Simulation of heavy ion ring and shell distributions downstream of the bow shock

Abstract

The behavior of heavy solar wind ions at the bow shock is studied using one‐dimensional electromagnetic hybrid computer simulations. Beginning from a synchronous flow of different ion species protons and heavy ions jump to different downstream velocities. Three significant downstream regions are found: (i) Immediately downstream of the shock the differential velocity between the protons and the heavy ions generates coherent pickup of the heavy ion minor component and this region is characterized by a gyrating heavy ion beam. (ii) In the intermediate downstream region pitch‐angle scattering transforms the heavy beam within a few heavy ion gyrations to a ring‐like distribution in case of a quasi‐perpendicular magnetic field or to a shell‐like distribution in case of quasi‐parallel magnetic field. (iii) In the far downstream region energy diffusion thermalizes these distributions to become Maxwellians. Though in (ii) the heavy ion distributions are unstable their contribution to the downstream magnetic wave spectrum is unimportant.