Shock Formation in a Collision of Two Plasmas with Their Relative Velocity Oblique to the Magnetic Field

Abstract

Shock formation processes arising from a collision of two plasmas in an external magnetic field B 0 are studied with electromagnetic particle simulations, for the case in which one plasma (exploding plasma) has a high velocity v 0 while the other (surrounding plasma) is at rest with a lower density; the ion gyroradius for the speed v 0 is much greater than the width of the shock transition region. The ion motion across B 0 induces strong electric field in the direction - v 0 × B 0 , which accelerates the surrounding ions in this direction in the early phase. Then, the change in the velocities of the two groups of ions due to the magnetic force leads to the formation of two pulses near the front of the exploding ions, which evolve into forward and reverse shock waves. The effect of the angle θ between v 0 and B 0 on plasma behavior is examined. The two pulses appear in time of the order of the ion gyroperiod. As θ decreases from 90°, however, it takes a longer time for the two pulses to form.