Abstract

Stability limits for the ideal internal kink mode are calculated analytically for the Shafranov current profile using the large aspect ratio expansion. For equilibria with q(a) > 2 and circular cross-section, the maximum stable poloidal beta is below 0.1. In the absence of a conducting wall, an equilibrium with q(a) < 2 is unstable at arbitrarily small positive poloidal-beta or shear inside the q = 1 surface. The effects of non-circularity are discussed and quantitative results are given for elliptic cross-sections.

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