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Title: Measured improvement of global magnetohydrodynamic mode stability at high-beta, and in reduced collisionality spherical torus plasmas

Global mode stability is studied in high-β National Spherical Torus Experiment (NSTX) plasmas to avoid disruptions. Dedicated experiments in NSTX using low frequency active magnetohydrodynamic spectroscopy of applied rotating n = 1 magnetic fields revealed key dependencies of stability on plasma parameters. Observations from previous NSTX resistive wall mode (RWM) active control experiments and the wider NSTX disruption database indicated that the highest β{sub N} plasmas were not the least stable. Significantly, here, stability was measured to increase at β{sub N}∕l{sub i} higher than the point where disruptions were found. This favorable behavior is shown to correlate with kinetic stability rotational resonances, and an experimentally determined range of measured E × B frequency with improved stability is identified. Stable plasmas appear to benefit further from reduced collisionality, in agreement with expectation from kinetic RWM stabilization theory, but low collisionality plasmas are also susceptible to sudden instability when kinetic profiles change.
Authors:
; ;  [1] ; ; ; ; ; ; ;  [2] ;  [3]
  1. Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)
  2. Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)
  3. Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States)
Publication Date:
OSTI Identifier:
22252833
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 5; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CONTROL; HIGH-BETA PLASMA; MAGNETIC FIELDS; NSTX DEVICE; PLASMA INSTABILITY; SPECTROSCOPY; SPHERICAL CONFIGURATION; STABILIZATION