Collisionless Shocks Driven by Supersonic Plasma Flows with Self-Generated Magnetic Fields

Collisionless shocks are ubiquitous in the Universe as a consequence of supersonic plasma flows sweeping through interstellar and intergalactic media. These shocks are the cause of many observed astrophysical phenomena, but details of shock structure and behavior remain controversial because of the lack of ways to study them experimentally. Laboratory experiments reported here, with astrophysically relevant plasma parameters, demonstrate for the first time the formation of a quasiperpendicular magnetized collisionless shock. In the upstream it is fringed by a filamented turbulent region, a rudiment for a secondary Weibel-driven shock. This turbulent structure is found responsible for electron acceleration to energies exceeding the average energy by two orders of magnitude.

无碰撞激波（Collisionless shocks）广泛存在于宇宙之中，其源于超音速等离子体流扫过星际与星系际介质的过程。这类激波是诸多已观测到的天体物理现象的诱发因素，但由于缺乏实验研究手段，激波的结构与行为细节至今仍存在争议。本文报道的实验室实验采用与天体物理相关的等离子体参数，首次证实了准垂直磁化无碰撞激波的形成。该激波的上游区域被丝状湍流区包裹，该区域是韦贝尔（Weibel）驱动的次级激波的雏形。研究表明，这一湍流结构能够将电子加速至超出平均能量两个数量级的能级。