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