Speaker
Description
Astrophysical collisionless shocks are efficient particle accelerators, for which some pre-acceleration mechanism is needed in order for electrons to participate in diffusive shock acceleration. In this work, we investigate how pre-existing turbulence may be able to modify the shock structure, plasma instabilities, and ultimately particle acceleration. We perform linear analysis of wave modes in fully-kinetic simulations of oblique non-relativistic high-Mach-number shocks propagating into a turbulent upstream medium with oblique large scale magnetic field. The upstream medium carried decaying compressive turbulence with density fluctuations of amplitude on the order of 15%, consistent with measurements of the local interstellar medium. We found that the simulation with pre-existing turbulence yields more efficient electron acceleration than the homogeneous one. In both simulations, we see electromagnetic modes in the turbulent inner electron foreshock region, which is consistent with previous studies of oblique high-Mach-number shocks, but with larger structures in the turbulent case. Through Fourier analysis, we investigate the polarisation of these modes and deduce that they are whistler-like. We also compare the impact on the wave modes of pre-existing turbulence to that of a homogeneous upstream on the momentum distribution of shock-reflected electrons and ions. Finally, through the linear dispersion analysis using the momentum distribution of electrons and ions in the inner foreshock region, we characterise the growth rate and frequency of the whistler waves within the inner foreshock region that is present in both simulations and compare it with our results from the Fourier analysis.
