Parametric study of non-relativistic electrostatic shocks and the structure of their transition layer
Parametric study of non-relativistic electrostatic shocks and the structure of their transition layer
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DOI：
10.1063/1.4801447
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发表时间：
2013-04
影响因子：
2.2
通讯作者：
M. Dieckmann;H. Ahmed;G. Sarri;D. Doria;I. Kourakis;L. Romagnani;M. Pohl;M. Borghesi
中科院分区：
文献类型：
--
作者：
M. Dieckmann;H. Ahmed;G. Sarri;D. Doria;I. Kourakis;L. Romagnani;M. Pohl;M. Borghesi
在实验室等离子体中经常观察到非相对论静电非磁化激波，它们很可能存在于天体物理等离子体中。它们的最大速度，以激波上游较远的离子声速为单位表示，仅取决于如果没有二元碰撞的情况下电子与离子的温度比。在此，我们用粒子模拟的方法研究了大范围激波速度下激波的形成和演化。电子和400倍重的离子的初始温度相同。马赫数在1.7和2.2之间时，激波在电子时间标度上形成。马赫数高达2.5的激波是在数十次逆离子等离子体频率后形成的。激波反射的离子束密度随激波马赫数的增加而增加，穿过激波的离子数也随之减少，从而导致其静止坐标系中下游区域的扩展变慢。相对于遥远的上游，这种离子束占据的间隔是正势。即使在没有束流不稳定性的情况下，这种势能也会在激波前预热电子，并将激波前的前震中的电子温度与远上游等离子体中的电子温度分离。电子加热降低了激波的有效马赫数。这种效应可以潜在地稳定非相对论静电激波，其移动速度与超新星残余激波的速度一样快。
Nonrelativistic electrostatic unmagnetized shocks are frequently observed in laboratory plasmas and they are likely to exist in astrophysical plasmas. Their maximum speed, expressed in units of the ion acoustic speed far upstream of the shock, depends only on the electron-to-ion temperature ratio if binary collisions are absent. The formation and evolution of such shocks is examined here for a wide range of shock speeds with particle-in-cell simulations. The initial temperatures of the electrons and the 400 times heavier ions are equal. Shocks form on electron time scales at Mach numbers between 1.7 and 2.2. Shocks with Mach numbers up to 2.5 form after tens of inverse ion plasma frequencies. The density of the shock-reflected ion beam increases and the number of ions crossing the shock thus decreases with an increasing Mach number, causing a slower expansion of the downstream region in its rest frame. The interval occupied by this ion beam is on a positive potential relative to the far upstream. This potential pre-heats the electrons ahead of the shock even in the absence of beam instabilities and decouples the electron temperature in the foreshock ahead of the shock from the one in the far upstream plasma. The effective Mach number of the shock is reduced by this electron heating. This effect can potentially stabilize nonrelativistic electrostatic shocks moving as fast as supernova remnant shocks.