Instability theorem in magnetohydrodynamics revisited

A previous theorem by Pfirsch and Tasso [Nucl. Fusion 11, 259 (1971)] concerning "resistive wall modes" is extended in a "weak sense" to the case of time-dependent wall resistivity. Instability growth behavior remains, however, an open problem. (C) 2004 American Institute of Physics. Physics of Plasmas