Effects of a resistive wall on magnetohydrodynamic instabilities

Abstract

The paper presents linear and non-linear MHD calculations to examine the effect of a finite conductivity (resistive) wall on plasma stability. At a limiting safety factor qψ of approximately 2 in the tokamak and generally in the RFP, ideal modes are found, with a growth rate that varies inversely with the wall time constant. Resistive tearing modes can also be destabilized by a finite conductivity wall, but sufficiently fast plasma rotation can in turn stabilize these instabilities. It is shown that, non-linearly, the eddy currents driven in the resistive wall, by rotating MHD activity, produce a torque which opposes and slows the plasma rotation. This effect can be particularly strong in the RFP and leads to mode lock times which are shorter than in the tokamak.