Electron Preacceleration Mechanisms in the Foot Region of High Alfvénic Mach Number Shocks
Electron Preacceleration Mechanisms in the Foot Region of High Alfvénic Mach Number Shocks
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DOI：
10.1086/341733
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发表时间：
2002-11
期刊：
影响因子：
--
通讯作者：
H. Schmitz;S. C. Chapman;R. Dendy
中科院分区：
文献类型：
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作者：
H. Schmitz;S. C. Chapman;R. Dendy
已知高马赫数、无碰撞的垂直激波通过扩散激波加速将电子加速到强相对论能量。这是以存在温和相对论性电子为前提的，其来自较低环境能量的预加速机制（注入问题）仍然是一个悬而未决的问题。在这里，一个粒子在细胞模拟被用来调查的预加速机制。取决于上游等离子体的参数和冲击速度，在冲击的脚的不稳定性的增长率可以是显着的，导致非线性模式的存在和电子相空间空穴的形成。研究发现，这些都与电子预加速，这可以分为三个阶段。在初始阶段，电子在激波脚中通过表面加速器机制加速，该机制涉及非线性波模式中的粒子捕获。这种机制与孤立电子相空间空穴的存在密切相关。第二阶段的特征是磁场强度的波动和电子的μ守恒运动。最后，在第三阶段，磁矩μ不再守恒，可能是由于湍流散射过程。能量高达10.6洛伦兹因子实现，模拟中，上游电子的流入动能为3.5千电子伏。
High Mach number, collisionless perpendicular shocks are known to accelerate electrons to strongly relativistic energies by diffusive shock acceleration. This presupposes the existence of mildly relativistic electrons, whose preacceleration mechanism from lower ambient energies (the injection problem) remains an open question. Here a particle in cell simulation is used to investigate the preacceleration mechanism. Depending on the parameters of the upstream plasma and the shock velocity, the growth rate of instabilities in the foot of the shock can be significant, leading to the existence of nonlinear modes and the formation of electron phase space holes. It is found that these are associated with electron preacceleration, which can be divided into three phases. In the initial phase electrons are accelerated in the shock foot by the surfatron mechanism, which involves particle trapping in nonlinear wave modes. This mechanism is strongly linked to the existence of solitary electron phase space holes. The second phase is characterized by fluctuations in the magnetic field strength together with μ-conserving motion of the electrons. Finally, in the third phase the magnetic moment μ is no longer conserved, perhaps due to turbulent scattering processes. Energies up to Lorentz factors of ≃6 are achieved, for simulations in which the inflow kinetic energy of upstream electrons is 3.5 keV.