Hybrid simulations of weakly collisional/collisionless shocks in laser produced plasmas

等离子体冲击在许多情况下起着重要作用，从爆炸的恒星到激光驱动的聚变实验。实验能力的最新进展激发了人们努力将实验室产生的冲击与天体物理学对应物联系起来。这是一个快速发展的研究领域，在实验室等离子体物理学和天体物理学社区之间产生新的合作。建立和隔离在两个系统中应该发生的清晰和可区分的物理效应是首要目标。然后，这些可以用来在发生在不同尺度上的过程之间建立物理上有意义的联系。数值模拟是这一努力的有力辅助。该方案涉及到构建一个新的混合等离子体模拟程序，该程序将探索具有任意碰撞水平的等离子体中冲击波的物理学，特别强调在过渡区的系统，在弱碰撞到无碰撞等离子体之间移动。在大多数观测到冲击波发生的天体物理系统中，库仑平均自由程比所关心的宏观尺度大得多。因此，流体性质（密度、温度等）的突然转变，必须通过无碰撞效应，即通过带电粒子和电磁场之间的集体相互作用来介导。这是物理学的一个迷人的领域，在微观尺度上发生的集体过程对宏观行为产生了巨大的影响。在天体物理学中，理解这种冲击的动力学具有巨大的意义，因为冲击产生的热粒子和非热粒子的辐射为我们提供了关于宇宙的重要信息。虽然无碰撞冲击是天体物理学的标准，但在地球实验中，再现必要的等离子体条件以确保库仑碰撞可以忽略不计是具有挑战性的。在利弗莫尔国家点火装置（NIF）使用世界上最大的激光器进行的实验可以提供必要的条件，但进入该设施的机会有限。然而，数值研究可以用来确定在不同层次的碰撞性冲击的共同特点，打开了研究碰撞冲击物理在更温和的激光能量的可能性。这将使人们能够利用卢瑟福·阿普尔顿实验室的火神激光器等设施，对与天体物理学有关的冲击物理学进行更深入的研究。最近在火神星上进行的一项实验的初步结果表明，这确实是可能的。我们将开发一种新的数值工具，以促进此类调查。该代码基于KALOS形式主义（Bell等人，2006年，PPCF），其中使用福克-普朗克描述准确地模拟碰撞。一个新的混合等离子体计划，使用伏拉索夫-福克-普朗克处理的离子将开发，能够调查冲击等离子体与任意水平的碰撞。我们预计这将提高我们的预测能力，提供进一步的洞察力的物理碰撞冲击。这些结果将对天体物理学和激光等离子体界都有意义。该守则还将在这两个领域有进一步的应用。

Plasma shocks play an important role in a number of situations, ranging from exploding stars to laser driven fusion experiments. Recent advances in experimental capabilities have inspired efforts to connect shocks produced in the laboratory with their astrophysical counterparts. This is a rapidly developing research area generating new collaborations between the laboratory plasma physics and astrophysics communities. Establishing and isolating clear and distinguishable physical effects that should occur in both systems is the primary goal. These can then be used to make physically meaningful connections between processes occurring on vastly different scales. Numerical simulations are a powerful aid in this effort. This proposal concerns the construction a novel hybrid plasma simulation code, that will explore the physics of shock waves in plasmas with arbitrary levels of collisionality, with a particular emphasis on systems in the transitional regime, moving between weakly collisional to collisionless plasmas.In most astrophysical systems in which shock-waves are observed to occur, the Coulomb mean free path is considerably larger than the macroscopic scales of interest. Thus, the abrupt transition in the fluid properties (density, temperature, etc.), must be mediated by collisionless effects, i.e. through the collective interaction between charged particles and electromagnetic fields. This is a fascinating area of physics, whereby collective processes occurring on microscopic scales have a dramatic effect on the macroscopic behaviour. In astrophysics, understanding the kinetics of such shocks is of enormous significance, since the radiation from the thermal and non-thermal particles produced by the shock provide us with vital information about the Universe. While collisionless shocks are the norm in astrophysics, in terrestrial experiments, reproducing the necessary plasma conditions to ensure Coulomb collisions are negligible is challenging. Experiments using the world's largest laser at the National Ignition Facility (NIF), Livermore, can provide the necessary conditions, but access to this facility is limited. However, numerical investigations can be used to identify common features of shocks at different levels of collisonality, opening the possibility of investigating collisionless shock physics at more modest laser energies. This would allow more in depth investigations of astrophysically relevant shock physics to be carried out, using facilities such as the Vulcan laser at Rutherford Appleton Laboratories. Preliminary results from a recent experiment on Vulcan indicate that this is indeed possible.We will develop a new numerical tool to facilitate such investigations. The code is based on the KALOS formalism (Bell et al., 2006, PPCF), where collisions are accurately modelled using a Fokker-Planck description. A novel hybrid plasma scheme, using a Vlasov-Fokker-Planck treatment of the ions will be developed, capable of investigating shocks in plasmas with arbitrary levels of collisionality. We anticipate this will improve our predictive capability, providing further insight into the physics of collisionless shocks. The results will be of interest to both the astrophysics and the laser plasma communities. The code will also have further applications in both fields.