2D PIC Simulation of Oblique Pickup Ion Mediated Shock

We investigate the multi-dimensional microstructure of pickup ion mediated collisionless shocks using PIC simulations.In simulations with a shock angle of 50 degrees, some of the pickup ions escape upstream from the shock front, necessitating a sufficiently large system length along the shock normal direction.In this study, we performed long-time simulations with a significantly extended system length compared to previous studies (2000 times the ion inertial length), reproducing the multi-dimensional microstructure of shock transition region.The backstreaming pickup ions excite large-amplitude upstream waves propagating different directions with respect to the magnetic field, which are convected by the upstream plasma flow and induce shock front reformation through shock surface modulation.Additionally, these large-amplitude waves influence the downstream electromagnetic field structures.The upstream waves propagate obliquely to the magnetic field lines, possessing both electromagnetic and electrostatic components.Near the shock front, steepening of the electrostatic potential associated with the waves occurs.As a result, some pickup ions undergo shock surfing acceleration followed by the shock drift acceleration, gaining significant energy.