The sensitivity of tokamak magnetohydrodynamics stability on the edge equilibrium
Abstract
Due to the Xpoint singularity, the safety factor tends to infinity as approaching to the last closed flux surface. The numerical treatments of the near Xpoint 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 updown symmetric equilibrium without Xpoint 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 cuttingoff. 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 »
 Authors:

 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)
 OSTI Identifier:
 1497845
 Grant/Contract Number:
 FG0204ER54742
 Resource Type:
 Accepted Manuscript
 Journal Name:
 Physics of Plasmas
 Additional Journal Information:
 Journal Volume: 24; Journal Issue: 10; Journal ID: ISSN 1070664X
 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. https://doi.org/10.1063/1.4986036.
Zheng, L. J., Kotschenreuther, M. T., & Valanju, P. The sensitivity of tokamak magnetohydrodynamics stability on the edge equilibrium. United States. https://doi.org/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. https://doi.org/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 Xpoint singularity, the safety factor tends to infinity as approaching to the last closed flux surface. The numerical treatments of the near Xpoint 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 updown symmetric equilibrium without Xpoint 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 cuttingoff. 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}
}
Web of Science
Figures / Tables:
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