Kinetic simulations of electron acceleration at shock waves in plasma with pre-existing turbulence

Shocks that propagate obliquely relative to the upstream magnetic field are ubiquitous in astrophysics and are observed to accelerate electrons to relativistic energies. Since shock acceleration is generally a highly coupled and nonlinear problem, numerical simulations are widely used. However, simulations that assume a homogeneous upstream medium do not always reproduce efficient electron energization, and our studies aims to reveal whether pre-existing turbulence may have an effect. Using a novel simulation framework, we perform fully kinetic simulations of shocks propagating in turbulent media. Our results indicate that at nonrelativistic high-Mach-number oblique shocks, which model conditions in supernova remnants, pre-existing compressible turbulence with amplitudes of density fluctuations of approximately 15% affects the shock microphysics. We demonstrate that the main plasma instability ahead of the shock develops stronger fluctuations and larger nonlinear structures that further impacts the dynamics of the shock-reflected electrons. Moreover, we observe more efficient electron acceleration. Extending our investigations to relativistic shocks, which can be found in powerful extragalactic sources such as active galactic nuclei, we examine the influence of turbulence driven by proton cosmic rays through the non-resonant streaming instability. We discuss the properties of the turbulence, its saturation mechanism, and its injection method into a shock simulation. Finally, we present the latest results from shock simulations.