Nonthermal High Energy Electron Acceleration from Shock Transition Region to Downstream Region

无碰撞激波在宇宙中的作用是超音速等离子体体能转化为粒子/热能的关键机制。然而，对非热粒子加速机制的了解仍然很少。以激波冲浪加速度为研究对象，对其加速效率、能量谱和激波动力学进行了研究。在这次助学金研究期间，我们获得了以下结果：(1)由双流不稳定性(Buneman不稳定性)产生的大幅度静电波对电子激波冲浪的加速起着重要作用。我们发现，在非线性阶段，静电波可以与离子声波耦合，并且波的幅度可以进一步提高。在斜激波中，由于洛伦兹力和高能电子逃逸的竞争效应，冲浪加速效率在激波角约为70度时达到最大。(3)在双流不稳定性产生的相干静电波背后的湍流也有助于粒子加速的增强。(4)在超高马赫数激波中，激波重塑过程随着马赫数的增加而减弱。

The role of collisionless shock waves in the Universe is important as the key mechanism of energy conversion from super-sonic plasma bulk flow energy into particle/thermal energy. However, the understanding of the non-thermal particle acceleration mechanism remains poor. By focusing on the shock surfing acceleration, we investigated the acceleration efficiency, energy spectrum, and shock dynamics. During this Grant-in-Aid research period, we obtained the following results :(1)The large amplitude electrostatic waves generated by two-stream instability (Buneman instability) plays an important role on the electron shock surfing acceleration. We found that the electrostatic wave can couple with the ion acoustic waves in the nonlinear stage, and the wave amplitude can be further enhanced. Also we discussed that the emission of the large amplitude waves occurs when the plasma frequency is larger than the electron cyclotron one.(2)In oblique shock waves, due to the competing effect between the Lorentz force and the escape of high energy electrons, the maximum efficiency of the surfing acceleration occurs when the shock angle becomes about 70 degree.(3)The turbulence behind the coherent electrostatic waves generated by two-stream instability also contributes to the enhancement of particle acceleration.(4)In super-high Mach number shock waves, the shock reformation process becomes weak as increasing Mach number.