Stability of current-driven modes in reversed field pinches with resistive walls and plasma rotation

The linear stability of reversed field pinches (RFP’s) to current driven modes is investigated including the effects of resistive walls at a finite distance from the plasma and mode rotation. A comprehensive study is made of the stability to ideal and resistive modes and the implications for long-pulse operation of RFP’s are discussed. Stability to resistive modes of poloidal mode number m=1 requires conducting walls at a distance b/a<1.11 (a is the plasma and b the wall radius) for optimally peaked current profiles. Stability to m=0 requires very close-fitting conductors, b/a<1.03. The requirements on wall times and mode rotation frequencies posed by these modes are discussed. Nonresonant m=1 modes cannot be stabilized by resistive walls and require active feedback.