Stochastic Electron Acceleration in High-Mach-Number Collision-less Shocks

Elucidating acceleration mechanisms of charged particles have been of great interests in laboratory, space, and astrophysical plasmas. Among other mechanisms, a collision-less shock is thought as an efficient particle accelerator. The diffusive shock acceleration (DSA) theory has provided a solution to observational evidences for efficient accelerations at collision-less shocks, as it predicts a power-law energy spectrum of particles having a spectral index that is close to the values suggested by multi-wavelength observations. As the DSA theory presumes pre-existing mildly energetic particles, pre-acceleration mechanisms are required to provide a seed population for DSA, particularly for electrons. The connection between pre-acceleration and DSA remains a critical issue in shock acceleration theory.

In this talk, we present our recent progresses on electron accelerations at collision-less shocks in weak magnetic field regimes. Large-scale particle-in-cell simulations have revealed that in such high Alfven Mach number cases, the ion Weibel instability plays dominant roles in energy dissipation through generating strong magnetic field turbulence in the shock transition layer. Electrons are efficiently accelerated during interacting with the strong magnetic field turbulence in stochastic manners.