SUBCRITICAL MULTIPLE-ION SHOCKS

Low Mach number collisionless shocks in a multiple-ion plasma are investigated theoretically using multiple-ion Rankine-Hugoniot relations (MIRHR) and hybrid simulations. The derived MIRHR permit tractable solutions for perpendicular shocks. It is found that starting from a synchronous flow of a mixture of different ion species, light ions and heavy ions jump to different downstream velocities. Although the resulting differential velocities between the species are unstable, they produce coherent gyration of the ion species around each other. This gyration excites standing ion hybrid waves in the downstream region. Both of these effects (the jump of different ion species to different downstream velocities and the excitation of the ion hybrid waves) are confirmed by hybrid simulations.