ELECTRON SHOCK SURFING ACCELERATION IN MULTIDIMENSIONS: TWO-DIMENSIONAL PARTICLE-IN-CELL SIMULATION OF COLLISIONLESS PERPENDICULAR SHOCK
ELECTRON SHOCK SURFING ACCELERATION IN MULTIDIMENSIONS: TWO-DIMENSIONAL PARTICLE-IN-CELL SIMULATION OF COLLISIONLESS PERPENDICULAR SHOCK
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DOI：
10.1088/0004-637x/690/1/244
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发表时间：
2008-05
期刊：
影响因子：
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通讯作者：
T. Amano;M. Hoshino
中科院分区：
文献类型：
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作者：
T. Amano;M. Hoshino
利用自洽二维粒子胞内模拟研究了高马赫数无碰撞冲击在弱磁化介质中传播的电子加速机制。模拟结果表明，在激波过渡区前缘的电子-离子静电双流不稳定性激发了强静电波，与先前的一维模拟结果相同。我们观察到与激波过渡区湍流静电波有关的强电子加速度。激波过渡区的电子能谱呈明显的幂律分布，能谱指数在2.0 ~ 2.5之间。通过分析加速电子的运动轨迹，我们发现其加速机制与离子的激波加速非常相似。然而，与离子冲击冲浪相反，高能电子在冲击过渡区被电子尺度的静电波动所反映，而不是被离子尺度的交叉冲击静电势所反映。然后，反射的电子被激波前的对流电场加速。我们认为多维效应和自一致激波结构是高马赫数激波下强电子加速的必要条件。
Electron acceleration mechanisms in high-Mach-number collisionless shocks propagating in a weakly magnetized medium is investigated using a self-consistent two-dimensional particle-in-cell simulation. Simulation results show that strong electrostatic waves are excited via the electron–ion electrostatic two-stream instability at the leading edge of the shock transition region as in the case of earlier one-dimensional simulations. We observe strong electron acceleration that is associated with the turbulent electrostatic waves in the shock transition region. The electron energy spectrum in the shock transition region exhibits a clear power-law distribution with spectral index of 2.0-2.5. By analyzing the trajectories of accelerated electrons, we find that the acceleration mechanism is very similar to shock-surfing acceleration of ions. In contrast to the ion shock surfing, however, the energetic electrons are reflected by electron-scale electrostatic fluctuations in the shock transition region and not by the ion-scale cross-shock electrostatic potential. The reflected electrons are then accelerated by the convective electric field in front of the shock. We conclude that the multidimensional effects as well as the self-consistent shock structure are essential for the strong electron acceleration at high-Mach-number shocks.