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Title: A current-driven resistive instability and its nonlinear effects in simulations of coaxial helicity injection in a tokamak

An instability observed in whole-device, resistive magnetohydrodynamic simulations of the driven phase of coaxial helicity injection in the National Spherical Torus eXperiment is identified as a current-driven resistive mode in an unusual geometry that transiently generates a current sheet. The mode consists of plasma flow velocity and magnetic field eddies in a tube aligned with the magnetic field at the surface of the injected magnetic flux. At low plasma temperatures (~10–20 eV), the mode is benign, but at high temperatures (~100 eV) its amplitude undergoes relaxation oscillations, broadening the layer of injected current and flow at the surface of the injected toroidal flux and background plasma. The poloidal-field structure is affected and the magnetic surface closure is generally prevented while the mode undergoes relaxation oscillations during injection. Furthermore, this study describes the mode and uses linearized numerical computations and an analytic slab model to identify the unstable mode.
Authors:
 [1] ;  [2]
  1. Woodruff Scientific, Inc., Seattle, WA (United States)
  2. Univ. of Wisconsin, Madison, WI (United States)
Publication Date:
OSTI Identifier:
1328138
Report Number(s):
LLNL-JRNL-698022
Journal ID: ISSN 1070-664X; TRN: US1701570
Grant/Contract Number:
AC52-07NA27344; AC02-05CH11231; FC02-05ER54813
Type:
Published Article
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 10; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION