Asymmetric ion acceleration in laser-produced magnetized collisionless shocks

Quasi-hemispherical magnetized collisionless shocks have been generated at the SG-II laser facility through the interaction between a laser-produced supersonic plasma flow and a magnetized ambient plasma, exhibiting an angular asymmetric shock profile accompanied by asymmetric ion acceleration. We have conducted test particle simulations using the electromagnetic fields derived from 2D MHD simulations to investigate the asymmetry of ion acceleration. The simulations reproduce the angular asymmetry of the shock and the ion acceleration observed in experiments. The results indicate that shock drift acceleration is the primary mechanism for ion energization in the present quasi-perpendicular magnetized shock. The asymmetric shock structure caused by nonuniform ambient plasma forms an asymmetric accelerated electric field, ultimately leading to angular asymmetric ion acceleration, which is consistent with space observations and our experimental results. Our study provides a plausible explanation for the discrepancies reported in previous ion acceleration experiments, and could contribute to understanding of the collisionless shock acceleration.