We examine with particle-in-cell (PIC) simulations how a parallel shock in pair plasma reacts to upstream waves, which are driven by escaping downstream particles. Initially, the shock is sustained in the two-dimensional simulation by a magnetic filamentation (beam-Weibel) instability. Escaping particles drive an electrostatic beam instability upstream. Modifications of the upstream plasma by these waves hardly affect the shock. In time, a decreasing density and increasing temperature of the escaping particles quench the beam instability. A larger thermal energy along than perpendicular to the magnetic field destabilizes the pair-Alfven mode. In the rest frame of the upstream plasma, the group velocity of the growing pair-Alfven waves is below that of the shock and the latter catches up with the waves. Accumulating pair-Alfven waves gradually change the shock in the two-dimensional simulation from a Weibel-type shock into an Alfvenic shock with a Mach number that is about 6 for our initial conditions.

中文翻译：

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上游波将成对等离子体中的 Weibel 型转变为 Alfvenic 激波

我们通过胞内粒子 (PIC) 模拟研究了成对等离子体中的平行冲击如何对上游波做出反应，上游波是由逃逸的下游粒子驱动的。最初，冲击在二维模拟中由磁丝化（束-韦贝尔）不稳定性维持。逃逸的粒子会在上游驱动静电束不稳定。这些波对上游等离子体的修改几乎不会影响冲击。随着时间的推移，逃逸粒子的密度降低和温度升高会抑制光束的不稳定性。比垂直于磁场更大的热能破坏了对-阿尔芬模式的稳定性。在上游等离子体的静止坐标系中，增长对阿尔芬波的群速度低于激波的群速度，后者赶上波。