Toroidal MHD stability in complex magnetic configurations

Abstract

Mercier's localized perturbation criterion near the magnetic axis is examined for a particular type of toroidal configuration of non-planar magnetic axis of variable curvature and torsion with non-circular (elliptically and triangularly deformed) plasma cross section for the 'resonance case'. As an application, a numerical calculation is carried out for a class of equilibria that belongs to the above configuration with constant torsion. In the absence of longitudinal current, it is possible to have a domain of stability in a system with a horizontally elliptical (and triangular) deformation with an ellipticity corresponding to (a=2b) i.e. the minor axis is twice the major axis. In the presence of a longitudinal current, a domain of stability is also possible and it depends on the direction of the current. Horizontally elliptical and triangular deformations are favourable for stability.