Systematically characterising the exotic material properties of weakly collisional plasmas

天体物理学前沿科学研究目前正在解决的许多最具挑战性的难题涉及巨大尺寸和/或能量的奇异物体之间的相互作用，通常会导致非凡的能量释放：伴随着黑洞合并的电磁烟花，随着引力波和多信使天文学的出现，现在可以观察到；-星团中的星系形成；-吸积盘和喷流，现在可以通过事件视界射电望远镜网络连续观测到；-伽马射线和快速射电暴；超高能宇宙射线；还有很多其他的事情。为了模拟这些现象，一个关键的挑战是详细了解构成这些事件发生的天体物理环境的稀释热气体（称为“等离子体”）。不出所料，人们认为这种等离子体的行为与我们日常生活中遇到的气体非常不同，因为它的温度要高数百万度，密度只有气体的六分之一！尽管物理学家已经对这种物质状态进行了近一个世纪的研究——最著名的是在恒星和核聚变能研究的背景下——但它的性质仍然存在许多令人惊讶的基本不确定性：例如，等离子体如何传导热量，它们的粘度是多少？然而，我们的计算能力和高能激光设备的最新技术进步意味着我们现在可以在实验室和超级计算机上前所未有地研究等离子体的行为。在这个研究项目中，我将承担一个系统的项目，这将大大提高我们对在天体物理环境中通常遇到的等离子体类型（其热能超过其磁能）的基本特性的理解。更具体地说，我会用最先进的代码进行数值模拟，以研究几种不同的特性：粘度，导热性和导电性，以及具有异常高能量的带电粒子的自发产生。我对与传统气体明显不同的行为特别感兴趣。然后，我将测试在“实验室天体物理学”实验中开发的理论框架，这些实验使用激光来实现地球上与相关天体物理环境有许多相似之处的极端条件。除了天体物理观测之外，我还对利用磁化等离子体的异常特性来辅助惯性约束聚变（ICF）的工作感兴趣。在ICF方案中，一个装有氘-氚燃料的小胶囊用激光束点燃；如果该方案成功，所产生的核聚变反应产生的能量比最初使用激光产生的能量大得多。目前，ICF计划尚未取得成功；然而，我相信，通过考虑使用外加磁场，可以对目前的尝试进行重大改进。

Many of the most challenging conundrums currently being addressed by frontier scientific research in astrophysics involve interactions between exotic objects of colossal sizes and/or energies, typically resulting in instances of extraordinary energy release: - the electromagnetic fireworks accompanying black-hole mergers, which are now observable with the advent of gravitational- wave and multi-messenger astronomy; - galaxy formation in clusters; - accretion discs and jets, which are now serially observable by the Event Horizon radio-telescope network; - gamma-ray and fast radio bursts; ultra-high-energy cosmic rays; and many other occurrences. To model these phenomena, a key challenge is to have a detailed understanding of the dilute hot gas (known as `plasma') making up the astrophysical environments where these events occur. Unsurprisingly, this plasma is believed to behave very differently to the gases we all encounter in everyday life, on account of being millions of degrees hotter, and one sextillionth the density! While this state of matter has been studied by physicists for nearly a century - most famously, in the contexts of stars and nuclear fusion energy research - there remain a number of surprisingly fundamental uncertainties about its properties: for example, how do plasmas conduct heat, and what is their viscosity? However, recent technological advances in both our computing capabilities and high-energy laser facilities mean that we can now investigate the behaviour of plasmas as never before in the laboratory and on supercomputers. In this research project, I will be undertaking a systematic programme that will significantly advance our understanding of the fundamental properties of the type of plasma typically encountered in astrophysical environments (whose thermal energy exceeds their magnetic energy). More specifically, I will run numerical simulations with state-of-the-art codes to investigate several different characteristics: viscosity, thermal and electrical conductivity, and the spontaneous generation of charged particles with anomalously high energies. I am particularly interested in behaviours which depart markedly from conventional gases. I will then test theoretical frameworks developed in "laboratory astrophysics" experiments, which use lasers to realise extreme conditions on Earth with many similarities to relevant astrophysical environments. In addition to the astrophysical observations, I am also interested in leveraging anomalous properties of magnetised plasmas to aid inertial confinement fusion (ICF) efforts. In ICF schemes, a small capsule of deuterium-tritium fuel is ignited using laser beams; if the scheme is successful, the resulting nuclear fusion reactions produce much more energy than initially applied with the lasers. At present, successful ICF schemes have not yet been achieved; however, I believe that significant improvements to current attempts could be attained by considered use of applied magnetic fields.