Magnetohydrodynamic Stability of Spheromak Plasma in Spheroidal Flux Conserver–Application of Mercier Criterion–

Abstract

The MHD equilibrium configurations of spheromak plasmas in an oblate spheroidal flux conserver are determined for a pressure distribution whose derivative d p /dψ vanishes on the magnetic axis, and for an optimized distribution which is neutrally stable for localized perturbations. Here ψ is the flux function. These equilibria are shown to be stable for symmetric modes. The stability for localized modes is investigated by the Mercier criterion. The values of the maximum beta ratio β max are evaluated for both pressure distributions and are shown to become about 1.5 times larger by optimization. The beta ratio is defined by the value of 2 p / B ϕ 2 on the magnetic axis, where B ϕ is the toroidal magnetic field. If the condition, q axis <1 is required, the values of β max are found to be less than 23%. Here q axis is the value of the safety factor on the magnetic axis.