Effect of a strong-current ion ring on spheromak stability

Abstract

The stability of a spheromak with an energetic ion ring, carrying a current comparable to the plasma current, to the tilt mode is considered. For small departures from sphericity a perturbative approach is applied to an appropriate energy principle in order to calculate the lowest nontrivial kinetic contribution of the ion ring. An analytic stability criterion is obtained. It is seen that the prolate configuration becomes more stable while the oblate one is less stable than in the absence of the ring. The prolomak becomes stable when the ring kinetic energy exceeds the magnetic energy within the separatrix.

A 3-D Darwin–EM Hybrid PIC Code for Ion Ring Studies

“…They have also shown that the unstable rings will naturally evolve, through increase in the axial ion temperature, to stable shapes if in the initial formation process they are axially short. It has also been predicted that ion rings could stabilize compact torus configurations [11,12,13,14]. A linearized 3-D hybrid code was constructed for stability studies of field-reversed ion rings [15] but lacked the ability to examine nonlinear ef-FIG.…”