Transmitted, reflected, quasi-reflected, and multiply reflected ions in low-Mach number shocks

The dependence of ion dynamics on the cross-shock potential and upstream β_i in low-Mach number marginally critical shocks is studied using advanced test particle analysis,. The directly transmitted ions provide the main contribution to the downstream ion pressure. The fraction of reflected ions increases with the increase of the cross-shock potential and β_i. This fraction is small and their contribution to the downstream ion pressure is negligible in marginally critical shocks. A population of quasi-reflected ions is identified. These ions make a loop inside the ramp and do not appear upstream. They acquire energies comparable to the energies of the true reflected ions, are observed as a halo in the downstream ion distribution, and contribute significantly to the downstream pressure. Thus, the transmitted and quasi-reflected ions shape the downstream magnetic profile. At higher cross-shock potentials and β_i the reflected ions cause formation of a magnetic dip just ahead of the ramp. A small fraction of ions are multiply reflected at the shock front. All these ions escape into the upstream region and all escaping ions are mutliply reflected.