Influence of equilibrium flows on tearing modes

Early investigations of resistive instability assumed that the plasma was at rest. However, recent work showed that the influence of the natural diffusion velocity (v∼η/a) on resistive tearing modes was important even in the limit η→0. Here, the effect of a more general velocity, of the same order as the natural resistive diffusion velocity, but otherwise arbitary, is investigated. It is found that as η→0 the effect on the stability threshold is finite and independent of the velocity except for its sign. Hence, the threshold is discontinuous at v=0. There is an additional effect of velocity on modes of finite growth rate which may be stabilizing or destabilizing according to the sign and magnitude of the velocity. The present calculations of these effects agree well with numerical simulations of tearing modes.