Electron energization at oblique SNR shocks in turbulent media

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Where and how cosmic rays are produced in the Galaxy is an important question in modern physics. Observations of nonthermal X-rays and high-energy gamma-rays from shell-type supernova remnants (SNR) imply that nonrelativistic collisionless shocks can efficiently accelerate charged particles. Diffusive shock acceleration is a likely process for the acceleration to very high energies, but requires a preacceleration of electrons to about 50 MeV for SNR shocks. We conduct extensive particle-in-cell (PIC) simulations of collisionless shocks to investigate the processes of electron acceleration and heating at shocks. Building on earlier simulations of collisionless shocks in homogeneous environments, we now propose to study the impact of pre-existing fluctuations in the upstream medium. We know from measurements in the heliosphere that such fluctuations exist and expect that they do so also in the environment of SNRs. We also know that fluctuations on large scales can drive magnetic field amplification at, and induce rippling of, the shocks. Here we are interested in the effect of turbulence on small scales. We shall investigate the effect of pre-existing turbulence on the electron dynamics and on the driving and saturation of plasma waves. If pre-existing turbulence enhances the efficiency of electron energization, it would indicate an answer to the question of electron injection. This long-standing unsolved problem is crucially important to our understanding of particle acceleration at shocks.