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arXiv · 1409.7671

High-m Kink/Tearing Modes in Cylindrical Geometry

J. W. Connor·R. J. Hastie·I. Pusztai·P. J. Catto·M. Barnes
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Abstract

The global ideal kink equation, for cylindrical geometry and zero beta, is simplified in the high poloidal mode number limit and used to determine the tearing stability parameter, $Δ^\prime$. In the presence of a steep monotonic current gradient, $Δ^\prime$ becomes a function of a parameter, $σ_0$, characterising the ratio of the maximum current gradient to magnetic shear, and $x_s$, characterising the separation of the resonant surface from the maximum of the current gradient. In equilibria containing a current "spike", so that there is a non-monotonic current profile, $Δ^\prime$ also depends on two parameters: $κ$, related to the ratio of the curvature of the current density at its maximum to the magnetic shear, and $x_s$, which now represents the separation of the resonance from the point of maximum current density. The relation of our results to earlier studies of tearing modes and to recent gyro-kinetic calculations of current driven instabilities, is discussed, together with potential implications for the stability of the tokamak pedestal.

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J. W. Connor, R. J. Hastie, I. Pusztai, P. J. Catto, M. Barnes. 2014-09-26. High-m Kink/Tearing Modes in Cylindrical Geometry. https://doi.org/10.1088/0741-3335%2F56%2F12%2F125006

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