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