Collins G W, Valenzuela J C, Speliotopoulos C A, Aybar N, Conti F, Beg F N, Tzeferacos P, Khiar B, Bott A F A, Gregori G
Center for Energy Research, University of California at San Diego, San Diego, California 92093, USA.
Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave, Chicago, Illinois 60637, USA.
Phys Rev E. 2020 Feb;101(2-1):023205. doi: 10.1103/PhysRevE.101.023205.
Currently there is considerable interest in creating scalable laboratory plasmas to study the mechanisms behind the formation and evolution of astrophysical phenomena such as Herbig-Haro objects and supernova remnants. Laboratory-scaled experiments can provide a well diagnosed and repeatable supplement to direct observations of these extraterrestrial objects if they meet similarity criteria demonstrating that the same physics govern both systems. Here, we present a study on the role of collision and cooling rates on shock formation using colliding jets from opposed conical wire arrays on a compact pulsed-power driver. These diverse conditions were achieved by changing the wire material feeding the jets, since the ion-ion mean free path (λ_{mfp-ii}) and radiative cooling rates (P_{rad}) increase with atomic number. Low Z carbon flows produced smooth, temporally stable shocks. Weakly collisional, moderately cooled aluminum flows produced strong shocks that developed signs of thermal condensation instabilities and turbulence. Weakly collisional, strongly cooled copper flows collided to form thin shocks that developed inconsistently and fragmented. Effectively collisionless, strongly cooled tungsten flows interpenetrated, producing long axial density perturbations.
目前，人们对创建可扩展的实验室等离子体以研究诸如赫比格 - 哈罗天体和超新星遗迹等天体物理现象的形成和演化背后的机制有着浓厚兴趣。如果实验室规模的实验符合相似性标准，表明相同的物理原理支配这两个系统，那么它们可以为这些外星天体的直接观测提供经过良好诊断且可重复的补充。在此，我们展示了一项关于碰撞和冷却速率对激波形成的作用的研究，该研究使用紧凑脉冲功率驱动器上相对的锥形线阵列产生的碰撞射流。通过改变为射流供料的线材来实现这些不同的条件，因为离子 - 离子平均自由程（λmfp - ii）和辐射冷却速率（Prad）随原子序数增加。低Z值的碳流产生了平滑、时间上稳定的激波。弱碰撞、适度冷却的铝流产生了强烈的激波，这些激波出现了热凝聚不稳定性和湍流的迹象。弱碰撞、强冷却的铜流碰撞形成了薄激波，其发展不一致且破碎。有效无碰撞、强冷却的钨流相互渗透，产生了长轴向密度扰动。
