Kinetic Simulations of Strong Nonrelativistic Shocks Propagating in a Turbulent Medium*

Strong nonrelativistic shocks are known to accelerate particles up to relativistic energies. However, for Diffusive Shock Acceleration electrons must have a highly suprathermal energy, implying the need for very efficient pre-acceleration. Most published studies consider shocks propagating through homogeneous plasma, which is an unrealistic assumption for astrophysical environments. We have developed a novel simulation technique that provides a framework for studying shocks propagating in turbulent media. I will present results from fully kinetic simulations of nonrelativistic high-Mach-number shocks propagating in an electron-ion plasma with a preexisting compressive turbulence. We explore the impact of the density fluctuations with realistic amplitudes on electron acceleration and the driving of plasma instabilities. Such turbulence at perpendicular shocks enhances variations in the upstream magnetic field, but their levels remain too low to affect the behavior of electrons significantly. At oblique shocks, however, the turbulence modifies the properties of the shock-reflected electrons and plasma instabilities driven by these particles. Furthermore, the energy spectrum of downstream electrons shows a well-pronounced non-thermal tail.