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