Multi-scale simulation of intense laser plasma interactions

通过中央激光设施的工作，英国处于高功率激光等离子体研究的前沿，在国际评论中一直获得最高赞誉。最近成立的等离子体物理协同计算项目（CCPP）将其研究工作的很大一部分用于模拟激光等离子体相互作用，特别是在CLF现有的实验项目和将其扩展到更高强度的Vulcan 10PW项目的建议的推动下。两个极其重要的新发展是欧洲基于激光的惯性约束聚变演示器的HiPER项目，以及激光等离子体在x射线和伽马射线光谱中的超短脉冲光源应用的迅速兴起。超高功率激光等离子体的实验室应用还包括利用辐射和粒子束进行诊断和治疗的医疗应用，其中一些等离子体的极端条件可作为天体物理物体的实验室模拟物。至关重要的是，计算机代码可以帮助推进等离子体物理学的这些新发展。这些实验获得的物理学通常是非线性的，相对论性的，并且在尺度长度和时间尺度上有许多数量级的耦合。为了理解实验并帮助提高性能，计算建模是不可或缺的工具。与这些高度动态等离子体相关的长度和时间尺度的范围使得用单一的数值技术来模拟整个问题变得困难。例如，在HiPER聚变目标的情况下，MHD流体模型适用于压缩阶段，而随后的加热和燃烧阶段需要详细的动力学建模和颗粒在四个数量级的密度范围内的传输。Vulcan 10PW激光器的实验计划将在电子康普顿长度的尺度上探测量子电动力学（QED）现象，而磁重联的实验室实验可能涉及长达1厘米的长度。目前还没有一种方法可以适用于激光等离子体实验的全部情况，但细胞内粒子方法（PIC）非常健壮，对许多高强度实验立即有用，并且有可能在短长度尺度上扩展到量子状态，也有可能在长尺度上扩展到流体状态，使用的方法虽然在物理方面非常不同，但在计算要求方面是相似的。这种对等离子体物理新体制的探索需要开发新的软件来包含这种新的物理。这个项目将在几个方向上扩展目前用于等离子体模拟的代码。它们将被优化，以利用最大的计算机，使用国家超级计算设施上的1000个处理器。这些代码将以一种新颖、快速的方式扩展到包括粒子碰撞，从而扩展到更长的长度和时间尺度。包括QED效应将扩展其适用性到更短的尺度长度和更强的激光。来自单个电子的辐射，包括相干辐射，将有助于探索有望提供下一代短脉冲光源的新体制。最后，所有这些都将被整合到一个单一的计算工具中，使英国等离子体物理学家能够轻松地利用他们需要的工具来了解下一代实验，并为英国计算激光等离子体物理建立世界领先的地位，以补充它在实验激光等离子体科学方面已经建立的声誉。

The UK is at the forefront of high power laser-plasma research through the work of the Central Laser Facility, which has consistently received the highest praise at international review. The recently formed Collaborative Computational Project in plasma physics (CCPP) directs a substantial part of its research effort towards modelling laser-plasma interactions, driven particularly by the existing experimental programme at the CLF and the proposal to extend this to even higher intensities with the Vulcan 10PW project. Two extremely important new developments are the European HiPER project for a laser based inertial confinement fusion demonstrator and the rapidly emerging application of laser-plasmas to light source applications for ultra-short pulses in the X-ray and gamma-ray spectrum. Laboratory applications of ultra-high power laser-plasmas also include medical applications using radiation and particle beams for diagnosis and therapy and the extreme conditions in some of these plasmas serve as laboratory analogues for astrophysical objects.It is vital that computer codes are available to help progress these new developments in plasma physics. The physics accessed by these experiments is often non-linear, relativistic and couples across many orders of magnitude of scale lengths and time scales. To understand the experiments and help improve performance computational modelling is an indispensable tool. The ranges of length and time scales that are relevant to these highly dynamical plasmas make it difficult to model the whole problem with a single numerical technique. For instance, in the case of HiPER fusion targets, MHD fluid models are appropriate during the compression phase, while the ensuing heating and burn phases require detailed kinetic modelling and the transport of particles across a density range of four orders of magnitude. Experiments planned for the Vulcan 10PW laser will probe quantum electrodynamic (QED) phenomena at the scale of the electron Compton length while laboratory experiments on magnetic reconnection may involve lengths up to 1 cm. There is still no single method which is applicable to the entirety of circumstances of laser plasma experiments but the Particle in Cell method (PIC) is remarkably robust, immediately useful for many of the high intensity experiments, and has the potential to be extended at short length scales towards the quantum regime and also at long scales towards the fluid regime using methods which, while very different in terms of physics, are similar in terms of the computational requirements.This exploration of new regimes of plasma physics requires new software to be developed to include this new physics. This project will extend the current codes used for plasma simulations in several directions. They will be optimised to make use of the largest computers, using 1000's of processor on national supercomputing facilities. The codes will be extend to include particle collisions in a novel, and fast, way enabling the extension to longer lengths and time scales. Including QED effects will extend their applicability down to shorter scale lengths and more intense lasers. Radiation from individual electrons, including coherent radiation, will help probe the new regimes expected to deliver the next generation of short pulse light sources. Finally all of this will be combined into a single computational tool allowing UK plasma physicists to easily exploit the tools they need to understand the next generation of experiments and establish a world leading role for UK computational laser plasma physics to compliment it's already established reputation in experimental laser plasma science.