Resistive wall mode stabilization of high-β plasmas in the National Spherical Torus Experiment

Aaron C. Sontag, S. A. Sabbagh, W. Zhu, J. M. Bialek, J. E. Menard, D. A. Gates, A. H. Glasser, R. E. Bell, B. P. Leblanc, M. G. Bell, A. Bondeson, J. D. Callen, M. S. Chu, C. C. Hegna, S. M. Kaye, L. L. Lao, Y. Liu, R. Maingi, D. Mueller, K. C. ShaingD. Stutman, K. Tritz

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45 Citations (Scopus)

Abstract

The resistive wall mode (RWM) poses a limit to the maximum Β that can be sustained in magnetic fusion experiments. RWM stabilization physics at low aspect ratio is studied in high- Β National Spherical Torus Experiment (NSTX) [M. Ono, S. M. Kaye, Y.-K. M. Peng, Nucl. Fusion 40, 557 (2000)] plasmas (Βt up to 39%; ΒN up to 6.8) to understand and alleviate this constraint. Plasmas with increased q in NSTX have been maintained with Β above the computed ideal no-wall Β limit for more than 20 wall times with no signs of RWM growth in cases where toroidal rotation ωφ > ωA 4 q2 across the entire plasma cross section. Plasmas that violate this stability criterion can suffer a RWM induced collapse within a few wall times. This critical rotation profile for stabilization is in agreement with drift-kinetic theory applied to low frequency magnetohydrodynamics modes [A. Bondeson and M. S. Chu, Phys. Plasmas 3, 3013 (1996)]. A toroidally symmetric array of internal sensors has been used to observe n=1-3 RWMs in NSTX. This array consists of Bp and Br sensors both above and below the midplane at 12 toroidal locations instrumented to detect toroidal mode numbers of n=1-3. RWM perturbations exceeding 30 G have been measured with mode growth rates on the order of 5 ms. Small modes (δB<10 G) which cause minor drops in Β, with growth rates ~1500 s-1 have been observed when ΒN exceeds 6. Resonant field amplification of an externally applied error field by the stable RWM has been observed.

Original languageEnglish
Article number056112
Pages (from-to)1-7
Number of pages7
JournalPhysics of Plasmas
Volume12
Issue number5
DOIs
Publication statusPublished - 2005 May

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics

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