Resistive wall mode stabilization of high-{beta} plasmas in the National Spherical Torus Experiment

Journal Article · Sun May 15 00:00:00 EDT 2005 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.1883668· OSTI ID:20736577

Sontag, Aaron C; Sabbagh, S A; Zhu, W; Bialek, J M ^[1]; Menard, J E; Gates, D A; Bell, R E; LeBlanc, B P; Bell, M G; Kaye, S M; Mueller, D ^[2]; Glasser, A H ^[3]; Bondeson, A; Liu, Y ^[4]; Callen, J D; Hegna, C C; Lao, L L; Shaing, K C ^[5]; Chu, M S ^[6]; Maingi, R ^[7]

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1. Princeton Plasma Physics Lab (Columbia U.), James Forrestal Campus, Princeton, New Jersey 08543 (United States)
2. Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)
3. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
4. Institute for Electromagnetic Field Theory, Chalmers University, Goteborg (Sweden)
5. University of Wisconsin, Madison, Wisconsin 53706 (United States)
6. General Atomics, San Diego, California 92186 (United States)
7. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 (United States)

The resistive wall mode (RWM) poses a limit to the maximum {beta} that can be sustained in magnetic fusion experiments. RWM stabilization physics at low aspect ratio is studied in high-{beta} National Spherical Torus Experiment (NSTX) [M. Ono, S. M. Kaye, Y.-K. M. Peng et al., Nucl. Fusion 40, 557 (2000)] plasmas ({beta}{sub t} up to 39%; {beta}{sub N} up to 6.8) to understand and alleviate this constraint. Plasmas with increased q in NSTX have been maintained with {beta} above the computed ideal no-wall {beta} limit for more than 20 wall times with no signs of RWM growth in cases where toroidal rotation {omega}{sub {phi}}>{omega}{sub A}/4q{sup 2} 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 B{sub p} and B{sub r} 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 ({delta}B<10 G) which cause minor drops in {beta}, with growth rates {approx}1500 s{sup -1} have been observed when {beta}{sub N} exceeds 6. Resonant field amplification of an externally applied error field by the stable RWM has been observed.

• OSTI ID: 20736577
• Journal Information: Physics of Plasmas, Vol. 12, Issue 5; Other Information: DOI: 10.1063/1.1883668; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
HIGH-BETA PLASMA
KINK INSTABILITY
MAGNETOHYDRODYNAMICS
NSTX DEVICE
PLASMA DIAGNOSTICS
WALL EFFECTS