Particle Energization at a High Mach Number Perpendicular Shock: 1D Particle-in-cell Simulations

In this paper, we use a 1D particle-in-cell simulation code to study particle preaccelerations at a high Mach number perpendicular shock. Our simulation results show that almost all of the injected particles can be reflected at the shock front, and then they immediately gyrate back to upstream for a long distance. That facilitates the formation of a large-scale shock foot where they dominate the average velocity of particles and the formation of resultant electric fields with several subareas, unlike a low Mach number shock with fewer reflected particles. In the large-scale shock foot with subareas, these reflected particles can be energized by the motional electric fields and unexpected electrostatic fields, which means they may undergo multiple stages of preacceleration processes when gyrating just before the high Mach number perpendicular shock front with high-intensity particle reflection.