Formation and evolution of a pair of collisionless shocks in counter-streaming flows.
Formation and evolution of a pair of collisionless shocks in counter-streaming flows.
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逆流中一对无碰撞激波的形成与演化
DOI：
10.1038/srep42915
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发表时间：
2017-03-07
影响因子：
4.6
通讯作者：
Zhang J
中科院分区：
文献类型：
--
作者：
Yuan D;Li Y;Liu M;Zhong J;Zhu B;Li Y;Wei H;Han B;Pei X;Zhao J;Li F;Zhang Z;Liang G;Wang F;Weng S;Li Y;Jiang S;Du K;Ding Y;Zhu B;Zhu J;Zhao G;Zhang J
在激光诱导的逆流流相互作用中，首次观察到一对沿相反方向传播的无碰撞激波。在神光-II（SG-II）激光装置上，用八束激光束照射一对相对的铜箔，产生流动。实验结果表明，激发的冲击波是无碰撞的静电冲击波，与静电冲击波的理论模型符合较好。粒子模拟结果证实了强静电场的存在对激波的形成有重要作用。这种演变是由上游和下游之间的热压力梯度驱动的。理论分析表明，在两股气流相互渗透过程中，激波强度随密度比的减小而增强。正反馈可以抵消冲击波的衰减过程。这可能是我们实验中静电冲击能保持较长时间稳定的主要原因。
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.