The sensitivity of tokamak magnetohydrodynamics stability on the edge equilibrium

Zheng, L. J.; Kotschenreuther, M. T.; Valanju, P.

doi:10.1063/1.4986036

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

Journal Article · 18 October 2017 · Physics of Plasmas

DOI: https://doi.org/10.1063/1.4986036 · OSTI ID:1497845

^[1]; Kotschenreuther, M. T. ^[1]; Valanju, P. ^[1]

Univ. of Texas, Austin, TX (United States)

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.

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Research Organization:: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: FG02-04ER54742

OSTI ID:: 1497845

Journal Information:: Physics of Plasmas, Vol. 24, Issue 10; ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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