EPOC++ a future-proofed kinetic simulation code for plasma physics at exascale

许多等离子体物理研究计划的核心是要求捕获等离子体的全部动力学性质。这是最常见的使用粒子在单元(PIC)代码，它移动样本的等离子体粒子在自洽的电磁场。十多年来，华威最初与牛津大学和约克大学合作，一直在为英国等离子体研究人员开发这样的代码-纪元代码。核心PIC方案处理的是粒子之间的碰撞被忽略的等离子体--无碰撞的等离子体。Epoch已经扩展到包括二元碰撞、量子电动力学(QED)过程和辐射。这使得EATCH成为世界上使用最广泛的PIC代码之一，应用于粒子加速器、下一代光源、高功率激光QED研究以及用于磁和惯性约束聚变的聚变科学。为了满足英国用户群的需求，英国纪元需要进行一些关键的科学扩展。以上目标部分详细介绍了这些内容。然而，维护时代变得越来越令人担忧。这是因为Epoch是从较旧的Fortran PIC代码演变而来的，虽然在添加更复杂的边界、诊断或物理包时，对于无碰撞等离子体来说，这是相对容易修改的，但Fortran的有限功能集使这些添加变得越来越麻烦。也许可以在Fortran的旧遗产上再坚持一段时间，但还有其他或许更紧迫的问题。现代高性能计算机(HPC)系统正在远离完全由相同类型的处理器构建。相反，混合了由GPU加速的传统CPU的HPC系统正在变得流行起来。其他使用ARM处理器甚至是现场可编程门阵列的系统正在安装中。这种向异类HPC系统和复杂HPC环境的转变是由对计算能力持续增加的需求推动的。用于处理这些较新的异类系统的工具集主要是C++，而不是Fortran。将Eegch转移到C++实现(结果是重命名为EPOC++)打开了对这些通向Exascale HPC的较新路线的访问。同时，它使代码更易于维护，并为将来的更改提供了更大的灵活性。该项目将完成所有这些变化，并提供一个EPOC++代码，能够满足英国和国际纪元用户的需求，性能和并行代码几十年来经得起考验。

Central to many research programmes in plasma physics is the requirement to capture the full kinetic properties of the plasma. This is most commonly done with a particle-in-cell (PIC) code which move samples of plasma particles in the self-consistent electromagnetic field. For over a decade Warwick, initially in collaboration with Oxford and York, has been developing such a code for UK plasma researchers - the EPOCH code. The core PIC scheme deals with a plasma in which collisions between particles are ignores - a collisionless plasma. EPOCH has been extended to include binary collisions, Quantum Electro-Dynamics (QED) processes and radiation. This has made EPOCH one of the most widely used PIC codes worldwide with application to particle accelerators, next generation light sources, high-power laser QED studies and fusion science for both magnetic and inertial confinement fusion. There are key science extensions required to UK EPOCH to meet the needs of the UK user base. These are detailed in the Objectives section above. However, maintaining EPOCH has become increasingly fraught. This is because EPOCH evolved out of an older Fortran PIC code and while this was relatively easy to modify for the collisionless plasma when adding more sophisticated boundaries, diagnostic or physics packages the restricted feature set of Fortran made these additions increasingly cumbersome. It may be possible to persevere with the old legacy Fortran for a while longer but there are other perhaps more pressing problems. Modern high-performance computer (HPC) systems are moving away from being built all from the same processor type. Instead HPC systems with a mixture of traditional CPUs accelerated with GPUs are becoming prevalent. Other systems are being installed which use ARM processors or even FPGAs. This move towards heterogeneous HPC systems and a complex HPC landscape is been driven by the need for continued increases in computing power. The toolsets for working with these newer heterogeneous systems are primarily in C++, not Fortran. Moving EPOCH over to a C++ implementation (renamed EPOC++ as a result) opens up access to these newer routes towards Exascale HPC. At the same time it makes the code easier to maintain and more flexible for future changes. This project will complete all these changes and deliver an EPOC++ code able to meet the needs of UK and International EPOCH users with a performant and parallel code future proofed for decades.