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Title: The sensitivity of tokamak magnetohydrodynamics stability on the edge equilibrium

Abstract

Due to the X-point singularity, the safety factor tends to infinity as approaching to the last closed flux surface. The numerical treatments of the near X-point behavior become challenging both for equilibrium and stability. The usual solution is to cut off a small fraction of edge region for system stability evaluation or simply use an up-down symmetric equilibrium without X-point as an approximation. In this work, we assess the sensitivity of this type of equilibrium treatments on the stability calculation. It is found that the system stability can depend strongly on the safety factor value (qa) at the edge after the cutting-off. When the edge safety factor value falls in the vicinity of a rational mode number (referred to as the resonant gap), the system becomes quite unstable due to the excitation of the peeling type modes. Instead, when the edge safety factor is outside the resonant gaps, the system is much more stable and the predominant modes become the usual external kink (or ballooning and infernal) type. It is also found that the resonant gaps become smaller and smaller as qa increases. The ideal magnetohydrodynamic peeling ballooning stability diagram is widely used to explain the experimental observations, and themore » current results indicate that the conventional peeling ballooning stability diagram based on the simplified equilibrium needs to be reexamined.« less

Authors:
ORCiD logo [1];  [1];  [1]
  1. Univ. of Texas, Austin, TX (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1497845
Grant/Contract Number:  
FG02-04ER54742
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 10; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Zheng, L. J., Kotschenreuther, M. T., and Valanju, P. The sensitivity of tokamak magnetohydrodynamics stability on the edge equilibrium. United States: N. p., 2017. Web. doi:10.1063/1.4986036.
Zheng, L. J., Kotschenreuther, M. T., & Valanju, P. The sensitivity of tokamak magnetohydrodynamics stability on the edge equilibrium. United States. doi:10.1063/1.4986036.
Zheng, L. J., Kotschenreuther, M. T., and Valanju, P. Wed . "The sensitivity of tokamak magnetohydrodynamics stability on the edge equilibrium". United States. doi:10.1063/1.4986036. https://www.osti.gov/servlets/purl/1497845.
@article{osti_1497845,
title = {The sensitivity of tokamak magnetohydrodynamics stability on the edge equilibrium},
author = {Zheng, L. J. and Kotschenreuther, M. T. and Valanju, P.},
abstractNote = {Due to the X-point singularity, the safety factor tends to infinity as approaching to the last closed flux surface. The numerical treatments of the near X-point behavior become challenging both for equilibrium and stability. The usual solution is to cut off a small fraction of edge region for system stability evaluation or simply use an up-down symmetric equilibrium without X-point as an approximation. In this work, we assess the sensitivity of this type of equilibrium treatments on the stability calculation. It is found that the system stability can depend strongly on the safety factor value (qa) at the edge after the cutting-off. When the edge safety factor value falls in the vicinity of a rational mode number (referred to as the resonant gap), the system becomes quite unstable due to the excitation of the peeling type modes. Instead, when the edge safety factor is outside the resonant gaps, the system is much more stable and the predominant modes become the usual external kink (or ballooning and infernal) type. It is also found that the resonant gaps become smaller and smaller as qa increases. The ideal magnetohydrodynamic peeling ballooning stability diagram is widely used to explain the experimental observations, and the current results indicate that the conventional peeling ballooning stability diagram based on the simplified equilibrium needs to be reexamined.},
doi = {10.1063/1.4986036},
journal = {Physics of Plasmas},
number = 10,
volume = 24,
place = {United States},
year = {2017},
month = {10}
}

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Figures / Tables:

Figure 1 Figure 1: Cross section of the ITER H-mode confinement as computed by the CORSICA code. The radial grids are compacted at the rational surfaces by the AEGIS code.

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