Evolution of slow electrostatic shock into a plasma shock mediated by electrostatic turbulence
Evolution of slow electrostatic shock into a plasma shock mediated by electrostatic turbulence
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DOI：
10.1088/1367-2630/16/7/073001
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发表时间：
2014-05
影响因子：
3.3
通讯作者：
M. Dieckmann;G. Sarri;Domenico Doria;Hamad Ahmed;M. Borghesi
中科院分区：
文献类型：
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作者：
M. Dieckmann;G. Sarri;Domenico Doria;Hamad Ahmed;M. Borghesi
两个等离子体云以超过离子声速的速度碰撞会导致激波的形成。这种现象不仅在天体物理场景中观察到，例如超新星遗迹（SNR）爆炸壳传播到星际介质中，而且在基于实验室的激光等离子体实验中也观察到。因此，这些实验和支持模拟被视为实验室小规模再现和研究天体物理冲击的有吸引力的平台。我们通过二维细胞内粒子模拟对两个由电子和离子组成的等离子体云进行建模。两个云的离子温度相差十倍。两个云的碰撞速度对于实验室研究和后期演化阶段的信噪比冲击来说是现实的，就像 RCW86 那样。与模拟平面正交的磁场的强度与 SNR 冲击的强度相当。在等离子体云和具有较冷离子的云的重叠层之间形成前向激波。在重叠层和具有较热离子的云之间观察到大振幅离子声波。它不会陡峭地变成反向激波，因为它的速度低于离子声速。当前向激波压缩磁场时，磁场幅度的梯度会在前向激波附近建立。该梯度引起的电子漂移快到足以引发不稳定。静电离子声波湍流在激波之前发展，加宽其过渡层，并使离子热化，但前向激波保持不变。
The collision of two plasma clouds at a speed that exceeds the ion acoustic speed can result in the formation of shocks. This phenomenon is observed not only in astrophysical scenarios, such as the propagation of supernova remnant (SNR) blast shells into the interstellar medium, but also in laboratory-based laser-plasma experiments. These experiments and supporting simulations are thus seen as an attractive platform for small-scale reproduction and study of astrophysical shocks in the laboratory. We model two plasma clouds, which consist of electrons and ions, with a 2D particle-in-cell simulation. The ion temperatures of both clouds differ by a factor of ten. Both clouds collide at a speed that is realistic for laboratory studies and for SNR shocks in their late evolution phase, like that of RCW86. A magnetic field, which is orthogonal to the simulation plane, has a strength that is comparable to that of SNR shocks. A forward shock forms between the overlap layer of both plasma clouds and the cloud with cooler ions. A large-amplitude ion acoustic wave is observed between the overlap layer and the cloud with hotter ions. It does not steepen into a reverse shock because its speed is below the ion acoustic speed. A gradient of the magnetic field amplitude builds up close to the forward shock as it compresses the magnetic field. This gradient gives rise to an electron drift that is fast enough to trigger an instability. Electrostatic ion acoustic wave turbulence develops ahead of the shock, widens its transition layer, and thermalizes the ions, but the forward shock remains intact.