Electron heating and acceleration in high Mach number shocks

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It is known that the efficient energy transfer from ions to electron occurs in the shock transition layer, where the supersonic flow in upstream is transformed into the subsonic flow in downstream. It is also expected that the non-thermal, high-energy electron are simultaneously produced by the wave-particle interaction under the turbulence electromagnetic fields. In our study, we found the rapid energization of high-energy electron which time scale is much shorter than that for the standard diffusive/Fermi acceleration mechanism by using particle-in-cell simulations. So far the turbulent plasma waves is thought to play an important role in the shock transition layer, but it is discovered by in situ satellite observations that a large amplitude, electrostatic solitary wave is also excited in the shock transition layer. Having the solitary wave in mind, we studied how the solitary wave can be generated in the shock region, and how the solitary wave can contribute to the electron acceleration. Our new results are summarized as follows : 1) the electrostatic, solitary wave can be generated by the two-stream instability under the reflected ions from the shock and the incoming electrons in a super-critical Mach number regime, 2) some electrons can be effectively trapped by the electrostatic field through the shock surfing acceleration, which results in the formation of the nonthermal electrons, and 3) the electrons can be infinitely accelerated up to the relativistic energy if the shock Mach number exceed about several 10s. We also discussed that the electron shock surfing acceleration can be applied for the high-energy population observed in super-nova shocks as well as the interplanetary shocks.