DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 158: Marginal island for 2/1 NTMs | ||
| Name: | Robert J. La Haye ( |
Affiliation: | General Atomics |
| Research Area: | Stability | Presentation time: | Requested | Co-Author(s): | R. Buttery, M. Maraschek, S. Sabbagh, E. Strait |
| Description: | The marginal island is where the small island threshold physics kicks in, dominates, and rapid stabilization occurs below this size. It determines both how low a beta one has to operate at to remove the metastable space, or how much ECCD has to drive an island down to to remove it. | ||
| Experimental Approach/Plan: | Excite a 2/1 mode, reduce betap slowly, stay in H-mode, and look for spontaneous stabilization of the 2/1 mode. | ||
| Background: | 3/2 NTM marginal island widths in either betap ramp down or ECCD removal are about twice the ion banana width. This suggests that the wpol threshold is more important than the wd threshold. Collaboration between DIII-D, AUG, JET, and JT-60U on the 3/2 mode allowed a bigger range in ion banana width and has been published. This empirical scaling seems to work for 2/1 removal but no systematic study has been made. Recent 2/1 beta ramp down exps in NSTX also yield twice the ion banana width. NSTX experiments with 2/1 mode have recently been done and fitted and this is a good test of the aspect ratio effect.
Previous DIII-D experiments dropped out of H-mode before the 2/1 mode stabilized. | ||
| Resource Requirements: | Standard sawteething H-mode plasma but at high q95
to stay in H-mode as beam power is reduced. | ||
| Diagnostic Requirements: | Usual. | ||
| Analysis Requirements: | Code is written for fitting the time dependent MRE
with either the wpol or the wd threshold models. | ||
| Other Requirements: | -- | ||
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