Feedback stabilization of resistive shell modes in a reversed field pinch

A reactor relevant reversed field pinch (RFP) must be capable of operating successfully when surrounded by a close-fitting resistive shell whose L/R time is much shorter than the pulse length. Resonant modes are largely unaffected by the shell resistivity, provided that the plasma rotation is maintained against the breaking effect of nonaxisymmetric eddy currents induced in the shell. This may require an auxiliary momentum source, such as a neutral beam injector. Nonresonant modes are largely unaffected by plasma rotation, and are expected to manifest themselves as nonrotating resistive shell modes growing on the L/R time of the shell. A general RFP equilibrium is subject to many simultaneously unstable resistive shell modes; the only viable control mechanism for such modes in a RFP reactor is active feedback. It is demonstrated than an N-fold toroidally symmetric arrangement of feedback coils, combined with a strictly linear feedback algorithm, is capable of simultaneously stabilizing all intrinsically u...