Effect of the parallel current density on the local ideal 3D MHD stability of HELIAS configuration

摘要

We study the local ideal three-dimensional magnetohydrodynamic stability for the Wendelstein 7-X (W 7-X) configuration. We confirm a volume average beta limit of 5% with a nearly optimal pressure profile using two methods to calculate the parallel current density: the magnetic method that uses magnetic information of the configuration (in particular, the condition of charge conservation (nabla).j = 0 is explicitly used in the resolution) and the geometric method that uses the geometry of the configuration itself. We show that the ballooning stability does not depend on the method of the parallel current calculation. In contrast, the value of Mercier criterion depends sensitively on which method is used. Not only is the geometric method not sensitive to resonant surfaces (in particular, the i(sub p) = 1 /6), but there is a systematic error in the Mercier criterion for nonresonant surfaces when not enough modes are used to calculate the equilibria numerically with a spectral method. However, this systematic error does not change the average beta limit of W 7-X because ballooning stability is more stringent than Mercier stability for this configuration. (author) 8 figs., 13 refs. (Atomindex citation 25:024368)