Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China.
National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Sci Rep. 2017 Mar 7;7:42915. doi: 10.1038/srep42915.
A pair of collisionless shocks that propagate in the opposite directions are firstly observed in the interactions of laser-produced counter-streaming flows. The flows are generated by irradiating a pair of opposing copper foils with eight laser beams at the Shenguang-II (SG-II) laser facility. The experimental results indicate that the excited shocks are collisionless and electrostatic, in good agreement with the theoretical model of electrostatic shock. The particle-in-cell (PIC) simulations verify that a strong electrostatic field growing from the interaction region contributes to the shocks formation. The evolution is driven by the thermal pressure gradient between the upstream and the downstream. Theoretical analysis indicates that the strength of the shocks is enhanced with the decreasing density ratio during both flows interpenetration. The positive feedback can offset the shock decay process. This is probable the main reason why the electrostatic shocks can keep stable for a longer time in our experiment.
一对在相反方向传播的无碰撞激波首先在激光产生的反向流动相互作用中观察到。这些流动是通过在神光二号（SG-II）激光装置上用八束激光辐照一对相对的铜箔产生的。实验结果表明，激发的激波是无碰撞的和静电的，与静电激波的理论模型非常吻合。粒子模拟（PIC）验证了从相互作用区域生长的强静电场有助于激波的形成。这种演化是由上游和下游之间的热压力梯度驱动的。理论分析表明，在两个流相互穿透的过程中，随着密度比的减小，激波的强度增强。正反馈可以抵消激波衰减过程。这可能是静电激波在我们的实验中能够保持更长时间稳定的主要原因。
