Electron and ion heating in high-Mach number collisionless shocks

Collisionless shocks are ubiquitous in astrophysical plasmas and play an important role in plasma heating, magnetic field amplification, and in accelerating high energy cosmic rays. A fundamental open question in collisionless shock physics is what are the mechanisms that control the difference in the temperature of ions and electrons in the downstream. Observations of high-Mach number shocks have shown that T_e/T_i ≥ 0.1, indicating that electrons gain significantly more energy than that corresponding to simple thermalization of their initial kinetic energy. In this work we use fully-kinetic 3D simulations to investigate the electron and ion heating mechanisms in collisionless shocks. In the high Mach number regime, we find that T_e/T_i is dictated by the interplay between the ion current-filamentation and the drift-kink instability. The connection of these results with recent experimental studies and their dependence on the Mach number will be discussed.