By using particle-in-cell simulations, we study the collision of two plasma flows with one of them carrying a magnetic field. Ion interpenetration results in the formation of a magnetic piston with the magnetic field compression proportional to the density ratio of the colliding plasmas. The counterpropagating ions in the nonmagnetized plasma upstream from the piston excite the ion Weibel instability, which turns into magnetic turbulence. The thickness of the piston increases with time, and it turns into a reverse magnetized shock after less than one ion gyro period. In front of the piston, the time needed to decrease the nonmagnetized ion anisotropy using the magnetic turbulence is much larger than the ion gyroperiod in the piston. Consequently, particles are reflected by the piston, which acts as a wall initiating a transient phase. After several ion periods, the formation of this electromagnetic forward shock is, then, accelerated by the piston, and at large timescale, the dissipation of energy is eventually mediated only by the Weibel turbulence. We report here a new configuration of shocks, where a reverse magnetized and a forward electromagnetic shock coexist separated by a tangential discontinuity. Particle acceleration and heating in the two shock structures and relevance of this scenario of collisionless shock formation to laboratory experiments and astrophysical conditions are discussed.

中文翻译：

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磁性活塞形成的轻度相对论无碰撞激波

通过使用细胞内粒子模拟，我们研究了两个等离子体流与其中一个携带磁场的碰撞。离子互穿导致形成磁性活塞，磁场压缩与碰撞等离子体的密度比成正比。活塞上游的非磁化等离子体中的反向传播离子激发离子 Weibel 不稳定性，从而转变为磁湍流。活塞的厚度随着时间的推移而增加，在不到一个离子陀螺周期后变成反向磁化冲击。在活塞前，利用磁湍流降低非磁化离子各向异性所需的时间远大于活塞内的离子回旋周期。因此，粒子被活塞反射，活塞充当启动瞬态阶段的壁。经过几个离子周期后，这种电磁前向激波的形成被活塞加速，在大的时间尺度上，能量的耗散最终仅由威贝尔湍流介导。我们在这里报告了一种新的冲击配置，其中反向磁化和正向电磁冲击共存，被切向不连续性隔开。讨论了两种激波结构中的粒子加速和加热，以及这种无碰撞激波形成场景与实验室实验和天体物理条件的相关性。其中反向磁化和正向电磁冲击共存，被切向不连续性隔开。讨论了两种激波结构中的粒子加速和加热，以及这种无碰撞激波形成场景与实验室实验和天体物理条件的相关性。其中反向磁化和正向电磁冲击共存，被切向不连续性隔开。讨论了两种激波结构中的粒子加速和加热，以及这种无碰撞激波形成场景与实验室实验和天体物理条件的相关性。