Full particle simulations of quasi-perpendicular shocks: mass ratio dependence of shock properties

Properties of low beta quasi-perpendicular shocks for various ion-to-electron mass ratios are studied by using a one dimensional full particle simulation code. It is shown that the shock reformation process changes depending on the mass ratio. In unrealistically low mass ratio runs, the reformation is due to the accumulation of gyrating specularly reflected ions at the upstream edge of the foot. At realistic mass ratios, on the other hand, the above process is strongly modified by ion thermalization associated with the modified two-stream instability in the foot. At sufficiently low mass ratio, the Buneman instability gets excited in the foot while it is stabilized at higher mass ratios. The two reformation mechanisms are compared in detail by additional runs.