DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| 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: | -- | ||
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