exactly the same as mentioned for high torque case.
To assess the robustness of the model-based controllers (related to Goal 3), we will do beta scans. As for high torque plasmas, the beta scan will be equivalent to growth rate scan. Thus, the beta scan can directly address the robustness of the model-based controllers, as well as allow us to assess the need of gain scheduling. Meanwhile, considering that the low torque plasmas show rather weak dependency on the RWM growth rates in a wide range of beta scans beyond ideal no-wall limit, the model-based controller performance in high C_beta is not expected to be different from that in low C_beta.
As a result, we will be able to evaluate the robustness of the eigenmode model-based controllers.
As a note, although the eigenmode-based DIII-D/RWM model is developed without taking into account the plasma rotation so far, the performance of eigenmode-based Kalman filter appears to fit in high torque plasmas, where an ideal MHD assumption is deemed appropriate. |
| Background: | In recent high beta, high torque RWM experiments, a picture-frame model (modeled open-loop RWM growth rate, gamma =120 rad/s) was experimentally confirmed to be reasonable to describe the DIII-D/RWM system, in that the dynamic Kalman filter (based on picture frame wall model) was effective in discriminating the ELM-noise from RWM [Y. In et al., Phys. Plasmas 13, 062502 (2006)].
As a more advanced model, FAR-TECH's eigenmode-based DIII-D/RWM model was predicted to be superior to picture frame wall model in terms of its effectiveness and computation times. For example, the computation times of 11 eigenmode-based Kalman filter was found to be ~ 12 us. However, considering that the performance of 3 eigenmode-based Kalman filter (i.e. requiring 6 wall states) was almost the same or slightly better than that of the successful 72 picture frame wall model mentioned above, further reduction with fewer wall states is believed to be feasible. As a result, we may shorten the computation times below DIII-D/PCS cycle time (9 us as of 2007) without compromising the capability to effectively discriminate non-RWM noise from RWM.
In 2007, there was a systematic checkup for vacuum shots, whose analysis provided us with the measured L/R times, as well as the time delay between PCS commands and control coils. This helped us to properly characterize the additional connecting lines between power supply and control coils. The corresponding measurements were incorporated into DIII-D/RWM model, which led to a successful vacuum shot benchmark. Based on the latest DIII-D/RWM model, several types of model-based controllers including linear-quadratic-Gaussian (LQG) controller, are being designed in the same manner studied for preliminary model-based controllers [D. Humphreys et al., Nucl Fusion 47, 943 (2007); J. Blair et al., APS-DPP (2006)].
While all the ITER controllers are expected to be model-based, no validated RWM model exists applicable to controller design. The eigenmode-based DIII-D/RWM model is one of the candidates, which needs to be validated. |
| Resource Requirements: | 5 co-beams and 2-counter beams, 2 gyrotrons for ECCD |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | Vacuum test results prior the run-campaign and simulation results need to be confirmed first |
| Title |
268: Study of turbulence effects on anomalous particle and momentum pinches |
| Name: | Lei Zeng ( ) |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | E. J. Doyle, T. L. Rhodes, A.E. White, G. Wang, L. Schmitz, W.A. Peebles |
| Description: | In this experiment, we study the effects of core turbulence on anomalous particle and momentum pinches and transports, and the dependence of the pinches on collisionality. By comparing experimental data to theoretical models (GS2, GYRO and others), the mechanisms of anomalous pinch can be further studied. |
| Experimental Approach/Plan: | In RF heating plasma (without NBI core particle source), when scaning collisionality from low to high, measure Te and ne fluctuations in the core. Use modulated momentum and particle transport technique, to separately determine diffusion and pinch calculations (co/counter NBI blips can be used for momentum study). Also, by using impurity pellet injection or modulated He NBI, analyze particle transport. The measurements of ne, Te, q and rotation profile variations in the core (rho< 0.6) are needed.
Experimental data is used to compare with the simulations from GS2 and GYRO. |
| Background: | The understanding of the mechanisms of core particle and momentum transports is important for ITER and other fusion plasmas. Recently, the anomalous inward particle pinch has been observed in several tokamaks. The inward pinch velocity is much larger than the expected value via neoclassical theory. In Tore Supra, the ICRH heating during non-inductive LHCD experiment shows the inward pinch is driven by turbulent thermo-diffusion for rho<0.3, while the inward pinch is driven by turbulence equipartition for 0.3<rho<0.6. In AUG and JET experiments, it is observed that the density peaking increases with decreasing collisionality, consistent with the GS2 simulation. Currently, a novel momentum pinch mechanism is proposed by T.S. Hahm et al.
In DII-D, with the updated diagnostic measurements for turbulence and profiles, these mechanisms can be further tested and investigated. We will study the dependence of anomalous pinch on collisionality, the effects of ne fluctuations from low to high k, and Te fluctuation. Comparison between experimental results and simulation results from GS2, GYRO and others will also be proceeded. |
| Resource Requirements: | Fast wave heating, ECH |
| Diagnostic Requirements: | FIR, CECE, reflectometers , BES |
| Analysis Requirements: | GS2, GYRO |
| Other Requirements: | -- |
| Title |
269: Enhanced erosion from deuterium saturated materials during ELMs |
| Name: | Karl Umstadter ( ) |
Affiliation: | University of California, San Diego |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Not requested |
Co-Author(s): | Clement Wong, George Tynan, Russ Doerner |
| Description: | All prior heat pulse testing of PFCs have been completed in vacuum environments without the presence of a background plasma. ELMs will not be this kind of isolated event and one should know the effect of a plasma background during these transients. The retention of gas in PFCs may lead to enhanced erosion or explosions of material that will behave differently if ionized near the surface. Current models may underestimate the damage caused by ELMs due to this phenomena. |
| Experimental Approach/Plan: | DIMES samples of graphite and tungsten will be saturated with deuterium in the PISCES A device. Saturated and unsaturated samples will be loaded into the DIMES system. During H2 experiemnts, the strike point will be moved onto the DIMES system simulating an ELM strike. |
| Background: | Heat pulse experiments have begun in the PISCES A device utilizing laser heating in a divertor-like plasma background. Initial results indicate that the erosion of PFCs is enhanced as compared to heat pulse or plasma only tests. This enhanced erosion may be caused by self-sputtering of material that is ejected during the transient, ionized by the plasma near the surface and subsequently driven back to the surface. Gas retention in PFCs and ELM energy are currently indicated as the cause. |
| Resource Requirements: | A few shots during H2 experiments where the strikepoint can be moved onto the DIMES system. |
| Diagnostic Requirements: | High speed video of the DIMES system during the event. MDS of ablated material - C and W. |
| Analysis Requirements: | SEM imaging, TDS and mass loss analysis will be completed at UCSD PISCES lab. |
| Other Requirements: | -- |
| Title |
270: Simultaneous correction of B-coil bus and F-coil offset errors |
| Name: | Michael J. Schaffer () |
Affiliation: | General Atomics |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | LaHaye, Strait, Scoville (expected) |
| Description: | Develop an improved empirical correction for left-handed (standard) plasmas, by independently and simultaneously correcting the two main known sources of error, (a) the F-coil offsets from the B-coil, and (b) the B-coil current feed at 30 degrees. The I-coil and the C-coil should both be tried for the F-coil offset correction role. It is expected that one or both of these corrections will be better than the presently used empirical corrections. The result will also be used to test J-K Park's new theory of error correction. |
| Experimental Approach/Plan: | Use the previously developed Ohmic, low-density, locked-mode error field test plasma and technique. The starting point for the empirical search for best correction will start from past experiments and from calculations of error fields informed by J-K Park's new theory. If time permits, empirical corrections will be developed using the I-coil for both functions |
| Background: | An exploratory experiment in 2007 showed that the I-coil nearest to the 30 deg feed (the IL30 coil) applied alone is effective at reducing the locked mode error symptom. On the other hand, The C-coil and especially the I-coil are thought to be good at correcting the F-coil offset error. Therefore, it is hypothesized that independently correcting both error fields simultaneously will be more effective than previously used corrections.
New theory by J-K Park et al, PRL (accepted 2007) explains previous DIII-D empirical error correction semiquantitatively, via the coupling between the external error and correction fields with the least stable ideal MHD plasma mode, whose non axisymmetric currents strongly dominate inside the plasma. This theory will be used to help choose the starting point for the empirical best correction search. |
| Resource Requirements: | I-coil and C-coil systems essential.
Ohmic plasmas --- no NBI. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
271: ECH Modification and Control of Pedestal Profiles |
| Name: | Phil Snyder () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Because turbulent transport is very sensitive both to details of the temperature profiles, as well as Ti/Te, eta_i and eta_e, it is possible in certain regimes to strongly modify profiles, including the density profile by using local ECH heating. In ELMing H-mode discharges, confinement in the edge barrier region is generally so good that profiles continuously rise until an ELM is triggered. At low density, it appears that the Te profile can approximately saturate, but density remains uncontrolled and rises until ELMs are triggered. Most ELM control techniques (eg RMP and QH) appear to work by providing additional particle transport in order to control the density profile and avoid ELMs. Here we would attempt to achieve a similar effect by modifying the turbulent transport in the edge region with ECH. Preliminary studies of both ECH heating efficiency in various edge regimes, as well as TGLF studies of various mode growth rates and expected fluxes are needed to do a detailed experimental plan. |
| Experimental Approach/Plan: | Locate a regime in which turbulent transport, particularly particle transport, in the pedestal region is expected to be strongly sensitive to the Te profile and/or Ti/Te, and in which ECH can be efficiently coupled to the edge. Use ECH at varying power and radius to impact local transport. Goal is to control the density profile. Use discharges with a long initial ELM free period and a long ELM period and study detailed profile evolution and turbulent fluctuations. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
272: Hydrogen Isotope Scaling of Turbulence and Transport |
| Name: | George R. McKee () |
Affiliation: | University of Wisconsin, Madison |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | K. Burrell, C. Holland, C. Petty, M. Shafer |
| Description: | Measure the dependence of transport and turbulence characteristics on working ion mass using hydrogen and deuterium. |
| Experimental Approach/Plan: | Establish baseline discharges similar to well-characterized discharges in a dimensionless scaling experiment. Perform steady state L-mode edge inner wall limited discharges very similar to previous rho* scan discharges, but in Hydrogen. The aim to run discharges in an operationally similar manner to a baseline in deuterium (101391), similar beam power and torque, field, current and density, and document this discharge. Assuming confinement changes with isotope, nondimensional parameters (beta, collisionality) will not be matched and rho-star is already not matched by the change in isotope. Ideally, we would then then try and match the dimensionless parameters, with the obvious exception of ion mass, A, to the past discharges by adjusting toroidal field, current, heating power, torque, gas puffing, etc., to examine how transport and turbulence scales while varying only A. This would require going to lower field in Hydrogen to match rho-star from the baseline deuterium discharge (at 2 Tesla), and adjusting heating and density accordingly.
Measure turbulence throughout with BES, FIR, CECE, Correlation Reflectometer, PCI and Langmuir probes. Temperature profiles are measured for transport studies (may require beam swapping). Also, perform particle transport studies with Helium gas puffs. |
| Background: | Previous experiments have demonstrated increased confinement with higher atomic-mass isotopes. This issue has obvious implications for future experiments. DIII-D may perform experiments in hydrogen in 2008 allowing for such experiments to compare turbulence and transport parameters in well documented discharges, and to compare the results with comparable deuterium discharges. Results, both in terms of transport and turbulence, would be compared with transport simulations. By varying ion mass and keeping charge constant, thus changing gyroradius, these results can complement those obtained with a proposed rho* scan (C. Holland). |
| Resource Requirements: | Hydrogen fueling with D-beams. This experiment would be more feasible if there are significant hydrogen dischages planned in the ITER physics area. |
| Diagnostic Requirements: | Profile and fluctuation diagnostics and any modifications required for use in hydrogen. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
273: Simultaneous correction of B-coil bus and F-coil offset errors |
| Name: | Michael J. Schaffer () |
Affiliation: | General Atomics |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | LaHaye, Strait, Scoville (expected) |
| Description: | Develop an improved empirical correction for left-handed (standard) plasmas, by independently and simultaneously correcting the two main known sources of error, (a) the n=1 F-coil offsets from the B-coil, and (b) the local B-coil current feed at 30 degrees. The I-coil and the C-coil should both be tried for the F-coil offset correction role. It is expected that one or both of these corrections will be better than the presently used empirical corrections. The result will also be used to test J-K Park's new theory of error correction. |
| Experimental Approach/Plan: | Use the previously developed Ohmic, low-density, locked-mode error field test plasma and technique. The starting point for the empirical search for best correction will start from past experiments and from calculations of error fields informed by J-K Park's new theory. If time permits, empirical corrections will be developed using the I-coil for both functions |
| Background: | An exploratory experiment in 2007 showed that the I-coil nearest to the 30 deg feed (the IL30 coil) applied alone is effective at reducing the locked mode error symptom. On the other hand, The C-coil and especially the I-coil are thought to be good at correcting the F-coil offset error. Therefore, it is hypothesized that independently correcting both error fields simultaneously will be more effective than previously used corrections.
New theory by J-K Park et al, PRL (accepted 2007) explains previous DIII-D empirical error correction semiquantitatively, via the coupling between the external error and correction fields with the least stable ideal MHD plasma mode, whose non axisymmetric currents strongly dominate inside the plasma. This theory will be used to help choose the starting point for the empirical best correction search. |
| Resource Requirements: | I-coil and C-coil systems essential.
Ohmic plasmas --- no NBI. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
274: Edge current measurement |
| Name: | Phil Snyder () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The edge current profile is very important both for conventional models of edge stability (peeling-ballooning) and for micro-instabilities in the edge (strong dependence on local magnetic shear). Measurements of the edge current using the lithium beam have been very useful in the past, though long time windows have been needed for this analysis. The (possible?) availability of a dual MSE system creates an opportunity to measure this highly important quantity with a different technique. |
| Experimental Approach/Plan: | Create diagnostic optimized plasmas, with low density and very high expected bootstrap current, as well as a long ELM-free period and long ELM periods. Look also at high collisionality plasmas to investigate expected reduction of Jbs. Allow time for whatever diagnostic testing and calibration is needed. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | This expt ought to be done early in the year to develop edge current measurements, so that they can be usefully employed in later expts. Measuring the edge current is very useful in essentially all pedestal and ELM expts. |
| Title |
275: Optimization w.r.t. plasma rotation of the error field correction from I-coil |
| Name: | Andrea M. Garofalo () |
Affiliation: | Columbia University |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Use a rotating n=1 field applied with the I-coil to produce fluctuations in the rotation measurements. Exploit DIII-D's capability to measure rotation at different toroidal locations to separate n=1 from n=0 components of the fluctuations and learn what is the optimal correction of the n=1 error field w.r.t. plasma rotation. The error correction is perfect when the plasma becomes insensitive to the phase of an additional, rotating n=1 field. |
| Experimental Approach/Plan: | Previous experiment's phase scan: Apply an n=1 rotating field (I1), in addition to the feedback-driven error field correction (I0). Use analysis of the CER fluctuation to determine the times when the phase of the applied n=1 I-coil field is the optimal correction phase. At these times the amplitude and phase of I1 are: A1x, phi1opt. Future experiment's amplitude scan: Vary A1 slowly (over several seconds) from A1x to zero and from zero to maximum allowed. This gives a total apllied field (It) with varying amplitude and phase. In addition to this varying It, again apply an n=1 rotating field, this time at higher frequency, e.g. 20 Hz A time dependent Fourier analysis of the Mirnov loops will give the amplitudes of the n=0 and n=1 magnetic fluctuations. The time of minimum n=0/n=1 amplitude should give the optimal error-field correction. An I-coil helicity scan may then improve the match to the intrinsic error field structure. The error correction is perfect when the plasma becomes insensitive to the phase of an additional, rotating n=1 field. Look for improved angular momentum confinement (at beta above the no-wall limit). |
| Background: | Complete 2003 experiment (scan of the toroidal phase) carrying out scan of the amplitude and of the helicity of the n=1 error correction field applyied by the I-coil. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
276: Pedestal width in Hydrogen discharges |
| Name: | Phil Snyder () |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | A number of theoretical models of the pedestal width produce a width related to the ion gyroradius or poloidal gyroradius. Because of the tight coupling between pedestal width and height (pedestal height is expected to scale roughly as width^3/4 if the pedestal is peeling-ballooning stability constrained), and because of the difficulty of separating gyroradius dependence from beta or beta_p dependencies in deuterium plasmas, it is useful to look at the mass ratio dependence. |
| Experimental Approach/Plan: | Optimize plasma for pedestal diagnostics in a hydrogen plasma. Measure the pedestal width in several different regimes, reproducing a series of common discharge shapes. Focus on strongly shaped low density discharges where pedestal width is expected to be somewhat wider and more precisely measurable. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
277: Test of Neoclassical Toroidal Viscosity theory using modulated I-coil currents |
| Name: | Keith Burrell ( ) |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | A. Garofalo, G. Jackson, M. Schaffer, |
| Description: | Use modulated I-coil currents to investigate the theory of braking of plasma toroidal rotation by non-resonant error fields |
| Experimental Approach/Plan: | Create non-resonant, n=3 error fields in L-mode and/or QH-mode plasmas using the I-coil. Modulate the I-coil currents to modulate the non-resonant drag on the plasma. Investigate the effects as a function of modulation frequency, background plasma rotation, collisionality and I-coil parity. |
| Background: | The theory of braking of plasma rotation by non-resonant error fields predicts that the magnitude of the drag on the plasma increases with the square of the error field amplitude and that the drag vanishes when the plasma rotates toroidally at a non-zero, offset velocity related to the ion temperature gradient. By creating non-resonant, n=3 error fields using the I-coil and then modulating these at frequencies up to 100 Hz, we can impose a periodic variation in the drag term. By analyzing the amplitude and phase of the resulting changes in the toroidal rotation, we can determine the size of the drag term. In addition, by doing this experiment at various different toroidal rotation speeds, we can investigate the offset velocity. The results can then be compared with theoretical predictions to test the theory. |
| Resource Requirements: | I-coil system connected to do both error field correction and n=3 braking, if possible. If not, use C-coil for error correction and I-coil for n=3 braking. Reversed plasma current is needed for the QH-mode portion of the experiment. 7 NBI sources needed for rotation scan. |
| Diagnostic Requirements: | All profile diagnostics. CER at high enough speed to have 10 samples per I-coil modulation period. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
278: Density pump-out studies in USN divertored, RMP discharges |
| Name: | Zeke Unterberg ( ) |
Affiliation: | ORISE/ORNL |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | T. Petrie |
| Description: | The goal of these discharges would be to assess the effect of divertor geometry on edge particle transport during the RMP and to expand the database of RMP effects to different divertor geometries. In particular, the upper divertor geometry is more ITER-like with the dome between inner and outer strike point plenums as opposed to the lower divertor with only an outer baffle. The different geometry of the upper divertor would lead to different neutral particle and recycling characteristics during RMP discharges. These would most likely be caused by the proximity of the OSP (ISP) to the throat of the outer (inner) plenum. The OSP proximity to the plenum throat is known to have strongly coupled influence on density control and ELM suppression during LSN, RMP discharges with grad_B toward the divertor. USN discharges have the benefit of: a) an inner plenum and cyro-pump, and b) fast-neutral-particle (ASDEX) ionization gauge heads in ISP plenum, OSP plenum, and private flux region of the divertor. This could lead to more detail measurements of temporal and spatial neutral particle evolution during the RMP. Combined with the D_alpha and the upper divertor Langmuir probe array data, this could give a relatively full assessment of particle transport in the divertor during an RMP discharge. It is thought with potentially greater access to plenum pumping there would be a greater effect on particle pumpout and/or transport during the RMP. Another potentially interesting question is how pumping on in the ISP region effects ELM suppression in the RMP? |
| Experimental Approach/Plan: | A fiducial USN RMP discharge would be the initial focus. This experiment could either be a piggyback with Petrie�??s ROF ID169 proposal where grad-B would be out of the divertor or a flip of the B-tor to focus on discharges with grad-B toward the x-point, which have shown ELM suppression in LSN RMP shots. From there, scans of I_coil magnitude at different q95s to determine the optimal resonances for density pump out, and sweeps of the OSP and/or ISP for optimal particle exhaust and/or to assess changes in pumping would be desirable. For instance, the latter would provide information on the density pump out as a function of perturbation strength even without ELM suppression. Finally, variations in plasma shape with the aim being to access lower-triangularity, ITER-like shapes (similar to shot 126006 in LSN discharges) would further help in characterizing the effects of this divertor type on future machines. |
| Background: | -- |
| Resource Requirements: | Standard for H-mode and RMP experiments. Would need to reverse the direction of B-tor for experiments with grad-B toward the divertor. |
| Diagnostic Requirements: | upper divertor Langmuir probe array; upper filterscope array, upper divertor ASDEX gauges, plus standard diagnostics for RMP experiments. |
| Analysis Requirements: | possibly 2D and/or 3D edge fluid code modeling |
| Other Requirements: | -- |
| Title |
279: Extrapolation of H-modes and Hybrids to ITER |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Create discharges on DIII-D with exactly the ITER shape and dimensionless parameters identical to ITER except for rho*. Perform a rho* scan to access the extrapolation to ITER. This should be done for a hybrid plasma with beta_N>2.5, and for a "Scenario 2" plasma with beta_N=1.8.
The ITER plasma shape is not a cyropumping shape for DIII-D. In this experiment, we will use RMP from the I-coil to control the H-mode density. The I-coil has been shown to very effectively reduce the H-mode density pedestal on DIII-D. Balanced NBI should be used to give a low Mach number. |
| Experimental Approach/Plan: | Study small rho* plasmas first. (1) Reproduce exactly the ITER plasma shape, close to 125068 at 3700 ms but with lower triangularity. (2) For beta_N=1.8, q95=3 "ITER Scenario 2" case, need Ip=1.6 MA and Bt=1.9 T. Adjust gas puffing to obtain same collisionality as ITER. If ELM frequency is too low for effective density control, use the I-coil to reduce the density pedestal (alternatively lower the triangularity some more). (3) For large rho* comparison shot, decrease Ip to 0.8 MA and Bt to 0.95 T. Still have beta_N=1.8. Use PCS control of I-coil current to reduce density by factor-of-2.5 from the small rho* plasma. (4) Repeat rho* scan for hybrid plasma with beta_N>2.5. Same toroidal field, but plasma current is reduced to Ip=1.2-->0.6 MA to obtain q95=4. |
| Background: | A previous attempt at a beta_N=1.8 rho* scan in an ITER-like shape on DIII-D utilized a higher-than-ITER triangularity to optimize the divertor cyropumping. For this low beta_N value, the high triangularity resulted in a very low ELM frequency and very poor density control. This experiment will use the actual (lower) ITER value of triangularity, which will result in a higher ELM frequency, and obtain density control by means of RMP from the I-coil. |
| Resource Requirements: | NBI: All 7 sources required. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
280: DiMES Investigation of Helium Plasma Induced Nanostructured Morphology on Tungsten |
| Name: | Matthew Baldwin ( ) |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary |
Presentation time: |
Requested |
Co-Author(s): | R Doerner, C Wong, P West, D Rudakov |
| Description: | The diverted reactor exhaust in confinement machines like ITER and DEMO will be intense-mixed plasmas of fusion (D, T, He) species characterized by tremendous heat and particle fluxes. In both devices, the divertor walls are to be exposed to such plasma and must operate at high temperature for long durations. Tungsten, with its high-melting point and low-sputtering yield is currently viewed as the leading choice for divertor-wall material in this next generation class of fusion devices, and is supported by an enormous amount of work that has been done to examine its performance in hydrogen isotope plasmas. However, studies of the more realistic scenario, where ionized He is present, are considerably less. Current helium plasma on tungsten experiments on the linear machines NAGDIS II and PISCES-B have lead to the observation of plasma induced nanoscopic tendril like morphology. Such morphology may influence the thermal properties of the surface, have a significant impact on fuel retention and also contribute to in-vessel dust accumulation.
A experiment involving DiMES, outfitted with a high temperature tungsten sample that is exposed to successive He plasma shots will help to elucidate the magnitude of this effect in a tokamac environment. To date, there has been no experiment that capitalizes on the opportunity to explore the formation of these structures in an actual divertor plasma. |
| Experimental Approach/Plan: | Exposure of a polished DiMES W target at 900 degrees C to as many detached He or D2/He plasma discharges as possible. |
| Background: | The conversion of a hot W surface into tendril like nano-structures has very recently been observed in the divertor plasma simulators NAGDIS-II and PISCES-B. Experiments in LHD also show precursor bubble formation/pitting on hot W surfaces after as little as 1 s of exposure to He plasma. NAGDIS experiments have revealed that He ion bombardment at energies greater than 10 eV leads to the observation of this effect. PISCES investigations show that the formation rate of the nano-structures is a diffusion limited process. Both sets of experiments provide the necessary background to be able to predict the conditions of formation in a tokamac experiment. |
| Resource Requirements: | Some modification to DiMES system to facilitate higher temperature (900 degrees C) operation. |
| Diagnostic Requirements: | DiMES (RUDAKOV, WEST, WONG) |
| Analysis Requirements: | Ex-situ surface analysis provided at UCSD PISCES LAB (BALDWIN, DOERNER) |
| Other Requirements: | -- |
| Title |
281: Production of a Mass gradient in DIII-D Discharges |
| Name: | Jim Leuer ( ) |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | J. Leuer, A. Hyatt, M. Schaffer, T. Jernigan |
| Description: | In DIII-D most discharges use D as the primary gas; occasionally H or He is used. However, considerable differences in plasma transport and MHD (ie ELM'S) are observed using different gas species. We propose establishing a mass species gradient in DIII-D using H gas puffing or recycling at the edge and D beam and/or pellet injection in the core to establish the largest gradient permissible in the device. If we can achieve a large gradient in mass we would expect standard core D plasmas with favorable edge H parameters. This has direct bearing on ITER with the ability to vary the reactivity, MHD characteristics near the edge. This could add another tool for the control internal plasma profiles. |
| Experimental Approach/Plan: | This experiment will try to establish a mass gradient over the plasma radius. We will use beam/pellet and gas_puff/recycling to control the core and edge, fuel sources, respectively. Nominally we will use D for the core and H for the edge. We want to balance the core/edge fueling to maximize the the gradient while maintaining the plasma below global density limits. Initial testing will be with L-mode plasma since it is expected we can achieve the best control over the sources and thus establish the largest gradients. We would run 4 discharges types, identical except for fueling sources: 1) All D 2) All H, 3) D-core, H-edge, 4) H-core, D-edge. Diagnostics techniques to measure the gradients are expected to be difficult. However, using four different types above should enable us to compare global parameters and infer the impact on transport and MHD the mass variation provides. We might even try (H and He) to maximize the mass ratio effect. If successful we would extend the studies to H-mode plasmas and infer any benefits to ITER type discharges. |
| Background: | Most all tokamaks explore uniform mass (all D or all H) over the cross section of the device. The primary assumption is that a final single 50/50 mixture of D/T is ideal for a fusion power plant. However, toward the edge of a ignited plasma the low temperature would greatly reduce the importance of the edge to overall energy balance. A 50% DT mixture is not needed. However, edge region is critical to the success of reactors and a number of phenomena could be modified by different isotopes in the edge. In a device like ITER it could run with a larger fraction of deuterium in the plasma edge to reduce the tritium uptake in the wall. Transport is expected to be much different in a deuterium edge and will impact interactions in the divertor. Alternatively, we may increase the edge mass number by introducing only T at the edge while fueling a 50/50 mixture in the core. We need to explore how far edge species migrate up stream and what impact a lighter (or heavier) mass will have on the edge behavior. Ultimately, this gives us another knob to control profiles in the tokamak and an area that has not been explored to date. |
| Resource Requirements: | NBI sources especially tangential, upper and lower cryopumps, inner pellet injectors |
| Diagnostic Requirements: | Full set of diagnostics - with emphasis on spectroscopic analysis to determine H/D/(He) Isotope gradients. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
282: Test J-K Park theory of tokamak error field correction |
| Name: | Michael J. Schaffer () |
Affiliation: | General Atomics |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | LaHaye, Strait, Scoville, J-K Park (expected) |
| Description: | Find the best empirical correction by varying more I-coil degrees of freedom than the usual amplitude and toroidal phase angle in an otherwise hard-wired current distribution. Specifically, connect a 1.7 kA SPA to each I-coil so that all 12 coil currents can be independently set. Then vary the toroidal "phasing" angle between the upper and lower I-coil sets, in addition to the usual parameters. Compare the best empirical correction with analysis by J-K Park with his IPEC code. The result may help to further establish the theory. |
| Experimental Approach/Plan: | Use the previously developed Ohmic, low-density, locked-mode error field test plasma and technique. Connect one 1.7 kA SPA to each of the 12 I-coils, in order to make any physically possible current distribution. Operate the plasma at sufficiently low Bt, Iplas and density that locked modes can be made with no more than 1.7 kA maximum in any coil. Vary the "phasing" angle between the upper and lower I-coil sets, in addition to the usual current magnitude and global toroidal phase of the current distribution. Start from the past experimental correction and, if available, a prediction from J-K Park. Determine empirically the best correction. |
| Background: | Tokamaks are distressingly sensitive to non axisymmetric magnetic field errors. A new theory by J-K Park et al, PRL (accepted 2007) explains previous DIII-D empirical error correction semiquantitatively, via the coupling between the external error and correction fields with the least stable ideal MHD plasma mode, whose non axisymmetric currents strongly dominate inside the plasma. If this theory is verified, it will provide a systematic, practical way to design and operate tokamak error field correction systems. |
| Resource Requirements: | I-coil system essential.
Ohmic plasmas --- no NBI. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | Compare experiment result with theory. Requires collaboration by J-K Park with his IPEC code. |
| Other Requirements: | -- |
| Title |
284: Test contribution of edge ion orbit loss to intrinsic toroidal rotation |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Investigate intrinsic rotation in H-mode plasma with reduce edge ion orbit loss |
| Experimental Approach/Plan: | Run inner-wall limited H-mode plasma using shape with X-points well beyond the last closed flux surface. A possible discharge is 129470, which has no X-points in the vacuum vessel. Adjust plasma interaction with centerpost to achieve H-mode with convenient input power (< 7.5 MW). Change beam co-counter balance to scan toroidal rotation from counter to co with the goal of finding the point where the net torque is zero. Measure toroidal rotation profiles for all cases and determine intrinsic rotation. Compare magnitude of intrinsic rotation with results from previous experiments. |
| Background: | C.S. Chang has proposed a theory of the intrinsic toroidal rotation says that the effect is due to loss of counter-going ions at the plasma edge. These leave behind a distribution with net angular momentum in the co-direction, thus producing the rotation. Calculations by C.S. Chang indicate that most of the thermal ion orbit loss in H-mode plasmas is through the X-point. Accordingly, running a plasma without X-points should reduce this loss substantially. Fast ion orbit loss can be reduced by running a large outer gap. The experiment will investigate whether the intrinsic rotation follows the same scaling with toroidal beta that this seen in D III-D X-point discharges. If it is much lower, then that would indicate that ion orbit loss is a significant player. |
| Resource Requirements: | All profile diagnostics. Modulate 30LT and 330LT out of phase for improved CER measurements. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
288: Measurement of internal structure of RFA |
| Name: | Andrea M. Garofalo () |
Affiliation: | Columbia University |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | M. Lanctot, H. Reimerdes |
| Description: | Measure the internal structure of the RFA during application of a slowly rotating n=1 I-coil field at beta above the n=1 no-wall limit. Compare to the predicted structure of the stable RWM. |
| Experimental Approach/Plan: | We propose to calculate the radial profile of the n=1 plasma displacement due to a slowly rotating n=1 field, from the ECE measurement of the Te fluctuations at two opposite toroidal locations. Yes, you read that right: two opposite toroidal locations of measurements of the entire Te profile. We have that unique capability right here at DIII-D. It cannot be used for rapidly rotating tearing modes, but it will work just fine for a 10 Hz rotating RWM. The idea is to use the standard ECE radiometer, located at the 81° port, in combination with the Michelson interferometer (HECE), located at the 270° port: almost exactly 180° apart!
The limitation is that the fastest that the HECE can measure the profile is every 25 ms. For a 10 Hz rotating field, that gives 4 measurements every period. To increase the sampling, we propose to add data from repeat discharges with time-shifted start of the measurements. With just a handful of good repeat discharges we can collect high quality profile information on the amplitude and toroidal phase of the n=1 RFA, to compare with codes like GATO and MARS. In particular, comparing the toroidal phase profile with MARS will give us information on the dissipation physics. |
| Background: | The internal structure of the RFA excited by a rotating I-coil field has never been measured. It is a necessary step to conclude that the RFA is due to the stable RWM. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
289: Main ion poloidal rotation measurements in helium plasmas |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | J.S. DeGrassie, W.M. Solomon |
| Description: | The goal of this experiment is to test the neoclassical theory of poloidal rotation by measuring the rotation of the main (helium) and impurity (carbon) ions under a variety of conditions. These will be in Ohmic, ECH and NBI H-modes. |
| Experimental Approach/Plan: | These experiments will build on the ECH H-mode developed in helium plasmas during the 2003 and 2004 campaigns. In addition, they will utilize the ability of the CER system to make high time resolution measurements of the plasma rotation just after beam turn on. This allows us to use the beams to make the measurement before they have had time to alter the rotation. Using combinations of ECH and beams, we will make L-mode and H-mode plasmas, some totally RF dominated and others beam dominated. The beam dominated shots will cover cases with significant co-injection, balanced injection and counter injection. |
| Background: | Because of its role in affecting E x B shear stabilization of turbulence, developing a predictive understanding of plasma rotation is an essential part of transport studies. Measurements in 2004-2005 presented by W. Solomon at the 2005 APS DPP meeting showed that the impurity poloidal rotation did not agree with neoclassical predictions in QH-mode and RMP ELM-suppressed H-mode plasmas. However, to date, there has not been a good test of the theoretical predictions for the main ion rotation. One possible explanation for the discrepancy seen by Solomon et al is the effect of friction with the neutral beam ions. Performing experiments both with and without NBI will allow us to investigate this possibility. In addition, having measurements of the main and impurity ions allows provides significantly more information, since the coupling to the fast ions is different. During the LTOA, we installed a improved detectors for the poloidal views for the CER system; we are now in a position to make much better measurements of poloidal rotation. |
| Resource Requirements: | 4 gyrotrons. CER beams plus 2 more |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
290: Develop an L-mode error correction test plasma |
| Name: | Michael J. Schaffer () |
Affiliation: | General Atomics |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | LaHaye, Strait, Scoville (expected) |
| Description: | Test whether plasma toroidal rotation in an L-mode plasma can be used to test magnetic error correction, and if so, develop it. This test plasma might be easier to use than Ohmic, low-density plasmas sensitive to locked modes. |
| Experimental Approach/Plan: | Use a DND plasma biased upward, like the present Ohmic error field test plasmas, to avoid easy L-H transition. Begin with just the beam needed for CER toroidal rotation measurement. Apply known error correction and anti-correction fields to see whether rotation is affected enough to be a useful indicator of error status. Try low and moderate densities and NBI. If a useful effect is present, scan the applied non axisymmetric field over a wider range, to verify its usefulness. |
| Background: | Error field studies at DIII-D have used low-density, Ohmic test plasmas that are reproducibly sensitive to locked mode onset. As errors have been reduced, operating densities have become inconveniently low. Rapidly rotating, H-mode, high-beta_N, RWM test plasmas have also been used, in which toroidal plasma rotation is maximized by error correction. They require a clean machine and considerable resources to produce. A recent attempt to develop a plainer H-mode test plasma failed, because the plasma evolved too much as correction fields were applied, thus making it unreproducible for error work. L-mode plasmas are easy to run, and they have moderate plasma rotation and CER. It would be helpful for future error field research if a reliable L-mode test plasma could be developed. |
| Resource Requirements: | NBI for L-mode and CER toroidal rotation |
| Diagnostic Requirements: | CER toroidal rotation |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
291: Prompt torque and zonal flow damping |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | J.S. DeGrassie |
| Description: | The goal of this experiment is to determine the damping rate of the zero mean frequency zonal flow and the plasma poloidal rotation by periodically perturbing the plasma rotation using modulated co and counter neutral beam injection. The beam modulation will be fast compared to the fast ion slowing down time, so that the modulation will primarily be due to the prompt torque caused by fast ion orbit shift. |
| Experimental Approach/Plan: | This experiment is best done in QH-mode plasmas, because they are high temperature and low density, which leads to long ion-ion collision times. In addition, they have long steady periods, which allows significant averaging. Use the prompt torque from the beam orbit shift to apply periodic co and counter torques to the plasma by modulating the co and counter beams out of phase. Orbit shift calculations show that the 210LT and 330 RT beams give approximately equal prompt torque profiles out to rho=0.6. This allows 330 LT and 30LT to be run continuously to get CER data. Experimentally, what we are looking for is the evolution of the induced poloidal rotation (or radial electric field) after the initial jump which occurs when we add an extra co or counter beam. The beam modulation period will be chosen so that there are several ion collision times within one beam on time; this will be between 10 and 40 ms. CER will be set to short a integration time, something like 2 ms. We can average over multiple pulses to improve the quality of the rotation measurement. We will scan ion-ion collision time by changing the ion temperature using different power levels and by changing the core density by using ECH to induce density pumpout. The ECH will also provide extra electron heating to increase the fast ion slowing down time. |
| Background: | When neutral beams deposit toroidal angular momentum in the plasma, they do so on two time scales, one for the momentum deposited perpendicular to the magnetic field and another for the momentum deposited parallel. The parallel momentum couples to the background plasma on the time scale of the collisions between fast ions and the background ions. The perpendicular momentum is deposited much more quickly, through a process involving radial currents. When a beam neutral ionizes, the resulting D+ ion travels on a orbit whose guiding center is shifted from the ionization point. For D+ ions born outside the magnetic axis, this shift is outwards (towards larger minor radius) for counter injected neutrals and inwards (towards smaller major radius) for co-injected neutrals. This shift represents a radial current of fast ions. Processes in the background plasma produce on offsetting radial current, which then imposes a torque on the background plasma. However, this offsetting radial current grows up on the ion-ion collision time. During this time, the poloidal rotation and the radial electric field both evolve. If we use out of phase modulation of the counter and co beams, we can periodically reverse this torque, creating a square wave modulation. If the modulation period is fast compared to the fast ion slowing down, we only need to consider the prompt torque. For a plasma with 15 keV central temperature and 5 x 10^19 m^-3 density, the fast ion slowing down time is greater than 100 ms even for the 1/3 energy component. The damping of the overall plasma poloidal rotation is the same as the damping time of the plasma electric field. Accordingly, CER measurements of any impurity ion can be used to determine the overall poloidal rotation damping. More importantly, this damping time of the plasma electric field is the zonal flow damping time, which is crucial to turbulence behavior. Theory predicts that this damping time is of order the ion-ion collision time which is around 20 ms in our candidate plasmas. |
| Resource Requirements: | Reverse Ip. 7 NBI sources |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
292: ELM suppression with I-coil error correction |
| Name: | Michael J. Schaffer () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | Evans, Fenstermacher, Moyer, Joseph expected |
| Description: | Use improved error correction to extend ELM-suppressed plasmas to lower rotation speeds. Demonstrate that ELMs can be suppressed by n=3 RMP, applied by the I-coil, while simultaneously applying the empirical n=1 error correction field, also with the I-coil. Optimize the error correction for the test plasma. Using best error correction, use counter injection to see how slow the plasma can go without problems. |
| Experimental Approach/Plan: | Set up the necessary special I-coil patch panel connection. Establish one of the RMP ELM-control test plasmas and verify ELM suppression using the normal I- and C-coil combination. This can be done with the special connection. Next, repeat the ELM suppression test while using the I-coil correction along with the RMP. If successful, optimize the I-coil n=1 error correction amplitude and toroidal phase for best plasma rotation. Finally, use NBI counter injection to reduce plasma rotation and see whether the ELM-suppressed plasma survives to lower rotation speeds than it does with C-coil error correction. |
| Background: | n=3 RMP ELM control experiments in DIII-D have been done with C-coil error correction, which is important. The I-coil does better error correction, at least in Ohmic, low density, locked mode test plasmas. An I-coil patch panel was developed in 2007 to permit both the n=3 RMP and the n=1 error correction currents to be supplied simultaneously and varied independently. |
| Resource Requirements: | Special patch panel connection of I-coil |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
293: Minimum Contact Startup in DIII-D |
| Name: | Jim Leuer () |
Affiliation: | General Atomics |
| Research Area: | Model based Control |
Presentation time: |
Not requested |
Co-Author(s): | A. Hyatt, M. Walker, D. Humphreys |
| Description: | Plasma breakdown and initial plasma current ramp are produced primarily with a circular plasmas. The plasma edge is scraped-off on the inner or outer wall. This leads to loss of volt-second and impurity influx. Presently, only when substantial current is present in the plasma is is possible to divert and move the plasma off the wall surface. We will attempt to divert the plasma at the earliest possible time to limit the interactions with the wall. Low magnetic signal and issues with vertical feedback of elongated plasmas presently preclude early divertor formation. We will investigate the signals and determine if feed back is possible at an earlier time. Model based studies (including eddy currents) to improve the signal resolution required for early vertical stabilization will be explored. Other methods of detecting vertical position will also be explored to determine if other non-magnetic signals can be used for stabilizaiton. These signals include light emission from the inner and outer walls and impurity radiation from the core. Early ECH or diagnostic N-Beam may provide some indication of the plasma center and allow feed-back for vertical control. |
| Experimental Approach/Plan: | Initially effort will be to observer the signals of typical breakdown to develop those diagnostics that can provide positional plasma position resolution required for early utilization of feed back vertical control. We will request early EC and beams to quantify if these systems can be used diagnostics for centroid detection. Much of this work will be done in a piggy-back, observer, mode without need for experimental time. However, some diagnostic systems may require modification and/or timing changes to provide the required signal and time resolution. Following model/diagnostic development, we anticipate staged implementation of the techniques in the PCS to augment our existing startup scenario. |
| Background: | Traditional breakdown is based on simple null formation and feed-forward current or flux programing. Many modern modeling tools and non-magnetic diagnostics signals can be used to expand the capability of optimizing breakdown and initial current ramp. DIII-D is the perfect machine to explore this area of research and will provide ITER, KSTAR, EAST and other machines with new tools, diagnostics and methods to optimize their plasma startup. |
| Resource Requirements: | NBI sources especially tangential, EC |
| Diagnostic Requirements: | All diagnostics with significant signal at breakdown and initial current ramp |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
294: Search for Structures Predicted in RMP ELM control modeing |
| Name: | Richard A. Moyer () |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | Evans, Joseph, Kruger, Izzo, Park, Menard, Boozer, Schmitz |
| Description: | An outstanding issue for understanding RMP ELM control is the plasma response to the applied n=3 RMP. The goal of this experiment is to test predictions of various models for the magnetic field in the plasma by searching for structures in 2D Thomson scattering data. We will run upper and lower single null, low collisionality, ITER-similar shape discharges, apply n = 3 RMP from the I-coil to suppress ELMs, and shift the plasma rigidly across the Thomson view chord to build 2D images of electron density and Te. Islands, convective cells, and/or significant displacement of the equilibrium flux surfaces should be visible on the Thomson scattering data. This proposal has significant overlap with Schimitz #100. |
| Experimental Approach/Plan: | 1) Establish good RMP ELM suppression with n = 3 RMP in LSN, ITER-similar shape discharges. 2) Move the plasma boundary across the Thomson view chord on a timescale slow compared to the laser spacings. 3) construct 2D images of the boundary of the discharges, looking for evidence for islands, ExB convective cells, or plasma equilibrium displacements near the crown of the discharge where they are predicted to occur and to be easiest to see due to flux expansion. 4) Scan I-coil current 5) vary momentum input with co/ctr beams 6) repeat with USN discharges time permitting to image the region near the Xpoint. |
| Background: | Understanding the plasma response to the applied n = 3 RMP is crucial to understanding how RMP ELM suppression works. We have several models which make predictions about structures that form in the flux expanded regions near the crown and Xpoints. TRIP3D provides a vacuum field model (no plasma response) which predicts remnant islands with maximum physical size near the crown and Xpoint. NIMROD and JORIK extended MHD codes predict formation of ExB convectice cells in this region of the plasma that drive enhanced particle transport without significantly increasing thermal transport (relative to e.g. ripping open closed field lines in a stochastic layer). Most recently, the IPEC code has begun to be used to predict the plasma response to the I-coil RMP, and predicts significant plasma displacements near the crown and xpoint regions.
We propose to use the Thomson scattering diagnostic to build 2D images of electron density and pressure by moving the plasma boundary across the Thomson view chord on a time scale slow compared to the laser spacing. This technique has been used successfully for example in ASDEX-Upgrade to image "blobs" in the SOL and "holes" in the pedestal, and should be useful here to image the predicted structures if they exist.
Rick Moyer has written and IDL tool for constructing such 2D images from existing data in which the edge was "breathed" past the Thomson chords to improve the spatial resolution of the measured profiles. This tool is being developed to optimize the image construction but the discharges available have little Rmajor movement which limits the "field of view". |
| Resource Requirements: | 4-5 co sources; 2 counter sources
cryopumps
n = 3 I-coil with 6.5 kA capability |
| Diagnostic Requirements: | CER and Thomson scattering
fluctuation diagnostics
pedestal and boundary diagnostics |
| Analysis Requirements: | TRIP3D runs to: 1) test the vacuum field/island overlap model against imaged structure sizes and to provide RMP fields to other models, 2) validate IPEC predictions of flux surface displacements; 3) NIMROD and/or JORIK runs for validation of convective cell predictions. 4) EMC3/EIRENE runs for comparison with data. |
| Other Requirements: | -- |
| Title |
295: ELM suppression by single-row coil sets |
| Name: | Michael J. Schaffer () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | Evans, Fenstermacher, Moyer, Joseph expected |
| Description: | Apply n=3 magnetic perturbations up to the full allowable coil currents from single-row coil arrays, e.g., the C-coil and the upper or lower row I-coils. Determine how much ELM reduction and possibly suppression is obtained before effects like slow rotation and the onset of internal instabilities degrade the plasma. Measure the accompanying plasma profile changes and compare with conventional two-row ELM suppression. A single I-coil row is vertically narrower than the C-coil, and the proposed ITER port plug coils are narrower than either. |
| Experimental Approach/Plan: | -- |
| Background: | Complete ELM suppression has been demonstrated in DIII-D over a substantial range of plasma conditions using the two-row I-coil applying n=3 fields. Attempts to suppress ELMs by single-row coil sets have been unsuccessful at DIII-D and elsewhere, but substantial ELM amplitude reduction was obtained at JET. ITER just chose a single-row ELM control coil. Single-row arrays produce large non-resonant helical harmonics that might non resonantly brake plasma rotation; this might bu undesirable. Because DIII-D has the world's most extensive experience with ELM suppression and the most extensive non axisymmetric coil sets, we should make a dedicated effort to see if we can get complete suppression at DIII-D. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
296: Test neoclassical poloidal rotation prediction as a function of toroidal rotation speed |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | W.M. Solomon, S.K. Wong |
| Description: | Test predictions of an extended version of neoclassical theory which
says that the poloidal rotation of ions in the plasma should vary as
the the toroidal rotation changes |
| Experimental Approach/Plan: | Utilize QH-mode plasmas with modulated neutral beams for best rotation
measurements in a high temperature, H-mode plasma. Scan toroidal
rotation by varying the co-counter beam mix. Investigate poloidal and
toroidal rotation speed of various impurities: helium, carbon, neon
and argon. |
| Background: | Measurements of carbon and neon poloidal rotation by Solomon et al.
[Phys. Plasmas 13, 056116 (2006)] showed a significant discrepancy
between experimental measurements and the predictions of neoclassical
theory embodied in the NCLASS code. Recently, S.K. Wong has pointed
out that the standard neoclassical prediction for poloidal rotation
needs to be modified when the main ions or the impurities are rotating
at speeds comparable to their individual thermal speeds. In the
experiment by Solomon et al, the carbon and neon impurities were
rotating at near their thermal speeds. The goal of this experiment is
to make a detailed test of this extension of neoclassical theory. |
| Resource Requirements: | Reverse Ip. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
297: Effect of Error Fields and RMPs on H-mode power threshold and transport barrier |
| Name: | Richard A. Moyer () |
Affiliation: | University of California, San Diego |
| Research Area: | Transport |
Presentation time: |
Requested |
Co-Author(s): | Evans |
| Description: | Goals: 1. Use the I-coil to create controlled "error field" mode spectra and strengths 2. Measure the H-mode power threshold versus RMP mode spectrum and amplitude 3. Quantify changes to the edge Er, plasma flows, fluctuations, and transport 4. If available, use dedicated midplane probe heads for 1) electrostatic Reynolds stress and 2) Maxwell stress (i.e. magnetic component of the turbulent Reynolds stress) to quantify the effect of the RMPs on the turbulent Reynolds stresses (requires separate run days for the two stresses) |
| Experimental Approach/Plan: | Experimental approach: 1. Use ECH L-mode and H-mode discharges to facilitate probe measurements in the H-mode pedestal as in last year's experiment 2. Apply I-coil perturbations with varying current 3. Increase ECH power to determine change/increase in H-mode power threshold while plunging reciprocating probes 4. Switch to modulated beams to repeat determination of power threshold while acquiring edge CER and BES measurements. |
| Background: | Motivation: 1. Plasma flows, radial electric field, turbulence, and transport are all closely coupled in the plasma boundary. 2. Error fields and externally applied RMPs can significantly alter the edge Er shear and plasma flows, and consequently the plasma turbulence and transport 3. Last year, externally applied RMPs were observed to raise the H-mode power threshold from 1/4 neutral beam source (about 0.6 MW) to more than 4 sources, confirming that RMPs can significantly alter the physics of the L-H transition and transport barrier formation. |
| Resource Requirements: | complete control of the initial portion of the discharge (power, shape, diagnostics) to optimize probe data from inside the separatrix
1 run day
4 gyrotrons for ECH H-modes
electrostatic Reynolds stress head on midplane probe |
| Diagnostic Requirements: | midplane and Xpoint probes; midplane with Reynolds stress head
BES and CER with discharge shape to allow measurements on the same flux surfaces as the midplane probe.
Fluctuation diagnostics consistent with ECH heating
pedestal diagnostics |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
298: Balance between FW edge absorption by far-field sheaths and central absorption |
| Name: | Robert I. Pinsker () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | J.C. Hosea, F.W. Baity, E. Fredd, M. Porkolab |
| Description: | DIII-D experiments have shown that the central FW current drive efficiency can be accounted for quantitatively only if an edge loss on the order of a couple of percent per bounce is assumed. Experiments in ELMing H-modes showed that the edge loss increases significantly if the ELMs are so frequent that the FW cutoff moves near to the wall. These facts can be explained if the edge loss is predominantly due to rectified rf sheaths at the wall. If the edge losses are at all comparable to the central absorption, by changing only the edge loss, the fraction of power absorbed in the core should change, despite the core absorption per pass being held constant. In this proposed experiment, we measure the FWCD efficiency in L-mode, using the minimum amount of beam power necessary to obtain MSE data and using ECH to prepare the sawtooth-free portion of the discharge in which the current drive is measured. We vary the conditions in the plasma edge such that the dissipated power in sheaths should be reduced by increasing the separatrix/wall clearance in different poloidal locations, in an attempt to get a better idea where the important sheaths are located. When the outer gap is increased, the lower antenna loading will mean that the power per antenna will have to be lowered to be able to keep the total coupled FW power constant. Hence, the scan should begin with the maximum outer gap case in order to find the maximum reliably coupled FW power, and as the outer gap is reduced, it should be easy to keep the power constant. The prediction is that when the plasma/wall clearance in the important poloidal location is reduced, the core absorbed power will drop and hence the driven current will decrease. |
| Experimental Approach/Plan: | See description. |
| Background: | Experiments in NSTX on HHFW heating have arrived at a similar conclusion. In those experiments, by increasing the density at which the FW begins to propagate, the distance between that cutoff layer and the wall is increased, the edge losses decrease, and the core heating efficiency increases substantially. For NSTX, this increase in the cutoff density is achieved by raising the toroidal field. The complementary experiment in DIII-D, in which the toroidal field would be lowered and observe a decrease in central absorption, is difficult, because many things would change at the same time (proximity to the H-mode power threshold, electron thermal transport, ECH location). Hence in this proposal, we would vary the edge loss by changing the distance between the plasma edge and the wall, which should not affect the core absorption at all. |
| Resource Requirements: | 1 day experiment. 30L beam, 4 gyrotrons, all three FW systems. |
| Diagnostic Requirements: | MSE is the main diagnostic; all standard profile diagnostics. Edge reflectometry would be very useful to monitor edge density profiles directly. |
| Analysis Requirements: | Standard current drive analysis. |
| Other Requirements: | -- |
| Title |
299: QH-mode studies as a function of edge rotation |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | W.M. Solomon, M.E. Fenstermacher, P. Gohil, C.J. Lasnier,T.H. Osborne, P.B. Snyder |
| Description: | Determine whether the QH-mode can be achieved with balanced or even
some co-injection. Investigate effects of edge rotation on QH-mode
plasmas with emphasis on changes in EHO-induced particle transport. |
| Experimental Approach/Plan: | Start the experiment in QH-mode plasmas similar to 128502. Utilize
RMW feedback to null out the remaining intrinsic error field.
Investigate this QH-mode as rotation is made more and more co.
Important questions are the nature of the EHO and its effect on
particle transport. |
| Background: | During the 2006 and 2007 campaigns, we made significant progress in
producing QH-mode plasmas with reduced counter rotation. This was
achieved by optimizing the plasma shape for peeling-ballooning mode
stability and by reducing the intrinsic error fields. The latter is
the key to preventing locked modes at low toroidal rotation. In
moderate beta QH-mode plasmas, we have seen error field amplification
on the ESLD detectors. This effect indicates that we still do not
have optimal error field correction; however, this effect is also what
is needed to use the RWM feedback system to null out the remaining
intrinsic error fields. Unfortunately, we did not have time to apply this
RWM feedback technique in 2007. We have also seen that the particle
transport due to the EHO decreases as the magnitude of the toroidal
rotation decreases. This leads to higher density and higher pedestal
pressures, which in general are destabilizing to the peeling
ballooning modes. However, using the optimized high-triangularity,
double-null shape provided enough stability margin that we remained in
QH-mode. |
| Resource Requirements: | Reverse Ip. 7 NBI sources |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
300: QH-mode with co-injected neutral beams |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | M.E. Fenstermacher, P. Gohil, W.M. Solomon, C.J. Lasnier,T.H. Osborne, P.B. Snyder |
| Description: | Attempt to create QH-mode with dominant co-injection. |
| Experimental Approach/Plan: | Start with a plasma similar to 128502 but which the plasma current in
the standard direction. Utilize the usual QH-mode recipe to minimize
particle inventory to keep density as low as possible. Explore
variations in plasma up-down balance and strike point location
relative to the pumps to minimize density. Do current scan from 1.3
MA down to 0.7 MA to exploit the improved peeling-ballooning stability
at high q. Explore use of I-coil perturbations to induce increased
particle transport |
| Background: | The peeling-ballooning mode theory has allowed us to understand
QH-mode operation. ELM-free QH-mode edges lie in the region of
parameter space that are predicted to be stable to ELMs. This is
achieved by working to lower the edge density and pressure to move the
H-mode edge into this region of parameter space. The enhanced
particle transport due to the EHO is a key part of this. The
peeling-ballooning mode theory, however, makes no prediction of the
sign of the plasma current. Accordingly, if we can achieve the
correct edge density and pressure, the theory predicts that we can
achieve QH-mode with co neutral beam injection. In the 2006 and 2007
campaigns, we developed plasma shapes with enhanced edge stability
margins. These are high-triangularity, double-null plasmas which
exploit the new cryopumps for density control. The goal of the
present experiment is to see if our density control is good enough
for this shape to achieve QH-mode with all co-injection. A companion
experiment proposed by T. Osborne will explore use of the I-coil
perturbations at non-resonant q-values as a means of density control. |
| Resource Requirements: | Standard current direction. 7 NBI sources. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
301: Does RMP ELM suppression have hysteresis? |
| Name: | Michael J. Schaffer () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | Evans, Fenstermacher, Moyer, Joseph expected |
| Description: | This experiment will investigate whether ELM suppression can be maintained after a steady state has been reached by a smaller RMP field than was required to initiate suppression (hysteresis). The presence of hysteresis might help identify those aspects of the pedestal profiles that are most important for suppression. |
| Experimental Approach/Plan: | In a conventional RMP ELM suppression experiment, slowly reduce the RMP amplitude after the pedestal and core profiles have attained steady state. |
| Background: | In most past experiments, the I-coil n=3 RMP field is applied to a strongly ELMing plasma and kept constant. However, it is observed that pedestal profiles are strongly modified by the RMP and the pedestal itself is narrowed. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
302: Diagnostic spatial cross calibration using edge sweeps in QH-mode |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | C. Holcomb, G.R. McKee, W.M Solomon |
| Description: | Perform spatial cross calibration of the CER, BES and MSE systems
using edge sweeps in QH-mode discharges |
| Experimental Approach/Plan: | Run QH-mode discharges like 128542 with edge sweeps which change
Rmidout from 2.29 m to 2.16 m. Tune the CER system to look at the
Doppler-shifted D-alpha from the neutral beams. (BES and MSE already
view this wavelength). Modulate the beams to obtain the needed data.
The various beam combinations typically take 6 shots to complete. |
| Background: | In order to successfully combine data from the CER, BES and MSE
systems for edge plasma studies, we need to know the relative spatial
calibration of these system to millimeter accuracy. This has been
done before using edge sweeps in QH-mode plasmas. This calibration
needs to be done again so that we can finally include the MSE views of
the 210 beam and so we can recalibrate the BES system after the work
done in the vent at the end of 2007. The MSE portion of the calibration
is particularly important, since the relative location of the 210
system relative to the other MSE systems has never been established. |
| Resource Requirements: | Reverse Ip. 7 NBI sources |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
303: RF sustained QH-mode |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | R.D. Stambaugh |
| Description: | Investigate whether beam injection is essential in sustaining a
QH-mode plasma. The experiment will switch from all neutral beam
injection to ECH during the quiescent phase. If the plasma survives in
QH-mode for a time long compared to the fast ion slowing down time in
the plasma edge, then we will be able to conclude that beam injection
is not necessary for sustainment of the QH-mode and fast ion physics
at the plasma edge plays no role in QH-mode |
| Experimental Approach/Plan: | The plasma used here will be based on 128502, a high triangularity,
double-null QH-mode with reversed Ip. Neutral beam injection will be
used to create the QH-mode and sustain it until about 3000 ms into the
shot. At this point, the beams will be turned off and ECH will be
used. We will need at least five gyrotrons to obtain the needed
power. If QH-mode can be sustained for significant periods of time,
neutral beam blips will be used during the RF phase of subsequent
shots to obtain complete ion temperature profiles. |
| Background: | A key question for QH-mode plasmas is the role of counter injection
and beam injection in general. We know from experiments in the 2003
campaign that QH-mode can be created and sustained with right sources
only, which indicates that fast ion orbit loss is not essential for
QH-mode. We will be investigating further in the 2008 campaign
whether QH-mode is possible with balanced or dominantly co-injection.
Even if we achieve that, we still need to determine whether the
presence of fast ions orbiting beyond the separatrix is essential. |
| Resource Requirements: | Reverse Ip. 7 NBI sources. 4 gyrotrons |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
304: Turbulence spreading experiment in plasma core |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The goal of this experiment is to determine whether we can
experimentally detect the spatial spreading of turbulence which
is predicted by various analytic calculations and gyrokinetic
code runs. |
| Experimental Approach/Plan: | Use the same plasma and ECH configuration that J. DeBoo used to do the
ECH swing experiment--modulated ECH at two different radial locations
in an L-mode, sawtooth-free plasma. Modulate ECH out of phase at the
two locations so that grad Te is modified in the region between the
two radial positions. From rho_2 outward, the plasma sees constant
power input and, hence, should have constant gradients. Look for
modulation in the turbulence and transport in the outer region
correlated with the ECH modulation. We need to worry that there
might be a transient modulation due to the fact that the heat from the
inner gyrotron has to travel further to get out. Accordingly, right
after the switch, there may be a transient alteration in the radial
flux. Hence, we need to use long enough ECH modulation that this can
die out. For this experiment to work, we need to match the powers
from the gyrotrons very exactly. We know that we can make the basic
plasma and perform the modulation; however, we didn't acquire the
proper turbulence measurements in the last experiment. |
| Background: | Recent theoretical work indicates that there is a nonlocal character
to turbulence in magnetized plasmas. Turbulence can be driven from
free energy sources in one location and manifest itself both at
that location and in more distant areas. The issue is that, in most
cases, the plasma is also unstable to microturbulence in that more
distant location. Accordingly, to do a meaningful experiment, we need
to find ways to separate the local and nonlocal effects. |
| Resource Requirements: | 4-5 gyrotrons |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
305: Turbulence spreading experiment in the plasma edge |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The goal of this experiment is to determine whether we can
experimentally detect the spatial spreading of turbulence which
is predicted by various analytic calculations and gyrokinetic
code runs. |
| Experimental Approach/Plan: | Look at changes in turbulence across the L to H transition in the
region just inside the edge pedestal using BES and/or reflectometry.
See if the turbulence decreases much more rapidly than can be
explained by the change in local profiles. In order to give an exact
time marker, we want a sharp, single step transition during a period
when the beam power has been constant for some time. One possible way
to do this is to use a Drsep change to change the power threshold. |
| Background: | Recent theoretical work indicates that there is a nonlocal character
to turbulence in magnetized plasmas. Turbulence can be driven from
free energy sources in one location and manifest itself both at
that location and in more distant areas. The issue is that, in most
cases, the plasma is also unstable to microturbulence in that more
distant location. Accordingly, to do a meaningful experiment, we need
to find ways to separate the local and nonlocal effects. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | Edge turbulence diagnostics |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
306: Completion of MP 2007-01-02: Investigate direct effect of RMP on ELM Stability |
| Name: | Richard A. Moyer () |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | Moyer, Evans, Joseph, Fenstermacher, Wade |
| Description: | The goal of this experiment is to determine whether or not the RMP has a direct effect on ELM stabilization independent of the enhanced transport which leads to a reduction in the pedestal pressure gradient. We will use the separability of time scales between the transport/density pumpout (= 250 ms) and MHD response (< 1 ms) in order to separate these two effects by applying an a.c. oscillation (a few tens of Hz) around a sub-critical RMP amplitude for ELM suppression. This a.c. oscillilation will carry the RMP amplitude over the threshold for suppression and back on a time scale with is too fast for the transport to follow, but slow relative to the Alfven, reconnection and resistive times that govern MHD response. |
| Experimental Approach/Plan: | 1) Re-establish robust n = 3 RMP ELM suppression in a low collisionality, ITER-similar shape as on June 24, 2007. 2) Reduce the d.c. I-coil current below the level needed for suppression and add an a.c. oscillation on a 10-30 Hz frequency. 3) Characterize the ELM behavior, and the pedestal and boundary plasma response. |
| Background: | RMP ELM control results in ITER-similar shapes suggest that ELM suppression may be the result of not only reducing the edge pressure gradient, but of also shifting the stability boundary. This result raising the possibilty of a direct effect of the RMP on ELM stability separate from the effect of enhanced transport reducing the pedestal pressure gradient.
This experiment was initially attempted during the June 24 2007 run day, but due to limited machine availablity, we were not able to obtain a conclusive result. This proposal is to complete this portion of the experiment, describes in MP 2007-01-02 |
| Resource Requirements: | 1/2 run day
lower cryopumps
n = 3 a.c. I coil operation |
| Diagnostic Requirements: | CER, Thomson scattering, profile reflectometry
fast and Mirnov magnetics
pedestal diagnostics, filterscopes, SXR
reciprocating probes
BES, FIR scattering, PCI, reflectometry, correlation ECE
IRTVs (fast TEXTOR camera if available)
fast framing UCSD camera, DiMES camera, Xpoint tangential TV |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
307: ELM suppression by multi-harmonic RMPs |
| Name: | Michael J. Schaffer () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | Evans, Fenstermacher, Moyer, Joseph expected |
| Description: | Using special I-coil patch panel connection, apply approximately equal magnitudes of n=3 and n=2 pitch resonant magnetic perturbation fields simultaneously. Computation shows that such multi- harmonic fields can fill in some island gaps, and they also create richer stochasticity. Furthermore, depending on how the n=2 current component is distributed in the I-coil, the magnitude of side band n=4 harmonics can be varied, thus enabling a limited test of a three-harmonic RMP. Look for experimental similarities and differences with respect to conventional, pure n=3, RMP ELM suppression. |
| Experimental Approach/Plan: | -- |
| Background: | Computations of the helical Fourier spectra of magnetic fields produced by many coil concepts proposed for ITER revealed some spectral fill-in advantage to the combined use of two or more toroidal harmonics. DIII-D experiments have shown that this concept works, by adding extra n=1 from the C-coil. However, n=1 is prone to unstable mode locking. Pitch resonant n=2 can be made by the I-coil, and it is expected to induce less mode locking than n=1. |
| Resource Requirements: | Special I-coil patch panel connections. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
308: Resonant vs non-resonant braking |
| Name: | Andrea M. Garofalo () |
Affiliation: | Columbia University |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | Degrassie, Cole, Hegna, Callen |
| Description: | A systematic study of the braking physics that includes data in plasmas with co-Ip NBI, ctr-Ip NBI, and no NBI (ECH only) is necessary to further our understanding of the interaction between a rotating plasma and error fields, both resonant and non-resonant. This is important in order to assess the thresholds of tolerable error fields for ITER (ITPA Joint Experiment MDC-12). This proposal includes braking scans in normal Ip, reverse Ip, D plasmas and He plasmas. |
| Experimental Approach/Plan: | This is the continuation and extension of experiments started in FY07 (MPs 2007-04-02 and 2007-04-04). We will use the C-coil for optimal correction of the n=1 error field, determined via DEFC. We will use the I-coil to apply braking. The braking is applied after all profiles have reached nearly stationary conditions. We plan to increase the braking slowly, through a succession of torque equilibrium states, and remove the braking field quickly, to also observe the response to a step. Crucial requirements are to maintain the plasma density, beta and the injected NBI torque constant during the application of the braking, which requires careful setting of the PCS feedback control of the NBI and of the density.
We will carry out shot-to-shot scans of the NBI torque, of beta, of the density, and of q95.
The scan of the NBI torque is aimed at investigating the existence of an offset rotation in NTV physics for n=3 braking, and the threshold for rotation bifurcation in the induction motor model for n=1 braking. For a clear understanding of the results in very low torque cases, a day of experiments in Helium plasma is essential.
The scan of beta is aimed at investigating the effect of the plasma response during n=1 braking, and the NTV dependence on Ti and dTi/dr for n=3 braking.
The scan of the density is aimed at investigating the NTV dependence on collisionality.
The scan of q95 is aimed at investigating the effect of the plasma response during n=3 braking.
In addition to study braking by n=1 fields and by n=3 fields separately, we propose to study the combined effect of n=1 and n=3 braking, since a recent paper by Cole, Hegna, and Callen predicts an ameliorating effect of the n=3 field on the thresholds for bifurcation. |
| Background: | MPs 2007-04-02 and 2007-04-04 have begun on the effort to generate systematic scans of various parameters. Several discharges from these experiments could be use as starting points for the new experiments. In particular, these experiments have shown:
- that rotation bifurcation requires smaller vacuum field at higher beta, but with sufficiently large applied field it occurs at low beta as well
- that an island forms during the bifurcation of rotation with n=1 braking
- that the bifurcation occurs at rotation=half of the unperturbed rotation, at least for unperturbed rotation large enough that the C vs. D difference can be neglected
- that the NTV offset rotation is in the counter-Ip direction, and of the order of the ion diamgnetic rotation
- that a significant n=3 error field is present in DIII-D discharges, presumably due to the B-coil bus feed
- that odd parity vs. even parity of the n=3 field leads to the same braking, at least for the discharges considered |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
309: Simple as possible fast-ion transport by TAEs |
| Name: | William W. Heidbrink ( ) |
Affiliation: | University of California, Irvine |
| Research Area: | Energetic Particles |
Presentation time: |
Requested |
Co-Author(s): | Van Zeeland, Nazikian, Gorelenkov |
| Description: | Operate with super-Alfvenic beam ions in a regime with only a few TAEs and limited low-frequency MHD. Acquire FIDA and BES data in order to measure the TAE eigenfunction and its effect on the fast-ion profile. |
| Experimental Approach/Plan: | Use co-going Left beams. Operate at low field--probably 1.0 or 1.2 T--so the circulating beam ions satisfy the fundamental TAE resonance condition. Try to keep q95 relatively high to avoid large sawteeth or fishbones. Switch 330LT and 150LT beams to get both FIDA and BES data. |
| Background: | Attempts to explain our accurate measurements of fast-ion transport in reversed-shear plasmas have failed despite excellent measurements of the mode structure. The goal is to obtain data of comparable quality that should be easier to model theoretically as a first step to resolving this perplexing & important discrepThe expanded BES array permits the possibility of excellent eigenfunction measurements at lower fields (where ECE is unavailable). This is an ITPA experiment, MDC-11. |
| Resource Requirements: | Three co Left beams required; some other sources desirable. |
| Diagnostic Requirements: | FIDA, BES (new radial array) essential. |
| Analysis Requirements: | Match eigenfunctions with NOVA. Input modes into ORBIT. TRANSP and FIDA analysis. |
| Other Requirements: | -- |
| Title |
310: Giant sawteeth that never crash |
| Name: | William W. Heidbrink () |
Affiliation: | University of California, Irvine |
| Research Area: | Energetic Particles |
Presentation time: |
Requested |
Co-Author(s): | Kramer, Pinsker, Van Zeeland, Petty |
| Description: | Create giant sawteeth with 4th and 6th harmonic heating of deuterium beam ions. Use ECCD to arrest current diffusion, allowing operation without sawtooth crashes at q0 < 0.9 |
| Experimental Approach/Plan: | Attempt to reproduce the giant sawteeth observed in 1998, i.e., discharge 96043, using 4th harmonic heating of beam ions in a L-mode plasma. Use ECCD in two ways to increase the sawtooth period. (1) to flatten the magnetic shear near the q=1 surface. (2) As an off-axis current source to arrest current diffusion. In practice, the ECCD deposition layer will be scanned to both destabilize and stabilize the giant sawteeth. |
| Background: | There was a combined experiment with this objective in 2007. Due to the unavailability of 60 MHz power, we tried 3rd harmonic acceleration of hydrogen beams at 90 MHz but that failed to create giant sawteeth. Now we want to go back to our original plan of using 4th harmonic acceleration of deuterium beam ions. This experiment has multiple purposes: apply our outstanding Alfven eigenmode diagnostics to a new regime, accurate validation of sawtooth trigger models, and relevance to high-li AT operation. It is also an ITPA joint experiment. |
| Resource Requirements: | 1 MW of 60 MHz power essential; 2 MW of 90 MHZ power desirable. 330LT and 30 LT beams essential; others desirable. At least 2 MW of ECCD. |
| Diagnostic Requirements: | FIDA, MSE, and ECE essential, as well as all plasma profile diagnostics for sawtooth trigger validation. |
| Analysis Requirements: | Fit AE eigenfunctions with NOVA. Model fast-ion distribution with CQL3D and ORBIT-RF. Model sawtooth stability with MHD codes. |
| Other Requirements: | -- |
| Title |
311: Off-axis NBCD with a small, upward-shifted plasma |
| Name: | Masanori Murakami ( ) |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Requested |
Co-Author(s): | J.M. Park, T. Luce, W. Heidbrink, P. Gohil, D. Schissel, etc. |
| Description: | |
| Experimental Approach/Plan: | 1) Reproduce the small, upward-shifted plasmas (83300.03000) with the existing (horizontal) NBI. -2.1T/ 0.6 MA, ~10 MW. Bring the plasma back to mid-plane quickly (within 50-ms) to assure the MSE measurement.
2) Repeat the experiment with an opposite BT direction (this can be done in other Working Group)
3) Change the plasma conditions: reduce BT to 1.6 T (q95~5); Increase nebar to 6x1019. |
| Background: | |
| Resource Requirements: | Machine Time: 2 days, one day with positive (reverse) BT and negative (normal) BT on the other. (one day can be done in other Working Group area)
Number of gyrotrons: 4 desirable
Number of neutral beam sources: 7 |
| Diagnostic Requirements: | FIDA (UC, Irvine), MSE with counter-system (LLNL) |
| Analysis Requirements: | Scenario modeling with TRANSP, NUBEAM/GLF23/ONETWO |
| Other Requirements: | -- |
| Title |
312: test off-axis NBI with a small, upward-shifted plasma |
| Name: | Masanori Murakami () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | J.M. Park, T. Luce, W. Heidbrink, J. DeGrassie, P. Gohil, D. Schissel, etc.
J.M. Park, T. Luce, W. Heidbrink, J. DeGrassie, P. Gohil, D. Schissel, etc. |
| Description: | |
| Experimental Approach/Plan: | 1) Reproduce the small, upward-shifted plasmas (83300.03000) with the existing (horizontal) NBI. -2.1T/ 0.6 MA, ~10 MW. Bring the plasma back to mid-plane quickly (within 50-ms) to assure the MSE measurements.
2) Repeat the experiment with an opposite BT direction (this can be done in other Working Group)
3) Change the plasma conditions: reduce BT to 1.6 T (q95~5); Increase nebar to 6x10^19 |
| Background: | |
| Resource Requirements: | Machine Time: 2 days, one day with positive (reverse) BT direction and the second day with negative (normal) BT direction (one day can be done in Advance Scenario Development area)
Number of gyrotrons: 4 desirable
Number of neutral beam sources: 7 |
| Diagnostic Requirements: | FIDA (UC, Irvine), MSE with counter-system (LLNL) |
| Analysis Requirements: | Scenario modeling with TRANSP, NUBEAM/GLF23/ONETWO |
| Other Requirements: | No |
| Title |
313: Extend full noninductive, high performance operation |
| Name: | Masanori Murakami () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Requested |
Co-Author(s): | T. Luce, J. Ferron, JM Park, C. Greenfield, E. Doyle, et al. |
| Description: | Extend 100% noninductive, high performance for 2*tauR (~4s) |
| Experimental Approach/Plan: | 1) Start with 129830
2) Bring the start of the high power phase earlier to optimize q-profile and save NB energy
3) Work on PCS control of substituting the low power phase NB power with EC and FW heating power to save NB for high power phase
4) DND operation if we encounter beta limit problem |
| Background: | |
| Resource Requirements: | Machine Time: 2 days
Number of gyrotrons: >4
Number of neutral beam sources: 7 |
| Diagnostic Requirements: | Fast ion diagnostic (UC, Irvine), MSE(LLNL), edge reflectometer (UCLA) |
| Analysis Requirements: | |
| Other Requirements: | fast wave (both 60 and 100 MHz) |
| Title |
314: ITER steady state scenario demonstration |
| Name: | Masanori Murakami () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | T. Luce, J. Ferron, J.M. Park, E. Doyle, J. DeBoo, et al |
| Description: | |
| Experimental Approach/Plan: | |
| Background: | |
| Resource Requirements: | Machine Time: 3 days
Number of gyrotrons: >4
Number of neutral beam sources: 7 |
| Diagnostic Requirements: | Fast ion diagnostic (UC, Irvine), MSE (LLNL), edge reflectometer (UCLA) |
| Analysis Requirements: | Scenario modeling with GLF23/ONETWO, TRANSP, ONETWO analysis; CURRAY/ONETWO |
| Other Requirements: | 5-6 gyrotrons, fast wave (90 MHz and 60 MHz) |
| Title |
315: L-mode RMP thermal footprint |
| Name: | Michael J. Schaffer () |
Affiliation: | General Atomics |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Ilon Joseph, Lasnier, Boedo, Moyer, others TBD |
| Description: | Test whether an L-mode plasma displays stronger signs of stochastic THERMAL transport when subjected to resonant magnetic perturbations (RMP) than H-mode plasmas. Such behavior might be expected, because an L-mode plasma rotates less rapidly and its edge is cooler and more resistive than an H-mode plasma. The most detectable sign of stochastic thermal transport is splitting of the THERMAL divertor footprint. Such a result would establish this as a good test plasma to study stochastic thermal transport across the separatrix of a diverted tokamak. |
| Experimental Approach/Plan: | Use an DND shape with its divertor biased away from the ion grad B drift in order to postpone L-H transition. The choice of upper or lower divertor will depend on diagnostic considerations. Run relatively low density to maximize power arriving at the divertor. |
| Background: | Split particle footprints have been associated with non axisymmetric resonant magnetic pertrubations (RMP) applied to H-mode plasmas, but the power footprint seems to rarely spread beyond a nearly axisymmetric circle. This may be evidence that the H-mode pedestal was not very stochastic, even when predicted to be so by vacuum field calculations. This might happen if the RMP field were e.g. electromagnetically shielded by plasma rotation. L-mode plasmas have cooler, more resistive edge plasmas that rotate less rapidly, so they are more likely to exhibit stochastic edges and, then, split divertor footprints. If so, this would be an interesting finding in its own right. It would also make available a good test plasma to study stochastic thermal transport across the separatrix and into a spirally broadened footprint. |
| Resource Requirements: | Positive Bt if experiment is run with lower divertor. |
| Diagnostic Requirements: | Divertor and SOL diagnostics. IR TV essential for divertor power profile measurements. |
| Analysis Requirements: | Trip3d |
| Other Requirements: | -- |
| Title |
316: effect of toroidal rotation on sawtooth period |
| Name: | Ed Lazarus () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Stability |
Presentation time: |
Not requested |
Co-Author(s): | Luce, Turnbull |
| Description: | Repeat bean/oval experiments with counter beam and balanced beams.
This will explore the effects of toroidal rotation and the fast ions. The goal of this experiment is to separate the roles of thermal trapped ions, fast ion precession, and toroidal rotation on sawtooth stabilization in bean & oval shapes.
in stabilizing the sawtooth. |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | NBI, 30L & 210R
ECH, 3 gyrotrons (need heating equivalent of 1 NBI source). |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
317: localized heating in the sawtooth region in oval plamas |
| Name: | Ed Lazarus () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Do the experiment on the ECH heating (10 ms pulse) in the oval but
this time scan the radius
of heating out beyond the inversion radius.
This will provide some insight into the nature of the electron
energy transport. |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
318: Bean & Oval Sawteeth without fast ions |
| Name: | Ed Lazarus () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Stability |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Do bean/oval comparisons with bulk heating from ECH. This is at a
density high enough
for exchange heating of the ions. The purpose is to see the effect
of ion temperature on
the sawtooth period without fast ion effects (Kruskal-Oberman term).
This will also give an idea of how these shapes would respond in a more ITER-like situation.
Combine this with 316. It does fit: we want to find the stabilizing effects of toroidal rotation, fast ion precession, and thermal ions on the sawtooth for bean and oval plasmas |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
319: Stochastic thermal transport in DND |
| Name: | Michael J. Schaffer () |
Affiliation: | General Atomics |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Ilon Joseph, Petrie, Lasnier, others TBD |
| Description: | Apply a RMP field to a double-null diverted (DND) plasma. Measure footprint splitting in both upper and lower divertors and compare offline with computed footprints. Can the target powers be balanced between the two divertors? |
| Experimental Approach/Plan: | If my idea #315 for an L-mode test plasma for stochastic thermal transport experiments is successful, the present experiment should be tried with both H- and L-mode DND plasmas. |
| Background: | Most observations of split divertor footprints in DIII-D have been with single null diverted plasmas. For double nulls, one expects an stochastic edge to couple to spiral footprints in both outer divertors, but much weaker footprint splitting in the inner divertors. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | Must have IRTV data from both upper and lower divertors. |
| Analysis Requirements: | Trip3d |
| Other Requirements: | -- |
| Title |
320: Control VH-mode density rise by RMP |
| Name: | Michael J. Schaffer () |
Affiliation: | General Atomics |
| Research Area: | General FS |
Presentation time: |
Not requested |
Co-Author(s): | Jackson?, Hyatt? |
| Description: | Apply a non axisymmetric resonant magnetic perturbation (RMP) field to a VH-mode plasma in an attempt to enhance cross-separatrix particle transport and limit VH-mode particle accumulation to a tolerable level. |
| Experimental Approach/Plan: | -- |
| Background: | VH-mode has excellent confinement, but the particle confinement is so good that VH-mode is always terminated by excess density. Resonant magnetic perturbations (RMP) enhance particle transport across the separatrix. Therefore, RMP might limit the VH-mode particle accumulation to a tolerable level. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
321: RWM feedback control in ITER-like low rotation plasmas |
| Name: | Ted Strait () |
Affiliation: | General Atomics |
| Research Area: | RWM Physics |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | The goal of this experiment is to determine whether active RWM feedback control improves the stability of low-rotation plasmas above the no-wall beta limit. In contrast to previous attempts at this goal, the starting point here will be a plasma with active feedback. The key issues to be addressed are
(1) does the stability become poorer when feedback is turned off?
(2) what instabilities are encountered with and without feedback: ideal or resistive? |
| Experimental Approach/Plan: | Use a low-triangularity LSN plasma with a low no-wall beta limit. Begin with I-coil feedback turned on, using feedback parameters based on previous experience.
With beta above the no-wall limit, reduce the rotation at constant beta using counter NBI until omega_E is zero (derate the toroidal field a little, if necessary). Look for the onset of an RWM or other instability at low rotation. Document the rotation profile at onset, and the radial structure of the mode.
Repeat with feedback turned off. Also compare with intermediate values of feedback gain. |
| Background: | RWM feedback experiments in 2007 reinforced the need for active feedback control in high-beta AT plasmas to provide stability during ELMs and other transient events. These experiments also gave us confidence that the feedback system, with its present configuration and gain settings, is indeed capable of stabilizing RWMs.
However, the need and efficacy of active feedback at low rotation remains an open question. This issue has been clouded by two questions:
(1) Is feedback actually required in a quiescent plasma, or do kinetic effects stabilize the RWM down to zero rotation?
(2) At low rotation, are we still addressing the ideal-kink RWM, or is there a larger coupling to non-rotating islands which are less amenable to feedback control?
A separate proposal addresses stability at low rotation without feedback. Here we attempt to address the role of feedback at low rotation.
This issue is highly relevant to ITER design. ITER's anticipated strategy is to reserve space for "port plug" coils for RWM control. However, to make this design change credible and to keep the space from being reclaimed for other uses, we need a clear demonstration of RWM feedback control in an ITER-relevant low-rotation regime. |
| Resource Requirements: | I-coils and 24 audio amplifiers. |
| Diagnostic Requirements: | All available diagnostics should be used to determine whether the observed non-rotating modes have an ideal kink or island structure: SXR toroidal array, ECE, Thomson scattering, CER (Ti profile), MSE, maybe BES.
CER rotation measurement is also critical. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
322: Dynamic error field control for ITER |
| Name: | Ted Strait () |
Affiliation: | General Atomics |
| Research Area: | Error Fields |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | The goal of this experiment is to develop the use of feedback-controlled dynamic error field correction in low beta plasmas.
Such plasmas can develop non-rotating n=1 modes at low density, driven by error fields. As such a mode becomes marginally stable it should amplify the error field, just as RWMs do at high beta, providing input for the feedback system. |
| Experimental Approach/Plan: | Use a low-density ohmic plasma with all error correction turned off. Ramp the density down in the current flattop phase until a locked mode appears. Then turn on "slow" feedback (time constant 10-50 ms) using C-coils and SPAs. We expect to see that the feedback calls for something close to the "standard" error correction currents, and thereby avoids the locked mode.
Repeat the process in an ELMing H-mode plasma, well below the no-wall beta limit. |
| Background: | ITER is likely to have little or no capability to measure field errors directly. The field errors may also change as the coils and their support structures are cooled in the cryostat. Therefore "dynamic error field correction" in real time is likely to be required for all scenarios in ITER. However, this technique has so far been applied only in plasmas above the no-wall limit. The proposed experiment would provide the first demonstration of the technique in a wider range of operating conditions. |
| Resource Requirements: | C-coils and SPAs |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | A prerequisite is a good compensation matrix (C-matrix) in the control system to remove direct coupling of the sensors to the toroidal field, F-coils, etc. This is likely to be more critical than for dynamic error field correction at high beta. The reason is that in the high beta case, the feedback is typically turned on when the plasma current is at flattop and beta is approaching its maximum, so there is relatively little change in the coils currents. In the present low-beta case, it may be necessary to enable the feedback control early in the discharge, as the coil currents are still ramping. |
| Other Requirements: | -- |
| Title |
323: Separating role of E x B and magnetic shear in stabilization of turbulence (DOE Milestone 166) |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | J. Kinsey |
| Description: | The goal of this work is to separate the effects of magnetic shear and
E x B shear on transport in the core of tokamak discharges. |
| Experimental Approach/Plan: | Create plasmas with strong negative central magnetic shear by using a
combination of early ECH and NBI heating. The goal is to create a
q-profile similar to that in shot 117984. Referece shot used 4.5 MW
NBI starting at 50 ms to create strong NCS discharge. Replace as much
of this power with ECH as possible (5 gyrotrons desired) in order to
minimize input torque. Contrast shots with all co-injected beams with
balanced beams to vary the E x B shear while keeping the magnetic
shear the same. Determine the effect on transport and core barrier
formation. |
| Background: | Theoretical calculations indicate that both E x B shear and magnetic
shear can be stabilizing for the microturbulence which drive tokamak
transport. Prior to 2006, it was difficult to separate these effects
in experiments, since we did not have independent control of the E x B
shear in negative central shear discharges. Creation of these
discharges requires significant early heating, which required a
substantial amount of co-NBI. The co-NBI also produced significant
plasma rotation, resulting in increased E x B shear. |
| Resource Requirements: | 5 gyrotrons desired. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
324: Dependence of non-resonant magnetic braking on nu_i and v_phi profile |
| Name: | Steven A. Sabbagh ( ) |
Affiliation: | Columbia University |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | H. Reimerdes, A.M. Garofalo, W. Solomon |
| Description: | Examine the dependence of ion collisionality and rotation profile on neoclassical toroidal viscosity theory (joint experiment with NSTX) |
| Experimental Approach/Plan: | Create plasmas with weak or no low frequency rotating MHD modes (especially n = 1). Vary ion collisionality and rotation profile in relatively high stored energy plasmas. Change ion collisionality in most effective way for DIII-D, preferably (but not necessarily) at fixed q. Change rotation profile by changing NBI mix.
Operate at highest controllable elongation with good H-mode to best compare to NSTX. |
| Background: | Research on NSTX over the past several years (e.g. S.A. Sabbagh, et al., PoP 5 (2002) 2085.) has identified broad radial braking of the plasma rotation profile during RWM activity and non-resonant applied fields with the theory of neoclassical toroidal viscosity (NTV). This correlation has also been recognized in JET, and magnetic braking has been used for many years in DIII-D. Experimental results have shown quantitative agreement with NTV theory when trapped particle effects are included (W. Zhu, et al., PRL 96 (2006) 225002.). Testing the saturation of the viscosity at low collisionality and the dependence on rotation profile shape is of particular importance to ITER. The experiment can be conducted in joint fashion with NSTX to best verify the theory (e.g. aspect ratio dependence ~ (1/A)^1.5). |
| Resource Requirements: | Expect that full NBI power is needed, with maximum counter-NBI capability to best vary rotation profile. |
| Diagnostic Requirements: | Toroidal rotation profile measurement, MSE measurements |
| Analysis Requirements: | Most accurate EFIT reconstructions possible (Kinetic reconstructions with MSE, flux-isotherm constraint if available). First-principles calculation of NTV will be performed with equilibrium reconstructions as input. |
| Other Requirements: | (present with other PPPL presentations) |
| Title |
325: Comparison of RWM stabilization physics in DIII-D and NSTX |
| Name: | Steven A. Sabbagh () |
Affiliation: | Columbia University |
| Research Area: | RWM Physics |
Presentation time: |
Requested |
Co-Author(s): | H. Reimerdes |
| Description: | Test theories of RWM stabilization physics, in particular the dependence on ion collisionality, relevance of Alfven frequency, and rotation profile (joint experiment with NSTX) |
| Experimental Approach/Plan: | Compare existing DIII-D and NSTX databases on RWM marginal stability to determine what data needs to be filled in for comparison of most recent results. Analogous scans determining RWM marginal stability vs. ion collisionality and plasma rotation will be needed in plasmas with similar proximity to passive conducting structure. Comparison of the DIII-D and NSTX databases between now and the time of the experiment may yield further desired scans in otherwise similar conditions.
Create plasmas with weak or no low frequency rotating MHD modes (especially n = 1). Variations of parameters should be conducted at fixed q. Change rotation profile by changing NBI mix. Operate at highest controllable elongation with good H-mode to best compare to NSTX. |
| Background: | A first-principles understanding of the physics of RWM stabilization is a critical, but elusive goal in RWM research. Various physical theories have been proposed for RWM stabilization, however, a unified physics model has not yet been found to explain results observed in all devices. A large database of results has been generated by DIII-D and NSTX, and initial joint experiments yielded some common understanding (H. Reimerdes, et al., PoP 13 (2006) 056107.) Experiments conducted on both DIII-D and NSTX since the original joint experiments have generated new questions and insights (e.g. influence of error field, rotation profile, and ion collisionality). The potential of RWM stabilization at low rotation via trapped particle precession drift resonance also suggests comparison between DIII-D and NSTX to examine experimental differences due to aspect ratio. |
| Resource Requirements: | Expect that full NBI power is needed, with maximum counter-NBI capability to best vary rotation profile. |
| Diagnostic Requirements: | Toroidal rotation profile measurement, MSE measurements |
| Analysis Requirements: | Most accurate EFIT reconstructions possible (Kinetic reconstructions with MSE, flux-isotherm constraint if available). |
| Other Requirements: | (present with other PPPL presentations) |
| Title |
326: Exploring the assumptions built in the RWM models: Hu-Bettie-Manickam and MARS codes |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | M. Chance, M. Chu, J. Manickam, A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | Theoretical models for the RWM stabilization have been developed by several groups including various complex stabilizing processes. Among them, MARS code and Hu-Betti-Manicham codes are very comprehensive and should reflect the realistic experimental conditions. These predictions have been found in the range of experimental observations. The detailed comparison between the experiments and the models is the next step we should pursue.
However, through recent workshops and conferences, we have started to notice that there exist potentially- significant differences in the built-in assumptions, which could be important more than simple agreement with experimental results.
Here, some differences are summarized. We propose to design the experiment for assessing their built-in assumption by examining one aspect of their predictions. Our aim is to assist the refinement of these codes as well as our understanding |
| Experimental Approach/Plan: | Details
According the materials presented at workshops by the two groups, there seem to exist potentially important differences between these codes.
Here, some differences of their built-in assumption are summarized.
MARS-F
Particle bouncing
(Including trapped particle and drift) ---yes
Diamagnetic drift---------------------------no
Ex B------------------------------------------yes
Eigen-mode pattern used------------------consistent with rotation profile
Volume integration scheme---------------large aspect ratio approximation
Bo-Hu-Manicham
Particle bouncing
(Including trapped particle and drift)---yes
Diamagnetic drift--------------------------yes
Ex B-----------------------------------------yes
Eigen-mode pattern used-----------------with no rotation profile
Volume integration scheme--------------full 2D geometry integral
One of conclusion of RWM driving energy source
MARS-F---------------------------------------------strongly localized near the off-axis
Bo-Hu-Manicham----------------------------------peaked near the central area
Experiment
This difference of stability localization could be related to the diamagnetic effect, eignmode pattern and the volume integration scheme. As an initial step, we propose to examine that pressure profile or q-profile dependence. Especially, the study of pressure profile peaking dependence can provide insight in the modeling.
The plasma condition can be made with low rotation target like 127941. The NBI energy may be needed to be adjusted for modifying the pressure profile peakingness |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
327: Understanding the role of wall sources and sinks during RMP H-modes |
| Name: | Todd E. Evans () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | tbd |
| Description: | The goal of this experiment is to understand the relative importance of wall sources and sinks in determining the rate of density decay and the saturated density level during RMP ELM control experiments. Can the density decay rate and final density in the ELM suppressed state be altered with plasma shape changes, the lenght of the glow between plasma discharges or the delay between the L-H transition and the I-coil pulse. |
| Experimental Approach/Plan: | Establish long reproducible ELM suppressed RMP H-modes with the largest possible I-coil current starting at approximately the same time as the first ELM following the L-H transition with 7 minute glow between plasmas. Reproduce this case at lease 4 times or until the rate of density decay remains constant from shot to shot. Delay the start of the I-coil pulse by 1 s and compare the denstiy decay rate and saturated density level with the previous shots. Repeat this sequence several times adding a 1 s delay in the I-coil pulse at each step. Reduce the length of the glow to 3 minutes and repeat that last few steps of the previous case. Repeat with no glow. If time premits repeat the 7 minute glow sequence with dRsep increased to approximately zero and the upper x-point positioned for maximum pumping with the upper cyropumps. |
| Background: | Previous RMP H-mode experiments have shown significant differences in the amount of density pump out that appears to be related to changes in wall conditions (i.e., the relative contributions of neutral sources and sinks dur to the walls). In some cases the saturated density during the ELM suppressed phase is of order 50-60% of that before the I-coil pulse and in other cases it is of orser 5-10% of the pre-I-coil density. An analysis of the cryopump data indicated that these differences are not due to changes in the pumping throughput. It is important to understand the wall are involved in the density pump out effect because the wall conditions in ITER will be very different than those in DIII-D and the RMP may not result in a large density pump out in that case. There is also evidence that the level of the saturated density is not a critical parameter for ELM suppression suggexting that the physics of RMP EM suppression may not be uniquely related to changes in the pedestal pressure gradient. |
| Resource Requirements: | 7 kA I-coil and stable wall conditions (i.e., ths experiment should not be scheduled following any days that will have an adverse effect on the condition of the walls). |
| Diagnostic Requirements: | ELM and pedestal diagnostics |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
328: Fast wave heating and current drive in AT plasmas |
| Name: | Masanori Murakami () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Not requested |
Co-Author(s): | C. Petty, R. Pinsker, W. Heidbrink, W. Baity, and Adv. Scenario Develop groups |
| Description: | (1) Robust coupling to AT plasma
(2) Characterize beam ion absorption of FW power at 90HZ and 60MHz
(3) Validate scenario modeling of FWCD in AT |
| Experimental Approach/Plan: | 1) Reproduce shot #123159 and/or baseline NBI-plasmas ) [BT=1.85T, Ip=1.2 MA,nebar=3.5e19, NB=9.3 MW]
2) Study q0 control using co- and counter-FWCD in the AT plasmas.
3) Use PCS control of q0 if available. The push-pull operation with two ICRF systems is highly desirable. |
| Background: | |
| Resource Requirements: | Machine Time:1 day Experiment; after successful demonstration of FWCD in AT plasmas (for ICRF and PCS operation); minimum residual hydrogen
Number of gyrotrons: 4
Number of neutral beam sources: 5 |
| Diagnostic Requirements: | Fast ion diagnostic (UC, Irvine), edge reflectometer (UCLA) |
| Analysis Requirements: | CURRAY/ONETWO, TRANSP, ONETWO; SciDAC-RF [AORSA/CQL3D; ORBIT-RF/TORIC, etc]; RANT3D |
| Other Requirements: | Fast wave systems (90 and 60 MHz) required |
| Title |
329: Role of ECCD in sustaining steady state NCS scenario |
| Name: | Masanori Murakami () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Not requested |
Co-Author(s): | T. Luce, C. Petty, M. Wade, R. Prater, C. Greenfiled, etc. |
| Description: | Document the role of off-axis ECCD in sustaing 100% noninductive, AT operation, in particular, broad versus narrow and radial location of ECCD deposition |
| Experimental Approach/Plan: | |
| Background: | |
| Resource Requirements: | Machine Time: 1 day
Number of gyrotrons: 5 (or >2.5)
Number of neutral beam sources: >5 |
| Diagnostic Requirements: | Fast ion diagnostic (UC, Irvine) |
| Analysis Requirements: | TRANSP; PEST3; ONETWO;TWIST,GATO,DCON |
| Other Requirements: | -- |
| Title |
330: ITER accessibility to hybrid regime using RF |
| Name: | Masanori Murakami () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | J.M. Park, R. Pinsker, W. Baity, D. Rasmussen, J. Hosea, C. Petty, et al., |
| Description: | 1) Study the accessibility of hybrid regime using substantial RF power in ITER-shape plasmas
2) Sustain q(0)>1 with FWCD while 3/2 or 4/3 tearing modes feedback stabilized
3) Gain experience of FW operation with ELMing H-mode with a relatively large gap |
| Experimental Approach/Plan: | 1) Scenario modeling study to seek optimal strategy for accessibility and sustainment of hybrid scenario in ITER-shaped plasma in DIII-D
2) Reproduce shot like 119733, and apply counter-FWCD
3) Adjust power to find L-H threshold power, and lowest betaN for hybrid operation
4) Settle at a baseline (ITER-like) condition and characterize RF operation (optimal coupling, etc)
5) Study maintenance of q(0)>1 with FWCD while ECCD stabilize 3/2 or 4/3 NTM |
| Background: | |
| Resource Requirements: | Machine Time: 2 days
Number of gyrotrons: 4
Number of neutral beam sources: 7 |
| Diagnostic Requirements: | Fast ion diagnostic (UC, Irvine), edge reflectometer (UCLA) |
| Analysis Requirements: | |
| Other Requirements: | fast wave (both 90 and 60 MHz) |
| Title |
331: ITB in ITER steady state scenario |
| Name: | Masanori Murakami () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | J.M. Park, E. Doyle, J. DeBoo, T. Luce, J. Ferron, et al., |
| Description: | |
| Experimental Approach/Plan: | 1) Scenario modeling study to seek optimal strategy for accessibility and sustainment of high-qmin AT with ITER-shape
2) Reproduce DIII-D classical high-qmin AT discharge (111203) [or possibly BT-ramp-down betaN=4 shot (122976)], but ITER-shape like 125946.
3) Adjust timinig of the high power phase
4) Add broadly distributed ECCD
5) Apply FWCD to control q(0) and increase off-axis ECCD |
| Background: | |
| Resource Requirements: | Machine Time: 2 days
Number of gyrotrons: 4
Number of neutral beam sources: 7 |
| Diagnostic Requirements: | fluctuation diagnostics; Fast ion diagnostic (UC, Irvine) |
| Analysis Requirements: | |
| Other Requirements: | 5-6 gyrotrons, fast wave (90 MHz and 60 MHz) |
| Title |
332: Comparison of high beta_p small ELM regime in DIII-D and JT-60U |
| Name: | Naoyuki Oyama ( ) |
Affiliation: | JAEA |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | A.Leonard, T. Osborne, Y. Kamada, H. Urano, K. Kamiya |
| Description: | Final goals of this inter-machine experiment are to establish H-mode plasma operation with small ELMs and extension of operational regimes for these small ELM regimes to ITER relevant plasmas. Especially, the effect of the toroidal rotation should be confirmed by using the unique capability of rotation control with co- and counter- NBs in DIII-D and JT-60U. (ITPA inter-machine experiment PEP-17) |
| Experimental Approach/Plan: | A search through the extensive DIII-D database of high beta_p discharges did not reveal grassy ELM regime so far. In JT-60U, on the other hand, grassy ELMs with ELM frequency of ~400 Hz was obtained with zero plasma rotation in high q (q95>6) and high delta(d>0.5) plasmas.
Therefore, following experiments will be proposed in DIII-D.
1) The first attempt will be a beta_p scan to reproduce small ELMs in DIII-D following the grassy ELM recipe with balanced NB injection (balanced NB injection + more co NBIs to increase beta) in high q and high delta plasmas.
2) Once we obtain small ELM similar to grassy ELM in DIII-D, parametric dependence of important parameters (delta , q95, beta_p and VT) to enter the grassy ELM regime will be compared between DIII-D and JT-60U. |
| Background: | Small ELM regimes have been intensely studied in several devices. The grassy ELM regime discovered by JT-60U is a candidate for a small ELM operation in ITER to combine tolerable ELM energy losses at low pedestal collisionality, and no degradation of pedestal pressure. Since the grassy-like ELMs has been observed in AUG and JET following the grassy ELM prescription developed in JT-60U, we expect that similar small ELM regime can be established also in DIII-D. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
333: Turbulence dependence on rho_* via working gas species (Hydrogen and Helium) |
| Name: | Terry L. Rhodes ( ) |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | Peebles |
| Description: | Use dimensionally similar helium and hydrogen plasmas with matched Te, Ti, �?� to compare fluctuation and transport properties. Direct tests of turbulence simulation will be performed. |
| Experimental Approach/Plan: | Use helium and hydrogen plasmas with matched Te, Ti values. Te, Ti ratios and profiles will be adjusted using ECH, co and counter neutral beams. The rotation and radial electric fields will also be monitored and matched as possible. Use will be made of all the available turbulence and other diagnostics as appropriate. If successful the approach can be modified to examine shaped plasmas, H-mode/QH-mode plasmas, etc. |
| Background: | There is a well known dependence of the plasma confinement on the mass of the working gas, varying approximately as (Mass)^0.5. This variation will be addressed by comparing helium and hydrogen plasmas with Ti, Te matched as closely as possible. This should give approximately the same rho_i,e but of course different working gas masses. Theoretical turbulence expectations appear to depend upon the value of rho_i,e rather than the mass itself so the naïve expectation is that the plasmas should be very similar. Comparison of low, intermediate, high k turbulence, transport analysis, etc. will be made between the plasmas and theoretical expectations (analytic, numerical �??GYRO, GS2,�?�) . |
| Resource Requirements: | Hydrogen and helium plasmas, ECE, co and counter NBI |
| Diagnostic Requirements: | low, int, high k scattering diagnostics, Doppler
backscattering, CECE, BES |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
334: Deuterium and carbon SOL flows in USN plasmas using toroidally symmetric CD4 injection |
| Name: | Mathias Groth ( ) |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Integrated Modeling |
Presentation time: |
Requested |
Co-Author(s): | G.D. Porter, and the integrated modeling and boundary physics groups |
| Description: | Validate UEDGE SOL model with cross-field drifts by measuring the deuterium and low-charge state carbon ion velocities in the main SOL/pedestal regions in well-characterized L-mode and ELMing H-mode plasmas |
| Experimental Approach/Plan: | Use upper single-null magnetic configurations to give reciprocating probe access to crown of the plasma, use CD4 puffing from lower outer plenum to enhance carbon emission in the crown for lower divertor tangential cameras;
1) L-mode density scan in forward and reversed BT configuration,
2) ELMing H-mode density scan in forward and reversed BT configuration |
| Background: | Anamalously large scrape-off layer flows have been measured in the main SOL at the crown of the plasma. These flows can significantly affect/determine divertor detachment and impurity migration from the main chamber to the divertor plates. Our previous measurements in low-density L-mode plasmas have shown that the carbon injected into the crown of the plasma gets entrained in the deuterium ion flow, reaching Mach speeds of up to 0.5 of the plasma sound speed. Our proposal extends the range of measurements to plasmas at higher density in both L-mode and H-mode confinement regimes. |
| Resource Requirements: | 2x1-day experiment in forward and reversed BT configurations, repeat discharges for additional diagnostic settings, density scan: attached to detached divertors |
| Diagnostic Requirements: | Reciprocating probes at outer midplane and crown (x-point probe)
MDS spectrometer (tangential views)
MDS spectrometer for Te measurements in inner divertor
Tangential cameras (divertors, inner and outer midplane)
Langmuir probes
Filterscopes
CER |
| Analysis Requirements: | Profiles of Jsat, ne, Te, and D+ v (RCPs, fixed probes)
Flow velocities of C1+, C2+ ions (MDS)
High-n Balmer line analysis for divertor Te
Image analysis CD, CI, CII, CIII, CIV (tangential TVs)
CVI and CIV CER analysis |
| Other Requirements: | UEDGE analysis |
| Title |
335: Deuterium and carbon SOL flows in LSN or USN ELM-suppressed H-mode plasmas |
| Name: | Mathias Groth () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | M.E. Fenstermacher, and the ELM Control, Integrated Modeling, and Boundary Physics groups |
| Description: | Measure the deuterium and low-charge state carbon ion velocities in the main SOL/pedestal regions in well-characterized ELM-suppressed H-mode plasmas |
| Experimental Approach/Plan: | Use lower single-null or upper single-null (preferred!) configurations that permit ELM-suppressed operation, use CD4 puffing from upper or lower outer plenum to enhance carbon emission in the crown for divertor tangential cameras |
| Background: | Anomalously large scrape-off layer flows have been measured in the main SOL at the crown of the plasma. These flows can significantly affect/determine divertor detachment and impurity migration from the main chamber to the divertor plates. Our previous measurements in low-density L-mode plasmas have shown that the carbon injected into the crown of the plasma gets entrained in the deuterium ion flow, reaching Mach speeds of up to 0.5 of the plasma sound speed. This proposal extends the range of plasmas to ELM-suppressed H-mode confinement regimes. |
| Resource Requirements: | 2x1/2-day experiment in forward and reversed BT configurations, repeat discharges for additional diagnostic settings; density scan, but stay in ELM-suppressed regime |
| Diagnostic Requirements: | Reciprocating probes at outer midplane and crown (x-point probe)
MDS spectrometer (tangential views)
MDS spectrometer for Te measurements in inner divertor
Tangential cameras (divertors, inner and outer midplane)
Langmuir probes
Filterscopes
CER |
| Analysis Requirements: | Profiles of Jsat, ne, Te, and D+ v (RCPs, fixed probes)
Flow velocities of C1+, C2+ ions (MDS)
Image analysis CD, CI, CII, CIII, CIV (tangential TVs)
CVI and CIV CER analysis |
| Other Requirements: | UEDGE analysis |
| Title |
336: Effect of core plasma rotation of deuterium and carbon SOL flows |
| Name: | Mathias Groth () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Boundary, integrated modeling, and rotation physics groups |
| Description: | Measure the deuterium and low-charge state carbon ion velocities in the main SOL/pedestal regions in unbalanced and balanced-beam H-mode plasmas |
| Experimental Approach/Plan: | Use upper single-null configurations to give reciprocating probe access to crown of the plasma, use CD4 puffing from upper or lower outer plenum to enhance carbon emission in the crown for divertor tangential cameras; change momentum input by NBI injection from co-current to balanced to counter-current |
| Background: | Anomalously large scrape-off layer flows have been measured in the main SOL at the crown of the plasma. These flows can significantly affect/determine divertor detachment and impurity migration from the main chamber to the divertor plates. One of the most pressing questions is how core rotation affects flows in SOL versus how SOL flows affect core rotation and the L-H threshold power. This proposal attempts to provide first SOL flow measurements in DIII-D in unbalanced and balanced H-mode plasmas. |
| Resource Requirements: | 1-day experiment in forward BT/IP configurations, repeat discharges for additional diagnostic settings |
| Diagnostic Requirements: | Reciprocating probes at outer midplane and crown (x-point probe)
MDS spectrometer (tangential views)
Tangential cameras (divertors, inner and outer midplane)
Langmuir probes
Filterscopes
CER |
| Analysis Requirements: | Profiles of Jsat, ne, Te, and flow (RCPs, fixed probes)
Flow velocities of C1+, C2+ ions (MDS)
Image analysis CD, CI, CII, CIII, CIV (tangential TVs)
CVI and CIV CER analysis |
| Other Requirements: | UEDGE analysis |
| Title |
337: Control of SOL flows by Puff & Pump |
| Name: | Mathias Groth () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Boundary physics group |
| Description: | -- |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
338: Carbon migration in the divertor using the C13 method |
| Name: | Mathias Groth () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Not requested |
Co-Author(s): | S.L. Allens and the Hydrogen Retention, Integrated Modeling, and Boundary Physics groups |
| Description: | Simulate carbon erosion at outer plate as the dominant carbon source and its migration using trace carbon-13; this experiment may be combined with oxygen bake |
| Experimental Approach/Plan: | Establish quiescent L-mode plasma, low density as in 2003 with outer strike inboard of the pumping plenum; inject methane C12H4 (or C12D4) at trace level from lower outer plenum into outer divertor common SOL -> establish lowest acceptable injection amount; characterize divertor conditions; repeat methane injection on the following day, but use C13H4; 10+ discharges to inject sufficient amount of C13; remove tiles during vent; this experiment requires to be run on the last day of the campaign!
Alternatively, this experiment could also be exectuted in low-density H-mode, however, ELMs will make interpretation of experimental results more complicated. Also, there will be no direct comparison to 2005 detached H-mode. |
| Background: | The 2003 and 2005 C13 experiments were performed in a lower single null configuration with C13H4 injection from the upper outer plenum to simulate carbon erosion being dominant from the main chamber above the midplane. The injected C13 is entrained in the SOL flow toward the inner plate, and deposited at the inner plate (2003 attached L-mode), and the inner plate and private flux region (2005 detached H-mode). The proposed experiment intends to contrast the 2003 results by injecting C13H4 into the outer divertor SOL (common flux region) and measuring the C13 deposition post-mortem. The following questions will be answered: will a dominant outer plate source lead to a similar deposition at the inner plate as seen in the 2003 experiment? What is the dominant mechanism of carbon transport between the outer and inner divertor: the 'long way' via the main SOL versus the 'short way' across the private flux region? |
| Resource Requirements: | 2 days of DIII-D operations at the end of the experimental campaign; C13H4 injection from the lower outer plenum; little requirement on heating power if executed in L-mode |
| Diagnostic Requirements: | All available SOL diagnostics, including MDS, tangential cameras, RCPs, DTS, fixed Langmuir probes; also CER |
| Analysis Requirements: | Analysis of SOL flows from tangential MDS and RCPs (midplane and lower divertor), UEDGE and OEDGE modeling of C13H4 injection and carbon transport |
| Other Requirements: | Experiment can be combined with oxygen bake |
| Title |
339: Control of the heat and particle flux in radiative divertors |
| Name: | Mathias Groth () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | General PCO |
Presentation time: |
Not requested |
Co-Author(s): | S.L. Allen, D. Humprheys, T.D. Petrie, and the Boundary Physics, Plasma Control, and Core-Edge Integration groups |
| Description: | Develop and demonstrate stable, feedback-control, radiative divertor scenarios. Identify suitable sensor (e.g., bolometer channel, filterscope, Langmuir probe, IRTV) and actuators (gas valves in the divertor). Test feedback in several operating regimes (e.g., with type-I ELMing toward detached divertor) |
| Experimental Approach/Plan: | Select one of our established radiative divertor scenarios as starting point. Identify sensors and actuators. Run this scenario in feedback control. Scan collisionality (density and power) to test feedback |
| Background: | Control of the detachment (ionization) front is instrumental in future devices (=ITER!) with strong heatfluxes to the target plate. To reduce the heat flux in ITER, the currently envisioned scenario foresees radiative divertors using Ne and Ar seeding. However, stable divertor operation must be demonstrated in present devices, including the feedback-controlled position of the detachment front. Large, type-I ELMs may still burn through the detachment front, requiring a novel feedback approach. |
| Resource Requirements: | As part of radiative divertor program (core-edge integration) develop feedback control. Dedicate run time when feedback loop is programmed in PCS. |
| Diagnostic Requirements: | Bolometer, floor Langmuir probes, filterscope, IRTV -> sensors must be accessible by PCS |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
340: Low triangularity, low nu*, RMP ELM control |
| Name: | Todd E. Evans () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | tbd |
| Description: | The goal of this experiments is study the heat flux splitting in RMP ELM suppressed H-modes by using the upper cryopumps to obtain low density (nu*) in a slightly downward biased plasma with the lower outer strike point positioned on top of the lower shelf where it can be seen by the IR and DiMES cameras. |
| Experimental Approach/Plan: | Using the shape described above, obtain the lowest possible density by optimizing the pumping due to the upper (inner and outer) and the lower outer cryopumps. This will require adjusting dRsep and the x-point positions. Do an I-coil current and phase scan with the highest NBI power possible (lowest nu*) to obtain strike point splitting data. Using the best ELM suppressed case, do an NBI power scan to assess how the splitting scales with nu*. If we are successful in obtaining RMP ELM suppression in this configuration future experiments will designed ot test other aspect of RMP physics will benefit. |
| Background: | In LSN ITER similar shapes the OSP is not within the giew of the IR cameras or the DiMES TV so the only way to measure strike point splitting is to move the OSP inward. This reduces the pumping due to the lower cryopump and the density increases until small ELMs return which then make it difficult to observe OSP splitting. A critical issues for understanding RMP ELM control and steady-state heat flux control in RMP H-modes is the level of heat flux on the target plates in the ELM suppressed state. These measurements will also help us understand the energy trnasport in RMP H-modes and the degree of RMP penetration (i.e., the level of stochasticity) across the pedestal. |
| Resource Requirements: | I-coil, upper and lower cryopumps, 7 NBI sources |
| Diagnostic Requirements: | lower divertor IR cameras (2 toroidal positions if possible), DiMES TV, filterscopes, tangential TVs and all the standard ELM diagnostics. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
341: Investigation of edge ne profile, fluctuations, and particle transport during RMP |
| Name: | Lei Zeng () |
Affiliation: | University of California, Los Angeles |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | T.E. Evans, R.A. Moyer, M.E. Fenstermacher, and UCLA group |
| Description: | The goal of this experiment is to investigate the edge density and fluctuations by reflectometers and turbulence measurements for different RMP amplitudes during ELM suppression phase in the low collisionality plasma, and compare to the theoretical models. |
| Experimental Approach/Plan: | Setup low collisionality ELM suppressed operation. For I-coil current scan, or different current, measure edge density profile via profile reflectometer, density fluctuations via FIR, correlation reflectometer, Doppler reflectometer, BES and Langmuir probe, Te fluctuation from CECE. Also, measure the Er from CER. Compare ne values at separatrix and top of pedestal, and others to the prediction from Tokar model. Study the mechanism of particle transport, ExB convection or charged particle flow. |
| Background: | Although ELM has been successfully suppressed by using a stochastic magnetic boundary which is generated by I-coil, the mechanism of particle and thermo transports is not very clear. It is believed that particle transport in low collisionality is possibly caused by ExB convection during ELM suppression. Currently, Tokar model shows particle transport is due to charged particle flow, and thermo transport is interpreted by the reduction of perpendicular neoclassical transport with decreasing density and nonlocality of parallel heat transport. In DIII-D, the advanced turbulence and profile measurements are good to test the model and mechanisms. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | turbulence measurements and reflectometer |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
342: Formation and radial propagation of ELM filament structure in DIII-D |
| Name: | Lei Zeng () |
Affiliation: | University of California, Los Angeles |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | UCLA group, D.L. Rudakov, J.A. Boedo, G.R. Mckee, M.E. Fenstermacher, M. Groth, C.J. Lasnier, P.B. Snyder |
| Description: | |
| Experimental Approach/Plan: | It is important to generate ELMing (type I) plasma with large outer gap (>= 20 cm, as large as possible). Use fast profile reflectometer, BES, Langmuir probe, Thomson scattering and fast camera to measure ELM filament structure. And use FIR scattering and fluctuation reflectometer to monitor the density fluctuations during ELM. Scan Bt from 1.7 to 2.1 T. Scan line-average density. |
| Background: | The ELM filament structure has been observed in DIII-D , MAST and other devices. Thomson scattering in MAST shows a bump structure in the outboard edge density profile during an ELM event, directly resolving the filament structure in radius. In DIII-D, we have fast profile reflectometer measurement with >= 10 micro-sec time resolution which is good to track the density profile evolution associated with ELM. Although the measurement can not resolve non-monotonic density profile, a flat shoulder in the measured profile may indicate a bump structure existed. Also, other diagnostics in DIII-D such as Langmuir probe, TS, BES and fast camera can resolve the filament as well. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
343: DiMES: Exposure of CVD diamond film |
| Name: | Steven Lisgo ( ) |
Affiliation: | UKAEA |
| Research Area: | Boundary |
Presentation time: |
Requested |
Co-Author(s): | D. Rudakov |
| Description: | Expose a chemical vapour deposited (CVD) diamond coated molybdenum DiMES sample to a detached divertor plasma. |
| Experimental Approach/Plan: | Restore discharge 130122 @ 3.5 s: detached L-mode with the outer strike-point at the DiMES radius. It is important to start the strike-point significantly outside the DiMES radius and only move it inward once the plasma is detached, in order to avoid exposure of the sample to an attached plasma. |
| Background: | Recent advances in CVD methods and technology have allowed the production of relatively low cost polycrystalline diamond films. Diamond is an interesting candidate plasma facing material because of its high thermal conductivity and very low reactivity with hydrogen, i.e. chemical sputtering is nominal in laboratory hydrogenic plasmas. Unfortunately, it is also an electrical insulator in it's pure form and has a very low coefficient of thermal expansion, which are issues due to the potential for arcing and delamination, respectively. However, diamond may be a suitable strike-point material for a detached divertor, where the reduced plasma flux could mitigate these unfavourable properties. |
| Resource Requirements: | 0.5 day: diamond exposure to a detached plasma to test for arcing
0.5 day: same as above, but with Ar/Ne seeding to test for erosion |
| Diagnostic Requirements: | Langmuir probes near DiMES radius, tangential divertor cameras (Dalpha, Dgamma, CII and C III), divertor Thomson, DiMES TV, MDS (DiMES view). |
| Analysis Requirements: | None. |
| Other Requirements: | None. |
| Title |
344: Search for the critical ExB velocity shear for ITG and ETG |
| Name: | Lei Zeng () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | UCLA group |
| Description: | The goal of this experiment is to search for the critical ExB velocity shear for ITG and ETG turbulences. |
| Experimental Approach/Plan: | Use CER and Doppler reflectometer to measure Er, in order to get ExB velocity shear. Use FIR to measure low-k , intermediate-k turbulence, and back scattering for high k. For the ITB plasma (maybe QDB operation), scan ExB velocity shear in ITB by changing the NBI and measure the turbulence associated and compare to simulations. |
| Background: | The results from many devices have observed short-k turbulence reduces and ExB shear increases after the formation of ITB. Theoretical simulation shows the critical ExB velocity shear is smaller than vti/Ln for suppression of ITG and short wavelength ion mode (SWITG), however, the critical shear for ETG is much larger [PoP, vol. 11, p. 3053]. In DIII-D, it is possible to search for the critical ExB velocity shear for ITG and ETG modes experimentally, since we have a verity of turbulence diagnostics covering a large range of k space, counter beams may provide velocity shear control. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
345: Is high-k turbulence a significant contributor to the transport dynamics in the pedestal of H-mode? |
| Name: | Terry L. Rhodes () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | Groebner, Schmitz, McKee, Wang, Zeng. Moyer |
| Description: | This is really a more general H-mode plasma experiment than the title indicates. We propose to characterize to the highest extent possible the plasma behavior leading up to and transitioning to H-mode utilizing the full extent of the upgraded, new, and existing turbulence diagnostics. In particular we will examine the role of the high k ETG scale fluctuations in H-mode however the scope will include low and intermediate k as well (i.e. ITG and TEM scales). We will also examine to the best extent possible the variation of the turbulence and transport in the radial transition region between the steep gradient region and in the flatter internal region. ECH and beam heated H-modes will be utilized to allow the largest diagnostic access. Note that set of companion discharges in hydrogen would likely produce significant information. |
| Experimental Approach/Plan: | Plasmas designed for significant diagnostic access. Different H-mode access routes will be investigated, NBI, ECH, USN going to LSN at constant power. The extension to hydrogen plasmas would be very desirable. |
| Background: | -- |
| Resource Requirements: | 1 day. |
| Diagnostic Requirements: | all fluctuation diagnostics, fast profile reflectometers. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
346: Effect of ECH on low, intermediate and high k turbulence during density pumpout |
| Name: | Terry L. Rhodes () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | Peebles, Casper, Schmitz, White, McKee, Zeng, Wang |
| Description: | |
| Experimental Approach/Plan: | Utilize ECH in Ohmic, L, and H-mode plasmas to modify the local drive terms. Select target plasmas based upon previous runs which either showed a strong or no effect. |
| Background: | -- |
| Resource Requirements: | ECH |
| Diagnostic Requirements: | all fluctuation diagnostics, fast profile reflectometers |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
347: Magnetic shear dependence of low, intermediate and high k turbulence and GK simulation predictions |
| Name: | Terry L. Rhodes () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport Model Validation |
Presentation time: |
Requested |
Co-Author(s): | Peebles, Holland, Schmitz, McKee, Wang |
| Description: | Both analytic and numerical results indicate an increase in ETG turbulence levels as the magnetic shear is increased. Analytic growth rate calculations show ITG growth rates decreasing with increasing shear. Analytic TEM growth rates appear to be insensitive to the magnetic shear. By varying the shear and keeping the other important drive parameters roughly constant (the difficult part!) we will determine if these predictions hold up. Compare results to theory and simulation (e.g. GYRO, GS2, ..). |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | all fluctuation diagnostics. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
348: Testing of VPS-W coating on Cu heat sink from ASIPP |
| Name: | Clement Wong ( ) |
Affiliation: | General Atomics |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Guang-Nan Luo, Dmitry Rudakov, Phil West, Matt Baldwin, Russ Doerner |
| Description: | W surface material is projected to be utilized for ITER, advanced tokamaks and DEMO. We would like to make use of the DiMES and MiMES system to test different thick W coatings on Cu heat sinks in DIII-D. Different W-coatings deposited by vacuum plasma spray (VPS) on Cu buttons will be exposed in helium plasma discharges. |
| Experimental Approach/Plan: | Different W coated Cu heat sink button samples, with different W coating thicknesses, will be loaded onto DiMES and MiMES samples. The samples will be exposed to as many detached He or D2/He plasma discharges as possible, and at different surface temperature provided by resistive heating or by plasma contact. |
| Background: | VPS-W/Cu heat sink design is proposed for the plasma facing components for EAST. But there is uncertainties on surface erosion, disruption tolerance and helium ion damage on W-surface materials at different surface temperatures. It is important to acquire integrated and controlled experimental data in an operation tokamak like DIII-D to study the effects for the design and fabrication of advanced limiter and divertor in EAST, ITER and future steady state operation tokamaks. |
| Resource Requirements: | DIII-D operation and DiMES and MiMES system with material button samples. |
| Diagnostic Requirements: | All the outboard chamber and lower divertor diagnostics and the core performance diagnostics. |
| Analysis Requirements: | Surface analysis from EAST and US laboratories like PISCES and SNL. (M. Bladwin, R. Doerner, W, Wampler) |
| Other Requirements: | -- |
| Title |
349: Test of importance of rotation in QH-mode using the I-coil for rotation and density control |
| Name: | Tom Osborne ( ) |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | K. Burrell, M. Fenstermacher, T. Evans, P. Snyder |
| Description: | The goal of this experiment is three fold: 1) The I-coil is used to vary the plasma rotation and thereby test the importance of rotational shear in QH-mode independent of the CO/CNTR beam (and therefore fast ion orbit) mix 2) The I-Coil is used to eliminate the density rise which occured in previous attempts to increase the CO beam fraction in QH-mode separating the effect of the density rise from the CO/CNTR beam fraction in loss of QH-mode at increased CO/CNTR fraction. 3) Develop the RMP as a pedestal density control method to extend QH-mode operation to less favorable discharge shapes which could impact the possibility of QH-mode operation in ITER. |
| Experimental Approach/Plan: | 1) Use I-Coil field (perhaps fully non-resonant odd parity) to reduce rotation in a QH-mode discharge and look for loss of QH-mode or changes in EHO character. 2) Apply resonant or near resonant RMP field to maintain density at fixed level during CO/CNTR beam fraction scan. 3) Use resonant RMP to reduce pedestal density while maintaioning central density to extend QH-mode operation to 'unfavorably' shaped (ITER shape) discharge otherwise poor access to low n peeling instabilites. |
| Background: | In a model proposed by Phil Snyder, QH-mode requires a combination of high rotational shear and access to the low n peeling/ballooning regime. In previous results QH-mode was lost and the discharge began to ELM when the CO/CNTR beam fraction reached 20%. As CO/CNTR fraction increased however there was also an increase in pedestal density as well as a change in fast ion orbits (and associated change in fast ion population in the pedestal) which made it difficult to separate the rotational effects. In these experiments the RMP coil will be used to control the plasma rotation. Braking of the plasma rotation may be achievable with only non resonant fields (odd parity I-coil connection). Density control with the I-coil has been shown to be effective over a wider range of q than required for ELM suppression and for the density control experiment then even parity will be used but q will not likely have to at 3.6. |
| Resource Requirements: | I-coil with possible flips from odd to even parity. Reverse Ip for primary CNTR injection. |
| Diagnostic Requirements: | Any QH-mode iexperiments in the future, particularly where ELMs and EHO will be mixed, should the have the possibility of getting BES and fast UCSD camera data to try to understand the EHO structure and its relationship to the ELM precurson. CER and TS are required |
| Analysis Requirements: | Profiles including rotation, kinetic EFIT, ELITE stability, etc. |
| Other Requirements: | Low recycling machine conditions (not after disruption mitigation or Ar puff experiments for example). |
| Title |
350: Giant Sawtooth control with Alfven Eigenmodes in ITER |
| Name: | Gerrit J. Kramer ( ) |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Energetic Particles |
Presentation time: |
Not requested |
Co-Author(s): | G.J. Kramer, R. Nazikian, M. van Zeeland, B. Heidbrink, N.N. Gorelenkov |
| Description: | Sawteeth in DIIID can be stabilized by a combination of NBI and ICRF heating.
The stabilization occurs when the fast particle pressure inside the q=1
surface is sufficiently high. Such fast particle pressures are created
by accelerating NBI ions with on-axis ICRF heating.
The sawtooth stabilization period, however, does only last for up to about
200 ms ending with a giant sawtooth.
In the period before the giant sawtooth energetic particle modes (EPMs)
or core-localized TAEs (C-TAE), localized inside the q=1 surface, are
often observed. When the ICRF power is increased not only C-TAEs but
also global TAEs (G-TAE), localized outside the q=1 surface, are excited.
It has been found that in discharges where core-localized and global TAEs
are observed simultaneously, the stored energy is reduced.
It was made plausible that the combination of C-TAEs and G-TAEs was
an efficient way to expel fast particles from the core, thereby reducing
the fast-particle pressure and setting of the sawtooth. |
| Experimental Approach/Plan: | We propose to study the influence of C-TAEs and G-TAEs on the fast-ion
transport by varying the the q at the edge between 3 and 5 with otherwise
identical plasma conditions. By varying q_edge the alignment of the TAE
gap is changed which in turn influences the spectrum of the TAEs which are
thought to be responsible for fast-ion transport. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | This experiment is well suited for DIIID because of the increased
capability of measuring part of the fast-ion distribution in the
plasma with the D_alpha diagnostic. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
351: Recovery of D from thick exfoliated C-codeposits mechanically or using localized thermal oxidation |
| Name: | Peter C. Stangeby ( ) |
Affiliation: | GA ,LLNL and U of Toronto |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Not requested |
Co-Author(s): | Phil West |
| Description: | DIII-D studies would be used to establish the conditions required to cause exfoliation of carbon codeposits and to optimize the process, e.g. to minimize dust formation and to avoid UFO exfoliated flakes entering the confined plasma where they could cause disruptions. Water-cooled surfaces in plasma-hidden regions, as used in JET (louvers) may be advantageous but heated ones may also have benefits, e.g. reduction of the D/C (simulating T/C) in the co-deposits. In initial studies, the exfoliated material created in the hidden region (lower pump entrance) would simply be collected in a tray which would be removed at the time of a vacuum opening. In later studies a conveyor-belt system could be tested. If heat-able co-deposition surfaces are used, then localized oxygen recovery of D (T) from the co-deposits could be used as an alternative to mechanical removal. The rest of the vessel would not need to be heated to the temperatures at which O-baking is effective at removing carbon co-deposits (and releasing the D (T)), i.e. 250-350C, but just the codeposits themselves would be heated while the (cold) vessel was filled with O2. If the O2 was introduced before exfoliation of the co-deposits occurred, then the heating would be applied to the deposition surface, while if after exfoliation, the heating would be applied to the tray into which the exfoliated material fell. Although lab studies have not yet been carried out on carbon co-deposition flakes/dust, it seems likely that their reactivity to hot O2 will be greater than for still-adhering co-deposit films. Such localized O-baking to recover tritium would not involve the problems caused by having to raise the entire vessel and all its internal components to high temperature.
Disruptions caused by exfoliated flakes entering the plasma was initially a problem in the Tore Supra DITS Project, (Deuterium Inventory in Tore Supra) although it was not a problem in the JET DTE1 campaign, presumably because of the basic differences in configuration between limiters and divertors: a limiter surface directly contacts the confined plasma, which is not the case for divertor target surfaces. In addition, if the co-deposits are formed largely at locations out of plasma contact, as occurred in JET, then the risk of exfoliated debris causing a disruption is further reduced and perhaps eliminated. Nevertheless, the risk that this process will cause a disruption is sufficiently serious that this aspect should be included as a central element in the project. |
| Experimental Approach/Plan: | DIII-D hybrid discharges would be ideal for creating thick carbon co-deposits [Luce, et al, NF 43 (2003) 321]. This could be done by operating for 1 - 2 weeks using such discharges, at the end of the 2008 campaign, with the outer strike point placed at the entrance to the lower pumping plenum. During the vessel opening tiles would be removed from this region for analysis of, and lab experiment on, the co-deposits. The tiles at the strike point location might be sufficiently worn that they would have to be replaced in any case.
Recent lab studies in Toronto using thick codeposits from JET have established that thermal oxidation erodes thick carbon co-deposits more rapidly than thin ones. Almost all earlier laboratory studies have employed thin, of order microns, codeposit films, e.g. the ones from DIII-D: Thin (~2 micron) DIII-D divertor codeposits with low impurity content (<5% B): Oxidation can remove > 85% of the initial D content in 2 h at 623 K and >20 kPa O2 pressure; higher B content, however, reduces the total amount of D removed. Thick (10-250 micron) JET MkII-GB divertor codeposits with high impurity content (up to 50% Be/(Be+C)): During oxidation at 623 K and 20 kPa O2 pressure the initial D removal rates increase nearly linearly with initial D content; ~55% of the initial D is removed in the first 15 minutes, independent of thickness and Be content. After 8 h of oxidation > 90% of the initial D was removed. This implies that the structure of the codeposit is highly porous such that erosion occurs throughout the layer, and not from the geometric surface inward. The different effects of B (DIII-D) and Be (JET) on the codeposit removal rates is attributed to different chemistry. Implication for a DT device: assuming codeposits have similar structure and impurity content as the JET codeposits, we would expect that thermo-oxidation at 623 K and 20 kPa O2 pressure would remove > 90% within a day, independent of the codeposit thickness. [Haasz, et al, US-BPO: ITER Summary/WG-1/Task 5/Topic #5, Sept 13 2007].
It will be important to confirm this highly promising JET-tile finding for thick carbon co-deposits formed in DIII-D. It seems likely that the rate of oxidation for exfoliated carbon co-deposit fragments would be still faster than for thick, still adhering ones, and perhaps lower O-baking temperatures will be adequate for tritium recovery. It will be an important objective of the DIII-D project to establish if this is the case.
In addition to providing data on thermal oxidative removal of thick, exfoliating codeposits, both in situ and ex situ, the 2008 campaign experiments would also be used to measure the amount of codeposit formation on the hidden region under the lower pumping entrance, providing the information required to design future experiments that used local heating of codeposits at that location. |
| Background: | In the JET DTE1 experiment, most of the tritium retained in the vessel was contained in
carbon codeposits which initially formed as adhering layers on the water-cooled louvers
in the (plasma-hidden) entrance to the inner pumping duct. When they became thick, these layers exfoliated spontaneously and the tritium-containing flakes/dust then fell to the bottom of the JET vessel. If JET had had a flake collection system in place at the time of the DTE1 campaign to catch this tritiated exfoliated material, then it could have been readily removed from the vessel and the tritium recovered by heating the material in vacuum to ~ 1000C. Various mechanical recovery methods have been proposed, including vibratory conveyor-belt systems that would allow the exfoliated tritiated material to be removed continuously from the vessel [EU TASK No:DV7A-T438 Development of dust detection and removal techniques in tokamaks, GF Counsell, Euratom/UKAEA Fusion Association, 30 November 1999.] JET had not anticipated the specific nature of the carbon codeposition process that occurred in the DTE1 campaign nor the exfoliation of the codeposits. Had it done so, then catchers (troughs) could have been installed in advance of the DTE1 experiment, into which the exfoliated tritiated material could have fallen, for later removal (not requiring anything so complex as a conveyor belt system) and ex situ tritium recovery. While JET did not exploit the opportunity to demonstrate tritium recovery by such a means, DIII-D is equally well placed to develop and demonstrate this method. The key requirement is the existence of a large opening that is itself shadowed from plasma contact but which directly and immediately faces the divertor target strike point. In JET this was the entrance to the lower inner pumping plenum, where water-cooled louvers are located and on which the carbon codeposits formed initially, before exfoliating. In DIII-D the entrance to the lower outer pumping plenum could be used similarly.
Reduction of the T/C ratio in carbon co-deposits by strong surface heating: in JT-60U the divertor locations where the plasma heating was so strong that the surface temperatures reached ~1000C had carbon co-deposits with very low hydrogen content. This is potentially an important way to reduce the amount of tritium retained in the first
place in carbon co-deposits, reducing the required frequency for applying any recovery
process such as O-baking. DIII-D hybrid discharges heat the targets to very high temperatures, ~ 1200C. These discharges will therefore be ideal for reducing the deuterium content in the carbon co-deposits formed in DIII-D and will permit study and quantification of this important tool for tritium control. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
352: Stabilization of Giant sawteeth by modifying the q-profile. |
| Name: | Gerrit J. Kramer () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Energetic Particles |
Presentation time: |
Not requested |
Co-Author(s): | G.J. Kramer, R. Nazikian, M. van Zeeland, B, Heidbrink, N.N. Gorelenkov |
| Description: | In sawtooth stabilization experiments sawtooth-free periods can be extended
to about 200 ms which are then followed by a giant sawtooth crash.
The sawtooth oscillation is stabilized by a sufficiently high fast
particle pressure inside the q=1 surface.
In the period before the giant sawtooth energetic particle modes (EPMs)
or core-localized TAEs (C-TAE), localized inside the q=1 surface, are
often observed. A sequence of toroidal mode numbers is excited starting
with the Highest toroidal mode number and gradually decreasing to lower
toroidal mode numbers. When the toroidal mode number decreases the
radial mode structure broadens and larger volume of the plasma is
affected by the mode from which fast particles can be expelled.
This my ultimately reduce the fast particle pressure inside the
q=1 surface to a value below which stabilization is possible and
a sawtooth is triggered.
The sequence of TAEs from high to low toroidal mode number is caused by
a slow decrease of q at the plasma center, usually from q_0=0.95 to
0.8 when the sawtooth is triggered. |
| Experimental Approach/Plan: | We propose to extend the sawtooth-free period by stopping the current
penetration to the core which stops the the evolution of the q_0.
This can be done by applying ECCD and/or ECRH near the q=1 surface
so that the current penetration is stopped. By varying the amount
of current drive we hope to vary q_0 and study the influence of
TAEs with high and low toroidal mode numbers on the sawtooth stability. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | Because the core of the DIIID plasmas is well diagnosed with fluctuation
diagnostics and MSE together with NBI, ICRH and ECCD heating capabilities
it is the ideal place to perform these experiments. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
353: Stabilization of giant sawteeth through the reduction of the fast particle pressure gradient. |
| Name: | Gerrit J. Kramer () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Stability |
Presentation time: |
Not requested |
Co-Author(s): | G.J. Kramer, R. Nazikian, M. van Zeeland, B, Heidbrink, N.N. Gorelenkov |
| Description: | Giant sawteeth are stabilized by the pressure of fast particles inside the
q=1 surface. Gradients in that population can excite core-localized
Alfven eigenmodes (C-TAE) (otherwise known as energetic particle modes).
It has been shown that these C-TAEs can transport fast ions from inside
to outside the q=1 surface which results in a reduction of the fast-ion
pressure to below a point where the the sawtooth is stabilized and a
giant sawtooth is triggered. |
| Experimental Approach/Plan: | We propose to modify the the fast-particle pressure gradient inside the
q=1 surface during the sawtooth stabilization period by varying the
toroidal magnetic field in such a way that the power from the ICRF is
spread more evenly inside the q=1 surface. This reduces the fast-ion
pressure gradients which drive the C-TAEs. A variation of about 0.05 Tesla
is needed on a 100-500 ms time scale. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | Studying the behavior of the fast ion population together with the
Alfven eigenmode activity is crucial for this experiment and DIIID
is the only place that has the diagnostic capability to do this. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
354: The effect of plasma rotation on core-localized Alfven eigenmodes. |
| Name: | Gerrit J. Kramer () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | G.J. Kramer, R. Nazikian, W. Solomon, N.N. Gorelenkov |
| Description: | Plasma rotation modifies the the measured spectrum of Alfven Eigenmodes
by Doppler shifting the modes with the toroidal mode number times the
toroidal plasma rotation frequency at the mode location. The Alfven
continua are also also Doppler-shifted. This can influence the
continuum damping of the Alfven eigenmodes. |
| Experimental Approach/Plan: | We propose to study the influence of the plasma rotation on the
stability of the the Alfven eigenmodes by varying the plasma rotation
from co- to counter-rotation with the new set of beams in otherwise
identical discharges. The fast-ion population that destabilized the
TAEs can be created by ICRH. |
| Background: | -- |
| Resource Requirements: | DIIID's rotated beam line makes these experiments possible and the
set of fluctuation and plasma rotation diagnostics that can probe
the plasma core are paramount for the success of such an experiment. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
355: Controlling q(0) with Elipticity induced Alfven Eigenmodes in DIIID |
| Name: | Gerrit J. Kramer () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Energetic Particles |
Presentation time: |
Not requested |
Co-Author(s): | G.J. Kramer, R. Nazikian, N.N. Gorelenkov |
| Description: | Ellipticity induced Alfven Eigenmodes have frequencies that are twice the
TAE frequency and they reside in the gap above the TAE gap. On JT60U
EAEs have been observed at the q=1 surface after giant sawtooth crashes.
In those experiments there was circumstantial evidence that those EAEs
induce fast-ion transport from the core to the edge regions of the
plasma thereby hampering the recovery of the full plasma performance
after such a crash. |
| Experimental Approach/Plan: | We propose to study these EAEs with internal measurements and try to
clarify the effect that those modes have on fast-ion transport.
Because those modes reside at the q=1 surface and close to the Alfven
continuum we also like to study the effects of plasma rotation on
the stability of those modes. The upgraded beam capabilities for
controlling the plasma rotation together with the excellent fluctuation
diagnostics are well suited for such an experiment. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
356: Measuring the contribution of the main wall to tritium retention |
| Name: | Peter C. Stangeby () |
Affiliation: | GA ,LLNL and U of Toronto |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The ability of DIII-D to affect a 2D wall system is highly valuable, not only because it makes possible quantifiable and interpretable measurements of the plasma-wall interaction, but also because it directly replicates ITER reference condition. When operating in LSN the toroidally symmetrical structure at the top of DIII-D protecting the upper, outer cryo pump, can be used as the wall since the gap to the separatrix can be made smaller than the other gaps, including to the non-toroidal limiters. When operating in USN, the lower divertor surfaces can be used similarly to affect a toroidally symmetrical wall at the bottom. The latter arrangement is especially useful since this region of DIII-D is especially well diagnosed, including uniquely DTS. This region also contains DiMES which permits material samples to be placed in the wall surface for one or more shots, with easy removal for surface analysis. The lower surfaces are extensively fitted with Langmuir probes for measuring the spatial distribution and intensity of plasma fluxes to the wall. Comprehensive spectroscopic diagnostics are concentrated in the lower region of DIII-D, enabling measurements of the plasma-surface interaction by deuterium and carbon emissions.
Specific questions that will be answered by these experiments and their interpretation:
1 What is the spatial distribution and magnitude of ion fluxes to the first-wall? and how do they depend on the size of the gap between the separatrix and the wall, i.e. the 2nd separatrix?
2 What is the strength of the impurity source and its spatial distribution? i.e. what is the gross erosion rate? and how does it depend on the size of the wall gap?
3 What are the spatial distributions and magnitudes of the net erosion, net deposition and codeposition rates at the wall?
4 How much of the material released from the walls ends up in codeposits in the divertor? and how much ends up in codeposits on the walls? where are the latter located? What is the relative importance of codeposition retention at the walls and divertor?
5 What is the spatial distribution and intensity of the charge exchange fluxes at the walls?
6 It is well known that for true SN there is a fast parallel flow in the SOL that convects low-Z impurities released from the walls, to the inner divertor, concentrating the codeposits there. If the 2nd Xpt is inside the vessel, does that flow still occur in the 1st SOL, i.e. the one between the 1st and 2nd separatrix? Presumably it does not occur in the 2nd SOL, i.e. the one outside the 2nd separatrix. What SOL flows exist there? What role do they play in the codeposition process?
7 Since the local ionization at the 2nd Xpt could be substantial, how much of the C sputtered from the surfaces subtending the 2nd SOL reaches the 1st SOL? How much reaches the wall proper? Is the wall still an important source of materials ending up in divertor codeposits when a 2nd Xpt is
present? |
| Experimental Approach/Plan: | 1 The primary focus will be on the reference plasma conditions for ITER, namely high density and high power H-mode, with and without ELM suppression.
2 The preferred configuration will be USN with the lower divertor surfaces being used to constitute the wall surface. Magnetic configurations with and without a 2nd X-point at the bottom will be used. The gaps to the edge structure on the low field side (which are not toroidally symmetrical) will be made large enough to prevent any significant plasma interaction from occurring there. The gap to the toroidally symmetrical inner wall, however, will be one of the variables explored in the experiment. The principal variable to be explored will be the distance between the 1st and 2nd separatrices (case of two X-points inside the vessel) or the distance from the separatrix to the last closed flux surface, LCFS, defined by the outermost magnetic flux surface that touches the wall at the bottom (case of one X-point in the vessel).
3 The source rate of carbon entering the plasma would be measured using filterscopes and MDS CI, CII, etc emissivities. The spatial distribution of the C-source (gross erosion) would also be measured with the tangential tv, TTV, system in CI, CII, CD, etc light.
4 The net erosion, net deposition and codeposition will be measured using DiMES. Such measurements have been made extensively in DIII-D over a number of years but with DiMES located in the divertor, while here it will be used to make such measurements at the wall.
5 A special PPI head will be made which injects methane over one half of the head only, using the rest of the head to register the local deposition resulting from the injection for ex situ surface analysis.
6 The PPI will also be used to create emission plumes in CII, CIII, etc light which will be recorded by the DiMES viewing camera system (which views DiMES almost directly from above). Such impurity plumes can be used to measure the local SOL flow field, both parallel and cross-field.
7 13CH4 will be injected toroidally symmetrically into both USN and LSN configurations, both for the two X-point and one X-point configurations, to measure the large scale impurity transport patterns. |
| Background: | For PFCs protected by C or Be tiles the most important T retention process is codeposition. If W is used the most important process is diffusion to traps created throughout the bulk by 14 MeV neutron damage [Haasz, et al, US-BPO: ITER Summary/WG-1/Task 5/Topic #5, Sept 13 2007]. T retention is due to plasma interaction at (a) the divertor and (b) the main wall. In order to reduce the peak power load on the divertor target, ITER will operate at high density to achieve detachment. The ion flux to the main wall increases as ne2 or ne3 and for high density the total fluxes to the divertor and walls are comparable, potentially making comparable the contribution of divertor and wall to T retention. Generally the wall is a major source of the low-Z C or Be that ends up in the divertor codeposits and may become the dominant impurity source at high density. Bombardment of W-walls by T ions/atoms drives T into the n-damage traps via permeation resulting in total T retention that may be comparable to that in the divertor at high density. Since the total sputtering yields of C and Be are comparable and since, for a given temperature, the T/C and T/Be ratios in codeposits are also comparable, the codeposition retention for a C-wall and a Be-wall system will be roughly similar. Therefore DIII-D is suitable for assessing the basic aspects of T codeposition retention in ITER for a wall tiled with either C or Be.
The plasma interaction with the wall is less well studied and understood than the interaction with the divertor, largely due to the fact that, while the divertor is toroidally symmetrical (2D), the wall structures are usually not, making for a 3D problem which is scarcely tractable. The present proposal is to make measurements in DIII-D of the plasma interaction with the wall by exploiting the unique feature of DIII-D to be able to affect a 2D wall.
The magnetic configuration in ITER will result in a plasma-wall interaction which is in fact primarily 2D since there is a strong tendency for a 2nd X-point to occur at the top. A toroidal limiter/target will have to be installed there in order to handle the high power load. Therefore the plasma interaction outside the divertor will tend to occur primarily in toroidal bands at the top of the vessel and at the entrance to the divertor at the bottom. Most of the wall proper may be located further out, magnetically, and may experience relatively little plasma interaction. With regard to T retention, the wall in ITER will therefore in large part be these toroidally symmetrical bands, although cx fluxes will reach the wall proper and this has to be included. In any case, so long as the plasma interaction is 2D, the interpretive analysis is tractable, even if the neutrals explore 3D solid structures. The 3D-EIRENE Monte Carlo code was successfully applied to a 2D OEDGE plasma background in C-Mod by S Lisgo to interpretively model neutral pressure measurements made in the 3D C-Mod divertor-structure. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
357: Test the feasibility of operating ITER steady-state scenario demonstration discharges in DIII-D |
| Name: | John Ferron () |
Affiliation: | General Atomics |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Make an initial attempt at producing a 100% noninductively driven discharge with the parameters envisioned for ITER. Assess any issues that arise having to do with the change in discharge shape and accessibility of values of q_min above 2. |
| Experimental Approach/Plan: | Produce a steady-state scenario discharge similar to what has been operated previously in DIII-D, except with the ITER shape. This would mean focusing on discharges with q_min between 1.5 and 2. Assess any observed changes in the ability to obtain a high noninductive current fraction. Then, attempt to raise the value of q_min closer to what has been envisioned for ITER (about 2.2 in scenario 4). Assess the noninductive current fraction and bootstrap current fraction as a function of beta and compare with the anticipated ITER scenario. |
| Background: | The focus of steady-state scenario research in DIII-D has been discharges with shape that is double null divertor (plus or minus a small, nonzero dRsep). These discharges depend on operation with beta well above the no-wall stability limit in order to produce sufficient bootstrap current. Because ITER will be operated with a single null divertor shape, the beta limits and the resulting achievable bootstrap fraction could be significantly different from what is normally achieved with the double null discharge shapes. The effect of the change in discharge shape would be the first issue to address. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
358: Te/Ti dependence of low, intermediate and high k turbulence |
| Name: | Terry L. Rhodes () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | McKee, Peebles, Schmitz, G.Wang |
| Description: | Both analytic and numerical results indicate that ETG and ITG turbulence levels should respond in opposite manners as the ratio Te/Ti is varied. We will test this utilizing the full range of turbulence and other diagnostics available on DIII-D. This is a continuation of previous work in this area with the important addition of measuring the turbulence response over a very large k range as well as with the low k CECE temperature fluctuation system. Previous experiments on DIII-D have found modest changes in the low k turbulence and chi_i with more substantial changes in chi_e. This could be explained by increased transport due to TEM and ETG scale turbulence. |
| Experimental Approach/Plan: | ECH heating will be applied to L-mode plasmas. co and counter NBI will be utilized to match plasma conditions (especially rotation and Er) as closely as possible. |
| Background: | -- |
| Resource Requirements: | ECH |
| Diagnostic Requirements: | all fluctuation diagnostics. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
359: Structure of EHO and Connection to ELM precursor |
| Name: | Tom Osborne () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | J. Yu, G. McKee, P. Snyder, K. Burrell |
| Description: | Study structure of EHO with fast UCSD camera, BES, Magnetics, SXR and compare to ELM precursor. |
| Experimental Approach/Plan: | Create discharge which is transitioning between QH-mode and ELMing H-mode by adding CO beam beam power near threshold and look at structure of EHO in comparison to ELM precursor. Current up ramps might also be used to induce ELMs in QH-mode discharges. |
| Background: | The theory of P. Snyder for QH-mode proposes that the EHO is a rotational shear destabilized low n peeling ballooning instability. In previous studies where the CO NBI power was increased in QH-mode until ELMs reappeared in some cases n=1 EHOs grew to large amplitude preceeding the first ELM. A more rapidly growing mode is observed on magnetis as a precursor to the ELM also in this case. The link between the EHO and the mode usually associated with the ELM is unclear from the magnetic measurements. Filaments are observed associated with ELMs on several tokamaks and one would expect if there were a connection between the EHO and ELM instability to observed a transition between a steady perturbation and a rapidly ejected filament which could be important in understanding both the ELM instability and the EHO. An examination of the structure of the EHO and ELM presursors with fast cameras, BES, SXR, and magnetics combined may help to shead light on both the EHO and ELM instability. |
| Resource Requirements: | Rerverse IP, CO and CNTR beams for QH-mode. |
| Diagnostic Requirements: | UCSD fast camera, BES, SXR. Some gas puffing will probably be necessary to see anything on the camera. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
360: Variation of Bootstrap Current with Collisionality in the H-Mode Pedistal |
| Name: | Bejamin F Hudson ( ) |
Affiliation: | LLNL |
| Research Area: | Heating & Current Drive |
Presentation time: |
Requested |
Co-Author(s): | K. Burrell, C. Holcomb, C. Petty |
| Description: | Make detailed comparison of bootstrap current profile and H-Mode pedestal gradients under differing collisionality regimes. |
| Experimental Approach/Plan: | We will isolate Bz using MSE (Bz + Er) and measuring Er with CER. To increase radial resolution, we will "Jog" the plasma position to scan pedistal region past the diagnostic field of views. The collisionallity will be varied with other key dimensionless parameters held constant. With a profile of Bz, we will use equilibrium reconstruction or Ampere's law directly to determine the bootstrap current. |
| Background: | Collisionality in the edge plays an important role in the achievable parameters in many DIII-D discharges. By studying the behavior of the bootstrap current under different collisionalities, we will be able to better validiate stability models. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | MSE, CER, TS |
| Analysis Requirements: | EFIT |
| Other Requirements: | -- |
| Title |
361: Scaling of H-mode pedestal width with rhostar |
| Name: | Tom Osborne () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | L. Horton (AUG), M. Beurskens(JET), A. Leonard, R. Groebner |
| Description: | The scaling of H-mode pedestal width with rhostar is determined by comparing otherwise dimensionally similar discharged on DIII-D/JET/Asdex-Upgrade. This would verify the results obtained on DIII-D which showed no rhostar dependence over a variation of about 50% in rhostar to a factor of 4 in rhostar by comparison with JET high field discharges and verify the result by comparison with Asdex-Upgrade. |
| Experimental Approach/Plan: | The recent completion of the JET high resolution thomson scattering system (HRTS) now allows the scaling of the pedestal width with rhostar to be determined over a wide range in rhostar by comparison of DIII-D/AUG with small size at low field (large rhostar) to JET with large size and high toroidal field (small rhostar). For each machine discharges would first be made with all dimensionless parameters matched in the H-mode pedestal region, then AUG and DIII-D would push to low Bt increasing rhostar while keeping the other dimensionless parameters fixed while JET would push to high field and small rhostar. It is though a range of a factor of 4 in rhostar should be obtainable. |
| Background: | Simple theoretical arguments suggests that the H-mode pedestal width should decrese with decreasing rhostar. Even a small dependence on rhostar would reduce the preformance of a large, small rhostar, machine like ITER by reducing the obtainable pedestal pressure within the edge stability constraing. The importance of determining this scaling for ITER lead to it being listed as ITPA experiment PEP-2. The previous JET/DIII-D pedestal comparison experiment gave similar normalized pedestal widths when all dimensionless parameters were matched and showe no dependence of the width on rhostar in a scan of about 50% on DIII-D alone. In these experiments good profile data could not be obtained from JET at high field and the experiment could not be completed as planned. JET's new high resolution Thomson system will low allow each machine to independently do a rhostar variation while overlapping at the dimensionally matched point to give a wide rhostar range and finally complete PEP-2. Previous results also showed an increase in ELM size with increasing rhostar that could be helpful for ITER. |
| Resource Requirements: | Discharge shapes will be matched between JET, DIII-D and AUG possibly requiring some discharge development. |
| Diagnostic Requirements: | Profile diagnostics are essential. ELM diagnostics. |
| Analysis Requirements: | Profiles including rotation, kinetic EFIT, ELITE. |
| Other Requirements: | AUG and JET participants would travel to GA to take part requiring careful scheduling |
| Title |
362: Comparison of Bootstrap Current in ELMing and non-ELMing H-Modes |
| Name: | Bejamin F Hudson () |
Affiliation: | LLNL |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | K. Burrell, C. Holcomb, C. Petty |
| Description: | Make a detailed comparision of bootstrap current profile and H-Mode pedistal gradients for ELMy and ELM-surpressed plasmas. |
| Experimental Approach/Plan: | We will combine MSE (Bz + Er) and CER (Er) to isolate Bz. Radial resolution will be increased by "Jogging" the plamsa position to scan pedestal region past the diagnostic field of views. To mitigate ELM activity we will use counter NBI to create a QH-mode plasma. Another method will be to use the I-coils to create a stochastic edge. With a profile of Bz, we will use equilibrium reconstruction or Ampere's law directly to determine the bootstrap current. |
| Background: | Boostrap current is an important component of edge stability models. One issue in model validation is the variation in bootstrap current in the presence of ELM's. |
| Resource Requirements: | Counter NBI, NBI for MSE views, I-Coils |
| Diagnostic Requirements: | TS, CER, MSE |
| Analysis Requirements: | EFIT |
| Other Requirements: | -- |
| Title |
363: Current versus voltage control of plasma shape |
| Name: | Bingjia Xiao ( ) |
Affiliation: | ASIPP |
| Research Area: | General PCO |
Presentation time: |
Not requested |
Co-Author(s): | Dave Humphreys, Mike Walker, Jim Leuer, Qiping Yuan |
| Description: | |
| Experimental Approach/Plan: | 1. Plasma current and position control only. First use the voltage control scheme for the RZIP control. Then shift to the coil current scheme. Gain matrix with proper PID operation is used to generate coil current requirement. PID operation on the difference between the required and measured coil currents generates the commands to the PF power supplies. For the current control scheme, first apply the measured coil currents in the voltage control scheme as the feed forward portion of the current demand and gradually remove this feed forward component.
2. Emulate EAST reference shape and make plasma shape controlled. Apply the PF power supply voltage controlled first and then shift to be current controlled. Using feed forward current more or less just like what was done in the first step. |
| Background: | |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
364: Tungsten surface treatments for thermography |
| Name: | Charles Lasnier () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | West, Rudakov, Wong |
| Description: | Apply ELMing H-mode plasma to a DIMES sample containing tungsten buttons with different surface treatments. Observe the effect of plasma exposure on the emissivity. |
| Experimental Approach/Plan: | Insert the DIMES sample and sweep the strike point across DIMES while in lower single-null ELming H-mode. Use tungsten buttons that are variously polished, sandblasted, knurled, and castellated. |
| Background: | The infrared emissivity of tungsten varies greatly depending on surface conditions. This is of concern for a high-power tokamak using tungsten in the divertor, because thermography is needed to monitor the surface temperature. |
| Resource Requirements: | ELMing H-mode, beams |
| Diagnostic Requirements: | DIMES, IRTV viewing DIMES at high resolution |
| Analysis Requirements: | Process IRTV measurements and compare with DIMES thermocouple measurements, and between different tungsten buttons in the sample which started with different surface treatments. Perform surface analysis on the exposed tungsten to quantify the effect on the differently prepared surfaces. |
| Other Requirements: | -- |
| Title |
365: Visualization of 3-D SOL structures in RMP discharges |
| Name: | Neil H Brooks ( ) |
Affiliation: | General Atomics |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | I. Joseph |
| Description: | |
| Experimental Approach/Plan: | |
| Background: | Some evidence for the 3-D structure around the core plasma has already been obtained experimentally. The LLNL tangential camera in the top of the vessel has seen stripe-like interactions with the dome in LSN plasmas and the fast pressure gauges in the upper plenums have detected pressure pulses during application of RMP coil current which are 30% as great as that observed in the pumping plenum of the active divertor. Also, the UCSD tangential fast framing camera has seen helical like structures in the outer edge. |
| Resource Requirements: | Standard items for H-mode, RMP experiments: beams, i-coils, cryopumps |
| Diagnostic Requirements: | DiMES TV, IR camera, lower tangential TV |
| Analysis Requirements: | TRIP3D |
| Other Requirements: | -- |
| Title |
366: Effect of rotation, nonresonant field perturbation, betap, and triangularity on ELM size |
| Name: | Tom Osborne () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | N. Oyama (JT60-U), M. Fenstermacher |
| Description: | This will look at the effect of rotation and non resonant field perturbation on ELM size, particularly in relation to the grassy ELM regime which was obtained on JT60-U. |
| Experimental Approach/Plan: | Starting with discharge similar to 128464 (q=7.5 dicharge which showed large reduction in ELM size with large non-resonant I-coil field) explore the effect of rotation and nonresonant field perturbation by varying CO/CNTR bream mix and I-coil current. Effect of betap and triangularity/closeness to double null on ELM size would also be explored. It would be highly desirable to obtain data, possibly from the fast UCSD camera to identify any difference in ELM structure through the hoped for variation in ELM size. |
| Background: | ELM size has been tied to plasma rotation, betap and triangularity at low collisionality on JT60-U. In particular a regime of very small grassy ELMs was obtained with rotation low CO injection rotation, higher betap, higher triangularity discharges. Also on JT60-U, adding the ferritic inserts to reduce toroidal field ripple increased ELM size. THe grassy ELM regime is the only small ELM regime which offers high pedestal energy at low collisionality and is therefore attractive for future tokamaks. A search of the DIII-D archive did not reveal the presence of this small ELM regime at high betap and triangularity, with ELM size for low collisionality DIII-D dischages genarally > 10% of the pedestal energy. In RMP discharges with large resonant field component (q=3.7) when ELMs are not completely eliminated the ELM size is not reduced as a fraction of pedestal energy. However in a few discharges at high q (7.5) which used a secondary maxima in the resonant field to reduce the pedestal pressure there was a strong reduction in ELM size as a fraction of pedestal energy. The I-coil was producing a strong nonresont field in these discharges, the betap was somewhat higher due to the higher q value, and the rotation was reduced. The requirements of very small ELMs should make study of small ELM regimes a high priority. |
| Resource Requirements: | I-coil probably in odd parity. CO and CNTR NBI sources. |
| Diagnostic Requirements: | CER and TS essential. UCSD fast camera, BES. |
| Analysis Requirements: | Profiles, kinetic EFIT, ELITE. |
| Other Requirements: | N. Oyama would visit GA to participate in the experiment which may affect scheduling |
| Title |
367: Deuterium retention in tungsten |
| Name: | William R. Wampler ( ) |
Affiliation: | Sandia National Laboratories |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Requested |
Co-Author(s): | Dmitry Rudakov
Clement Wong |
| Description: | Retention of tritium in tungsten plasma-facing components might constrain operation of ITER. Although some studies of deuterium retention in tungsten exposed to plasmas have been done, the possibility of enhanced tritium retention due to trapping at lattice defects from neutron irradiation remains an open issue. It is known that energetic neutron irradiation creates lattice vacancies, and that vacancies in metals trap hydrogen isotopes. In tungsten vacancies are stable below 300 C whereas hydrogen diffuses at room temperature and above. Thus hydrogen isotopes injected from a plasma may diffuse to the vacancies and become trappped. The issue for ITER is how much tritium will become trapped. This depends on the concentration of trapped hydrogen, the depth it extends into the material, and how strongly the hydrogen is bound to the traps. The purpose of the proposed experiments is to answer these questions by measuring the retention of deuterium in tungsten samples exposed to DIII-D plasmas. Some of the samples would be pre-irradiated with energetic ions to produce atomic displacements similar to that resulting from fusion neutron irradiation. The experiments would look for a difference in deuterium content of damaged versus undamaged samples after exposure to divertor plasma in DIII-D. |
| Experimental Approach/Plan: | Tungsten samples would be irradiated with energetic ions at Sandia National Laboratories to produce displacement damage up to one displacement per atom (dpa) to depths of a few microns. These samples would be exposed to divertor plasma in DIII-D, along with similar undamaged samples using DiMES. After plasma exposure, the deuterium concentration versus depth would be measured using nuclear reaction analysis at Sandia. Increased deuterium retention in the irradiated samples would be evidence of enhanced retention due to trapping at displacement damage. |
| Background: | -- |
| Resource Requirements: | One DIII-D run day for setup and exposure of samples to lower single null attached divertor plasma. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | DiMES probe would be used to expose samples. |
| Title |
368: Dependence of C deposition and D co-deposition rates on the surface temperature |
| Name: | Dmitry Rudakov () |
Affiliation: | University of California, San Diego |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Requested |
Co-Author(s): | A. Litnovsky, V. Philipps, W. West, C. Wong, R. Boivin, W. Wampler, D. Buchenauer |
| Description: | Expose differentially heated metal strip mounted on DiMES holder to detached ELMing H-mode discharges. Because of the surface temperature variation, net deposition rates of C and D, D/C ratios, and deposited layer thickness will vary along the strip. |
| Experimental Approach/Plan: | Insert the DIMES holder with metal strip into the private flux zone of high-density LSN ELMing H-mode plasmas. Expose for ~8 plasma discharges. Remove and analyze deposit thickness and C and D areal density by various techniques (ellipsometry, IBA, SIMS, XPS). |
| Background: | During the 2004-07 experimental campaigns it was shown that a moderate increase of the surface temperature has a dramatic effect on C deposition and D co-deposition at recessed surfaces in a tokamak divertor under detachment. C deposition was observed on molybdenum mirrors recessed below the divertor floor at room temperature, and was fully suppressed at elevated temperature between 90 - 180ºC. At 200ºC carbon deposition down a simulated tile gap was reduced by about a factor of 2-4 and D co-deposition by an order of magnitude compared to those at room temperature. Here we are proposing to measure a continuous dependence of the deposition/co-deposition rates on the surface temperature. |
| Resource Requirements: | 1/2 day experiment; high density ELMing H-mode, NBI |
| Diagnostic Requirements: | DIMES with a specially built head, all available lower divertor diagnostics |
| Analysis Requirements: | Various surface analyses: IBA, ellipsometry, SIMS, XPS |
| Other Requirements: | -- |
| Title |
369: DiMES Erosion Measurements with Detached Plasmas Induced by Argon Injection |
| Name: | Dmitry Rudakov () |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | W. Wampler, W. West, T. Petrie, D. Whyte, C. Wong, R. Moyer, S. Allen, N. Brooks, P. Stangeby, J. Boedo, C. Lasnier |
| Description: | DiMES will be used to measure the rate of carbon and tungsten erosion at the outer strike point (OSP) of H-mode plasmas detached by argon injection. This experiment should determine whether argon-detached plasmas can be used with a carbon/tungsten divertor in a tritium fueled next step device. Results will be compared to those from a previous DiMES exposures to plasmas detached by neon injection and semi-detached plasmas with argon injection. |
| Experimental Approach/Plan: | This is a continuation of previous DiMES experiments with noble gas injection. A DiMES probe containing depth-marked graphite and tungsten (surface-deposited films or solid buttons) samples will be exposed to the OSP with LSN H-mode plasmas detached by argon injection. Plasma and machine parameters should be close to those used in the previous experiments with neon and argon injection. The OSP should be moved onto the DiMES probe during periods of detached H-mode for a total exposure time of 10-12 seconds (3-4 discharges). Heat flux reduction during Ar injection should be about a factor of 4 compared to the attached phase. Divertor plasma conditions should be characterized to allow comparison of experimental results with erosion/deposition models. Pellet ELM pacing may be used to prevent density runaway in ELM-free H-mode. |
| Background: | Carbon and tungsten are the materials currently in the ITER divertor design. A possibility of switching to all-tungsten divertor for D-T phase is being discussed. Divertor detachment is required to reduce heat flux and erosion rates of the targets. With all-tungsten divertor impurity injection will be required to reach the detachment. Previous studies using DiMES showed that net carbon erosion rate at the OSP with neon injection can be rather high even with detachment. Attempts have been made to repeat this experiment with argon injection, but due to various problems the desired plasma conditions were not achieved. During the latest attempt argon injection rate had to be limited because of the density runaway at detachment. As a result, OSP stayed attached through most of the exposure. Preliminary results indicate that tungsten from a surface-deposited strip has eroded. An experiment with better controlled conditions is needed for better extrapolation to ITER. |
| Resource Requirements: | 1/2 day experiment; ELMing H-mode, NBI, Ar puff |
| Diagnostic Requirements: | DIMES, all available lower divertor diagnostics |
| Analysis Requirements: | IBA analysis of the exposed samples |
| Other Requirements: | Pellet injection for ELM pacing |
| Title |
370: ECRH/ECCD Control of ELMs |
| Name: | Francesco Volpe ( ) |
Affiliation: | ORAU |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | J. Lohr, R. Groebner, R. Moyer, R. Prater |
| Description: | Modify the edge pressure gradient and/or edge current by means of ECRH/ECCD to affect ELM frequency and size and possibly suppress them. |
| Experimental Approach/Plan: | Heat the very edge of the plasma (pure ECRH), comparing deposition slightly inside/outside the separatrix. Repeat for oblique launch (both co- and ctr-ECCD). |
| Background: | A similar experiment was carried out with success at DIII-D by J.Lohr et al. in the late 80's and early 90's (Stambaugh et al., PPCF 1988; T.Luce et al., IAEA 1990): 1.2MW of ECRH at 60GHz deposited inside/outside the separatix, on the high field side, was observed to halve/double the ELM period; no ECCD was attempted at that time. The idea would be to repeat the experiment on the low-field side with the new 110GHz system and with the improved edge diagnostics (improved TS, to measure the edge pressure, and MSE, to measure the edge current) and codes (ELITE) that became available in the meantime. These offer the perspective of a deeper physical understanding in terms of peeling-ballooning limit.
From the point of view of MHD control, the minimum goal would be to reproduce the effect on the ELM period, and possibly improve it, thanks to the increased ECRH power, the improved focusing and the fact that the experiment would be repeated on the low field side, i.e. with the target closer to the launcher, and thus reduced broadening of the gyrotron beams.
Furthermore, ECRH tests on marginally ballooning-stable plasmas and ECCD tests on marginally peelng-stable plasmas have the potential for complete ELM (de)stabilization.
Note that for extreme off-axis deposition, ECRH is known to affect n_e more than T_e, for not well understood reasons. It is still a valuable knob to control the product of the two, i.e. the edge pressure, but extensive tests would help to clarify why the effect on n_e is dominant. |
| Resource Requirements: | Up to 6 gyrotrons |
| Diagnostic Requirements: | Good TS and MSE at plasma edge |
| Analysis Requirements: | ELITE |
| Other Requirements: | -- |
| Title |
371: Inducing 3/2 NTMs in hybrid discharges by means of ECRH |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Requested |
Co-Author(s): | R. La Haye |
| Description: | ECRH slightly outside q=3/2 to provoke a local flattening of pressure, thus a Bootstrap deficit and therefore a 3/2 NTM when desired, for example in hybrid discharges. |
| Experimental Approach/Plan: | Very simple, with ECRH, perpendicular launch and deposition slightly outside q=3/2. A toroidal field scan (within the shot, or from shot to shot) will allow to find the best location. |
| Background: | NTMs are not always undesired instabilities: small 3/2 NTMs, for example, are desirable in "hybrid" discharges, where they help to prevent sawteeth. Occasional difficulties were encountered recently (March 2007) in reproducing hybrid scenarios with "natural" 3/2 NTMs. The purpose of this proposal is to develop a tool to trigger these modes on demand, when required. It might also shed light on the physics of seeding, and permit accurate measurement of the NTM growth rate, although under "artificial" conditions, which can be contrasted with predictions from the Rutherford equation. In particular, the flattening of the pressure profile is expected to affect the Bootstrap term in the Rutherford equation and, to a higher order, to make Delta' less negative. The presence of other NTMs in the plasma (typically 4/3, in the absence of 3/2) is not expected to constitute a problem, as ECRH will be deposited outside the 3/2 surface and thus even farther from the 4/3 one. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
372: Inducing 3/2 TM or NTM in hybrid discharges by means of modulated ECCD |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Requested |
Co-Author(s): | R. La Haye |
| Description: | Drive current filament on the q=3/2 surface (around which island will form), by means of ECCD modulated at twice its CER rotation frequency. |
| Experimental Approach/Plan: | Measure with CER the toroidal rotation velocity of the 3/2 surface (identified/localized through MSE and EFIT). Repeat the shot with modulated ECCD at twice that frequency (because n=2). In case of excessive variation from-shot-to-shot or within-the-shot, some work on the PCS might allow to respond in real-time to the changes of CER frequency. Compare co- and ctr-CD, expected to drive classical and neoclassical TMs, respectively. |
| Background: | NTMs are not always undesired instabilities: small 3/2 NTMs are desirable in 'hybrid' discharges, where they help to prevent sawteeth. Despite the existence of consolidated experimental recipes, difficulties were recently encountered (March 2007) in developing hybrid scenarios with "natural" 3/2 NTMs. The purpose of this proposal and of #371 is to develop a tool to trigger these modes on demand, when required. The basic idea is that, in the absence of mode and therefore of filamentation, the 3/2 surface is "smooth" and consists of identical 3/2 current filaments, all carrying the same current. Artificially increasing or decreasing the current in one of them by means of co- or ctr-CD would break the axisymmetry and introduce the helical current perturbation around which an island would form. If sufficiently big (wider than 'marginal'), this island would evolve, grow and saturate. Tailoring the island to the hybrid discharge needs would then be a question of setting beta -or otherwise modifying the Rutherford equation- in such a way that the saturated width is tolerable. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
373: Prompt turn-off of ECCD when no longer required or detrimental for NTM stabilization |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | NTM Stabilization |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | PCS-control of ECCD timing, to turn it off as soon as the NTM stabilization is complete (according to Mirnov signals). |
| Experimental Approach/Plan: | The experimental approach is the same as in CW ECCD stabilization of 3/2 NTM, including alignment procedures. Once a reference stabilization discharge is obtained, the discharge should be repeated with a shorter ECCD pulse. In particular, ECCD should be turned off at the time at which stabilization was complete in the reference shot. If encouraging, one might automate the process by using BDOTEVENAMPL or similar trace in the PCS for a "dud detector" that would switch off the gyrotrons as soon as the mode is suppressed. |
| Background: | ECRH and co-ECCD are known to make Delta' more negative. Co-ECCD also replaces the "missing" Bootstrap current in a neoclassical island. The two effects stabilize NTMs, for deposition at the exact island centre. In reality, for full suppression it is sufficient to shrink the island below its marginal width (which relaxes the requirement on the alignment between ECRH/ECCD and the island), then the mode will automatically disappear, as shown at DIII-D. If well-aligned, continuous application of ECRH/ECCD after that moment is equivalent to pre-emptive ECCD, which has been shown to prevent the mode (re)appearance. If, on the other hand, the misalignment exceeds the marginal width, the island will be initially mitigated and its width will decrease but, eventually, it will become comparable with the misalignment and, at that point, a significant amount of current will be driven outside the island and have a destabilizing effect.
Note that the marginal width (hence, the alignment requirements) change with beta and tend to become more stringent as a result of NTM stabilization and of the accompanying increase in beta. Consequently, an initially good alignment might not be satisfactory later in the discharge, and the aforementioned destabilizing effect might take place even under conditions of initially good alignment.
Moreover, the technique would readily make ECRH/ECCD resources available for other tasks, such as q-profile tailoring in hybrid and AT plasmas. This is particularly appealing in devices like DIII-D and ITER equipped with steerable launchers. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
374: Assess optimal Error Field Correction by modulating I-coils at incommensurable frequencies |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | Error Fields |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Perform several non-destructive Error Field Correction (EFC) tests within a single discharge, including non-resonant components |
| Experimental Approach/Plan: | Feed AC currents of incommensurable frequencies to each pair of I-coils in order to generate error fields that are different at every instant. Infer from plasma rotation or other indicator what set of currents gives best error correction. |
| Background: | Most of the times, optimal EFCs are assessed by "trial-and-error", with a new EFC being tested in each shot. One of the reasons for this is that the current indicator of optimal EFC is the lowest density at which the plasma can be ramped down without locking. This usually results in a disruption and can thus be considered a "destructive test" (destructive of the plasma). Utilizing a non-destructive indicator such as the plasma rotation (faster or slower, depending on how strong the magnetic braking from the residual error field is) would allow multiple EFC tests within a single discharge. The limit on how many EFC configurations can be tested is set by the plasma rotation response time. At this point, there are various choices on how to conduct the EFC scan during the discharge. For example, one can fix the phases between the I-coil circuits and scan the currents, while keeping their ratios fixed. This would fix the 3D geometry of the EFC field and scan the overall strength of the correction. Alternatively, one can fix the strength and vary the phases so as to "rigidly" rotate the EFC. In reality, to maximize the number of configurations, one can change the amplitude and the phases, as well as the topology, including non-resonant components. The latter can be achieved by individually modulating the I-coils, which is technically possible. In particular, modulating them at different frequencies would permit to test various strengths, topology and directions of the resulting EFC. To maximise the number of configurations, distinct coils should be modulated at incommensurable frequencies (incommensurable over the duration of a discharge, or a number of discharges). |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
375: Test of causality: mode rotation vs. plasma rotation |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | In locking at low rotation, mode slows down the plasma? or plasma slows the mode down? And in rotational mitigation, it is well-known that the rotating plasma drags the mode, but can torque imparted to the mode drag the plasma? |
| Experimental Approach/Plan: | Use co/ctr NBI mixture to control plasma rotation, I-coils to control mode rotation, CER to measure plasma rotation and Mirnov spectrograms (newspec) to measure mode rotation. Then use an approach similar to K.Burrell's H-mode studies (PoP 1999): modulate the mode (plasma) rotation and measure the delay of the plasma (mode) response. Hysteresis curves will be obtained. |
| Background: | NTMs are approximately "frozen" in the plasma and spinning the latter (by momentum injection with NBI) also spins the former. Various proposals and some experimental evidence exists, suggesting that the opposite is also true, i.e. that torque imparted to the mode also spins the plasma. If confirmed, plasma rotation (and not just mode rotation) would represent one more application for internal coils in devices with low NBI momentum injection like ITER. Similar considerations apply to plasma and mode braking, and how they affect each other. For example, rotating modes are known to lock even in rotating plasmas which keep rotating. On the other hand, slow plasma rotation encourages mode locking. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
376: RFA assisted RMP-ELM control |
| Name: | Ilon Joseph ( ) |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | AH Boozer, JE Menard, JK Park, RA Moyer, TE Evans |
| Description: | Unlike the DIII-D I-coils which work well for ELM supression, the currently favored choice of ITER RMP-ELM control coils is localized on the outer midplane surrounding the outer port plugs. The advantage of this configuration is that one can attempt to use RFA to enhance the ELM-control efficiency of a high-n RMP localized on the outboard midplane. |
| Experimental Approach/Plan: | Investigate RFA for static n=2 and n=3 C-Coil and I-Coil fields. |
| Background: | The linear plasma response to external perturbations can enhance the magnitude of the resulting field by the ratio of delta W to the energy of the vacuum: delta Wvac. In general, the least stable mode is strongly localized on the outboard midplane in the region of unfavorable curvature. The localization has been shown to increase the effective width of the mode spectrum by roughly a factor of 2 over the vacuum calculation, which is precisely the amount needed to generate a sizeable field line pitch-resonant component of the spectrum. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | cameras: IR, DIMES, XPT-TAN-TV ...
Langmuir probes: array, reciprocating, ... |
| Analysis Requirements: | SURFMN, DCON, IPEC |
| Other Requirements: | -- |
| Title |
377: Beta limits for 3/2 NTM onset and locking, as a function of rotation |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | Rotation Physics |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Characterize 3/2 onset and locking (and compare with 2/1) by means of beta ramp and torque scan |
| Experimental Approach/Plan: | Ramp NBI power at fixed co/ctr mix in hybrid discharges until 3/2 forms and, eventually, locks. Repeat for various co/ctr mix. |
| Background: | The background of this proposal is twofold and related to two experimental observations from the last campaign.
On one hand, it will help to better understand the conditions for the onset of the 3/2 mode and -in combination with measurements by R.Buttery et al. for the 2/1 mode- will help to understand when to expect a 3/2 or a 2/1 mode. In turn, this might explain recent difficulties in reproducing earlier hybrid discharges, where 2/1 modes were obtained instead of 3/2. A possible explanation is that different beta thresholds apply to the two modes at different rotation velocities. What threshold a beta ramp hits first (thus, which NTM appears first), it depends on the rotation.
On the other hand, this study will also help to characterize the 3/2 mode locking, recently observed at DIII-D for the first time and experimentally determine its ITER relevance. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
378: Counter Ip RMP-ELM suppression |
| Name: | Ilon Joseph () |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | TE Evans, A Garofalo, M Heyn, I Ivanov, SV Kasilov, RA Moyer, AM Runov |
| Description: | The efficiency of RMP-ELM supression in counter Ip plasmas will be explored. The study should clarify the role of diamagnetic rotation physics on RMP penetration and the subsequent impact on ELM control. |
| Experimental Approach/Plan: | Run counter-Ip H-modes chosen for stability and field line pitch-resonant edge q95 ~ 3.5-3.7. Apply n=3 I-coil for good measure. |
| Background: | Both 2-fluid and kinetic theory of RMP penetration have shown a strong dependence of the amount of tearing on the rate of rotation relative to the rest frame of the electrons. This implies that, unlike the single fluid theory, the diamagnetic electron flow is the key player in the penetration physics. Since the electrons flow in the co-beam direction in a counter-Ip discharge, the plasma may be less sensitive to tearing by external perturbations. In fact, previous studies of resonant field braking in counter NBI plasmas have shown an improvements in particle confinement rather than particle pumpout! A serious study is needed to determine whether ELM control can be achieved, and if so, whether it will be the direct effect of the 3D field on ELM stability that is responsible for the change in behavior. |
| Resource Requirements: | counter-Ip |
| Diagnostic Requirements: | cameras: IR, DIMES, TAN-TV, Fast Camera, Langmuir probes |
| Analysis Requirements: | TRIP3D, SURFMN, IPEC, kinetic wave code |
| Other Requirements: | -- |
| Title |
379: Can RMP strike point-splitting spread divertor heat flux? |
| Name: | Ilon Joseph () |
Affiliation: | University of California, San Diego |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | JA Boedo, TE Evans, ME Fenstermacher, M Jakubowski, CJ Lasnier, RA Moyer, MJ Schaffer, O Schmitz, WP West |
| Description: | The goal is to widen the effective strike point heat flux area by increasing the size of the magnetic footprint. Carefully characterize the heat and particle flux deposition profiles and optimize over n. Obtain clear confirmation of splitting in n=3 case, using RFA if necessary. |
| Experimental Approach/Plan: | At least 2 run days: begin with n=1 case, rotating at slow ~10Hz rate in both L-mode and H-mode discharges based on ITER similar reference cases. Continue to n=2 and n=3 (non-rotating) optimization study on next run day. |
| Background: | RMP strike point splitting has been observed during application of RMP, as well as during locked modes. Recent E3D calculations by Joseph et al., showed that an increase in overall plasma wetting could be achieved in n=3 mode, along with a characteristic nonaxisymmetric structure. In contrast to changes in particle flux that are routinely observed in all cases, while heat flux splitting has been clearly observed for n=1, and to some degree n-2 RMPs, no confirmation of nonaxisymmetric deposition has yet been obtained in n=3. |
| Resource Requirements: | rotating I-coil |
| Diagnostic Requirements: | Cameras: ***IR***, DIMES, TAN_TV, fast camera
Langmuir probes: array, reciprocating |
| Analysis Requirements: | TRIP3D, SURFMN, IPEC, UDEGE, EMC3-EIRENE, FINDIFF |
| Other Requirements: | -- |
| Title |
380: Calibrate separatrix deformation to ideal response theory |
| Name: | Ilon Joseph () |
Affiliation: | University of California, San Diego |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | AH Boozer, KH Burrell, TE Evans, JE Menard, RA Moyer, JK Park, MJ Schaffer |
| Description: | Test the ideal theory of linear MHD plasma response by measuring surface deformations through Te symmetry point and Er well minimum. |
| Experimental Approach/Plan: | Choose stable n=1,2,3 plasmas where ideal theory should be valid. Send rotating ~10Hz n=1,2 RMP field through to measure surface deformations via TS and CER systems. |
| Background: | The linear plasma response to external perturbations has recently been to shown by Park, et al Phys Rev Lett 2007, to greatly modify the normal magnetic field at the seperatrix for low order n=1,2,3 toroidal modes. Due to the RFA effect, the ideal theory predicts that the normal field at the separatrix, and therefore, the deformation of the last closed outer surfaces can be much larger than the values anticipated by vacuum calculations alone. The theory has already worked well for the prediction of locked mode onset and error field cancellation. Should the predicted surface deformation match well to experimental results, one would obtain a method for systematically correcting TS and CER data for the effect of both applied RMPs and intrinsic error fields. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | TS working well and CER -- sweeps necessary
Cameras
Langmuir Probes |
| Analysis Requirements: | ER, Kinetic EFIT, SURFMN, IPEC |
| Other Requirements: | -- |
| Title |
381: Rapid-pulse Thomson Scattering scans in initial phase of RMP discharges |
| Name: | Zeke Unterberg () |
Affiliation: | ORISE/ORNL |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | B. Bray |
| Description: | The goal of this measurement would be to obtain high temporal resolution edge T_e and n_e profiles when the I-coils are first initiated. The fast time evolution of the T_e profile as the I_coils turn on would be of main interest. Langmuir probe data from past RMP discharges have shown a burst of fast electrons during the initial I-coil activation and there is thought to be an initial transient T_e decrease before n_e decreases and the edge temperature gradients then increase. These measurements would be an attempt to quantify this phenomenon. |
| Experimental Approach/Plan: | These measurements could piggyback on any RMP run day. The idea would be to multi-pulse the TS laser during the first few milliseconds of turning on the I-coils. This would most likely be done on the "Core" chord of the TS system. Although, the measurement could also be done on the divertor chord. The minimum time between pulses is 100 microsec (usec) and is limited by the data acquisition time. Therefore, this proposal would be to scan rapid pulse times from ~ 100 usec to ~ 1 msec in order to measure during the entire window of the fast tranisent in T_e. Ideally, this would be repeated for multiple shots for averaging with a range of times around the I_coil turn on. |
| Background: | -- |
| Resource Requirements: | Core chord TS setup to allow cascade firing of 7 lasers. This measurement chould piggyback on any run day with up to 4 lasers on the Core chord, but it would be most desirable to arrange the lasers to have all 7 on the core chord. This wourd take ~ 1 day to set up. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | TS profile fitting routines |
| Other Requirements: | -- |
| Title |
382: Oblique-ECE-assisted MECCD suppression of NTMs |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | NTM Stabilization |
Presentation time: |
Requested |
Co-Author(s): | M. Austin, R. La Haye, R. Prater |
| Description: | Use oblique ECE to check radial alignment of ECCD to island and determine the best frequency and phase of modulation for its suppression. |
| Experimental Approach/Plan: | Analyze two oblique ECE signals originating close to 2/1 or 3/2 target by software, within the PCS, and by hardware, by dedicated analogue electronics. PCS will determine the quality of the radial alignment and decide whether to move the plasma and/or the EC resonance, and by how much. The dedicated electronics will generate waveforms for the modulation of the gyrotrons and directly deliver them to their power supplies by means of optical isolators and fibres. The system was designed for 1-10kHz NTMs, but initially it would be preferable to stabilize a mode rotating more or less uniformly at 2-5kHz. This might require some scenario development. |
| Background: | All the hardware was assembled and individual parts were tested in April-June 2007. For example the oblique ECE radiometer was shown to work as far as absolute Te measurements are concerned, but measurements of the Te oscillations associated with a rotating NTM were not attempted yet. The electronics was also shown to correctly manipulate function-generated "fake" signals, and successfully modulated the gyrotrons at up to 5kHz. The experiment proposed here will be the first comprehensive test of the entire system on a real rotating island and the first ECCD stabilization experiment directly driven by oblique ECE emitted near the island, although similar experiments are under preparation at TEXTOR. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
383: Simultaneous control of ELMs and RWMs |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | Core-Edge Integration |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Simultaneously use I-coils for RMP control of ELMs and for RWM control. Look for conflicts or synergies. |
| Experimental Approach/Plan: | Simple superposition of AC, <1kA RWM control waveform, whatever algorithm or method it is based on, on DC, 6kA baseline for ELM control. Ramp down q95 in initial discharges, then continue at optimal values for ELM control. Try to obtain first ELM suppression above no-wall limit (and, for comparison, shots with ELM control only, RWM control only, and no control at all). |
| Background: | I-coils have been used with success at DIII-D to control ELMs or RWMs. It is important to assess conflicts or synergies between the two control techniques, on the way to an integrated coil system for ITER, which will have to fulfil these and other tasks, such as error field correction. The concern is that optimal current and helicity settings for RWMs might not be optimal for ELMs and viceversa.
For example, the n=1 dynamic correction for the RWMs might change the optimal q95 window for ELM control.
On the other hand, from a RWM perspective, ELM-suppressing RMPs are a static, typically n=3 error field affecting the plasma rotation and thus the RWM stability.
Hints of simultaneous RWM suppression and ELM mitigation can be found in A.Garofalo's shots 122591-594, where an n=3 magnetic braking field was applied with the C-coils, during n=1 RWM feed-back with the I-coils. Although the real goal of those experiments was to study RWM control in the presence of n=3 magnetic braking, they provide useful information on the interplay with RMPs for ELMs. For instance, they seem to confirm the above speculation on the modified q95 window. Although encouraging, the experiments will need to be repeated at increased n=3 current (6kA, as 3kA were marginal for ELM suppression). Moreover, the I-coils can be wired as to simultaneously apply an n=1 and n=3 perturbation. Finally it will be beneficial to drastically reduce the gas puff and move the strike point to improve the pumping and limit the collisionality, and to reduce the triangularity (was 0.6). All these modifications go in the direction of facilitating the ELM suppression. It will also be important to avoid ELM-free H-modes or temporary losses of H-mode, in order to isolate real ELM-suppression evidence.
n=3 RMPs were proposed here because they are the best known and most successful RMPs. However, if successful, the same experiment could be repeated with n=1 or n=2 RMPs, which showed promising results in recent ELM control experiments by R.Buttery. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
384: Preferential Locking |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | General IP |
Presentation time: |
Requested |
Co-Author(s): | R. La Haye, R. Prater, E.J. Strait |
| Description: | In case locking is imminent or has already happened, apply static n=1 error field "over-correction" to predetermine the toroidal phase of locking or readjust it, respectively, in such a way that the mode can be controlled by ECCD. |
| Experimental Approach/Plan: | Use three available dud detectors and a fourth one yet to be developed, based on real-time newspec, to predict or promptly recognize mode locking and trigger a control phase.
Control will consist of cw ECCD and various types of I-coil controls and NBI changes: in some initial shots, a slow travelling wave will be entrained to the mode to slowly drag it in the presence of ECCD. In this way, the island O-point and X-point will be illuminated, alternatively, with stabilizing/destabilizing consequences and an optimal set of I-coil currents will be determined. As a by-product, slowly dragging the island will also allow MSE measurements of current in its interior, which would represent the first measurement of current diffusion inside the island.
Once the optimal settings are found, preferential locking yielding ECCD in the O-point can be tried directly, i.e. without slowly rotating the island first. Mode mitigation is expected. The optimization and preservation during the shot of the ECCD alignment will enable full suppression.
Locking with ECCD in the X-point and no ECCD will offer terms of comparison.
The controls should preferably be applied before locking (pre-emptive control, expected to be more efficient). Anyway, pre- and post-locking intervention will be compared. |
| Background: | Piggyback experiments in Sept.2006 and 1.5 dedicated day in June 2007 have demonstrated locked mode mitigation from 6 to 3G, according to external saddle loop measurements. June experiments took advantage of increased ECRH power, marginally sufficient for stabilization, but optimal ECCD alignment was achieved only transiently. Repeating the experiments with equivalent or higher power has the potential for full stabilization, if the alignment will be maintained for >400ms. This requirement can be achieved by means of the PCS "active tracking" algorithm already applied with success to the stabilization of rotating NTMs. |
| Resource Requirements: | up to 6 gyrotrons, real-time newspec |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
385: Sustained rotation of 2/1 for locking prevention, rotational mitigation and to assist ECCD control |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | NTM Stabilization |
Presentation time: |
Requested |
Co-Author(s): | R. La Haye |
| Description: | |
| Experimental Approach/Plan: | Similar to #384, except that the applied field rotates, initially at 1Hz, and then is accelerated. Sustained rotation (a.k.a. entrainment) at up to 180Hz in the absence of ECCD has been already demonstrated. As a next step, on one hand we want to add ECCD (which will introduce a layer of complication, e.g. with respect to the alignment and maintaining it) and on the other we want even faster rotation. The concomitant linear increase of I-coil current during constant acceleration proved helpful. As a refinement, a non-linear current ramp taking into account partial cancellation by image current in the walls will be utilized.
We will also try to reproduce and understand the unexpected mode mitigation obtained during the frequency ramp at about 10Hz, which might be related to the natural frequency of the quasi-stationary mode (QSM). However, not that that was a mitigation. ECCD will be necessary for full stabilization, with the advantage that, once it is forced to rotate, the locked mode can be treated as a rotating NTM, and the same control strategies can be deployed against it. Furthermore, because the frequency and phase of rotation will be known and controllable, the control by modulated ECCD is expected to be easier.
Like #384, compare pre- and post-locking intervention. The former is expected to be more efficient, as it would "catch the mode" and sustain its rotation without letting it lock at all. |
| Background: | In June 2007, a mode previously locked to the wall was locked to a rotating n=1 field generated by a travelling wave in the I-coils. The mode was unlocked and accelerated at up to 180Hz, thanks to a concomitant I-coil current ramp, to compensate for shielding from image currents in the wall. During acceleration, mitigation was observed at about 10Hz.
This proposal is strictly related to #88 by G.Jackson and F.Volpe. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
386: Scaling of peak divertor heat flux and heat flux profile widths during MHD free L-mode operation |
| Name: | Phil West () |
Affiliation: | General Atomics |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | P. West, C. Lasnier, J. Boedo, T. Petrie, G. Porter, M. Groth. P. Stangeby, D. Hill |
| Description: | Validate (or not) the classical models of SOL and divertor heat flow contained in predictive and interpretive codes, specifically UEDGE and OEDGE. Use L-mode, MHD free plasmas as the closest as the closest experimental approximation to the simple 2D quasi-steady models. Perform connection length and density scans for scaling. |
| Experimental Approach/Plan: | |
| Background: | A cross machine database of heat flux profile scaling developed for ITER has not produced a convincing scaling for projection of heat flux profiles to ITER. This proposal is to benchmark the existing 2D codes based on classical parallel transport under the simple as possible plasma (SAPP) conditions. Validating this rather simple model of SOL plasma transport is key to the validation of models under more complex scenarios.
DIII-D is in a position to get a rather complete set of profile and relevant SOL transport
data and can fine tune the plasma parameters to optimize these physics scaling studies. |
| Resource Requirements: | |
| Diagnostic Requirements: | Essential:
IRTV
Thomson
CER
Bolometry,
X-point and Midplane plunging probes
Lower Langmuir Probes + Upper Baffle Knee Probe
CO2 interferometers
Filterscopes
Desired:
Thermocouple array
Visible Bremsstralung
SPRED
MDS Spectrometry |
| Analysis Requirements: | Standard Divertor Diagnostic Annalysis |
| Other Requirements: | -- |
| Title |
387: Chamber wall materials study |
| Name: | Clement Wong () |
Affiliation: | General Atomics |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | D. Rudakov, P. West, W. Wampler, N. Ashikawa, R. Bastasz, J. Brooks, T. Evans |
| Description: | PSI of the chamber wall surface material of a tokamak has not been studied or measured in detail. This proposal is to study the plasma surface interaction of different relevant chamber surface materials, with special interest on the plasma discharges that would generate bursty radial transport of the plasma. |
| Experimental Approach/Plan: | We plan to use the MiMES material module to expose well characterized graphite buttons with coatings of W, B and Al, (Al is used to simulate Be), and possibly other materials, to study the effects of erosion, H/D pickup, and surface material damage from L-mode type of discharges. Similar material buttons will be exposed concurrently with the DiMES system. A dedicated 1/2 day experiment will be requested to acquire as much plasma exposure time as possible. |
| Background: | PSI of the chamber wall of a tokamak has not been studied or measured in detail. We need to understand, quantify and be able to model the effects, especially from the bursty radial transport of the plasma. The understanding of these effects is very significant simply due to the fact that the first wall chamber has a much larger surface area than the divertor. The first wall chamber PSI effects can also become the significant contributor of core impurities contribution. MiMES system was designed for the study such effects. Material buttons of different materials can be exposed to different plasma discharges to quantify the effects of material erosion, H/D pickup and material surface damage. MiMES material exposure can be complemented by similar material buttons exposure using the DiMES system. Direction comparison can then be made between the chamber and divertor areas. |
| Resource Requirements: | MiMES and DiMES systems and initiated with repeated L-mode discharges for as long as possible. |
| Diagnostic Requirements: | Chamber wall, divertor and core diagnostics. |
| Analysis Requirements: | Edge plasma characterization, and will then be supported by modeling studies. |
| Other Requirements: | -- |
| Title |
388: Type II ELMs and the Evolution of Profiles Between Type I ELMs |
| Name: | Tom Osborne () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | P. Snyder, A. Leonard, J. Yu, J. Boedo, R. Moyer, J. Watkins |
| Description: | In this experiment we study the characteristics and stability properties of Type II ELMs in comparison to the Type I ELM regime. We test the hypothesis that Type II ELMs are pressure gradient driven while Type I ELMs require a peeling current drive. We also reexamine the effect of nonresonant fields on Type II ELMs. This work is motivated by the quest for an alternative to the Type I regime for ITER. |
| Experimental Approach/Plan: | We will establish a discharge with low frequency type I ELMs and significant Type II ELMs. We will look differences in filament and mode structure between ELM types on the fast UCSD camera, magnetics and the reciprocating probe. We will look at the effect of nonresonant filed perturbations, which have show strong effects on Type II ELMs in previous experiments, using the I-coil in odd parity. We will also have several repeat shots to gather data from the LiBeam and two view MSE to study the current profile evolution between Type I ELMs to test that hypothesis that the Type I ELM requires a current drive. We will also look at the effects of current ramps on Type I/II ELMs related to this same hypothesis |
| Background: | Small Type II ELMs appear near the end of the period between Type I ELMs in most DIII-D discharges. The small size of Type II ELMs compared to Type I ELMs makes their study important ans an alternative to the Type I regime which is unacceptable for ITER. In the rhostar scaling experiment on DIII-D Type II ELMs only appeared in discharges at small rhostar suggesting a favorable scaling to ITER. Discharges with exclusively Type II ELMs have only been obtained on DIII-D when a non-resonant field was applied with the I-coil (odd parity) at moderate collisionality (nustar_ped=1), suggesting a connection between Type II ELMs and non-axisymmetric fields. The fact that that Type II ELMs appear just before a Type I ELM suggests they are driven by a related instability. Typically the pedestal pressure profile reaches steady state well before the Type I ELM. This suggests a hypothesis for Type II ELMs as pressure gradient instabilities while the Type I ELM waits for the pedestal current density to increase to the peeling limit. Since peeling modes typically become more unstable as the pressure gradient decreases this may lead to much larger loss for the current driven Type I ELM. The rhostar scaling experiment and the association of type II ELMs with higher collisionality suggests an alternative hypothesis that the type II ELM is an instability of the foot of the pedestal pressure profile where current may decrease faster than the pressure gradient shutting off second stable access. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | UCSD fast camera, reciprocating probe, langmuir probes, Divertor IR TV. All profile diagnostics |
| Analysis Requirements: | Profiles, kinetic EFIT, ELITE stability, ONETWO simulation of current relaxation between Type I ELMs. |
| Other Requirements: | -- |
| Title |
389: Vertical Stability Control Using C-coil and I-coil |
| Name: | Dave Humphreys () |
Affiliation: | General Atomics |
| Research Area: | General PCO |
Presentation time: |
Not requested |
Co-Author(s): | D. Gates, S. Sabbagh, J. Leuer |
| Description: | The goals of this 1-day experiment are to study the potential for augmenting vertical control capability using the C-coil or the I-coil. |
| Experimental Approach/Plan: | |
| Background: | |
| Resource Requirements: | 0-4 beams (co), PCS modification |
| Diagnostic Requirements: | MSE, 5 kHz magnetics sampling |
| Analysis Requirements: | standard EFITs, TokSys, Corsica |
| Other Requirements: | -- |
| Title |
390: Measurement of RFA using the SXR Diagnostic |
| Name: | Matthew Lanctot ( ) |
Affiliation: | Columbia University |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | Andrea Garofalo and Holger Reimerdes |
| Description: | We will measure the internal mode structure of the plasma response (RFA) to externally applied magnetic field perturbations using the tools/techniques of active MHD spectroscopy and the SXR toroidal cameras. |
| Experimental Approach/Plan: | Apply slowly rotating (5-100 Hz) n=1 magnetic field perturbations with the Icoil while using feedback control of betan or control of the toroidal rotation. Analyze SXR data from these discharges to calculate a radial profile of the n=1 plasma fluid displacement. Compare these results with calculations of the mode structure of the external kink mode obtained from ideal MHD stability codes. Apply rotating error field in co and counter directions with respect to plasma rotation. Use neutral beam feedback control of the toroidal rotation to ramp down the rotation while applying the field to evaluate the effects of shielding. Scan beta and Icoil currents to maximize plasma response. |
| Background: | To date, on DIII-D, only arrays of magnetic sensors have been successfully used to investigate the RFA. Our goal is to extend the well-established methods of active MHD spectroscopy to include additional diagnostics. The newly refurbished SXR toroidal cameras can detect internal perturbations to the flux surfaces that result from externally applied fields. A more complete understanding of the internal RFA structure may help to elucidate the relationship between RFA and the RWM. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | MSE, CER, SXR, ECE, magnetics |
| Analysis Requirements: | CERFIT |
| Other Requirements: | -- |
| Title |
391: Optical Sensor for Feedback Control of Resistive Wall Modes |
| Name: | Matthew Lanctot () |
Affiliation: | Columbia University |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | Gerald Navratil, Andrea Garofalo, Holger Reimerdes, Ioan Bogatu, and Jin-soo Kim |
| Description: | We propose a proof-of-principle experiment whose primary goal is to demonstrate improved closed-loop performance of the n=1 RWM feedback control system by including soft x-ray photodiode detectors as optical sensors in the feedback algorithm. |
| Experimental Approach/Plan: | An evaluation of the method will be made by comparing the performance of the existing magnetic sensor algorithm to the multiple sensor algorithm. This experiment should follow other experiments that propose to measure the internal structure of the RWM at high and low rotation. Results from such experiments would aid in developing the new control algorithm. Tuning of the control system could occur during one or two two-hour experiments followed by a half-day session to demonstrate the effectiveness of the approach. |
| Background: | Initially, external radial magnetic field sensors were used to detect and track the n=1 resistive wall mode on DIII-D. Subsequent simulations suggested and experimental results indicated improved performance of the feedback control system using internal poloidal field probes. Johnson has shown that while magnetic probes can measure the helical mode structure at the plasma surface, the internal kink structure of the RWM can be detected using photodiodes that measure the soft x-ray emissivity. This is possible because the emissivity is a strongly varying function of density and temperature, two flux surface quantities, and the kink mode disturbs the equilibrium magnetic field. Since the present control system relies only on magnetic sensors, the RWM amplitude must exceed the magnetic noise level (~ 5-10 Gauss) at the vessel wall before triggering the feedback control system. This may be too late for the control system to provide full stabilization of the mode. Ongoing upgrades to the SXR diagnostic will make available at least three toroidally-separated measurements at 12 radial locations, which could in principle be used to track the slowly growing RWM before it is detected on the magnetic sensors. Early detection of a small amplitude RWM may improve the control system performance at low rotation. |
| Resource Requirements: | At least 4 real-time digitizer channels are needed to feed SXR signals to the PCS. Modifications to the existing feedback algorithm is necessary to include SXR measurements in the feedback logic. |
| Diagnostic Requirements: | 4 SXR cameras in R+1 ports at 45, 90, 165, and 195 degrees, MSE, CER, magnetics, Thomson |
| Analysis Requirements: | CERFIT |
| Other Requirements: | Success in this experiment depends upon the completion of work focused on characterizing the internal mode structure of the RWM using diagnostics located at multiple toroidal locations. |
| Title |
392: Resonant and Non-resonant magnetic braking |
| Name: | Matthew Lanctot () |
Affiliation: | Columbia University |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | A. M. Garofalo, H. Reimerdes, Gary Jackson |
| Description: | The purpose of this experiment is to investigate the effect of non-axisymmetric magnetic fields on rotating plasmas. This experiment is a continuation of previous efforts (MP 2007-04-04) to amass data from discharges where both resonant and non-resonant magnetic braking is applied to plasmas above and below the no-wall n=1 kink stability limit. To date, this experiment has received only 1/2 day of runtime. Data from discharges in both normal and reverse plasma current configurations are needed to compare with predictions from the neoclassical toroidal viscosity model of momentum dissipation. Analysis of these results may also indicate the presence of a significant n=3 error field on DIII-D. |
| Experimental Approach/Plan: | Using both normal-Ip and reverse-Ip configurations, we will measure the evolution of the plasma rotation while applying n=1 and n=3 magnetic braking using the I-coil. The phasing and/or the polarity of the I-coil configuration will be chosen to complement previous data. Magnetic, ECE and SXR data will be analyzed to detect the possible presence of error field induced magnetic islands after the braking phase of the discharge. |
| Background: | Operation in the high-beta regime, where plasmas exhibit a paramagnetic response to field asymmetries, is made possible by minimizing magnetic field errors. The optimal error field correction helps to maintain the plasma toroidal rotation, which has has been shown to have a stabilizing effect on potentially catastrophic MHD instabilities such as RWMs and tearing modes. A full understanding of the mechanism by which naturally occurring or injected angular momentum is lost from the plasma is lacking. Results from NSTX suggest the NTV theory should be considered when investigating questions of torque balance in toroidal plasmas. DIII-D results from this experiment will be compared with these NSTX results and similar experiments in JET. |
| Resource Requirements: | Toroidal field at 1.95 T for ECE measuremens. Normal and reversed Ip configurations. |
| Diagnostic Requirements: | Magnetics, ECE, SXR, MSE |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
393: NSTX/DIII-D simularity experiments |
| Name: | Eric Fredrickson ( ) |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Energetic Particles |
Presentation time: |
Not requested |
Co-Author(s): | (hopefully Heidbrink, Van Zeeland, Gorelenkov, other interested parties |
| Description: | Revisit NSTX simularity discharges previously developed to compare Alfven Cascade beta scaling, TAE avalanche thresholds and polarization measurements of CAE. |
| Experimental Approach/Plan: | Reproduce condition developed previously for TAE aspect ratio scaling experiment (e.g., 120190 etc). Lower density to reduce beta below stabilization threshold for Alfven Cascades (rsAE) as was done in NSTX experiments. Find condition where TAE present and do power scan to find threshold for TAE excitation. Attempt to reach threshold for TAE avalanching. CAE will likely be present in these shots and use new Mirnov coils to measure polarization of CAE, other modes. |
| Background: | Alfven Cascades seen in high field DIII-D plasmas and are suspected of fast ion redistribution. Operation at low field, and similar parameters to NSTX should put beta above threshold for "stabilization". First goal is to search for this beta-scaling of AC frequency sweeps. Second goal is to look for beta-fast threshold for onset of TAE, and then attempt to push beta-fast up to threshold for avalanch onset. Threshold might be higher in higher aspect ratio device. Finally, interesting results have been found regarding the polarization of TAE, AC and CAE on NSTX. Data from DIII-D could contribute to understanding the observed polarizations. |
| Resource Requirements: | Machine operation at 0.5 to 0.6 T and neutral beams at 80 kV. Possibly cryo-pumps to allow low density operation. Possibly need TF scan. |
| Diagnostic Requirements: | Fast Mirnov acquisition (5-10 MHz), reflectometers, BES, other fast internal mode diagnostics. MSE, CER, TS, neutrons and certainly FIDA. |
| Analysis Requirements: | EFIT and TRANSP. Higher level analysis by NOVA-k and/or M3D. |
| Other Requirements: | -- |
| Title |
394: High energy confinement, low density Type III discharges and study of Type III - Type I transition |
| Name: | Tom Osborne () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | P. Snyder, A. Leonard, J. Yu, J. Boedo, R. Moyer, J. Watkins, M. Fenstermacher |
| Description: | In this experiment we try to establish a low density Type III ELMing discharge with good energy confinement by operating near the Type III-Type I power threshold. We also continue a study of the Type III to Type I transition conditions. We will also look for differences in the structure between Type III and Type I ELMs. |
| Experimental Approach/Plan: | We will establish a Type III only discharge in with ITER shape operated near the Type III- Type I threshold power to obtain high energy confinement time and examine the Type III characteristics on the UCSD fast camera, magnetics and reciprocating probe to contract to the type I regime. We will then vary q and density to compare the Type III-Type I threshold conditions to previous results and theory. |
| Background: | The low density Type III ELM regime is generally though to be an unattractive alternative to the Type I regime for ITER due to the low pedestal pressure gradients obtainable in this regime relative to the Type I regime. However pedestal widths are typically larger in the low density Type III regime compared to the type I regime and previous results have show that much of the confinement is recovered if the discharge is operated near the threshold power for transition between the Type III and Type I regimes. Previous results from DIII-D showed that the power threshold for the Type III/Type I transition scaled as (n/n_GW)**-2, so that operating at low density gave a large margin of power above the H-mode threshold power where the Type III ELM regime could be achieved. In contrast to the Ighitanov/Poguetse theory which predicts a critical betaprime in the pedestal for transition out of the type III regime DIII-D results were more consistent with a critical alpha (q**2*betaprime). No measurements of the Type III ELM energy loss near were made on DIII-D and how Type III ELMs might fit into the filament ejection model for Type I ELMs has never been studied. Type III ELMs need to be reevaluated as an alternative to the Type I regime for ITER. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | UCSD fast camera, reciprocating probe, langmuir probes, Divertor IR TV. All profile diagnostics |
| Analysis Requirements: | Profiles, kinetic EFIT, ELITE stability |
| Other Requirements: | Low recycling machine conditions |
| Title |
395: Turbulence dependence on rho_* via working gas species (Hydrogen and Helium) (see transport area) |
| Name: | Terry L. Rhodes () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | Peebles |
| Description: | (Note that this proposal is being submitted here for completeness. The main submission is to the transport area.) Use dimensionally similar helium and hydrogen plasmas with matched Te, Ti, �?� to compare fluctuation and transport properties. Direct tests of turbulence simulation will be performed. |
| Experimental Approach/Plan: | Use helium and hydrogen plasmas with matched Te, Ti values. Te, Ti ratios and profiles will be adjusted using ECH, co and counter neutral beams. The rotation and radial electric fields will also be monitored and matched as possible. Use will be made of all the available turbulence and other diagnostics as appropriate. If successful the approach can be modified to examine shaped plasmas, H-mode/QH-mode plasmas, etc. |
| Background: | There is a well known dependence of the plasma confinement on the mass of the working gas, varying approximately as (Mass)^0.5. This variation will be addressed by comparing helium and hydrogen plasmas with Ti, Te matched as closely as possible. This should give approximately the same rho_i,e but of course different working gas masses. Theoretical turbulence expectations appear to depend upon the value of rho_i,e rather than the mass itself so the naïve expectation is that the plasmas should be very similar. Comparison of low, intermediate, high k turbulence, transport analysis, etc. will be made between the plasmas and theoretical expectations (analytic, numerical �??GYRO, GS2,�?�) . |
| Resource Requirements: | Hydrogen and helium plasmas, ECE, co and counter NBI |
| Diagnostic Requirements: | low, int, high k scattering diagnostics, Doppler
backscattering, CECE, BES |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
396: ELM interaction with main chamber wall |
| Name: | Dmitry Rudakov () |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | J. Yu, J. Boedo, N. Brooks, M. Groth, T. Evans, M. Fenstermacher, E. Hollmann, C. Lasnier, A. Leonard, R. Moyer, P. Stangeby, J. Watkins, P. West, C. Wong |
| Description: | Characterize ELM interactions with the main chamber wall under varying density/collisionality. Measure material erosion rates at the outer wall using MiMES. |
| Experimental Approach/Plan: | Synchronize as many fast edge/pedestal as possible to get reliable relative timing measurements. Perform measurements of the radial and poloidal propagation of ELM pulses at 3-4 different normalized densities n/n_GW of 0.4-0.9. Perform material sample exposure with MiMES. Turn on I-coil during the last second of the shot to attempt ELM reduction. |
| Background: | |
| Resource Requirements: | 1 day experiment; LSN H-mode, 4 sources of NBI, I-coils |
| Diagnostic Requirements: | All available fast edge and pedestal diagnostics; profile diagnostics |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
397: New ORNL pellet dropper to modify edge instability drives |
| Name: | Terry L. Rhodes () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | Jernigan, Boedo, Moyer, McKee, Schmitz, Wang, Zeng |
| Description: | Use new pellet dropper to modify edge instability drives in both L and H mode. We will utilize this new capability to probe the edge instabilities by periodically modifying the edge n_e and Te while simultaneously measuring with all available turbulence and profile diagnostics. |
| Experimental Approach/Plan: | -- |
| Background: | Identification of edge fluctuations, drive, etc. (pedestal and SOL) is not complete. The edge is a complicated interconnected system and there is not yet a complete picture of the dynamics there. The pellet dropper may allow a way to probe this system by locally modifying the edge drives in a new manner. |
| Resource Requirements: | pellet dropper (new ORNL system) plus all relevent turbulence and profile diagnostics |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
398: RMP pedestal transport and stability at normal density |
| Name: | Ilon Joseph () |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | TE Evans, ME Fenstermacher, RA Moyer, TH Osborne |
| Description: | Compare pedestal transport in an ELMing plasma versus an RMP plasma at the SAME density. The two major goals are to determine: 1. WHERE transport changes occur, and 2. HOW the ELM stability boundary is affected.
Reconstruct diffusivity profile to determine WHERE local transport changes have occurred: at the top of the pedestal, or only near the separatrix and SOL. Directly measure HOW the ELM stability boundary changes in RMP plasmas with the same density. |
| Experimental Approach/Plan: | Move plasma far enough away from pump to achieve the same line-averaged density before and after application of the I-coil pulse. Characterize pedestal transport by using edge breathing to develop high-resolution TS and CER profiles across the pedestal. |
| Background: | Attempts to understand changes in RMP transport and stability have been frustrated by the significant changes of temperature and density profiles between the original ELMing plasma and the final low density RMP plasma. A simple method to mitigate such changes is to move the strike point far enough away from the pump to maintain the same density before and after the I-coil is applied. The pedestal profiles of the before and after states can then be directly compared. If the diffusivities are shown to change at the top of the pedestal, one could conclude that effects deeper in the plasma such as the production of an island, or stochastic region, or in a model with complete shielding: by neoclassical transport in the resonant components of delta B^2 due to a perfectly ideal mode (compare to EHO). If, however, transport is only changed near the separatrix and SOL, one would need to assume that only a small of the plasma is sensitive to RMP induced transport changes.
By working in plasmas at relatively similar density and temperatures, one will be able to directly determine the effect of the RMP on the ELM stability boundary. |
| Resource Requirements: | n=3 I-coil, edge breathing to develop high resolution TS and CER edge profiles. |
| Diagnostic Requirements: | Turbulence diagnostics. |
| Analysis Requirements: | ONETWO, TRANSP |
| Other Requirements: | -- |
| Title |
399: Co-Injected QH-mode access using edge EC/ECCD |
| Name: | Phil West () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | K. Burrell, C. Lasnier, D. Thomas, M. Fenstermacher |
| Description: | Use ECH/ECCD in the region of the pedestal to increase the edge current and decrease the edge density and enhance access to QH-mode in co-injected discharges |
| Experimental Approach/Plan: | Work with the RF heating experts to establish a good scenario for edge ECH and ECCD. Establish a strongly pumped, low-density ELMing H-mode in a shape suitable for good edge ECH/ECCD and good pedestal and ELM diagnostics. Tweek the shape and EC aiming to optimize pedestal heating. Do ECH power and location scans. Document the pedestal conditions and ELM properties. Aim the EC power for ECCD and repeat the scans. |
| Background: | The ELM-free QH mode is a good candidate for ITER and beyond due to its good confinement properties and the absence of ELMs. The one disadvantage is that is has been observed only in discharges with counter injection. Of the many characteristics of QH-mode that are not typically achieved in co-injected discharges are two are address in this proposal: 1)an enhanced particle transport across the ETB, connected with the EHO and 2) a high edge current density due to low collisionality and high bootstrap drive. ECH has been observed to provide enhance particle transport in the presence of core transport barriers and has been used to reduce density and impurity peaking in these cases. A test of enhancing the particle transport across the ETB is proposed. In addition ECH edge heating can be expected to increase the edge current density by increasing the edge collisionality through both the density decrease and electron heating. Use of ECCD at the edge may further increase the current density. If successful we should be able to bring the co-injected edge plasma closer the hhe conditions observed in counter-injected QH-mode. |
| Resource Requirements: | Normal co-injection configuration
Bt and shape adjusted for needs of ECH/ECCD
Ip chosen to achieve q95~4.5
6 Beams, including 30L and both 330�??s
4 Gyrotrons (pending ECH modeling)
Cryopumping |
| Diagnostic Requirements: | Essential:
Thomson
CER
Edge Reflectometry
BES
Fast magnetics for ELM delW, EHO
SPRED
CO2 Interferometry
Desired:
Li Beam Polarimeter
IRTV
Bolometry
Divertor Tangential TVs |
| Analysis Requirements: | Standard ELM and pedestal analysis
Level of detail depends on qualitative success |
| Other Requirements: | -- |
| Title |
400: Continue development of reactor optimized hybrid plasmas |
| Name: | Edward Doyle () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Attempt to maximize reactor compatible features of hybrid operation on DIII-D, specifically pressing to Te/Ti~1 and combining with low rotation operation. These goals address IEA/ITPA Transprt Physics joint experiments on effect of Te/Ti ratio and operation with low momentum input. |
| Experimental Approach/Plan: | Two approaches possible: (1) Continue 2007 experiments (see background section), at low to moderate q95 (~3-4). Progress here could be made by: (a) Using additional ECH heating (6 gyrotrons required?), to further raise Te/Ti ratio, and/or (b) Use counter-NBi capability to simultaneously lower rotation rates in hybrid plasmas with maximal Te/Ti ratio. (2) Change target plasmas so as to increase relative effect of ECH on plasma. |
| Background: | Experiments in 2007 (20070627 and 20070709) at q95 of ~3.3 and 4.2, attained Te/Ti~0.8 with four gyrotrons (~2.4 MW at plasma). Plasma rotation with ECH was matched in NBI only discharges by making use of co-/counter-NBI capability. |
| Resource Requirements: | 5 gyrotrons minimum, 7 beams required |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
401: Dedicated Experiments to Check Cross Section Correction forCER Rotation Measurements |
| Name: | Keith Burrell () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | W.M. Solomon |
| Description: | Use dedicated scans of plasma temperature and rotation to check the
cross section correction used for CER measurements of plasma rotation. |
| Experimental Approach/Plan: | Perform NBI power and torque scans in steady state phase of L-mode
or QH-mode discharges. Goal is to vary Ti and v_phi as much as
possible to check cross section correction as a function of these
variables. L-mode provides the lowest temperature and rotation points
while QH-mode reaches the Ti and v_phi extremes. |
| Background: | Because the cross section for charge exchange between beam neutrals
and ion in the plasma depends on energy, ions moving with the beam
have typically a lower charge exchange cross section while those
moving against the beam have a higher cross section. This results in
an apparent shift in the ion velocity when that velocity is measured
using the post-charge-exchange spectrum. This correction depends on
the ion temperature and toroidal rotation speed of the background
plasma. The magnitude of the correction relative to the plasma
rotation speed is largest for high temperature, low rotation speed
plasmas, such a those created with high power balanced beam injection.
Such discharges are becoming increasingly important for the D III-D
program. We have an algorithm which we use to correct the C VI
rotation speed for the energy dependent cross section. This is fairly
complex, since it involves a significant amount of atomic physics.
Now that we have CER views of the co and counter neutral beams, we can
also directly measure the cross section correction since it has a
different sign for the co and counter beams whereas the actual plasma
rotation is the same. This experiment would produce high quality
CER data to compare the measured and calculated cross section
correction. |
| Resource Requirements: | NBI modulation with 30LT and 210RT modulated in phase is essential. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
402: |
| Name: | Yutaka Kamada ( ) |
Affiliation: | JAEA |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | A.Leonard, N.Oyama, H.Urano, Y. Sakamoto, M.Yoshida |
| Description: | By Utilizing the unique capability of rotation control with co- and counter- NBs in DIII-D and JT-60U and by utilizing the difference in the plasma shape and edge stability between the two tokamaks, we propose to conduct the inter-machine experiments on the rotation effects on the pedestal structure and type I ELMs. (ITPA Inter-machine experiment PEP-18) |
| Experimental Approach/Plan: | As the first step of the study, we propose the study on effects of rotation on Type I ELM, pedestal transport and core transport at different plasma shape. In JT-60U, effects of the toroidal rotation have been clarified at medium triangularity ~0.3. Based on the ITPA pedestal database, the pedestal structure in JT-60U and DIII-D are quite different: DIII-D has large pressure gradient and narrow pedestal width compared with JT-60U. This difference seems to be due to the plasma shape. In order to clarify the effects of rotation at different pedestal situation, we propose rotation scan experiments at higher triangularity in DIII-D and take the following data:
1) Frequency and energy loss (incl. ELM affected area) of type I ELMs, and Pedestal width and inter-ELM transport at the same _p-ped and q95 with JT-60U,
2) Frequency and energy loss of type I ELMs, and Pedestal width and inter-ELM transport at the same pedestal collisionality and q95 with JT-60U, and
3) Core thermal confinement of the plasmas in 1) and 2).
By comparing the data in DIII-D and JT-60U, we can clarify whether the rotation effects are universal, and the dependence of these effects on plasma shape. |
| Background: | Recent tokamak experiments have revealed that the pedestal and core transport of the H-mode plasmas are determined under the linkage among pressure, current and rotation profiles. The goal of this research is to understand this complex system in order to improve predictive capability for ITER, and to develop control schemes for the pedestal parameters and ELMs and core transport. Concerning the parameter linkage, plasma rotation and its radial profile seem to play critical roles. Recent JT-60U experiment has demonstrated a shift of toroidal plasma rotation VT into co-direction reduces the inter-ELM transport loss and increase the pedestal height and width. In addition, type I ELM energy loss normalized to the pedestal stored energy (_WELM/Wped) increases with increasing co-directed rotation. The critical importance is to clarify the rotation effects on the pedestal structure and ELMs over a wide range of the plasma shape. Is is also important to separate the effects of rotation and ripple loss on the pedestal structure and ELMs. As for the core confinement of H-mode plasmas, both DIII-D and JT-60U have shown improved performance with co-directed rotation compared with counter rotation. The purpose of this study is to clarify the roles of plasma rotation systematically by utilizing the unique capability of rotation control with co- and counter- NBs in DIII-D and JT-60U and by utilizing the difference in the plasma shape and edge stability between the two tokamaks. |
| Resource Requirements: | TBD |
| Diagnostic Requirements: | Charge Exchange Recombination, Thomson etc.. |
| Analysis Requirements: | TBD |
| Other Requirements: | Joint Work with ' Rotation Phys.' group |
| Title |
403: Aspect Ratio Scaling of Core Turbulence |
| Name: | Shigeyuki Kubota ( ) |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | T.L. Rhodes, G. Wang, W.A. Peebles, G.J. Kramer |
| Description: | Gyrokinetic microstability analyses indicate that low-k mode (ITG/TEM/micro-tearing) are sensitive to changes in the aspect ratio, beta, and Te/Ti. Here we propose similarity experiments in NSTX (A~1.3) and DIII-D (A~2-3) to look at the aspect ratio dependence of core turbulence properties. In particular, we will look at the turbulence radial correlation lengths determined from correlation reflectometry, since similar reflectometry hardware exists on both machines and the correlation length is a statistical property which allows a direct comparison between machines as well as with gyrokinetic codes. |
| Experimental Approach/Plan: | The matched target plasmas (from the standpoint of NSTX) should be L-mode, beam-heated plasmas with Bt~0.6 T and peaked density profiles with ne0~2-3x10^13 cm-3 for good reflectometer access. He working gas for good density control. The target shot should have a long MHD-free period. |
| Background: | Rewoldt et al. [Phys Plasmas 3, 1667 (1996)] initially demonstrated the stabilizing influence of the low aspect ratio on low-k modes, while more recent studies using linear GS2 analyses [Nucl Fusion 40, 677 (2000); Phys Plasmas 10, 2881 (2003)] with beta normal kept constant, have shown that beta is the dominant parameter and that the aspect ratio has little effect. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | Profile and fluctuation diagnostics. Profile and correlation reflectometers. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
404: QH mode comparison in DIII-D and JT-60U |
| Name: | Yoshiteru Sakamoto ( ) |
Affiliation: | JAEA |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | P. Gohil, N. Oyama, Y. Kamada, H. Urano |
| Description: | Purposes of this experiment are to clarify the roles of toroidal rotation, GAPOUT and EHO in accessing and maintaining QH-mode plasmas, and to investigate the pedestal structure in different edge toroidal rotation by utilizing the control capability of toroidal rotation in DIII-D and JT-60U. (ITPA inter-machine experiment TP-5/PEP-14) |
| Experimental Approach/Plan: | In JT-60U, QH-mode was observed in co-, ctr- and balanced injection plasmas with EHO. Optimum GAPOUT seems to depend on edge toroidal rotation. Increase in power during QH-mode leads to ELMy H-mode. Therefore we propose the following experiments on DIII-D. (1) GAPOUT scan during fixed edge toroidal rotation. (2) NB power scan in different edge toroidal rotation. The effects of toroidal rotation and GAPOUT on accessing QH-mode, and the change in pedestal structures in DIII-D will be compared to those in JT-60U. |
| Background: | The mitigation of the pulsed large heat load induced by ELM on the diverter plates is one of the important issues for a tokamak fusion reactor. QH-mode plasmas, found in DIII-D, with H-mode confinement but without such ELM-related physics issues can potentially offer an attractive regime for tokamak operations. In JT-60U, QH-mode was observed in co-, ctr- and balanced injected plasmas with large and optimum GAPOUT. Optimum GAPOUT seems to depend on edge toroidal rotation. The EHOs were observed in the edge channels of the ECE and BES diagnostics during QH-mode phases. The comparison of QH-mode properties in DIII-D and JT-60U is useful to improve understanding of QH-mode. |
| Resource Requirements: | Co and Counter NBs, cryopumps |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
405: Role of pedestal on global confinement in hybrid scenario: extend beta range with AUG shape |
| Name: | Costanza Maggi ( ) |
Affiliation: | IPP Garching |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | Richard Groebner |
| Description: | Study the relation between pedestal and global confinement in hybrid scenario as the input power (beta) is increased.The main physics goal is to determine if there is evidence of saturation of the pedestal beta as the input power is increased or if the pedestal beta continues to increase with power and total beta. A beta scan over as large a range as possible is desirable, for instance a factor of 2, but this has not yet been achieved. These experiments (following a proposal to ROF 2005) were performed in Spring 2007 and were successful. However, on the first experimental day we could not complete the power scan in the AUG shape due to frequent cut-outs of beam sources 330. This meant that we could not achieve stable operation at betaN>2.5. In addition, in the discharge (#128213) where betaN ~2.7 was achieved over a short time interval, no Thomson data could be collected. It would be highly desirable to be able to complete this power scan and obtain pedestal data also at high betaN in the AUG shape, since at present we are missing some information on the effect of shape on pedestal pressure at high betaN. |
| Experimental Approach/Plan: | Plasma shape: AUG hybrid shape as in shots #128198 >> 128213 - early heating scheme. This requires the AUG patch panel.
Requested betaN: repeat first part of power scan performed in March 2007 and add points at higher betaN: betaN=1.5 (#128206), 2.0 (#128198) , 2.5 (#128200), 2.7 for comparison with DIII-D shape (#128245), 2.9 for comp. with DIII-D shape (#128249), ~ 3.3 or max achievable, depending on available beam power.
Plasma density: 4x 10^19 m-3, as in the discharges performed on 26.03.07. |
| Background: | Experiments were performed in Spring 2007 at DIII-D to study the role of the pedestal on global confinement in hybrid discharges and to closely compare the pedestal in hybrid discharges of ASDEX Upgrade and DIII-D. The experiments were focussed on the study of the variation of the edge transport barrier (ETB) with power (beta) at fixed q95 ~ 4.5 and density (~ 4x 10^19 m-3) in two different shapes: a low triangularity (AUG) and a high triangularity (DIII-D) shape. The experiments were successful, except for the missing data at high beta in the AUG shape, and excellent pedestal data were collected using outer plasma sweeps to improve the spatial resolution of the Thomson scattering and CER diagnostics in the edge region. Analysis of the experiments shows that at a given betaN the confinement factor as well as the pedestal beta, betaN,PED, are higher in the higher triangularity shape. However, a different variation of the pedestal top pressure with power was observed in the two shapes: whereas betaN,PED increased with power (beta) in the AUG shape (up to betaN=2.5), it remained constant or even decreased with total betaN in the higher triangularity DIII-D shape (max total betaN=2.9). These data imply that the plasma is not stiff (as shown clearly by the kinetic profiles, especially Ti) in the DIII-D shape: the increase in confinement is due to an increase in core enrgy at essentially constant pedestal energy. The results of this power scan are at odds with other power scans in DIII-D and with previous analysis of the pedestal in hybrid discharges [1], which showed pPED to increase with power roughly as pPED~ P_NET^0.31, although the improved confinement at high betaN was due to improved core confinement. This difference is not yet understood, but analysis of the data is ongoing. The power scan in the AUG shape shows a variation of betaN,PED with power similar to what found in AUG up to betaN=2.5. Unfortunately, due to technical reasons, the high beta range of the scan is missing in this shape.
Further experiments are being proposed in improved H-modes on ASDEX Upgrade for 2008 to continue the characterization of the response of the ETB structure to input power (including high resolution measurements of the ion ETB).
[1] C.F. Maggi et al., Nucl. Fusion 47 (2007) 535. |
| Resource Requirements: | Machine time : 1/2 day |
| Diagnostic Requirements: | ne, Te profiles from Thomson scattering
ni, Ti, vtor profiles from CER
particular emphasis on pedestal region, therefore also outer plasma sweeping for improved spatial resolution at the edge
MSE |
| Analysis Requirements: | Thomson, CER data profiles |
| Other Requirements: | -- |
| Title |
406: Comparative study of RWM Excitation in low rotation plasmas on JT60U and DIII-D |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | Go Matsunaga, M. Takechi (JAEA) and DIIID RWM group |
| Description: | DIIID and JT60U have reported that the RWM critical rotation behaves in a similar manner with the low rotation plasmas (Phys. Rev. Lett. 98, 055002 (2007) / 055001 (2007). However, the RWM, the consequence of external kinks excitation interacted with the resistive wall, could behave differently depending upon the details of the plasma boundary condition as well as the resistive wall geometry. Here, it is proposed to carry out a series of comparative studies to generalize the experimental results. This should be extremely useful for designing future devices. |
| Experimental Approach/Plan: | Subjects for comparative studies are:
(1) RWM seeds, and the amplitude evolvement in time ( growth rate)
(2) RWM onset relative to the tearing modes onset
(3) the mode structure measurement: radial profiles by the soft x-ray arrays and poloidal mode structure by poloidal mirnov signals
(4) n=1residual mode activity above no-wall limit
(5) possibility of higher n RFA
Experiments
The plasma conditions will be similar to the conditions reported previously in these PRLs. Some of data are already available from the previous shots. Diagnostics essential for RWM documentation have be improved in coming experiments on both devices. In particular, soft x-ray arrays both in devices will be ready for the detailed mode structure analysis.
These experiments will provide information useful for designing future device, like ITER. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
407: ITER Mirror performance test. Active control over the deposition on the mirrors by the gas feed. |
| Name: | Andrey Litnovsky ( ) |
Affiliation: | Forschungszentrum Juelich |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | D. Rudakov (UCSD), V. Philipps (FZJ), C. Wong (GA), W. West (GA), R. Boivin(GA), N. Brooks (GA), P. Wienhold (FZJ), G. Sergienko (FZJ), R. Bastasz (SNL), J. Whaley (SNL), W. Wampler (SNL), J. Watkins (SNL), J. Brooks (ANL), T. Evans (GA), D. Whyte (UW), P. Stangeby (Univ. of Toronto), A.Mclean (Univ. of Toronto), J. Boedo (UCSD), R. Moyer (UCSD) |
| Description: | This experiment is the further continuation of the tests of ITER candidate mirror materials under ITER relevant plasma conditions. The goal is to study the efficiency of the gas feed in front of the mirror to mitigate the deposition on the mirror surface |
| Experimental Approach/Plan: | Following the results obtained in 2005 and 2006 when the dedicated experiments were done with diagnostic mirrors in the divertor of DIII-D, the continuation of this program is proposed. In the experiments made in 2005 and 2006, the suppression of carbon deposition was demonstrated in the experiment made in 2005 and the complete preservation of mirror optical characteristics was achieved in the experiment made in 2006. The gas feed in the vicinity of mirror is another attractive option to mitigate the impurity deposition and degradation of the optical properties of the diagnostic mirrors which should be tested in divertor environment.
It is planned to expose the set of mirrors in the private flux region for series of identical ELMy H-Mode discharges similar to those used in 2005-2006 experiments. The exposure is to be made using the DiMES Mirror holder. Molybdenum mirrors will be used for the experiment. The gas flow of D in the vicinity of mirrors will be realized using the existing gas feed system located near the DiMES transport system. Total exposure time of >40 seconds (>8 plasma discharges) is requested. |
| Background: | Metallic first mirrors are currently foreseen for all optical and laser diagnostics of ITER. The mirrors will be subject to erosion, deposition and particle implantation which will degrade their properties and impact the performance of entire respective diagnostic systems in ITER. The robust solution is needed to ensure the optimal performance of diagnostic mirrors in ITER throughout the whole lifetime of the machine. The development of the deposition mitigation techniques is of crucial importance to make such a solution possible.
The investigations on first mirrors are presently recognized as High Priority Task of the ITPA Topical Group on Diagnostics and are the subject of IEA-ITPA Joint Experiments Program (Task DIAG 2). The importance of the R&D program on first mirrors was outlined in the recent ITER Diagnostics review, carried out in Cadarache, France in July 2007.
The first-ever dedicated experiment with ITER-candidate mirror materials under ITER-relevant conditions was performed in DIII-D divertor in April 2005. This experiment confirmed that mirrors in detached divertor suffer from carbon deposition. It also delivered important information on the active deposition mitigation on divertor mirrors by elevated temperature. The subsequent experiment in 2006 has demonstrated the capability to prevent the carbon deposition and degradation of optical properties by heating the mirrors. Another promising technique presently being assessed for several ITER diagnostics, is the gas feed in front of the mirrors protecting them from deposition of impurities. In the pilot experiment performed in TEXTOR it was demonstrated that the gas feed is capable to prevent the carbon deposition on the mirrors directly exposed in plasma. We need to elaborate this technique further and to prove that the gas feed is efficient enough to gain the control under deposition in the ITER-relevant divertor conditions. |
| Resource Requirements: | Machine Time: 1/2 day experiment
Number of neutral beam sources: 3 |
| Diagnostic Requirements: | all SOL and lower divertor diagnostics, DiMES TV, core Thomson scattering, CER. |
| Analysis Requirements: | SIMS, XPS, Ellipsometry, Reflectivity measurements, NRA, DEKTAK profiling (the most of analyses will be provided by FZJ) |
| Other Requirements: | Plasma shape and discharge parameters similar to those of experiment with molybdenum mirrors performed on September 8, 2006 |
| Title |
408: Comparisons of L-mode and H-mode in hydrogen and deuterium |
| Name: | Robert Budny ( ) |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | Wayne Solomon, Keith Burrell, Craig Petty (?), Jeff Candy, Ron Waltz |
| Description: | We want to improve understanding of the isotopic scaling from present experiments to those anticipated in ITER. The first phase of physics experiments in ITER is expected to be L-mode and H-mode if accessible with hydrogen. The next phase is expected to be L-mode and H-mode in DT plasmas. Most of the present database is in deuterium plasmas. We plan to create pairs of H and D L-mode and H-mode plasmas with similar profiles, similar ELM characteristics if possible, and low rotation (but presumably different beam powers). |
| Experimental Approach/Plan: | Create matched L- and H-mode plasmas in separate runs with H and D. |
| Background: | Gyrokinetic theory implies that the scaling should follow gyro-Bohm, but there are various indications that this might not be the case. One example is a study of scaling of transport in JET H-modes with H, D, DT, and T plasmas (R.Budny et al, PoP 12 (2000) p5038-5050). The dimensionless coefficients of ion energy and momentum transport near the mid-radius scaled as isotopic mass to a power near minus unity instead of the gyrokinetic rho* prediction of plus 0.5. |
| Resource Requirements: | co & ctr NBI |
| Diagnostic Requirements: | plasma profiles including CX and MSE; turbulence measurements |
| Analysis Requirements: | We will GYRO code to compare their transport and turbulence. We can swap profiles and rho* to compare effects of different profiles and rho* on transport. We anticipate needing lots of nonlinear, extended-radial domain runs for the analysis |
| Other Requirements: | -- |
| Title |
409: Demonstrate TokSys to Tokamak Capability |
| Name: | Mickey R. Wade () |
Affiliation: | General Atomics |
| Research Area: | General PCO |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Demonstrate the capability to design a plasma scenario offline and
transfer this to the tokamak in a few number of shots. Such demonstration would improve the efficiiency of plasma operation and provide evidence that such capability would be possible
on ITER |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
410: Pedestal width dependence on Beta |
| Name: | Anthony W Leonard ( ) |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | R. Groebner, T. Osborne, P. Snyder |
| Description: | Use variations in shape, q95, and q profile to determine factors that affect the pedestal width dependence on global beta. |
| Experimental Approach/Plan: | 1. Confirm the lack of pedestal width scaling in the LSN hybrid case.
2. Confirm the high triangularity LSN case where the pedestal does scale with global beta.
3. Adjust case #2 for a similar shape and q95 as in case #1.
4. If case #3 pedestal still scales with beta, adjust the early heating to match the q profile and NTM activity of case #1. |
| Background: | During the previous year's experiment, a beta scan in a LSN hybrid did not produce a significant change in the pedestal height. This is the only case so far observed where the pedestal beta did not increase with global beta. The result appears robust and reproducible. This experiment will seek to determine which factor is responsible for this change in scaling. Isolating this controlling factor should provide insight into the physical mechanisms controllin the pedestal width. |
| Resource Requirements: | LSN with pumping and 5 sources of co-NBI |
| Diagnostic Requirements: | All pedestal diagnostics |
| Analysis Requirements: | Pedestal profile and stability analysis |
| Other Requirements: | -- |
| Title |
411: Poloidal Asymmetry of Separatrix heat flux in H-mode |
| Name: | Anthony W Leonard () |
Affiliation: | General Atomics |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Use a balanced double-null divertor to determine the in/out asymmetry of heat flux crossing the separatrix |
| Experimental Approach/Plan: | Create a balanced double-null configuration in L-mode and ELMing H-mode. Set up the H-mode to have regular well spaced ELMs. Measure the the heat flux to all 4 strike-points using IR cameras and four mounted probes. Compare the in/out asymmetry in L-mode to H-mode. For H-mode measure the heat flux between ELMs with the floor probes, and compare to the IR cameras. The particle flux will be more difficult to determine due to target plate recycling. |
| Background: | The in/out asymmetry of heat and particle flux across the last closed flux surface is well established in L-mode in a number of devices. The level of asymmetry in H-mode is less well characterized. This experiment would provide an estimate of this asymmetry in H-mode. It is likely the in/out heat flux can be estimated, but the particle flux will be more problematic. |
| Resource Requirements: | Double null configuration with 2-5 co-NBI sources |
| Diagnostic Requirements: | Pedestal and divertor diagnostics, particularly target plate probes and IR cameras. Fluctuation diagnostics would also be desirable. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
412: Pedestal Width dependence on Grad-B Direction |
| Name: | Anthony W Leonard () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | R. Groebner, T. Osborne, P. Snyder |
| Description: | Determine the effect of Grab-B drift direction on the pedestal width |
| Experimental Approach/Plan: | Reproduce the hybrid beta scan in LSN. Carry out similar beta scan but in USN with same toroidal field direction. Compare this to the case where there was not change in pedestal in USN vs. LSN. Systematically remove differences between these two scans to determine the controlling physics. |
| Background: | A number of beta scans in hybrid, or other high triangularity, configurations, has indicated that for the unfavorable Grad-B drift direction the pedestal density, and usually the pedestal pressure, is lower. This experiment will isolate the physical parameters controlling this scaling and determine if it comes primarily through a change in the pedestal width. |
| Resource Requirements: | USN and LSN high triangularity configurations. 5 co-NBI sources |
| Diagnostic Requirements: | All pedestal diagnostics |
| Analysis Requirements: | Pedestal profile and stability analysis |
| Other Requirements: | -- |
| Title |
413: RMP ELM suppression dependence on Grad-B drift direction |
| Name: | Anthony W Leonard () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Compare RMP ELM suppression in USN vs LSN for otherwise identical discharges. |
| Experimental Approach/Plan: | Use high triangularity configuration that can be easily switched between USN and LSN. Compare RMP ELM suppression in both cases. |
| Background: | Previous attempts at RMP suppression in Hybrid discharges found very different behavior in USN discharges versus most of the work done in LSN. This experiment will closely examine the differences to hopefully shed light on the transport and ELM stability changes |
| Resource Requirements: | High triangularity configuration to switch between USN and LSN. I-coils for ELM suppression and 5- co-NBI sources |
| Diagnostic Requirements: | All pedestal and ELM diagnostics |
| Analysis Requirements: | Pedestal profile and stability analysis |
| Other Requirements: | -- |
| Title |
414: Studies of ITER-like castellation in DIII-D: impact of castellation shape on fuel retention in gaps |
| Name: | Andrey Litnovsky () |
Affiliation: | Forschungszentrum Juelich |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Requested |
Co-Author(s): | D. Rudakov (UCSD), V. Philipps (FZJ), C. Wong (GA), W. West (GA), R. Boivin(GA), N. Brooks (GA), P. Wienhold (FZJ), G. Sergienko (FZJ), R. Bastasz (SNL), J. Whaley (SNL), W. Wampler (SNL), J. Watkins (SNL), J. Brooks (ANL), T. Evans (GA), D. Whyte (UW), P. Stangeby (Univ. of Toronto), A.Mclean (Univ. of Toronto), J. Boedo (UCSD), R. Moyer (UCSD) |
| Description: | This experiment is aimed at investigating the carbon transport and fuel accumulation in the ITER-like tungsten castellated structures. The essential goal of the experiment is to test the optimized shaping of the castellation cells to minimize the fuel accumulation in gaps. |
| Experimental Approach/Plan: | The experiments performed in DIII-D in 2005 with gap samples exposed in the DIII-D divertor using the DiMES system have demonstrated the positive effect of elevated temperatures on the carbon deposition and fuel accumulation in gaps. The next step in minimization of the impurity and fuel transport into gaps is the optimization of the shape of castellation.
It is planned to expose two sets of castellation samples in the private flux region for series of identical ELMy H-Mode discharges. The exposure is to be made using the DiMES transport system. Tungsten castellation will be used for the experiment, since the tungsten is planned to be used as a plasma-facing material in ITER divertor. Two shapes of castellation will be used: conventional (rectangular) shape and the optimized (dome-like) shape. Exposure time of >40 seconds (>8 plasma discharges) is requested per each castellation set. |
| Background: | The armor of the first wall and divertor of ITER will be castellated by splitting it into small-size cells to maintain the durability under the thermal excursions during plasma operation. However, there are concerns about the impurity deposition and fuel accumulation in the gaps of castellated structures. Past research demonstrated that the fuel inventory may become an issue for ITER, given the difficulties on fuel removal. To address this problem, dedicated investigations are ongoing on several tokamaks.
The investigations on fuel retention in the gaps of castellated structures are presently recognized as an important activity of the ITPA Topical Group on Divertor and SOL and are the subject of IEA-ITPA Joint Experiments Program (Task DSOL 13).
The optimization of the shape of castellation is the relatively natural way towards the minimization of the fuel retention in gaps.
The understanding of the physical processes behind the transport into gaps is of significant importance. The flexible design of the castellation allows the studies of deposition patterns in both toroidal and poloidal gaps, to reveal the effect of the gap orientation. Another advantage of this experiment is that the exposure of the castellated samples in private flux region of the DIII-D divertor will be performed at the shallow angles of castellation with respect to magnetic field, similarly as expected in ITER. |
| Resource Requirements: | Machine Time: 2x1/2 day experiment
Number of neutral beam sources: 3 |
| Diagnostic Requirements: | all SOL and lower divertor diagnostics, DiMES TV, core Thomson scattering, CER. |
| Analysis Requirements: | SIMS, XPS, Ellipsometry, NRA, DEKTAK profiling (the most of analyses will be provided by FZJ) |
| Other Requirements: | Plasma shape and discharge parameters similar to those of experiment with molybdenum mirrors performed on September 8, 2006 |
| Title |
415: Rapid pellets for lower density radiative divertor |
| Name: | Anthony W Leonard () |
Affiliation: | General Atomics |
| Research Area: | Core-Edge Integration |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Use rapid pellet injection with impurity puffing to produce a steady radiative divertor at a lower density than would be otherwise achievable. |
| Experimental Approach/Plan: | Set up a long pulse hybrid, or other high performance, discharge. Inject a radiating noble gas such as neon, or argon, while at the same time injecting rapid pellets, ~ 50 Hz, from the pellet dropper. Use pumping to control density. Adjust impurity injection to produce a radiative divertor with reduced heat flux. |
| Background: | Impurity injection for heat flux control typically results in core impurity accumulation and radiation which reduces the ELM frequency which further increases impurity acccumulation in a runaway process. Rapid pellet injection which induces ELMs offers the possibility of controlling the core impurity acccumulation keeping more of the impurities in the divertor where they can radiate away the heat flux. |
| Resource Requirements: | Pellet dropper, divertor pumping, and impurity injection |
| Diagnostic Requirements: | All divertor and pedestal diagnostics. Core impurity diagnostics. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
416: RWM n=1 Component Internal Structure in Low Rotation Plasma |
| Name: | Ioan N. Bogatu () |
Affiliation: | FAR-TECH, Inc. |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | Yongkyoon In (FAR-TECH, Inc.), Jin-Soo Kim (FAR-TECH, Inc.), Matt Lanctot (Columbia University), H. Reimerdes (Columbia University), K. Burrell (GA), W. Solomon (PPPL), E.J. Strait (GA) |
| Description: | To investigate the multi-faceted physics of the interaction of the internal structure of n=1 component of MHD activity (RWM ) with toroidal rotation and current density profile evolution in low rotation plasma. |
| Experimental Approach/Plan: | |
| Background: | |
| Resource Requirements: | Piggy-back on low-rotation RWM target plasmas. |
| Diagnostic Requirements: | SXR three TAs, CER (CERFIT with atomic data correction), MSE, and ECE |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
417: Injection of pre-characterized dust in using DiMES |
| Name: | Dmitry Rudakov () |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | P. West, C. Wong, J. Yu, M. Groth, B. Bray, N. Brooks, C. Lasnier, M. Fenstermacher, A. Pigarov, R. Smirnov, W. Solomon |
| Description: | Injection of pre-characterized graphite, diamond and boron dust in the lower divertor of DIII-D using DiMES. The objectives are: 1) study dust dynamics and migration in a tokamak; 2) benchmark DustT modeling, 3) calibrate cameras and Thomson scattering with known size dust |
| Experimental Approach/Plan: | Load well-defined size and composition dust into DiMES holder. Expose dust to LSN plasma discharges with strike point sweeps. Observe dust injection with available diagnostics (cameras, Thomson scattering, spectroscopy). Can be performed as piggyback on LSN cleaning discharges following maintenance periods. |
| Background: | A few dust injections in the lower divertor of DIII-D using DiMES have been previously performed. Dust used in those experiments was graphite dust with 6 micron median diameter and significant size spread (from sub-micron to over 10 micron). We have now obtained diamond dust with very uniform size in a few ranges (1-2 micron, 2-4 micron, etc.). Such dust would be useful to calibrate cameras, since it is generally very hard to deduce the dust size from camera images. Nanometer size carbon dust that could be used to calibrate Thomson scattering measurements is also available. Boron dust can be used to benchmark DustT modeling of different chemical composition dusts. |
| Resource Requirements: | 2-3 shot experiments: 1 setup shot, 1 reference shot (could be same shot as setup) + 1 injection shot. LSN patch panel, strike point sweeps. |
| Diagnostic Requirements: | DiMES, DiMES TV, lower divertor tangential TVs, UCSD fast camera, CER, Thomson (divertor and core), filterscopes, MDS, lower divertor Langmuir probes, SPRED |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
418: Does the Pedestasl spin the plasma? |
| Name: | Francis Perkins ( ) |
Affiliation: | University of Colorado |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | http://web.gat.com/diii-d_global/rof08/submit.php#http://web.gat.com/diii-d_global/rof08/submit.php# |
| Experimental Approach/Plan: | Measure trapped ions with large toroidal precession. |
| Background: | Remarks on Rotation.
As is the case for n, T, the pedestal region sets the boundary condition for angular momentum transport. This takes the form of a prescribed value for the pedestal angular rotation frequency. What physics determines this angular rotation frequency? The MHD answer is zero -- all open field lines are line-tied to the vessel.
Alcator C-Mod Ohmic-H data support a model in which angular momentum is created in the pedestal and diffuses inward. The boundary condition for angular momentum transport must be determined by pedestal physics. What physics can apply torque to the pedestal?
One possible scenario involves the potential determined by electron sheaths on open field lines just outside the separatrix. This sheath potential is several electron temperature. Alcator C-Mod observes very high temperature gradient just outside the separatrix, which implies a large radial electric field and a very high toroidal precession frequency for trapped ions. Collisions between trapped and passing ions would provide the friction to transfer momentum to the bulk plasma and create Ware pinches.
Note that this model uses trapped particles and would not be found by a fluid model code. It also suggests that divertor biasing could be used to insert angular momentum into a plasma. Experimentally, it would be interesting to distiguish trapped vs passng particles.
It strikes me that a common scenario for the pedestal, including direct ion-orbit loss, would serve your Rotaion, ELM Pedestal, Thermal Transport efforts well. |
| Resource Requirements: | Diagnostic capability to measre trapped ions |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
419: Fluid SOL model validation for helium plasmas |
| Name: | Mathias Groth () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Integrated Modeling |
Presentation time: |
Not requested |
Co-Author(s): | G.D. Porter |
| Description: | Perform edge diagnostic-optimized helium plasmato measure the recycling and physical sputtering behavior at the divertor and main chamber. Detailed validation of UEDGE and SOLPS codes using experimental data. |
| Experimental Approach/Plan: | Characterization of helium plasma in L-mode and ELMy H-mode; density scan to detach inner and outer divertor; use strike point sweeps for higher resolution of divertor conditions:
1) L-mode density scan: w/o conversion of beams, these plasmas can be Ohmic
2) H-mode with converted beams or ICRF/ECH, collisionality scan |
| Background: | Helium plasmas pose a significantly simpler situation in terms of SOL fluid code validation than their hydrogenic counterpart: carbon chemical sputtering is not present in helium plasmas, and wall pumping is zero as helium completely recycles. Both the UEDGE and SOLPS codes can be run for helium plasmas. Since chemical sputtering and wall pumping is 'turned off' experimentally, some of the uncertainties in the boundary conditions of the simulations are removed. |
| Resource Requirements: | Convert DIII-D to operate in 95%+ helium. H-mode operation with beams also requires conversion to helium beams;
2-day experiment: detailed characterization of plasma conditions in the SOL/pedestal |
| Diagnostic Requirements: | Diagnostics setup for helium: CER, filterscopes, tangential TVs |
| Analysis Requirements: | SOLPS and UEDGE simulations |
| Other Requirements: | -- |
| Title |
420: Rotation vs Ion Loss in L-H Transition Threshold |
| Name: | Mickey R. Wade () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Utilize electron heating to discriminate the need for low rotation from that of increased ion loss at the edge. |
| Experimental Approach/Plan: | Using the discharge shape of previous L-H transition studies, measure the L-H transition power threshold in cases in which 2.5 MW of ECH is applied continuously. This would essentially repeat the previous scans of torque but with 2.5 MW ECH applied. The goal is to determine if the L-H power threshold dependence on the co/counter NBI balance is different when a significant amount of the power is from torque-free sources. |
| Background: | Measurements on DIII-D have shown a clear dependence of the L-H power threshold on the co/counter NBI balance. A key question is whether the reduced threshold power at near balanced NBI is due to low rotation or due to increased ion loss at the edge due to the counter injection. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
421: q95 < 3 Hybrid Plasmas |
| Name: | Mickey R. Wade () |
Affiliation: | General Atomics |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Seek to determine ultimate limit of hybrid plasmas in terms of
achieveble fusion performance by operating with q95 ~ 2.8 or lower. |
| Experimental Approach/Plan: | Utlizing target plasmas at q95=3 in the ITER shape from the current campaign or target plasmas with q95 < 3 from the 2004 campaign, determine the beta limit and confinement quality of plasmas with q95 < 3. |
| Background: | Hybrid studies (really only two attempts) in 2004 showed that betaN ~ 2.8 could be maintained with q95 well below 3 (q95 ~ 2.8). In these cases, G = betaN*h89/q_95^2 ~ 0,7 were maintained for more than 1 sec. Because of the small number of shots, optimization was not done. Success in demonstrating G = 0.7 for several seconds (10 s would be great) would provide additional ammunition for the hybrid as the baseline regime for ITER and make an excellent IAEA viewgraph. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
422: Monitoring dust levels following entry vent |
| Name: | Dmitry Rudakov () |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | P. West, C. Wong, J. Yu, M. Groth, B. Bray, N. Brooks, C. Lasnier, M. Fenstermacher, A. Pigarov, R. Smirnov, W. Solomon |
| Description: | Monitoring dust levels following entry vent to compare with those during normal operations. Determine dust cleanup rates. |
| Experimental Approach/Plan: | At the beginning of plasma startup following an entry vent, turn on all available cameras, Thomson scattering and spectroscopic diagnostics to monitor change of the dust and impurity levels. |
| Background: | At the beginning of the CY2007 experimental campaign cameras were used to monitor dust levels. In the first 2-3 plasma discharges after the vent dust levels were quite high with thousands of particles observed in each discharge. After about 15 discharges dust was virtually gone during the stationary portion of a discharge, and appeared at much reduced levels during the plasma initiation and termination phases. We would like to repeat these measurements to check reproducibility and get better statistics. Thomson scattering that was not available in 2007 is highly desirable to monitor submicron dust levels. |
| Resource Requirements: | None - piggyback activity. |
| Diagnostic Requirements: | Essential: UCSD fast camera, DiMES TV, lower divertor tangential TVs; highly desirable: Thomson (divertor and core), SPRED, filterscopes, MDS, upper divertor and mid-plane TVs |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
423: ITER shutdown with li control |
| Name: | T. C. Luce ( ) |
Affiliation: | General Atomics |
| Research Area: | ITER Startup, Shutdown, Vertical Stability |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Normal shutdown of ITER scenarios has received virtually no attention either by simulation or experiment, yet it is perhaps the most likely time for the plasma to disrupt. This proposal entails looking at means to shutdown the various ITER scenarios without disruption. It includes li control by heating and current rampdown rate. |
| Experimental Approach/Plan: | In each ITER scenario, simulate the reduction in alpha power at end of burn by control of balanced NBI and add other heating sources by feedback control to stay in H mode and keep the plasma vertically stable. The current rampdown rate will also be controlled. |
| Background: | -- |
| Resource Requirements: | Need new feedback algorithm in PCS to simulate alpha power, maintain H mode, and control li simultaneously. |
| Diagnostic Requirements: | Only need RTEFIT parameters. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
424: Test of thermal ion ripple loss as key parameter for L-H transition |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Lots of dependencies have been observed for the L-H threshold that do not appear in the scalings derived from the international database. For example, the rise in threshold power at low density, the higher threshold with EC, the variation with co-NBI vs. balanced, the ion grad-B drift direction, and variation with current ramp up or ramp down have all been observed on DIII-D. The hypothesis here is that the true hidden parameter is the ripple cone loss of thermal ions, which, when large enough, leads to an L-H transition. |
| Experimental Approach/Plan: | The experiment would vary plasma shape and plasma parameters to change the ripple loss of the thermal ions and look for correlation with the L-H threshold power variation. It is essential to find the threshold by bracketing the L-H threshold in near stationary conditions. The sawtooth pulses would be minimized by operation at high q95. |
| Background: | -- |
| Resource Requirements: | Need EC power, co-NBI, and ctr-NBI. |
| Diagnostic Requirements: | Full edge diagnostics desirable, but not mandatory for exploratory experiment. Only filterscopes mandatory for transition info. |
| Analysis Requirements: | Need intensive analysis using model equilibria to examine thermal ion loss dependence on shape and other parameters (collisionality, ion grad(B) direction, etc.). |
| Other Requirements: | -- |
| Title |
425: Extension of advanced inductive domain to lower q95 |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The present database shows that the fusion gain figure of merit (G) continues to increase with lower q95. JT-60U has run transiently at q95=2.2 and JET has run at q95=2.7. The purpose of this proposal is to determine the minimum q95 below which either G begins to decrease or the disruption frequency becomes unacceptable. |
| Experimental Approach/Plan: | Begin with discharges from 2004 at q95=2.8. Decrease toroidal field. If problems with too low power, develop higher B and I discharges at equal q95 to increase the power demand. Then reduce q95 by reducing B. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
426: Confinement improvement or degradation with counter injection |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Continue scans shown in 2006 IAEA rotation post-deadline paper to counter torque to determine whether confinement depends on the sign of the rotation or the absolute value with an offset. See if the offset correlates with estimates of intrinsic rotation. |
| Experimental Approach/Plan: | Reverse Ip and reproduce scan parameters from Mach number scans shown in 2006 IAEA paper. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
427: High q95 hybrid as a test of current evolution models |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The expected presence of sawteeth complicates the prediction of current evolution and MHD stability. Try operation at high enough q95 that q(0) > 1 is expected from neoclassical Ohm's law with NBCD. |
| Experimental Approach/Plan: | Operate at high B to get high q95 and best MSE and ECE coverage. Compare experimenal and simulation results. Should require only a few shots. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
428: Bootstrap fraction as a function of q_min |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine how bootstrap fraction varies with q_min at fixed q95. |
| Experimental Approach/Plan: | Use 20 MW auxiliary power at highest B where beta_N=3.0 can be reached at high q_min. |
| Background: | Previous attempts ran at fairly low B. The NBCD overdrives J(0) leading to monotonic shear with q(0)<2. At higher B, there is more room for the central NBCD. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
429: Relative disruption frequency of hybrid and baseline scenario |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Take an extended run day (40 shots) with maximum rep rate. Run 20 baseline scenario pulses and 20 hybrid scenario pulses (developed previously). Document disruption frequency and causes. |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
430: Measure rotation screening of known applied error fields |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | There is no consensus regarding the screening of error fields from penetrating a rotating plasma. This proposal focuses on trying to measure the penetration by observing the rotation response to an applied error field at different fixed applied torques. Related to 20, 46, and 374. |
| Experimental Approach/Plan: | Set up pure co-NBI plasma that is stationary and robust. Apply oscillating non-resonant and resonant error fields with sufficient amplitude to detect the velocity variation with CER measurements. Repeat with decreasing torque input and compare magnitude and radial profile of velocity response. Switch to counter Ip and repeat. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
431: Develop method for optimization of error field correction |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | In the absence of complete characterization of the error fields of a future device (unlikely) and a complete theory of the plasma response to them, a rapid, automatic means of optimizing the error correction in any scenario within a single pulse will be needed. |
| Experimental Approach/Plan: | Apply constant torque and use simplex-type algorithms looking at plasma acceleration to determine the optimum error correction. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
432: Vertical stability of ohmic plasmas in ITER shape |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | ITER Startup, Shutdown, Vertical Stability |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | ITER will likely want to run ohmic plasmas at some point. Can they? |
| Experimental Approach/Plan: | Run ITER shape plasmas with q95 from 3-9 and see
them fly into the ceiling. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
433: ELM pacing and suppression by "plasma wobbling" 'a la TCV |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Use controlled vertical oscillations of the plasma to make it temporarily ELM-free, and fast oscillations for ELM-pacing. |
| Experimental Approach/Plan: | Starting with a DND H-mode, pre-program in the PCS vertical oscillations by +-1cm, initially with a period of 500ms. This should result in alternate ELM-ing and ELM-free periods. Then try faster oscillations. When the period becomes comparable with or faster than the "natural" inter-ELM period, ELM pacing should be obtained. |
| Background: | TCV has shown that controlled vertical oscillations of the plasma, sometimes referred to as "wobbling", can cause controlled transitions between ELM-ing and ELM-free H-modes [M.J.Dutch et al., Nucl.Fusion 1995] and even pace ELMs [A.W. Degeling et al., PPCF 2003]. Although not fully understood, the current interpretation is that the wobbling modulates the magnetic flux, thus inducing currents, predominantly in the edge.
DIII-D is intermediate between TCV and ITER both in size and with respect to the flexibility of vertical positioning. Therefore, it is a good test bed to check the exportability of this technique to ITER. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
434: Modulate I-coils to induce edge currents and affect/study ELMs |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Use ac currents in the I-coils to induce currents in the plasma edge and so perturb the edge current above/below the peeling boundary. |
| Experimental Approach/Plan: | Starting with a marginally peeling-stable plasma, modulate current in the I-coils on a time-scale comparable with the current-diffusion time. Several kA of current might be necessary. |
| Background: | External coils were used in COMPASS-D to induce currents in the plasma edge. Indirectly, they also affected the edge pressure gradient. Although not measured directly (COMPASS-D was not equipped with MSE, Li-beam or edge Thomson scattering), these perturbations were strong enough, according to EFIT, to cause a modulation across the peeling limit, which, in fact resulted in recursive stabilization/destabilization of ELMs [S.J. Fielding et al., EPS 2001, P5.014, Sec.2]. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
435: Modulate Ip to modulate edge current above/below peeling limit |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Requested |
Co-Author(s): | -- |
| Description: | Modulate the plasma current Ip to indirectly modulate the edge current above/below the peeling limit |
| Experimental Approach/Plan: | Pre-program oscillating plasma current. |
| Background: | Similar to proposal #434, except that the modulation in the edge current is not induced by the I-coils, but by the E-coil. This will cause a modulation of Ip and of the whole current profile. The shape of the current profile will also be modulated. The effect at the edge will be an oscillation of the local current density. Probably the edge pressure gradient will fluctuate too. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
436: Sheath factor measurement in Pisces compared with DIII-D |
| Name: | Charles Lasnier () |
Affiliation: | Lawrence Livermore National Laboratory |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | K. Umstadter, J. Boedo, J. Watkins |
| Description: | Measure the sheath factor for power transmission in Pisces using a DIMES sample which can then be used for the same measurement in DIII-D. |
| Experimental Approach/Plan: | use an instrumented carbon sample with a Langmuir probe in Pisces to measure electron temperature and density, and surface tmeprature using an IR camera. |
| Background: | We have measured sheath factors different from the theoretical value. The Pisces sheath will be simpler than DIII-D in th absence of a magnetic field, so we should look at that first. Then when we uderstand it, move the sample to DIII-D |
| Resource Requirements: | Pisces run time, Langmuir probe instrumented sample, IR camera
DIII-D shots or piggyback. |
| Diagnostic Requirements: | IR camera, Langmuir probe |
| Analysis Requirements: | Probe and IRTV analysis, compare with sheath model |
| Other Requirements: | -- |
| Title |
437: Study of turbulence during RMPs |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | Rudakov, Mueller, Holland, McKee, Evans, Hollmann, Yu |
| Description: | Still unknowns about how the RMP affects transport. Perform low power experiments to use probes and study convective cells, etc. |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
438: Momentum transfer across separatrix |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | Rudakov, Hollmann, Watkins, Mueller, Tynan, Yu |
| Description: | Use Mach probe to stufy momentum transfer. Add momentum in the core using co-Counter Beams and see the flow in the SOL to see if it is classical. Compare to obvious such as CX, viscosity, pinch, etc. |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
439: SHeath physics studies |
| Name: | Jose A. Boedo () |
Affiliation: | University of California, San Diego |
| Research Area: | Thermal Transport in the Plasma Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Lasnier, Tynan, Rudakov, Hollmann |
| Description: | There are clear problems with the understanding of the sheath treansmission factor in tokamaks. Use PISCES to study the effect of non-thermal populations and magnetic sheath |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
440: Plasma startup with compensating n=1(=3) error magnetic field components before the plasma ignition with I-coil feedback |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | General PCO |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Plasma startup is a complex process since the poloidal magnetic field pattern at the plasma ignition time t= 0 can be not only 2-dimensional but also 3-dimensional due to the non-axis-symmetric error field and the eddy currents induced on the metallic materials. The flux pattern, not only n=1, but higher n may exist in addition to the n=0 component around t = 0.
The 2-minensional Bp null point moves around inside the vacuum vessel and then the plasma will capture the helical flux in an unpredicted manner during low temperature period.
Here, it is proposed:
Using I-coil and/or c-coil, we turn on the feedback process to null out the magnetic field n=1 (=3 if needed) from before t=zero
This feedback should reduce the helical component in the vacuum field and reduce the helical flux capturing in break down.
This may minimize the appearance of magnetic island formation t=0-10 msec time range, improving the discharge evolvement in later time. |
| Experimental Approach/Plan: | Proof of principle experiment
(1) Fast feedback will be applied with taup =100 microsec of PCS before t=0. We will try first the I-coil with SPA connection.
(2) If the n=3 component is high, it will be tried to carry out the n=1 and n=3 feedback simultaneously. The C-coil will be used together, if needed
(3) The effectiveness of ECH before t=0 is tested |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
441: Does the LH threshold go back up with strong ctr-NBI? |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | A strong dependence of the L-H threshold power was observed when going from co-NBI to balanced to weak ctr-NBI. The question to be answered is whether the power threshold increases when negative torque equivalent to the co-NBI is applied. This would indicate perhaps that bulk rotation inhibits the transition. |
| Experimental Approach/Plan: | Apply strong ctr-NBI torque to reversed Ip plasmas. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
442: Rho* scaling of the LH threshold |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Present information shows a gyro-Bohm scaling of the H-mode energy confinement and a Goldston scaling of the LH threshold power. This implies the loss power in H mode will be insufficient to maintain H mode below some rho*. |
| Experimental Approach/Plan: | Measure the LH threshold power rho* scaling by carrying out rho* scans at different beta values. At some low beta, the high rho* power will be sufficient to have good H-mode confinement, while at the low rho* point, the edge will collapse if the gyro-Bohm power is applied. This will answer both the rho* scaling of the LH threshold and the margin above the LH threshold power that is required for good H mode confinement. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
443: Run hybrid plasmas to the ideal MHD limit |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Discharges with pre-emptive ECCD and active q=2 tracking achieved beta_N=3.4 which was at the no-wall n=1 limit. The beta was limited by the feedback request, not instability. The approach here is to add dynamic error field correction to ensure good rotation above the no-wall limit to stabilize the RWM, and ask for more. |
| Experimental Approach/Plan: | Repeat previous discharge with pre-emptive ECCD and active tracking of q=2. Add dynamic error field correction. Ask for full power. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
444: Rho* scaling in hydrogen L mode |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | OK, I know this sounds boring, but it is important to validate the models used for ITER startup. The electron temperature in hydrogen will determine the current profile in the initial phase of ITER operation. In order to plan this phase, it is important to be able to predict the electron temperature profile. A smart choice of parameters may allow us to derive a proper mass scaling of confinement by matching up with previous deuterium L mode discharges. |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
445: Effect of ECCD on sawteeth in H mode |
| Name: | T. C. Luce () |
Affiliation: | General Atomics |
| Research Area: | Stability |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The previous experiment to look for effects of ECCD on sawteeth saw only period lengthening, independent of the ECCD location. With higher power and perhaps more judicious choice of parameters, it should be possible to see the predicted current drive effect on the sawteeth. Either full co-ECCD or ctr-ECCD can be used, or a co/ctr-ECCD combination to give maximum shear variation can be tried. |
| Experimental Approach/Plan: | -- |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
446: Hydrogen Sensor Diagnostic for DIII-D |
| Name: | Dean Buchenauer ( ) |
Affiliation: | Sandia National Laboratories |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Not requested |
Co-Author(s): | D. Buchenauer, R. Bastasz, D. Rudakov, P. West, C. Wong |
| Description: | Understanding plasma-surface interactions in DIII-D requires knowledge of the flux and energy spectrum of plasma particles striking the walls and divertor. A diagnostic comprised of a number of solid-state hydrogen sensors, placed at various
locations in DIII-D, could provide much of this information. It is proposed that an initial component for this diagnostic be built and tested on the DiMES probe. It will be used to characterize the hydrogenic (H and D) particle flux striking the divertor floor in DIII-D at the DiMES location. Successful operation of the DiMES hydrogen sensor would lead to incorporation of hydrogen sensors in so-called smart tiles installed in the walls of DIII-D. |
| Experimental Approach/Plan: | |
| Background: | The sensors are metal-insulator-semiconductor (MIS) devices that can be configured as diodes, capacitors, or transistors. The detection mechanism is similar in each case. Hydrogen striking the sensor surface is accommodated into a metal overlayer, which is typically made from a Pd alloy that promotes rapid transport of the hydrogen to the metalinsulator interface. Hydrogen trapped at this interface induces a dipole and changes the barrier height in the device. The change can readily be sensed by measuring the leakage current, flatband, or gate voltage. Fluences as low as 1012 H/cm2 have been measured in vacuum. For energetic particle detection, the metal layer thickness should be greater than the range of the most energetic particle impacting the device. This is typically on the order of 100 nm. An additional layer of a hydrogen impermeable material, such as Au, can be added on top of the
active metal layer to reduce the energy of particles entering the sensor, filter out low-energy particles, and to provide a
means for energy discrimination. Each configuration has particular characteristics that must be considered when implementing the diagnostic. The diode is the most basic structure and is the simplest to operate. However, its temperature sensitivity makes it suitable for
use only in isothermal locations. The capacitor is a more robust device whose response is relatively temperature insensitive. It requires a measurement circuit capable of generating capacitance-voltage (CV) curves and determining the appropriate flatband voltage. The transistor is the most
complicated structure, but can be integrated into complex circuitry. All of these MIS sensor configurations are small in size and operate at low power. Depending upon the operating temperature and exposure conditions, these sensors
function either as fluence or flux monitors.
Diagnostic Description:
The diagnostic is small enough to mount inside a regular sized DiMES sample. Initially, an individual sensor chip containing four redundant devices, configured as capacitors, will be embedded in a graphite-faced DiMES sample with a
small viewing hole. A prototype has been designed and built. Nine connections to the sensor diagnostic are needed, four sensor contacts, a common, and two leads each for a small heater and thermocouple. The connections will be made using the existing DiMES electrical cable.
External instrumentation will consist of a low-voltage supply, a capacitance meter, and interface electronics, which will be connected to a computer in communication with the DIII-D data system. There are three possible modes of operation: dosimetric, real-time, and chopped. The dosimetric mode, in which the sensor integrates the incoming flux and reports a single H dose value based on measurements made before and after the exposure period, is the most straightforward mode to implement. |
| Resource Requirements: | Piggyback initially, possibly 1/2 day experiment if tests are successful |
| Diagnostic Requirements: | Edge and divertor diagnostics and magnetics |
| Analysis Requirements: | Magnetic analysis for stored energy and strike point location, divertor spectroscopy and IR analysis, and divertor probes and Tompson data |
| Other Requirements: | -- |
| Title |
447: Rho* Scaling of Alfvenic Activity Using Hydrogen Discharge |
| Name: | Michael Van Zeeland () |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges |
Presentation time: |
Not requested |
Co-Author(s): | W. Heidbrink, R. Nazikian |
| Description: | The primary goal of this experiment is to document the difference in Alfvenic activity and resultant fast ion transport by repeating the well-documented deuterium AE discharge 122117 in hydrogen. |
| Experimental Approach/Plan: | Begin with discharge 122117 as a reference and repeat in hydrogen. Carry out beam power scan as well as density scan. Document the variation in AE activity as well as impact on fast ion transport for comparison to equivalent discharges already carried out in deuterium. |
| Background: | The fast ion gyroradius/plasma radius is thought to be fundamental in determining the degree to which Alfvenic activity or other MHD induced fast ion transport impacts plasma performance. Additionally, the most unstable mode is expected to occur when the poloidal wavelength is approximately the fast ion gyroradius. Both of these ideas are fundamental to making reliable projections to ITER. Operating the well-documented AE discharge 122117 in hydrogen will provide a sensitive test of both of these predictions since essentially all relevant parameters including V_beam/V_Alfven will remain constant except rho*. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
448: Sensitivity of ELMs and Particle Control to Triangularity |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | ITER Demonstration Discharges |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine how close the designed ITER triangularity is to the ELM-free "cliff" for the baseline "Scenario 2" at beta_N=1.8. Will the ELM frequency be increased, and the divertor cryopumping improved, by small changes away from the standard ITER plasma shape? In the future, this could be expanded to the effect of plasma shape on RMP ELM-suppression. |
| Experimental Approach/Plan: | (1) Faithfully reproduce the ITER plasma shape and establish the baseline "Scenario 2" at beta_N=1.8 and q95~3. (2) With the lower divertor cryopump cold, scan the lower triangularity up and down either vary slowly or shot-to-shot. (3) Repeat triangularity scan, but this time use the density control from the I-coil (n=3 RMP) to maintain a constant, low density during the scan. (4) Repeat the triangularity scan, but this time warm up the lower divertor cryopump and do not use I-coil density control. |
| Background: | For the ITER "Scenario 2" baseline case with beta_N=1.8, the ELM frequency is very sensitive to the plasma triangularity. As the traingularity is increased, the plasma tends to become ELM-free and particle control via divertor cryopumping is lost. This is not an issue for high beta_N plasmas, which ELM vigorously for all traingularities. |
| Resource Requirements: | NBI: 4 sources required. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
449: Target Plate Heat flux, sheath power transmission factor, and Power Accounting |
| Name: | Jonathan G. Watkins ( ) |
Affiliation: | Sandia National Laboratories |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Lasnier,Schaffer, Murphy, Leonard, Evans, Joseph, West, Porter, Stangeby |
| Description: | To validate our measurements of heat flux, measure the target plate heat flux profile using several different methods and do a detailed power accounting of DIII-D plasmas at high and low density and for different power levels in both L and H mode and ELM - suppressed H mode. |
| Experimental Approach/Plan: | To better measure the target plate heat flux, the outer strike point must be run on the outer shelf in the lower divertor to get good views with the IRTV. Sweeps should be used to get better profiles with the Langmuir probes, and the calorimeter probe. Fixed strike point shots will be needed to simplify analysis of the thermocouple array and calorimeter probe data. The bolometer array will be used to measure the radiated power and generate a total power accounting. The inner strike point should be run on the lower divertor floor in view of the IRTV, Langmuir probes, and the floor TC array. |
| Background: | |
| Resource Requirements: | A working IRTV is required. Electronics are needed for the new tc array and analysis techniques need to be refined to remove magnetic pickup on the signals as was done with the calorimeter probe. |
| Diagnostic Requirements: | IRTV
Thermocouple array
calorimeter probe
Bolometry,
Lower Langmuir Probes
Thomson
CO2 interferometers
X-point and Midplane plunging probes
Filterscopes
Visible Bremsstralung
SPRED
CER
MDS Spectrometry |
| Analysis Requirements: | Proper analysis techniques need to be developed to generate heat flux from the tc array data. |
| Other Requirements: | -- |
| Title |
450: Search for a window of RWM instability at high rotation |
| Name: | Holger Reimerdes () |
Affiliation: | Columbia University |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Analyze the rotation dependence of RWM stability and possible saturation mechanism at intermediate or high rotation values. |
| Experimental Approach/Plan: | We plan to carry out slow NBI torque ramp-downs starting with fast rotating plasmas with uni-directional NBI heating. The transport measurements can be supplemented with active MHD spectroscopy measurements, which should accelerate the rotation slow-down and indicate less stable regions. |
| Background: | Hu & Betti's kinetic calculations of RWM stability [Hu, Betti, PRL 2004] predict stability at low and no rotation, but instability at high rotation before shear-Alfven damping is thought to be effective [Reimerdes, et al, EPS 2007]. Such a region could be hard to detect since the growing RWM would greatly enhance the torque, decrease the plasma rotation and, thereby, stabilize the RWM again. It should however be detectable by a deterioration of momentum confinement at values of plasma rotation in the window of instability. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | Calculation of momentum confinement time. |
| Other Requirements: | -- |
| Title |
451: Systematic study of in-situ boronization |
| Name: | Clement Wong () |
Affiliation: | General Atomics |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | D. Rudakov, P. West, N. Ashikawa, K. Holtrop, R. Lee |
| Description: | Systematic study of in-situ boronization, by injecting different mixture of helium and diborane gases, from different DIII-D injectors and under different plasma discharges. The boron coating distribution will be recorded on different graphite buttons on the MiMES and DiMES samples. |
| Experimental Approach/Plan: | Injection of a selected mixture of helium and diborane gas at the last discharge of other already planned dedicated experiment. This would only be requested right before the weekend of boronization, such that any remaining diborane gas in the plasma chamber can be cleared through normal boronization procedure. After boronization study, material samples will be extracted from MiMES and DiMES systems. Special safety procedure will be applied for button samples extraction. Safety procedure of this procedure will also need to be reviewed carefully. |
| Background: | C, Be will not be suitable plasma facing materials for DT steady state operation due to radiation damage. W, the remaining high-Z and low sputtering material could suffer significant damage from helium ions. A boron layer could protect the W surface, due to the small mean free path of helium ions. A systematic study is necessary to understanding the possibility of in-situ boronization, impacts to different plasma operation, coating uniformity, and B-migration in the plasma chamber during different plasma discharges. |
| Resource Requirements: | MiMES and DiMES system, and preparation for boronization from different gas injection locations and during plasma discharges |
| Diagnostic Requirements: | Different chamber wall and divertor diagnostics. |
| Analysis Requirements: | Characterization of coated B layer on graphite buttons will be performed in the US and Japan. |
| Other Requirements: | -- |
| Title |
452: Systematic study of in-situ boronization |
| Name: | Clement Wong () |
Affiliation: | General Atomics |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | D. Rudakov, P. West, N. Ashikawa, K. Holtrop, R. Lee |
| Description: | Systematic study of in-situ boronization, by injecting different mixture of helium and diborane gases, from different DIII-D injectors and under different plasma discharges. The boron coating distribution will be recorded on different graphite buttons on the MiMES and DiMES samples. |
| Experimental Approach/Plan: | Injection of a selected mixture of helium and diborane gas at the last discharge of other already planned dedicated experiment. This would only be requested right before the weekend of boronization, such that any remaining diborane gas in the plasma chamber can be cleared through normal boronization procedure. After boronization study, material samples will be extracted from MiMES and DiMES systems. Special safety procedure will be applied for button samples extraction. Safety procedure of this procedure will also need to be reviewed carefully. |
| Background: | C, Be will not be suitable plasma facing materials for DT steady state operation due to radiation damage. W, the remaining high-Z and low sputtering material could suffer significant damage from helium ions. A boron layer could protect the W surface, due to the small mean free path of helium ions. A systematic study is necessary to understanding the possibility of in-situ boronization, impacts to different plasma operation, coating uniformity, and B-migration in the plasma chamber during different plasma discharges. |
| Resource Requirements: | MiMES and DiMES system, and preparation for boronization from different gas injection locations and during plasma discharges |
| Diagnostic Requirements: | Different chamber wall and divertor diagnostics. |
| Analysis Requirements: | Characterization of coated B layer on graphite buttons will be performed in the US and Japan. |
| Other Requirements: | -- |
| Title |
453: Edge Ti (rotation) disturbance with residual stable RWM activity |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | 2007 Observation
The high-N plasmas with error field correction applied show the existence of residual stable n=1 activity. Typically, the stable RWM amplitude reaches ~ 5gauss in the midplane MPID sensors. Since these weak fluctuation occurs in slow time scale ~ 100 Hz or less, we have not paid attention to these activities.
However, we found that the direct RWM feedback reduced the amplitude by more than a factor of two and simultaneously reduced the edge Ti (rotation) disturbance. Here, the terminology of disturbance is used since the samping rate of Ti(rotation) was 2 ms.
A hypothesis is that the n=1 activity was caused by the RFA due to the small but finite residual error field. The RFA process does capture the helical flux and then expel with the appearance of other MHD like ELMs.
The dynamic error field correction (DEFC)-only is not sufficient to reduce this weak n=1 activity.
This disturbance propagates into q=2 surface area. It is quite possible that these disturbances can impact the edge profile as well as the onset of other edge-related phenomena |
| Experimental Approach/Plan: | Experiments
(1) Apply fast feedback above the no-wall limit in fast feedback mode in AT plasmas rather than the standard DEFC operation.
(2) The better feedback can be made with using upper/lower separated sensor signals and energizing independently upper/lower I- coils. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
454: The n=3 RFA excitation in the ELM-induced RWM by applying the n=3 extra error field |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | In the RWM buildup period, we often observe the ELM-induced RWM followed by the RFA period before the final collapse takes place. Since the ELM event produces many n-components, it is quite possible that the n=3RFA also should be excited along with the n=1 component in the event of the ELM-induced RWM events.
Before 2005, we observed frequently the excitation of n=3 components along with n=1 component in ELM-induced RWMs. However, strangely in 2006-2007 campaign, we seldom observed the n=3 component until very late period of the discharge termination. At present, this weak n=3 component remains as a little mystery.
Here, it is hypothesized that the n=3 error field component was indeed reduced by the coil lead correction in 2005 major opening period.
If this hypothesis is reasonable, the n=3 RFA should reoccur in the ELM-induced RWM by applying n=3 error field. If the n=3 RFA reappears, we will attempt to excite the n=2 RFA by applying n=2 field from C-coils. |
| Experimental Approach/Plan: | Experiment
(1) We introduce the n=3 component from I- or C- coil and then we observe the ELM event
(2) The DEFC of n=1 should be kept applied to minimize the n=1 component for better noise ratio.
(3) if n=3 RFA is observed in ELM-induced RFA, n=2 RFA possibility will be explored |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
455: Tearing Mode locking avoidance with toroidal phase advance in the feedback |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | The feedback experiment in last year has shown very interesting results on the tearing mode behavior. The feedback operated with toroidal phase shift can synchronize the I-coil currents to the tearing mode, and not only prevent the mode from locking, but also modify the mode characteristics. The scheme can be applied for successful maneuverability of tearing mode in ITER once RWM control coil is installed.
Observations were:
(1) The Feedback can shift freely the tearing mode direction and frequency without losing the stored energy.
The feedback fields accelerate/decelerate the mode and, interestingly, the mode frequency is lower by two-three times in the CTR direction (to the plasma rotation) compared to that in the CO direction.
(2) The synchronization transition from 0.5-1 kHz frequency to the feedback-controlled frequency (20-60 Hz) is smooth when the phasing is correctly adjusted.
The choice of +30 degrees (CTR-direction of the mode) is very favorable, but so far only one shot tried. On the other hand, the -30 degrees (CO- direction of the mode) causes mode locking and beta collapse, which was reproducibly observed more than several shots. The zero phase shift may be acceptable.
These results suggest that the tearing mode is quite maneuverable so that the mode can be slowed down to low frequency range, and then can be controlled. Although it is to be examined further whether the tearing mode can be quenched in time, it seems, at least, we can sustain as a forced rotation-tearing mode. However, caution is to be made that this can occur only when the error field correction is extremely well compensated and of course only with high bandwidth amplifier-coil system.
We conclude that it is worthwhile to pursue this subject further, considering the possibility of the ITER application with internal coils |
| Experimental Approach/Plan: | Proposed experiments
(1) To survey systematically the impact of feedback toroidal phase on tearing modes
(2) To explore possibilities of quenching by varying the phase/gain in time
(3) To explore the implication to ITER internal coil option. |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
456: Improvement of Dynamic Error Filed Correction by Active MHD Spectroscopy approach in closed feedback |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | A. Garofalo, Yongkyoon In, G. Jackson, R. LaHaye, H. Reimerdes, Ted Strait, H. Takahashi |
| Description: | In the 2007 campaign, we have shown that a simple model of dynamic error field correction iteration process can describe the experimental observations in a satisfactory manner.
The Dynamic Error Filed Correction (DEFC) approach is a power tool to minimize the resonant error field component and to improve the macro MHD activity. It is very attractive if the approach is extended to C_beta ~ 0 regime where many AT discharges have to go though in time for achieving higher betan conditions. The RFA is expected to be weak at C_beta ~ 0, however, the lower rotation may enhance the amplification as if a singularity.
The challenging part is to evaluate the plasma response and to set the complex gain in PCS system.
Here, it is proposed to determine the plasma response by using the Active MHD spectroscopy approach in closed feednback system mode. |
| Experimental Approach/Plan: | Approach
(1) To prepare the Active MHD spectroscopy technique along with closed feedback option
(2) To document the closed loop performance at various frequencies.
(3) To predicts the maximum gain in the PCS system for DEFC, including the possibility of complex gain setting
(4) To verify the predicted performance and improve the process |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
457: Plasma startup with compensating n=1(=3) error magnetic field components before the plasma ignition with I-coil feedback |
| Name: | Michio Okabayashi () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Plasma startup is a complex process since the poloidal magnetic field pattern at the plasma ignition time t= 0 can be not only 2-dimensional but also 3-dimensional due to the non-axis-symmetric error field and the eddy currents induced on the metallic materials. The flux pattern, not only n=1, but higher n may exist in addition to the n=0 component around t = 0.
The 2-minensional Bp null point moves around inside the vacuum vessel and then the plasma will capture the helical flux in an unpredicted manner during low temperature period.
Here, it is proposed:
Using I-coil and/or c-coil, we turn on the feedback process to null out the magnetic field n=1 (=3 if needed) from before t=zero
This feedback should reduce the helical component in the vacuum field and reduce the helical flux capturing in break down.
This may minimize the appearance of magnetic island formation t=0-10 msec time range, improving the discharge evolvement in later time.
The effectiveness can be enhanced by applying the ECRH before t=0. |
| Experimental Approach/Plan: | Proof of principle experiment
(1) Fast feedback will be applied with taup =100 microsec of PCS before t=0. We will try first the I-coil with SPA connection.
(2) If the n=3 component is high, it will be tried to carry out the n=1 and n=3 feedback simultaneously. The C-coil will be used together, if needed
(3) The effectiveness of ECH before t=0 is tested |
| Background: | -- |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
458: Massive Gas Injection during Ip Rampdown |
| Name: | Tom Jernigan ( ) |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Disruptions |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Test MGI mitigation/assimilation for gas injected during Ip rampdowon. |
| Experimental Approach/Plan: | Trigger a disruption using one valve of the medusa array, fire the other 5 valves of the array at various times after the thermal quench. Compare mitigation quality and gas assimilation vs delay time. |
| Background: | MGI has proven very effective at disruption mitigation in existing tokamaks. However, the model for the gas assimilation is that most of the gas moves into the core during the current re-connection event at the thermal quench. The purpose of this experiment is to investigate MGI efficiency if a disruption is not dedected until the Ip decay begins after the thermal quench. |
| Resource Requirements: | 3 beams |
| Diagnostic Requirements: | disruption diagnostics and standard plasma diagnostics. Vessel displacement, thermal imaging of floor, and tile current arrays are important. |
| Analysis Requirements: | Usual MGI analysis |
| Other Requirements: | -- |
| Title |
459: Massive Gas Injection of ECH Heated Plasma |
| Name: | Tom Jernigan () |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Disruptions |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Test MGI mitigation in ECH heated plasmas to compare with NBI heated plasma mitigation to see if ECH heating would provide a more reliable target plasma for MGI experiments. |
| Experimental Approach/Plan: | Use ECH H-mode plasmas to test ECH launcher compatibility with MGI disruption mitigation, especially with argon injection. Basically the plan is to run a series of MGI shots into ECH heated plasmas to test the compatibility of the ECH launchers with the large quanties of gas injected. Also check to see if there are obvious differences in the mitigation between beam heated and ECH heated discharges. |
| Background: | Contamination and subsequent un-reliability of the neutral beam sources has become a problem with the large quanties of gas injected with the Medusa fast valve array. This experiment is to see if the ECH heating system is compatible with MGI, particularly with heavier gases such as argon and provides a more reliable target for MGI experiments. |
| Resource Requirements: | 4 gyrotrons |
| Diagnostic Requirements: | Usual disruption diagnostics and usual plasma diagnostics (except those requiring beams) |
| Analysis Requirements: | Usual MGI analysis |
| Other Requirements: | -- |
| Title |
460: Performance sensitivity studies of steady-state scenario (low rotation, Te~Ti) |
| Name: | Edward Doyle () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Core Integration (Steady-State Scenario) |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | To date, work in the steady-state area has concentrated on obtaining an existence proof of the ITER Q=5 goal, i.e. G=0.3 coupled with 100% NI operaton. Now that this goal is close to achievement, it is an appropriate time to turn to the question of the extrapolability of these regimes to reactor conditions, specifally low rotation (low Mach no.) and Te/Ti~1. Specifically, attempt to perform Mach. no. scan, coupled with maximizing Te/Ti |
| Experimental Approach/Plan: | As was done for previous similar hybrid studies, select target plasmas to minimize power requirement for the "steady-state" phase. This is required in order to free NBI and ECH power for use in a Mach no. scan and as electron heating. Ths implies operation at as low a B as possible, and probably q_min~1.5. |
| Background: | This experiment addressed IEA/ITPA joint experiments on operation with low momentum input and Te~Ti |
| Resource Requirements: | 7 NBI sources, 5-6 gyrotrons |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
461: Affect of MHD stability on pedestal width at low triangularity |
| Name: | Richard Groebner () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Test theoretical predictions that pedestal width should not increase significantly with plasma beta in a very low triangularity discharge. |
| Experimental Approach/Plan: | Produce H-mode discharges with triangularity of about 0. Then, shot-by-shot, perform a beta scan in these discharges by changing the heating power. Each discharge should have a long steady-state period with edge breathing so that well-resolved pedestal profiles can be obtained. A second part of this experiment would be to increase the triangularity shot-by-shot at constant power and to see the response of the pedestal width, height in this scan. The ELM energy loss and frequency would be measured in this scan. |
| Background: | An outstanding question in pedestal physics has been whether or not the pedestal height increases in response to heating power or to increases in the core beta. Recent studies on DIII-D show that the pedestal width and height typically (but not always) increase in response to increased heating power. These studies have been performed in discharges with average triangularity of 0.3 and higher. Recent theoretical studies with the ELITE code (performed by Phil Snyder) predict that part of the increase in pedestal height is due to increased MHD stability as the global plasma beta increases. However, this modeling also predicts that in plasmas with very little shaping, such as with triangularity of about 0, that this effect will be absent. There is some old DIII-D data that supports this. We propose to perform a power (beta) scan in a zero-triangularity discharge, measure the pedestal width and height, and check the theoretical predictions with our best pedestal measurements. |
| Resource Requirements: | 5-6 beam sources |
| Diagnostic Requirements: | TS, CER, CO2, fast magnetics, photodiodes |
| Analysis Requirements: | Obtain pedestal profiles.
Determine width and height of total pedestal pressure.
Plot variation of pedestal beta vs global beta for zero triangularity discharges.
Plot variation of pedestal beta vs triangularity for discharges at constant power.
Produce kinetic efits.
Perform ELITE analysis on these discharges to determine theoretical predictions for pedestal variations due to modifications in MHD stability. |
| Other Requirements: | -- |
| Title |
462: Modulated ECH to study pedestal electron thermal transport in ELM-stabilized discharges via RMP |
| Name: | Richard Groebner () |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine if electron thermal transport is increased in ELM-stabilized discharges, via application of RMP, as opposed to standard ELM-ing discharges without the application of RMP. |
| Experimental Approach/Plan: | Apply modulated ECH at top of pedestal in ELMing and ELM-suppressed discharges (via RMP). Observe the temporal response of electron temperature at the top of the pedestal from ECE and in the pedestal from SXR. Determine if temperature decays more quickly after end of an ECH pulse with RMP applied as opposed to no RMP. |
| Background: | As is well known, Resonant Magnetic Perturbations (RMP) in DIII-D have been used to stabilize ELMs. It is quite clear that the perturbed edge magnetic fields lead to enhancements of particle transport. In turn, the increased particle transport leads to a reduction of the pedestal density and this allows the pedestal to remain within an MHD-stable zone, as computed with ELITE. In contrast, the Te profile is not much changed by the application of the RMP. This is an outstanding mystery because it is expected that edge perturbed magnetic fields would allow electrons to escape from the plasma and thus to reduct the electron temperature. We evidently are not observing this. However, the electron transport is difficult to study and is not well studied for these discharges. We propose to use techniques of modulated transport to determine if the RMP degrades the electron thermal transport relative to discharges without an RMP. |
| Resource Requirements: | 5 neutral beam sources
4 ECH gyrotrons, aimed at plasma edge |
| Diagnostic Requirements: | TS, CER, CO2, ECE, SXR |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
463: Real-time q and Te profile control based on dynamical model approach |
| Name: | Didier J Mazon ( ) |
Affiliation: | CEA Cadarache |
| Research Area: | Model based Control |
Presentation time: |
Not requested |
Co-Author(s): | D.Moreau (CEA) |
| Description: | In the so-called advanced operation scenarios, real-time control of current, temperature and density profiles is essential. We propose to use a model based approach to control the q-profile (and potentially Te profile if available in real time)in feedback during a high performance pulse. This task is crucial to sustain a stationary ITB. |
| Experimental Approach/Plan: | For the design of the controller, a linearized model of the plasma profile responses to the different heating and current drive devices must be identified on the basis of experimental results (modulations of the actuators in open loop). In order to improve the controller performance a dynamical model of the profile response is foreseen and will be used to design the controller. |
| Background: | Recently (March 2007) a model based approch has been used with sucess at JET for q profile control and feedback loop has been performed. The controller was using 4 actuators (LHCD, ICRH, NBI powers and the loop voltage) for controlling 5 points of the q profile while at the same time the shape of the plasma was controlled as well to optimize the coupling.See for example D.Mazon IEEE conference San Diego December 2006 for more details about the technique. |
| Resource Requirements: | Machine time:1 or 2 days for modulations and 1 day for experiments. In order to optimize the model and the controller few weeks between modulations and close loop experiments are needed. |
| Diagnostic Requirements: | RT EFIT, Beam, ECH, Core and tangential Thomson,magnetics, MSE, ECH diagnostics |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
464: Measurement of RFA using the SXR Diagnostic |
| Name: | Matthew Lanctot () |
Affiliation: | Columbia University |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | Holger Reimerdes, Andrea Garofalo, Michael J. Schaffer |
| Description: | We will measure the internal mode structure of the plasma response (RFA) to externally applied magnetic field perturbations using the tools/techniques of active MHD spectroscopy and the SXR toroidal cameras. |
| Experimental Approach/Plan: | Apply slowly rotating (5-100 Hz) n=1 magnetic field perturbations with the Icoil while using feedback control of betan or control of the toroidal rotation. Analyze SXR data from these discharges to calculate a radial profile of the n=1 plasma fluid displacement. Compare these results with calculations of the mode structure of the external kink mode obtained from ideal MHD stability codes. Apply rotating error field in co and counter directions with respect to plasma rotation. Use neutral beam feedback control of the toroidal rotation to ramp down the rotation while applying the field to evaluate the effects of shielding. Scan beta and Icoil currents to maximize plasma response. |
| Background: | To date, on DIII-D, only arrays of magnetic sensors have been successfully used to investigate the RFA. Our goal is to extend the well-established methods of active MHD spectroscopy to include additional diagnostics. The newly refurbished SXR toroidal cameras can detect internal perturbations to the flux surfaces that result from externally applied fields. A more complete understanding of the internal RFA structure may help to elucidate the relationship between RFA and the RWM. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | MSE, CER, SXR, ECE, magnetics |
| Analysis Requirements: | CERFIT |
| Other Requirements: | -- |
| Title |
465: Gas Puff Imaging |
| Name: | Jonathan Yu ( ) |
Affiliation: | University of California, San Diego |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | J. Boedo, T. Evans, E. Hollmann, R. Moyer, D. Rudakov, G. Tynan |
| Description: | Vary collisionality and use the fast framing camera with gas puffing to study filament dynamics during L-mode and during inter-ELM H-mode. |
| Experimental Approach/Plan: | Gas puffing might be possible during the 2008 run using existing capillary gas lines located near the midplane. |
| Background: | The UCSD fast camera is a useful tool for studying and validating ELM and intermittent transport models. However, the existing camera is limited by emission intensity to a marginal frame rate of ~ 10,000 fps, while the maximum capability of the camera is > 100,000 fps. Using a gas puff system combined with the existing fast camera, edge turbulence, ELM, and RMP studies may be enhanced. This proposal does not require new hardware for gas puffing; instead, we would like to use any existing capillary gas lines located near the midplane within the fast camera field-of-view. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
466: ECCD stabilization of non-rotating mode in high beta, low-torque plasmas |
| Name: | Holger Reimerdes () |
Affiliation: | Columbia University |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | F. Volpe |
| Description: | Use ECCD stabilization as mean to probe the nature of the high-beta, low-rotation non-rotating mode. Any success of ECCD in reducing the mode amplitude or even stabilizing the mode would be an indication of the tearing character. Moreover, complete stabilization would allow for a further increase of beta in order to test the RWM/plasma mode beta limit. |
| Experimental Approach/Plan: | Use a low torque high beta RWM target and apply co-ECCD at the o-point of an assumed 2/1 island (see proposals 384 and 385 by F. Volpe). The ECCD is triggered using the locked mode detector. The position of the island o-point is estimated from the typical toroidal phase with which the mode grows and mapping the field line to the ECCD location. Since this mapping has some uncertainties the location has to be varied when looking for an effect on the mode magnitude. If the mode can be indeed stabilized we plan to increase beta in order to investigate the next beta-limiting instability. |
| Background: | The n=1 modes in high beta, low-rotation plasmas have been classified as "tearing modes" and "RWMs" depending on whether they exhibit a rotating precursor. However, an analysis of the magnetic perturbation measurements at the low-field-side yields the same helicity suggesting that the "RWM" could be a tearing mode that is born locked. This conjecture is further supported by recent rotation scans of the NTM betaN threshold by Buttery and La Haye. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
467: NTM (de)stabilization by co-/ctr-ECCD in island O-/X-point |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | NTM Stabilization |
Presentation time: |
Not requested |
Co-Author(s): | R. La Haye |
| Description: | Drive current in the O-point or X-point of a neoclassical island in the co- or ctr-direction (4 cases). Compare NTM stabilization efficiency and characterize (de)stabilization mechanisms. |
| Experimental Approach/Plan: | Begin as #230 (Mirnov-controlled MECCD), #382 (oblique ECE-controlled MECCD) or #385 (MECCD on entrained mode) as far as co-CD in the O-point is concerned. Repeat with ECCD modulation out-of-phase for co-CD in the X-point. Tilt gyrotrons in the opposite direction for ctr-CD in the X-point. Repeat with O-point phasing for ctr-CD in the O-point. |
| Background: | The capability of modulating the ECCD power in a controlled manner in order to selectively drive current in the O- or X-point of a rotating island is relatively recent. Experiments of this type have been carried out at Asdex Upgrade (AUG) and are under preparation at DIII-D (see proposals #230, #382, #385). AUG results clearly showed that co-CD in the O-point has a stabilizing effect and co-CD in the X-point is destabilizing, although not as much as expected. The aims of this proposal are: a) to confirm such co-CD observations; b) to compare with ctr-CD in the O- and in the X-point, which is similar but not identical to co-CD in the X- and O-point, respectively. One possible difference is that ctr-CD might give rise to a 4/2 component that would make the 2/1 island narrower and thus easier to stabilize. Similar considerations apply to a 6/4 distortion of the 3/2 island. Further differences between co- and ctr-CD stabilization might be unveiled by the experiment, in particular by magnetic probe and ECE measurements of the island width evolution and of the poloidal and toroidal mode numbers. MSE measurements of the total local current and ONETWO and TORAY calculations of the Bootstrap and EC-driven currents will also be essential in the analysis. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
468: Pair formation during disruptions |
| Name: | Francesco Volpe () |
Affiliation: | ORAU |
| Research Area: | Disruptions |
Presentation time: |
Not requested |
Co-Author(s): | Alex James (UCSD) |
| Description: | Provide first evidence of disruption-generated positrons. |
| Experimental Approach/Plan: | Repeat #51 either with the scintillator array repositioned or with reverse Ip and BT to measure emission in the opposite direction. This will be a combination of backward emission from electrons (e-) and forward emission from positrons (e+). Because forward and backward emission of each specie are related to each other, it will be easy to recognize anomalies in the comparison with #51 (forward emission from e- and backward emission from e+) that might indicate the presence of disruption-generated positrons. Additionally it is proposed to discriminate between clockwise and counter-clockwise elliptical polarization in the oblique ECE. Finally, coincidence counters of the type used in accelerators or in positron emission tomography might be utilized. |
| Background: | P. Helander predicted that, during disruptions, electron-positron pairs will form in collisions between runaway electrons and thermal ions [PRL 2003]. Not only the first experimental evidence of such phenomenon would be interesting from a basic science point of view, but it might also pave the way to innovative disruption mitigation applications by channelling part of the disruption energy into electron-positron pairs which will then annihilate in 511keV photons, relatively innocuous for the tokamak walls |
| Resource Requirements: | -- |
| Diagnostic Requirements: | Essential: scintillator array. Desirable: oblique ECE, coincidence counters. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
469: Prompt Beam Ion Loss Reduction & Suppression |
| Name: | Yubao Zhu ( ) |
Affiliation: | University of California, Irvine |
| Research Area: | Energetic Particles |
Presentation time: |
Not requested |
Co-Author(s): | W. Heidbrink |
| Description: | The primary goal of this experiment is to actively reduce / suppress
prompt beam ion loss intensity based on our newly investigation results on
the fast ion loss conditions. This will build the baseline for other
enhanced beam ion loss behaviors and relevant mechanisms study. |
| Experimental Approach/Plan: | Piggyback.
Will be performed or combined with other Energetic Particles or MHD
experiments. |
| Background: | Fast ion confinement and loss are crucial issues for advanced Tokamak
plasmas and ITER/DEMO scale fusion reactors, with the
consideration of auxiliary heating & drive efficiency, plasma & fusion
performance, and facility safety.
Recently, we have confirmed that significant prompt beam ion losses are
produced under certain DIII-D plasma conditions. While we are currently
making a database for the classification of fast ion loss study, we are
seeking some technology for the active control of prompt beam ion loss as
our first step. |
| Resource Requirements: | Piggyback
NBI, modulated 210RT source is required |
| Diagnostic Requirements: | BILD, FIDA & Magnetics |
| Analysis Requirements: | ORBIT & EFIT |
| Other Requirements: | -- |
| Title |
470: Experimental emulation of ITER port-plug RWM coil asymmetries |
| Name: | Michael Walker () |
Affiliation: | General Atomics |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | Yuri Gribov |
| Description: | The ITER port plug coils cannot be placed so as to maintain translational symmetry in the toroidal direction. Therefore, it would be very useful to study experimentally in DIII-D the effectiveness of RWM stabilization by the C-coils when one of the coils does not take part in the stabilization. This experiment could also produce very important data for validation of codes with a multimode RWM model and 3-D model of feedback coils and conducting walls. In the same configuration, it would also be useful to attempt ELM suppression and/or error field correction on the same experimental day, to determine if such a non-symmetric configuration can be effective for these tasks. The results of this experiment can provide critical guidance for decisions regarding the effectiveness of the candidate port plug coils for the proposed multiple uses. |
| Experimental Approach/Plan: | Disconnect one of the opposing C-coil pairs and power only one half of that pair, leaving the other coil open-circuited to emulate the expected lack of rotational symmetry in ITER. Some re-optimization of the RWM correction matrices will very likely be required. |
| Background: | There is concern by the ITER team that, although the port plug coils have been shown to be effective in n=1 RWM suppression, they may negatively impact the n different from one mode spectrum. Of particular concern is the expectation that there will be some pressure to install only a limited number of the total planned set of these coils. Some understanding of this issue from actual experiments would be useful, but perhaps most useful is the provision of data that can be used to validate multi-mode models. In that case, the validated models can be used to investigate this question in more detail.
The effectiveness of these in-vessel coils for other proposed purposes is also of concern. In particular, the more urgent problem in ITER at the moment may be ELM suppression. Does such a non-symmetric configuration provide for magnetic perturbations that will suppress ELMs?
Also, the present plan for the error correction coils outside the vessel is to provide only DC current. There does not seem to be a clear plan for how to optimize the current in these static coils to correct ITER error fields. More importantly, it has been seen on DIII-D that the optimal compensation is actually plasma dependent, which the present use of dynamic error field compensation addresses. The question remains, however, whether this approach (using the port plug coils) is feasible in ITER in light of the fact that the field spectrum that the port-plug coils (the only coils planned with AC capability) may not be sufficiently controllable. |
| Resource Requirements: | 1 experimental day |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | re-optimization of RWM control matrices. Development of proposed ELM suppression m/n spectrum. Development of approach to use this non-symmetric configuration for error field correction. |
| Other Requirements: | -- |
| Title |
471: Dependence of core rotation on dRsep |
| Name: | Wayne M. Solomon () |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | C.C. Petty |
| Description: | The goal is to see how the edge plasma conditions related to the biasing of the plasma null affects the plasma rotation. |
| Experimental Approach/Plan: | The plasma will be modulated between upper and lower single null (dRsep modulation). The modulation period should be comparable but less than the energy/momentum confinement time, so 10 Hz is probably optimal. CER beams need to be modulated with a suitable matching period to allow proper Fourier analysis. This should be repeated for several fixed power conditions and different densities. |
| Background: | Preliminary investigations in hybrid plasmas have shown that the central rotation is strongly influenced by the biasing of the null. In these original studies, the dRsep modulations were performed at constant beta with beta-feedback control. The changes in confinement associated with the rotation modulation resulted in approximately a factor of 4 modulation peak-to-peak in the power, which confuses the interpretation. |
| Resource Requirements: | Number of neutral beam sources: 6+
Machine Time: 1 day Experiment |
| Diagnostic Requirements: | CER, Mach probe measurement of SOL flows if possible |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
472: "Simple as possible" tests of TEM to ITG transitions |
| Name: | Edward Doyle () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport Model Validation |
Presentation time: |
Not requested |
Co-Author(s): | Steve Scott, David Mikkelsen, Terry Rhodes |
| Description: | A density scan in ohmic plasmas is predicted to generate a transition from TEM to ITG turbulence, the appearance of the latter mode leading to the saturated ohmic confinement regime. The proposal here is to revisit this simple operating regime and document with the current (much improved) local diagnostic set, and compare with gyrokinetic code predictions. A key feature of this experiment is run with "simple" ohmic experimental conditions, well within the simulation capability of GYRO and other codes. |
| Experimental Approach/Plan: | Perform density scan in ohmic plasmas. Increase density until staurated confinement regime is obtained. Utilize short beam "blips" for diagnostic purposes. Compare measured turbulence characteristics to code predictions. |
| Background: | During the National Tomamak Planning Workshop there was widespread and strong support for returning to relatively simple plasmas, such as ohmic and L-mode for tests of transport models. While such comparisons have been performed before, the key point is that the capabilities of both turbulence diagnostics and gyrokinetic codes have been considerably enhanced, such that we can now perfrom better, more meaningful comparisons. |
| Resource Requirements: | All turbuelnce systems (BES, refelctometer, scattering, CECE). |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
473: Comparison of particle and momentum diffusivities and pinches in helium discharges |
| Name: | Rajesh Maingi ( ) |
Affiliation: | Oak Ridge National Laboratory |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | The diffusive and convective terms of particle transport have been separated with both Helium gas puffing from the edge and also with Helium NBI injection (Wade PRL 1997) . Recently Yoshida (NF 2007 p.856) has demonstrated a similar technique to evaluate the diffusive and convective momentum transport coefficients with NBI modulation in JT-60U. The particle pinch term is likely linked with the momentum pinch term, but a detailed comparison has not been made. The basic idea is to use Helium discharges with modulated Helium NBI to simultaneously measure the particle and momentum transport coefficients in the same discharges for the main ion species. |
| Experimental Approach/Plan: | Run Helium discharges with Helium NBI. Use modulation to enable a transient transport analysis, and determine the relation of the particle and momentum transport coefficients on input power/collisionality. These discharges may allow a simultaneous evaluation of thermal diffusivities and pinches also. |
| Background: | -- |
| Resource Requirements: | Helium discharges with Helium NBI and modulation. |
| Diagnostic Requirements: | Ability to compute helium density from CER diagnostic. This was possible in the past. |
| Analysis Requirements: | Particle transport coefficients with CACTI or other code. Momentm transport analysis technique may need to be developed, if not possible with TRANSP or ONETWO. |
| Other Requirements: | -- |
| Title |
474: L-H transition threshold with ECH induced H-modes |
| Name: | Edward Doyle () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | Determine L-H transition power in RF generated H-mode plasmas for both directions of grad-B. Is the threshold power the same as in NBI-heated plasmas at low rotation? This is a critical question in understanding the ubiquity and signiificance of the 2007 observation that the power theshold with NBI heating is lower at low plasma rotation, and approximately equal for both directions of grad-B |
| Experimental Approach/Plan: | Utilise same plasma shapes as for 2007 NBI rotation studies, but replace NBI heating with ECH. Determine L-H transition power with ECH heating only, for both directions of grad-B. Use beam blips for diagnostic purposes. |
| Background: | The discovery that the L-H transition power threshold is lower at low rotation is one of the most significant results from the 2006/7 DIII-D run period. However, previously it was claimed that the power threshold for NBI and RF driven plasmas was similar. As RF driven plasmas have low rotation, are these two results contradictory? Given the gap in time since the previous RF driven L-h transition studies, the only way to address this is via new RF experiments. There are also implications for QH-mode operation and projections to ITER in resolving this issue. |
| Resource Requirements: | 5-6 gyrotrons. |
| Diagnostic Requirements: | -- |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
475: Studies of C deposition and D co-deposition in tile gaps |
| Name: | Dmitry Rudakov () |
Affiliation: | University of California, San Diego |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Not requested |
Co-Author(s): | W. Jacob, K. Krieger, A. Litnovsky, V. Philipps, P.C. Stangeby, W.P. West, C.P.C. Wong |
| Description: | Study reduction of C deposition and D co-deposition rate in tile gaps at elevated temperature |
| Experimental Approach/Plan: | Repeat DiMES tile gap experiment at higher temperature, possibly with metallic catcher plates in the gap. |
| Background: | |
| Resource Requirements: | ½ day experiment, detached LSN L-mode. |
| Diagnostic Requirements: | DiMEs, lower divertor and profile diagnostics |
| Analysis Requirements: | Surface analysis by IBA, ellipsometry, etc. |
| Other Requirements: | -- |
| Title |
476: ECCD profile in presence of magnetic island |
| Name: | Ron Prater () |
Affiliation: | General Atomics |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | C. Petty, F. Volpe |
| Description: | Measure the equilibrium ECCD when it is appled to an island O-point or X-point. Use the I-coil and nearly-balanced neutral beam injection to obtain a stationary 3/2 island. Using the known toroidal phase of the island, drive ECCD at the island O-point or X-point and use MSE signals to compare the effects. Or use a slowly rotating entrained mode and modulate the ECCD in phase. |
| Experimental Approach/Plan: | -- |
| Background: | ECCD in an island O-point is key to stabilization of NTMs, as needed for success on ITER. But the profile of ECCD has never been measured in the presence of an island. There are some theories, but they are not well validated. If the ECCD in the island is modulated, it's important to know if it stays within the island or spreads to the entire annulus since this affects the power requirements. |
| Resource Requirements: | I-coil; at least 4 gyrotrons; 2 counter beams and 3 co beams. |
| Diagnostic Requirements: | MSE co and counter views. |
| Analysis Requirements: | Analysis would benefit from improvements to the NVLOOP code to account for non-axisymmetric effects. |
| Other Requirements: | -- |
| Title |
477: Dust Generation at Tile Leading Edges |
| Name: | Phil West () |
Affiliation: | General Atomics |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Dmitry Rudakov, Clement Wong |
| Description: | Use the DiMES leading edge sample to investigate the formation and transport of dust during intense plasma interaction at leading edges of tiles. The DiMES leading edge sample is designed to intercept parallel heat flux over a small region to simulate tile edges and other intense plasma-surface interaction zones. The sample is also designed to collect ablated material from the edge. In this experiment we would alos use the DiMES TV system to monitor the path of dust ejected into the divertor plasma and the Thomson scattering system to monitor dust transported to the divertor and SOL at 120° toroidal location. |
| Experimental Approach/Plan: | With DiMES retracgted prepare a standard lower single null discharge with DiMES in the private flux region. Sweep the OSP to DiMES for a prescribed length of time, roughly 1 second. Set gain and integration time for TV systems. After plasma is developed and diagnostic gains set (1-2 discharges) insert the DiMES probe with leading edge sample for 1-2 discharges. |
| Background: | Dust formation mechanisms in the tokamak are poorly documented. Data from DIII-D and other machines indicate that impulsive loading, such as ELMs and disruptions, are an important source of dust. Here we propose to examine the formation of dust at regions of intense plasma interaction over a longer duration of time. The previous work with the DiMES leading edge sample, massive amounts of ablated material was observed in the collection zone located under (away from the plasma) the interaction zone. The morphology of the collected material suggested that much of this material may have been ejected as dust. Here we propose to use the diagnostic techniques developed for monitoring dust to examine the dust ejected into the plasma. |
| Resource Requirements: | LSN, L-mode, ELMing H-mode
Normal Bt, Ip
1 to 4 beams |
| Diagnostic Requirements: | DiMES TV
Divertor and Core Thomson
Lower Divertor Tangential TV
IRTV
Lower Langmuir Probes
Bolometer
SPRED
CER |
| Analysis Requirements: | Standard Video analysis
Stasndard Thomson dust analysis
Surface analysis |
| Other Requirements: | -- |
| Title |
478: W Rod Armor Plasma Exposure |
| Name: | Clement Wong () |
Affiliation: | General Atomics |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | D. Youchison, S. Allen, P. West, D. Rudakov |
| Description: | To study the thermal and mechanical response of the W rod armor at the divertor location of DIII-D. The study will also include erosion response, material redeposition in the rod gaps, IR emissivity calibration and thermal couple data acquisition on DiMES. |
| Experimental Approach/Plan: | We propose to use the DiMES mechanism to insert the W-rod sample into the lower divertor of DIII-D, and to expose the sample to different plasma discharges, while collecting IR camera and thermal couples data. The sample can be exposed to different plasma and transient events including ELMs and disruption exposures. Subsequent examination of the sample can provide information on carbon and hydrogen deposition in rod gaps, surface coating impact to emissivity, and displacement or melting of the W-rod surface. |
| Background: | W surface is proposed in a portion of the ITER divertor. W rod armor is also proposed for CTF/FDF and DEMO designs. It is important to gather integrated experimental data on the behavior of W rod armor in a takamak divertor. |
| Resource Requirements: | DiMES system. |
| Diagnostic Requirements: | All the lower divertor diagnostics. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
479: Thermal Energy Scan for Helium MGI |
| Name: | John C. Wesley () |
Affiliation: | General Atomics |
| Research Area: | Disruptions |
Presentation time: |
Not requested |
Co-Author(s): | Team MGI |
| Description: | Previous experiments with argon MGI using the Mark IV 'directed jet' injection system demonstrate a significant increase in assimilated ion and electron content with increasing plasma thermal energy (W_th). Experiments with helium MGI using the 5-valve MEDUSA injector show high assimilation, ~30%, with W_th = 0.7 MJ ELMy H-mode plasmas. Increase in W_th is expected to increase assimilation. A 2-2.5 MJ target plasma will be more 'ITER-like' with regard to reaching a high Rosenbluth density fraction in terms of the ratio of W_th to added He and electron content. The basic concept will be to do 6-valve short-pulse He MGI into a maximum W_th 'ITER-like' ELMy H-mode plasma with 7-source NBI heating. Supplemental ECH and/or ICH is an option. Need to assess whether incremental benefit is significant. |
| Experimental Approach/Plan: | |
| Background: | Assimilation of injected neutral gas in MGI depends on plasma thermal energy. Past data and experience + theories indicate positive W_th dependence of assimilation fraction. With regard to achieving total electron densities = Rosenbluth density (~4e22 m-3), all present tokamaks, DIII-D included, have lower ratio, at 'maximum performance', of W_th/n_RB than ITER will have. Hence experiments with maximum W_th are needed to better approach 'ITER-like' conditions and elucidate W_th scaling in the otherwise most efficient short-pulse MGI (MEDUSA) regime. |
| Resource Requirements: | q ~ 3 'ITER-like' ELMy H-mode target with 1->7 source NBI, plus supplemental ECH or ICH if warranted and available. Option: 'advanced baseline' hybrid target rather than standard sawtoothing H-mode. MEDUSA six-valve injector, helium gas. Standard MGI/disruption diagnostics, especially fast magnetics, 4-chord fast C02 interferometer, DISRAD + TS etc. for before-injection characterization. Shot plan will have to accommodate need (~ 30 min) to recycle NBI cryopumping after each shot. Consider scenarios for a dedicated experiment day (or half day) with ca 4 MGI shots vs. four end-of-day experiments |
| Diagnostic Requirements: | See Resource. Also spectroscopic and/or probe measurements of current quench plasma attributes. |
| Analysis Requirements: | Characterization of pre-injection target; eventual modelling with 2-D codes and diagnostic simulations to interpret C02 data, etc. |
| Other Requirements: | Similar He MGI into a high-performance 'AT' plasma would be interesting. Need to examine possible options for 'end-of-day' piggyback tests on a variety of high-performance plasmas. Some expectation that MGI will affect subsequent target plasma, so 'during-day' piggybacks may not be advisable. |
| Title |
480: Physics and Power Threshold of Low Rotation L- to H-mode Transitions |
| Name: | Lothar Schmitz () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | G. Wang, E. Doyle, T.L. Rhodes, G. McKee, A White, W.A. Peebles, J. DeBoo |
| Description: | This experiment investigates the L-to H-mode transition physics and power threshold in low rotation NBI and ECRH-generated H-modes. In particular, the experiment addresses the ubiquity and significance of the 2007 observation that the power threshold with NBI heating is lower at low plasma rotation, and approximately equal for both directions of grad-B. Radial flow profiles and the effects of equilibrium (shear) flow and Zonal flows on plasma turbulence will be investigated with four-channel Doppler Reflectometry and BES across the L-to H-mode transition. A second experimental goal is to quantify density, and Bt dependence of the L-H transition power threshold at low rotation with the goal to extrapolate to ITER. |
| Experimental Approach/Plan: | Utilize same plasma shapes as for 2007 NBI rotation studies with early NBI and late ECRH (only) heating to induce L-H transitions and determine threshold power for both scenarios. Beam torque will be scanned for both directions of grad-B, focusing on the low torque range. A subset of scans will be repeated for two other plasma density values, and for 1-2 different values of Bt (time permitting). Diagnostic beam blips for CER/MSE will be used during the ECRH phase. The average and time dependent poloidal flow will be measured simultaneously with low-k and medium k density fluctuations spectra by Doppler reflectometry. (2cm-1< k pol < 5 cm-1), combined with BES (k pol < 3 cm-1). Doppler reflectometry can also measure the instantaneous correlation of the flow amplitude with the density fluctuation level. Four x-mode reflectometry channels (50-70 Ghz) can obtain a radial flow profile for pedestal densities n ped < 2.5x 10^13 cm^-3. |
| Background: | : The discovery that the L-H transition power threshold is lower at low rotation is one of the most significant results from the 2006/7 DIII-D run period. However, previously it was claimed that the power threshold for NBI and RF driven plasmas was similar. As ECRH driven plasmas have low rotation, are these two results contradictory? Given the gap in time since the previous ECRH driven L-H transition studies, the only way to address this is via new comparison experiments. There are also implications for QH-mode operation and projections to ITER in resolving this issue.
The 2007 BES results show significant differences in edge flow profiles and fluctuation characteristics as the torque is varied. Four-channel Doppler Reflectometry will be used for simultaneous measurements of the rotation profile, intermediate-k fluctuations, and Zonal Flows including GAMs (Geodesic Acoustic Modes). Zonal Flows are thought to regulate local turbulence levels. We propose simultaneous low and intermediate-k fluctuation measurements, along with poloidal flow measurements (<v pol> and v~ pol) in ELM-free H-mode in the L-mode edge and the H-mode transport barrier (pedestal) |
| Resource Requirements: | 7 beam sources, 5-6 gyrotrons. |
| Diagnostic Requirements: | BES, FIR low/intermediate k, CECE, profile reflectometry |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
481: Physics and Power Threshold of Low Rotation L- to H-mode Transitions |
| Name: | Lothar Schmitz () |
Affiliation: | University of California, Los Angeles |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | G. Wang, E. Doyle, T.L. Rhodes, G. McKee, A White, W.A. Peebles, J. DeBoo |
| Description: | This experiment investigates the L-to H-mode transition physics and power threshold in low rotation NBI and ECRH-generated H-modes. In particular, the experiment addresses the ubiquity and significance of the 2007 observation that the power threshold with NBI heating is lower at low plasma rotation, and approximately equal for both directions of grad-B. Radial flow profiles and the effects of equilibrium (shear) flow and Zonal Flows on plasma turbulence will be investigated with four-channel Doppler Reflectometry and BES across the L-to H-mode transition. A second experimental goal is to quantify density, and Bt dependence of the L-H transition power threshold at low rotation with the goal to extrapolate to ITER. |
| Experimental Approach/Plan: | Utilize same plasma shapes as for 2007 NBI rotation studies with early NBI and late ECRH (only) heating to induce L-H transitions and determine threshold power for both scenarios. Beam torque will be scanned for both directions of grad-B, focusing on the low torque range. A subset of scans will be repeated for two other plasma density values, and for 1-2 different values of Bt (time permitting). Diagnostic beam blips for CER/MSE will be used during the ECRH phase. The average and time dependent poloidal flow will be measured simultaneously with low-k and medium k density fluctuations spectra by Doppler reflectometry (2 cm-1< k pol < 5 cm-1), combined with BES (k pol < 3 cm-1). Doppler reflectometry can also measure the instantaneous correlation of the flow amplitude with the density fluctuation level. Four x-mode reflectometry channels (50-70 Ghz) can obtain a radial flow profile for pedestal densities n ped < 2.5x 10^13 cm^-3. |
| Background: | The discovery that the L-H transition power threshold is lower at low rotation is one of the most significant results from the 2006/7 DIII-D run period. However, previously it was claimed that the power threshold for NBI and RF driven plasmas was similar. As ECRH driven plasmas have low rotation, are these two results contradictory? Given the gap in time since the previous ECRH driven L-H transition studies, the only way to address this is via new comparison experiments. There are also implications for QH-mode operation and projections to ITER in resolving this issue.
The 2007 BES results show significant differences in edge flow profiles and fluctuation characteristics as the torque is varied. Four-channel Doppler Reflectometry will be used for simultaneous measurements of the rotation profile, intermediate-k fluctuations, and Zonal Flows including GAMs (Geodesic Acoustic Modes). Zonal Flows are thought to regulate local turbulence levels. We propose simultaneous low and intermediate-k fluctuation measurements, along with poloidal flow measurements (<v pol> and v~ pol) in ELM-free H-mode in the L-mode edge and the H-mode transport barrier (pedestal). |
| Resource Requirements: | 7 beam sources, 5-6 gyrotrons. |
| Diagnostic Requirements: | BES, FIR low/intermediate k, CECE, profile reflectometry |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
482: Test of resistive MHD linear stability threshold and saturated island structure against models |
| Name: | Lang L Lao ( ) |
Affiliation: | General Atomics |
| Research Area: | Integrated Modeling |
Presentation time: |
Not requested |
Co-Author(s): | M. Chu, V. Izzo, T. Luce, R. Prater |
| Description: | Test resistive MHD classical linear stability threshold and saturated magnetic island structure against theoretical models by variation of local current density gradient and magnetic shear using ECCD, target density, and current ramp techniques. |
| Experimental Approach/Plan: | Produce low NBI L-mode plasmas and excite 3/2 and 2/1 classical tearing modes by varying the local current density gradient and magnetic shear at the 3/2 and 2/1 surfaces using ECCD, gas puff, and current ramp techniques. Fully document plasma equilibrium pressure and current profiles and fluctuation data for comparison against models and predictions from resistive MHD codes such as PEST3 and NIMROD. For ease of comparison against NIMROD, use a plasma with low magnetic Reynolds number. Start with a moderately high q95 plasma so that the q=2 surface is not too close to the edge. Apply co-ECCD to excite 3/2 and 2/1 modes. Reduce beam power if necessary to keep the islands saturated at constant amplitude. Then slowly rotating the island by varying the co-counter beam mix to move the island past the profile diagnostics (CER, BES, Thomson, MSE, etc.) It is expected that the saturated island size is largest when the co-ECCD sweeps across the singular surface and then drops precipitously across when the current drive layer moves outside. Repeat with current ramp technique and reduced target density. |
| Background: | Resistive MHD instabilities such as tearing modes play an important role in plasma confinement and stability. Although ideal MHD has become well established as a reliable predictive tool for tokamak stability limits, resistive MHD is less well understood. Resistive MHD models and codes such as PEST3 and NIMROD are available for evaluation of these instabilities, but very limited benchmarkings against experimental data have been performed. In a tokamak, tearing instabilities are driven primarily by the radial gradient of the equilibrium current density. The free energy driving theses instabilities arises from the non-uniform distribution of the current density that is concentrated near the neighborhood of a rational magnetic surface. This driving force can be characterized by the delta' parameter. As a first step toward development of a predictive resistive MHD tool, we propose to validate their linear stability threshold and saturated island structure by testing their dependence on the local current density gradient and magnetic shear against PEST3 and NIMROD predictions. |
| Resource Requirements: | 1 day experiment, 3 gyrotrons, 4 NBI sources (co+counter) |
| Diagnostic Requirements: | Thomson, CER, MSE, ECE, BES, SXR |
| Analysis Requirements: | Kinetic EFITs, PEST3, NIMROD, TORAY-GA |
| Other Requirements: | -- |
| Title |
483: Parasitic edge losses during Fast Wave Current Drive and Heating |
| Name: | Miklos Porkolab ( ) |
Affiliation: | Mass. Inst. of Technology |
| Research Area: | Heating & Current Drive |
Presentation time: |
Not requested |
Co-Author(s): | R.I. Pinsker, C.C. Petty, R. Prater, F.W. Baity, R. Moyer, J. Watkins, J.C. Hosea |
| Description: | Study the edge losses due to RF sheaths at the wall and/or Parametric Decay Instabilities (PDI) in the sol/scrape-off layer plasma during FWCD and/or FW heating campaigns. |
| Experimental Approach/Plan: | We propose to measure the sheath potentials in the plasma near the walls and/or limiters during high power FW heating and current drive. Initially, for these studies we would use existing Langmuir probes in collaboration with the edge physics group. By varying plasma conditions, such as the outer gap and ELM frequency, as well as line integrated density, theory predicts that the cut-off for fast wave propagation moves toward or away from the walls, thus greatly affecting sheath formation and subsequent edge losses. As a consequence, central electron absorption will be modified. As part of the experimental scans, we would vary the injected FW power, change the antenna phasing, and study the dependence of the sheath potential on these parameters. The results would be compared with recent predictions of theory under the SCIDAC program. To monitor Parametric Decay Instabilities (PDI), we would initially use existing RF magnetic loop probes located on the outer wall and on the center post. The PDI measurements will be greatly facilitated by the new high speed (up to 1G sample/sec) data acquisition system that is on loan from ORNL for the coming campaign. In the future, it would be desirable to install emissive probes to directly measure the plasma potential in the presence of RF waves, thus making a comparison between theory and experiment easier. In addition, to improve the interpretation of PDI spectrum in terms of theory, it would be desirable to equip the reciprocating probe with a coax tip to measure the spatial variation of the amplitude and shape of the RF spectrum. This has consequences for predicting the RF pump wave depletion due to spatial growth of the decay waves. |
| Background: | It has been observed in nearly all Fast Wave experiments at DIII-D and elsewhere, that under conditions of weak single pass absorption, parasitic edge absorption may deteriorate the current drive or heating efficiency. This is in addition to absorption by energetic beam ions in the presence of intense NBI. Although at the present time the nature of such absorption is not well understood or documented, under some conditions it may dominate the desired electron heating or current drive by Fast Waves in the core of high performance DIII-D plasmas. Given the availability of 6 MW of source ICRF power at DIII-D, it is of great importance to understand the physics of edge loss mechanisms and set up conditions to avoid them. Such high performance plasmas are typically in H-mode, and/or at high density, aimed at the high beta regime. The previous paper by Petty et al (Nucl. Fusion 39, 1421(1999) explored various ELMy H-mode conditions where edge losses completely dominated as the ELM frequency was increased to 200-300 Hz. It was shown that the edge density rose to sufficiently high level that the right hand cut-off layer moved to the plasma edge, allowing the development of strong RF sheaths at the wall or limiter surfaces. However, these sheaths were never measured. Related observations have been made on NSTX very recently and presented by Hosea at the 2007 RF conference, as well as at the 07 November APS meeting. Another mechanism leading to edge losses is the Parametric Decay Instability (PDI) into ion cyclotron quasi modes and Ion Bernstein waves in the SOL (M. Porkolab, Fusion Eng. Design 12, 93(1990)). Such spectra was observed both in DIII-D (R. Pinsker et al, Nucl. Fusion 46, S416 (2006) ) and NSTX (R. Wilson et al, APS, Albuquerque, 2003) but its role was not assessed. By understanding the physics of these processes, we propose to explore the conditions under which these mechanisms can be avoided, thus optimizing central electron heating and current drive. Furthermore, both of these processes are under intense investigation by the SCIDAC RF theory programs. |
| Resource Requirements: | At least 1 MW total FW power, in combinations of 60 MHz and/or 90 MHz; up to 6 MW NBI power. |
| Diagnostic Requirements: | Probes as described above in addition to the usual profile diagnostics. Edge reflectometry. |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
484: The unexplored SN/DN transition zone in the SOL |
| Name: | Jonathan G. Watkins () |
Affiliation: | Sandia National Laboratories |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | Lasnier, Stangeby, Rudakov |
| Description: | explore the conditions in the near (SN) SOL around an unbalanced DN plasma |
| Experimental Approach/Plan: | |
| Background: | The balanced DN has both x-points on the same flux surface. If the
magnetic balance is shifted slightly (-1<drsep<+1), the near SOL is SN while the secondary SOL is DN. The secondary SOL still has significant plasma density and temperature in this near balanced region. There are several interesting things that happen in this region of magnetic balance that strongly affect the core plasma.
1)The H mode power threshold varies strongly with drsep. Both DIII-D, ASDEX, as well as MAST have observed this in DN. In MAST the H mode can only be achieved in a narrow range around the balance point.
2) Strong changes in the ELM behavior and the core density have been observed to depend on the magnetic balance. The strongest changes occur in the transition region between +1 and -1 in the drsep parameter.
The structure of this type of SOL has potentially important properties that have never been studied before. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | mid plane probe
xpt probe
IRTV
floor probes
filterscopes
visible cameras |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
485: Sheath Factor measurement in unbalanced Double Null |
| Name: | Jonathan G. Watkins () |
Affiliation: | Sandia National Laboratories |
| Research Area: | Boundary |
Presentation time: |
Not requested |
Co-Author(s): | lasnier, Stangeby |
| Description: | Test the sheath power transmission theory using a double null plasma. Vary the magnetic balance slightly around the balance point to shift the fast electron heat flux at the strike point from the lower divertor to the upper divertor while measuring the heat and particle flux to the strike point. |
| Experimental Approach/Plan: | Control fast electron content of lower divertor plasma with DN balance. Control collisionality with density. Measure heat flux with IR camera. Measure particle flux with Langmuir probes near strike point. Measure Te with Langmuir probes and Divertor Thomson near strike point. Plot heat vs particle flux*Te for different drsep and density values. |
| Background: | The heat flux balance varies very strongly with drsep near the balance point of a DN plasma. The particle flux does not vary as quickly. This difference in drsep dependence allows us to study the two quantities independently. |
| Resource Requirements: | cryo pumps |
| Diagnostic Requirements: | IRTV
Floor probes
midplane probe
xpt probe |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
486: RMP fueling effect on pressure profile and ELMs |
| Name: | Jonathan G. Watkins () |
Affiliation: | Sandia National Laboratories |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | Evans, Osborne, Fenstermacher |
| Description: | Explore the effect of secondary xpt fueling on ELMs and ELM suppression |
| Experimental Approach/Plan: | Try to simulate RMP fueling with xpt gas injector. Using the xpt gas fueling injector, inject enough gas in the flux expanded region to reduce the edge Te (and current) while fueling the density at a narrow region in the edge. Use this flux expanded fueling to perturb the pressure profile using drsep and gas flow for control. Experiment with other fueling locations as well. |
| Background: | Edge magnetic perturbations enhance particle and energy transport across the plasma boundary into the target plates and walls. The ELM suppression may be linked to the way the plasma gets fueled in this configuration from the recyling particles at the wall and strikepoints. |
| Resource Requirements: | icoils
beams
xpt gas puff |
| Diagnostic Requirements: | visible cameras
IRTV
floor probes
mid and xpt RCPs
DIMEs TV |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
487: Target plate conditions during ELM suppression |
| Name: | Jonathan G. Watkins () |
Affiliation: | Sandia National Laboratories |
| Research Area: | ELM Control & Pedestal Physics |
Presentation time: |
Not requested |
Co-Author(s): | Evans, Moyer, Lasnier, West, Schaffer |
| Description: | Look for target plate structures and plasma conditions during ELM suppression. Monitor evolution of structures with edge q and I-coil current. Verify heat flux with thermocouples and Langmuir probes. |
| Experimental Approach/Plan: | Position strike point on top of tc array and monitor temp rise during shot to get heat flux. Move strike point to get better profile with LP (and TC?). With the improved TC and Langmuir probe array we hope to produce better profiles and show the evolution of conditions during parameter scans (q95, density, Icoil current, rotation, ...) |
| Background: | Evidence of structures has been observed with the floor probes - especially in the floating potential. The heat flux measured has been lower than expected. With the new TC array, we hope to verify the IRTV and extend the measurement into the view-blocked baffle region. |
| Resource Requirements: | -- |
| Diagnostic Requirements: | TC array and electronics |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
488: Role of pedestal in beta scaling of confinement |
| Name: | Anthony W Leonard () |
Affiliation: | General Atomics |
| Research Area: | Transport |
Presentation time: |
Not requested |
Co-Author(s): | R. Groebner |
| Description: | Use two different configurations to carry out a dimensionless beta scan. In one configuration the pedestal height is sensitive to changes in beta and the other case the pedestal is not sensitive to global beta. Measure the confinement changes with global beta in each configuration. |
| Experimental Approach/Plan: | In the standard hybrid configuration create a two point dimensionless beta scan. Carry out this scan in LSN and then USN, i.e. change the grad B drift direction. |
| Background: | In the LSN, favorable GradB drift direction, the pedestal was found to not respond to changes in BetaN. Also a confinement degradation with B was measured. In USN, unfavorable GradB direction, but otherwise identical configuration, the pedestal responded signficantly with BetaN, essentially proportional to Beta. Examining both configuration would go a long ways towards determing what role the pedestal is playing for beta scaling of confinement. |
| Resource Requirements: | All co beams |
| Diagnostic Requirements: | all pedestal diagnostics |
| Analysis Requirements: | profile and stability analysis |
| Other Requirements: | -- |
| Title |
489: Relativistic effects on profile reflectometry and a new potential Te measurement |
| Name: | Lei Zeng () |
Affiliation: | University of California, Los Angeles |
| Research Area: | General IP |
Presentation time: |
Not requested |
Co-Author(s): | W.A. Peebles, E.J. Doyle, T.L. Rhodes, G. Wang |
| Description: | The goal of this experiment is, first to investigation the relativistic effects on the reconstruction of ne profile via reflectometry in high Te. Second, by using this effect and dual polarization (O- and X- mode) measurement of profile reflectometry, test a new potential Te profile measurements. |
| Experimental Approach/Plan: | Create discharge with BT ~ 1.5 T, major radius of magnetic axis ~ 1.83 m, and LCFS in mid-plane ~ 2.29 m, in order to make fce layer as flat as possible in low field and fce at the edge ~ 34 GHz. The ne profile is with ne0 ~ 2.9 x10^19 m^-3, and ~1.3 x10^19 m^-3 at the top of edge pedestal. By using ECH, increase Te (10 keV or higher) in the center. Using profile reflectometer (dual mode operation as usual), measure O- and X- mode phases simultaneously. Reconstruct ne and Te profiles via reflectometry. And the results compare to ece and TS measurement. |
| Background: | Profile reflectometry will be important diagnostic in ITER. However, with high Te in ITER, the cold-plasma electromagnetic theory doesn�??t work. Plasma cutoff frequencies will be downshift due to the relativistic effect, which bring a measurement challenge to reflectometry. In DIII-D with high power ECH, Te can be increased to above 10 keV, the relativistic effect can be evaluated. Furthermore, for the dual mode measurements of reflectometry (as currently running in DIII-D), both O- and X-mode measured phases are modified by the relativistic effect independently. Through the analysis for these two sets of phase, both ne and Te profile can be reconstructed. The novel measurement technique has been published in PPCF (vol. 49, p. 1277)this year. It is really good to test this new technique in DIII-D, since the reconstructed results can cross check with ECE and TS measurements. |
| Resource Requirements: | ECH |
| Diagnostic Requirements: | profile reflectometry, ECE, TS |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
490: Optimal Density Control in Double-null and near Double-null High Performance Plasmas |
| Name: | Thomas W. Petrie () |
Affiliation: | General Atomics |
| Research Area: | Core-Edge Integration |
Presentation time: |
Not requested |
Co-Author(s): | -- |
| Description: | |
| Experimental Approach/Plan: | |
| Background: | |
| Resource Requirements: | |
| Diagnostic Requirements: | Asdex gauges, core Thomson scattering, upper divertor and centerpost fixed Langmuir probes, and CER |
| Analysis Requirements: | UEDGE |
| Other Requirements: | -- |
| Title |
492: Particle balance in hybrid plasmas over a full day of operations with no helium glow conditioning |
| Name: | Phil West () |
Affiliation: | General Atomics |
| Research Area: | Hydrogenic Retention |
Presentation time: |
Not requested |
Co-Author(s): | Tom Petrie, Steve Allen, Mathias Groth, Neil Brooks, |
| Description: | Establish a baseline H retention in strongly-pumped, high-performance hybrid operation with no between shot helium glow cleaning. Use the hybrid scenario previously found to have no (or even negative) H retention over a single shot. |
| Experimental Approach/Plan: | Run a standard hybrid, USN, normal Bt at a Greenwald fraction of ~0.4 all day long with no between shot helium glow. Use all diagnostics related to particle balance, extending vessel pressure measurements to 8 minutes after t=0. Regenerate crypumps between each shot to measure accumulated D2. Step 2: repeat experiment using gas puff feedback to control Greenwald fraction at 0.6 |
| Background: | Wall retention of H isotopes is found to be excessive in many devices that operate with strong particle exhaust. This has lead to a serious worry for the ITER team, who have used extrapolations of these results to predict that in vessel T inventory would build up rapidly. The rate of buildup could be high enough to require frequent (e.g. daily) mitigation. Yet DIII-D has observed zero net wall retention in strongly-pumped hybrid discharges, and in some cases net removal of wall inventory has been documented. A clear demonstration of zero wall retention over a full day of operation (roughly 180 plasma seconds) might bring some optimism into the ITER first wall planning process. |
| Resource Requirements: | USN Hybrid
Bt direction TBD, but probably normal
6 beams, 7 better
Cryopumping, all pumps |
| Diagnostic Requirements: | All the usual suspects
ASDEX gauges
Capacitance manometers.
RGA |
| Analysis Requirements: | Good particle balance, work on decreasing error in net particle balance. |
| Other Requirements: | -- |
| Title |
493: Does Intrinsic Rotation Depend on Beam Ions? |
| Name: | C. Craig Petty () |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics |
Presentation time: |
Not requested |
Co-Author(s): | W. Solomon |
| Description: | Determine if and how the intrinsic rotation profile is related to the beam ion pressure profile for nearly balanced NBI discharges. Use the same technique to determine the intrinsic rotation profile as published by Solomon. Repeat this for plasmas with strong AE activity that redistributes the beam ions (as measured by FIDA and MSE) and for plasmas with no (or weak) AE activity. The AE activity can be varied by changing the NBI power and plasma density. |
| Experimental Approach/Plan: | (1) In medium to high density plasmas using the standard AT startup, inject ~1 co and ~1 counter beam with close to zero net torque. Verify that the AE activity is absence or weak. (2) Vary the co/counter beam mix to obtain rotation profile with both signs. (3) Lower the plasma density to get strong AE activity. Increase the NBI power if necessary to keep the global stored energy constant. (4) Repeat step (2). |
| Background: | Wayne Solomon has measured the intrinsic rotation profile by interpolating nearly balanced NBI dischagres to zero torque density at each radii. Since this intrinsic rotation appears to be greater than that measured by deGrassie using ECH, one may think that it is tied somehow to the beam ion pressure. |
| Resource Requirements: | At least two co sources (30LT and 330LT) and two counter sources. |
| Diagnostic Requirements: | CER, FIDA, MSE |
| Analysis Requirements: | -- |
| Other Requirements: | -- |
| Title |
494: RWM thresholds without tearing modes |
| Name: | Richard Buttery
() |
Affiliation: | UKAEA |
| Research Area: | RWM Physics |
Presentation time: |
Not requested |
Co-Author(s): | Rob La Haye (his idea!) |
| Description: | Use pre-emptive ECCD to prevent tearing at the q=2 surface, while exploring onset threshold (rotation, beta) for RWM. Do this at various injected torques (low to high). |
| Experimental Approach/Plan: | Replicate various RWM onset scenarios in the presence/absence of 2/1 pre-emptive tearing mode current drive control. Do this for balanced, low, medium and high rotation plasmas. Some time may be needed to optimise ECCD deposition, as it may be hard to discern/check q=2 location directly - use real time MSE, and try to make modes in some cases (either rotating, or if locked use 10Hz EF phase sweep to rotate it past ECE). ECCD could also be applied in reverse direction to help destabilise tearing mode (both to measure location and discern effect on RWM). |
| Background: | It is becoming clear that the role of error fields and generation of tearing modes are intimately related to the process of RWM onset. Indeed, recent studies at high rotation have shown an error field penetration like process. At low rotation, new D3D measurements with 10Hz forced phase sweeps of the mode (from applied error field) indicate RWM onset is accompanied by island structures from very close to the point of RWM onset.
Interstingly, the latest theoretical model (eg Liu) propose further stabilisation effects for the RWM physics from kinetic damping and precessional drifts, possibly making theoretical predictions too stable to match observations of RWM onset. This all suggests that an additional destabilising force may be playing a role in RWM experiments to date - this could be coming from the tearing mode physics, either directly from error field induced islands, or the changes to tearing stability (delta prime) that seem to come about in low torque plasmas (cite D3D baseline scenario NTM torque scan).
Indeed, this even raises the possibility that the "RWM" is just a facit of an error field mode or delta prime driven mode onset. Is the real physics governing mode onset that of the tearing mode, with RWM components (although remaining stable) modifying the plasma response and energetics of the plasma to assist in tearing mode formation and generate RWM like signatures? |
| Resource Requirements: | Up to 6 beams including 2 counter. ECRH at least 2 gyrotrons, real time targetting from MSE. I coils for error field minimsation and phase locking control. |
| Diagnostic Requirements: | ECE, magnetics, MSE, CER. |
| Analysis Requirements: | Results should be apparent in changes in RWM thresholds. |
| Other Requirements: | Experience of D3D RWM experts in making target regimes. |
| Title |
495: Can n=3 fields raise n=1 error field thresholds? |
| Name: | Richard Buttery
() |
Affiliation: | UKAEA |
| Research Area: | Error Fields |
Presentation time: |
Not requested |
Co-Author(s): | Cole, Schaffer, la Haye |
| Description: | Test whether application of n=3 fields can raise plasma viscosity to the point that n=1 error field thresholds are increased, using a simple 2 shot test. |
| Experimental Approach/Plan: | Pick vanilla flavour standatrd DIII-D Ohmic plasma. Ramp n=1 fields. Repeat with n=3 applied also. Further repeats may be desirable to test result as we vary density. Ideally it would be best if we can wire I coils for both n=1 and n=3 independently. Otherwise do n=1 with C coils.
It may also make sense to do some repeats with low level of beams and apply rotation feedback with beam balancing, so that q=2 surface has the same rotation in cases with and without n=3 field.
Nevertheless, the basic proof of principal is a 2 shot test - perhaps could be squeezed in at the start of a day, while NBI cranking up? |
| Background: | Error field scalings have been a longstanding theoretical problem, with robust experiment data (particularly density scalings) not matched by theoretical models. However a new model (Cole et al) appears to be able to explain the data in terms of resonant error fields being accompanied by non-resonant (NR) components. These NR fields increase plasma viscosity, thereby making the localised braking of q=2, and consequent error field penetration, harder. This modifies the density dependence of the threshold scaling.
This also raises the possibility of a new technique to reduce plasma sensitivity to error fields, by deliberate application of non resonant fields to increase the plasma viscosity. Indeed, such an effect may already play some of the role in D3D, where the correction of the C coils has historically been hard to understand in the context of in vessel intrinsic error measurements (although Park's ideal response model goes some way to explaining this also). |
| Resource Requirements: | Ohmic, I coils, C coils. Some NBI if 2nd part pursued. |
| Diagnostic Requirements: | magnetics. CER for second part. density profiles. |
| Analysis Requirements: | Some analysi of optimal phasing and plasma configuration for n=3 fields is needed - want large amplitude at q=2 surface. |
| Other Requirements: | -- |