INSTABILITY OF A TANGENTIAL DISCONTINUITY IN A COLD-PLASMA WITH A MAGNETIC-FIELD ORTHOGONAL TO THE JUMP IN VELOCITY

A study is made of the stability of a tangential discontinuity in a co ld plasma in the well-known case of a magnetic field orthogonal to the velocity. This discontinuity is shown to be unstable for any value of the jump in the velocity. The growth rates and the domains of the ins tability of magnetohydrodynamic and hydrodynamic discontinuities are c ompared. It is shown that, in the magnetohydrodynamic case, for high v elocities, the growth rates are substantially lower, and the domain of unstable wave vectors is substantially narrower than in the hydrodyna mic case. Thus, it can be expected that, due to the instability, the s preading of magnetohydrodynamic discontinuities will occur more slowly than that of the hydrodynamic ones.