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Stability of coupled tearing and twisting modes in tokamaks
A dispersion relation is derived for resistive modes of arbitrary parity in a tokamak plasma. At low mode amplitude, tearing and twisting modes which have nonideal magnetohydrodynamical (MHD) behavior...
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Toroidal phase locking phenomena and nonaxisymmetric flux perturbations in the Extrap T1 reversed-field pinch
The structure of the magnetic fluctuations in the Extrap T1 reversed-field pinch [Phys. Scr. 44, 358 (1991)] has been studied over the pinch parameter range 1.6<=B(a)/B<2.2. It is found that non...

Effect of a static external magnetic perturbation on resistive mode stability in tokamaks

Phys. Plasmas 1, 3337 (1994); doi:10.1063/1.870918

Issue Date: October 1994

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R. Fitzpatrick and T. C. Hender
Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712
The influence of a general static external magnetic perturbation on the stability of resistive modes in a tokamak plasma is examined. There are three main parts to this investigation. First, the vacuum perturbation is expanded as a set of well-behaved toroidal ring functions, and is, thereafter, specified by the coefficients of this expansion. Second, a dispersion relation is derived for resistive plasma instabilities in the presence of a general external perturbation, and finally, this dispersion relation is solved for the amplitudes of the tearing and twisting modes driven in the plasma by a specific perturbation. It is found that the amplitudes of driven tearing and twisting modes are negligible until a certain critical perturbation strength is exceeded. Only tearing modes are driven in low-beta plasmas with epsilonbetap<<1. However, twisting modes may also be driven if epsilonbetap>~1. For error-field perturbations made up of a large number of different poloidal and toroidal harmonics the critical strength to drive locked modes has a ``staircase'' variation with edge-q, characterized by strong discontinuities as coupled rational surfaces enter or leave the plasma. For single harmonic perturbations, the variation with edge-q is far smoother. Both types of behavior have been observed experimentally. The critical perturbation strength is found to decrease strongly close to an ideal external kink stability boundary. This is also in agreement with experimental observations. Physics of Plasmas is copyrighted by The American Institute of Physics.
History: Received 1 April 1994; accepted 17 June 1994
Permalink: http://link.aip.org/link/?PHPAEN/1/3337/1
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KEYWORDS and PACS

Keywords
PACS
  • 52.35.Py
    The physics of plasmas and electric discharges Waves, oscillations, and instabilities in plasma Plasma macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, RayleighTaylor)
  • 52.55.Fa
    The physics of plasmas and electric discharges Plasma equilibrium and confinement Tokamaks
  • 52.40.Hf
    The physics of plasmas and electric discharges Plasma interactions Solidplasma interactions; wall effects; probes; sheaths
  • 52.30.Jb
    The physics of plasmas and electric discharges Plasma flow; magnetohydrodynamics Resistive MHD effects
  • YEAR: 1994

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1070-664X (print)   1089-7674 (online)
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REFERENCES (24)
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