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Title: Peeling-off of the external kink modes at tokamak plasma edge

Abstract

It is pointed out that there is a current jump between the edge plasma inside the last closed flux surface and the scrape-off layer and that the current jump can lead the external kink modes to convert to the tearing modes, due to the current interchange effects [L. J. Zheng and M. Furukawa, Phys. Plasmas 17, 052508 (2010)]. The magnetic reconnection in the presence of tearing modes subsequently causes the tokamak edge plasma to be peeled off to link to the divertors. In particular, the peeling or peeling-ballooning modes can become the “peeling-off” modes in this sense. This phenomenon indicates that the tokamak edge confinement can be worse than the expectation based on the conventional kink mode picture.

Authors:
 [1];  [2]
  1. Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States)
  2. Graduate School of Engineering, Tottori University, Tottori 680-8552 (Japan)
Publication Date:
OSTI Identifier:
22303592
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 8; 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; BALLOONING INSTABILITY; CURRENTS; DIVERTORS; MAGNETIC RECONNECTION; MAGNETIC SURFACES; PLASMA; PLASMA CONFINEMENT; PLASMA SCRAPE-OFF LAYER; TEARING INSTABILITY; TOKAMAK DEVICES

Citation Formats

Zheng, L. J., and Furukawa, M. Peeling-off of the external kink modes at tokamak plasma edge. United States: N. p., 2014. Web. doi:10.1063/1.4894105.
Zheng, L. J., & Furukawa, M. Peeling-off of the external kink modes at tokamak plasma edge. United States. doi:10.1063/1.4894105.
Zheng, L. J., and Furukawa, M. Fri . "Peeling-off of the external kink modes at tokamak plasma edge". United States. doi:10.1063/1.4894105.
@article{osti_22303592,
title = {Peeling-off of the external kink modes at tokamak plasma edge},
author = {Zheng, L. J. and Furukawa, M.},
abstractNote = {It is pointed out that there is a current jump between the edge plasma inside the last closed flux surface and the scrape-off layer and that the current jump can lead the external kink modes to convert to the tearing modes, due to the current interchange effects [L. J. Zheng and M. Furukawa, Phys. Plasmas 17, 052508 (2010)]. The magnetic reconnection in the presence of tearing modes subsequently causes the tokamak edge plasma to be peeled off to link to the divertors. In particular, the peeling or peeling-ballooning modes can become the “peeling-off” modes in this sense. This phenomenon indicates that the tokamak edge confinement can be worse than the expectation based on the conventional kink mode picture.},
doi = {10.1063/1.4894105},
journal = {Physics of Plasmas},
number = 8,
volume = 21,
place = {United States},
year = {Fri Aug 15 00:00:00 EDT 2014},
month = {Fri Aug 15 00:00:00 EDT 2014}
}
  • An analytical theory of stabilization of external kink modes in a tokamak with rotating plasma is developed, which is of interest in connection with experiments on the DIII-D tokamak demonstrating such a stabilization. It is assumed that, in addition to the main poloidal harmonic, the mode includes one or more side-band poloidal harmonics with singular points lying inside the plasma. Near these singular points, plasma inertia and related toroidal effects, the compressible part of plasma pressure and longitudinal viscosity, are allowed for. These effects are described kinetically taking into account the toroidal trapping of the resonant ions, which is essentialmore » if the toroidal velocity is small compared to the ion thermal velocity. Thereby, the theory presented includes both ion Landau damping and its weakening due to toroidal trapping. Near the singular points high-beta effects, which result in the finiteness of the Mercier index {ital s}, are allowed for. It is shown that the influence of plasma rotation on the external kink modes is most significant in the case of {ital s}{lt}0, i.e., when the development of the instability in a non-rotating plasma is most highly favored. In this case, the plasma rotation plays a stabilizing role, even when the ion Landau damping is neglected. The analysis presented also confirms the hypothesis of Bondeson and Ward on the stabilizing effect of ion Landau damping if this damping is not too small.« less
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  • The effect of rigid toroidal rotation on the stability of a tokamak to external kink modes is examined. For simplicity a surface current model is assumed. For a high-[beta] tokamak it is shown that to leading order the equations governing stability in the presence of rotation are identical to those for a static plasma with [beta] replaced by [beta]+[ital S], where [beta] is the plasma beta and [ital S] is a parameter which provides a measure of the rotation rate. For a circular cross-section tokamak the critical beta for stability to external kink modes in the presence of rigid toroidalmore » rotation is given, to leading order in the inverse aspect ratio [epsilon], by [beta]=0.21[epsilon][minus][ital S]. For an elliptical cross-section tokamak the largest critical beta is obtained for a vertical elongation of 2.2 and is given, to leading order in [epsilon], by [beta]=0.37[epsilon][minus][ital S]. The lower limit on the kink safety factor [ital q]* or the Mercier [ital q] increases with increase in [ital S]. Quantitative estimates of this increase can be obtained from the stability boundaries for the static problem.« less
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