Simulation study of energy partition in non-relativistic magnetized collisionless shocks

Collisionless shocks are common in astrophysical plasmas and are known to be important for the magnetic field amplification and acceleration of both high energy electrons and protons. While the diffusive shock acceleration mechanism is well established, particle injection remains an important puzzle. In this work we present the results of large-scale one-dimensional particle-in-cell simulations of magnetized, non-relativistic, collisionless shocks to investigate how electron heating and the properties of the injected particles depend on the Alfvénic Mach numbers and the orientation of the ambient magnetic field. Quasi-parallel and quasi-perpendicular shocks are analyzed. Reflected particles exchange energy through wave-particle interactions, triggering instabilities in the upstream that promote electron heating. We discuss the nature of these instabilities, and the development of a non-thermal power-law-like tail in the energy spectra, finding that quasi-parallel shocks with high Mach number are the most efficient in terms of injecting and accelerating particles to the highest energies.