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