Drag Instability

With the ionization rate of neutral particles caused by cosmic rays and balanced by the recombination rate of ions for a cold, weakly ionized fluid threaded by stressed magnetic fields, we show that a local perturbation can evolve to a traveling wave with its perturbed quantities growing with time so long as the drift velocity between neutrals and ions is comparable to the Alfven speed of the fluid. Since the large drift velocity is one of the key assumptions to drive this instability, we name it the “drag instability”. We suggest that the drag instability might occur in the regions where magnetic fields are highly stressed such as a C-shock front or a collapsing proto-stellar cloud.