Plasma dynamics in the tokamak edge

托卡马克边缘和刮离层中的输运对决定磁约束聚变堆的性能起着至关重要的作用。边缘的湍流可能设置了在高限制模式放电中形成的底座的高度，相关的传输将热负荷设置到管壁上。例如，由于开放场线、中性粒子、磁几何结构的极端变化和大幅度波动的存在，EDGE和SOL中的等离子体动力学特别具有建模和模拟的挑战性。作为正在进行的王者之剑/海王星项目的一部分，牛津大学的一组研究人员与英国宇航局的同事合作，创建了一个新颖的、基于矩的漂移动力学代码，以研究EDGE和SOL中的动力学。该程序的基本目标是有效地求解漂移和/或陀螺动力学方程的自洽版本，同时实现与内核中的Far SoL和Delta-f陀螺动力学代码中的流体代码的直接连接。据我们所知，目前的所有代码要么对于常规物理研究来说昂贵得令人望而却步，要么使用简化的流体处理(可能会减少所考虑的维度数量)，或者使用不一致的动力学处理。我们正在追求的力矩-动力学方法应该允许在需要的情况下进行自洽的动力学处理，而不需要不必要的数值费用。目前，该程序只对平行动力学(有或没有力矩动力学方法)或均匀的螺旋磁场(只有标准漂移动力学)求解。两个版本的代码都假设电子的简化响应符合玻尔兹曼统计平衡。我们的建议是由牛津大学的博士生继续开发代码；继续进行更高级的验证、确认和性能基准；并最终使用代码进行基础物理研究。可以探索的程序开发的关键方面包括扩展以处理动能电子，增加带电粒子之间的碰撞，扩展到3D(非螺旋)几何结构，处理连接开放和封闭场线区域的分离线区域，添加更复杂的壁边界条件，以及在单一模拟中从漂移动力学模型转换到回转动力学或流体模型的方案。有很多方法可以探索，学生解决哪些方法将取决于学生掌握速度后代码的状态，什么将被视为最新颖和及时的贡献，它提供了获得物理结果的最直接途径，以及目标物理与反应堆设计研究的相关性。该项目属于EPSRC“等离子体和激光”和“英国磁融合研究计划”的研究领域。

Transport in the tokamak edge and scrape-off layer (SOL) plays a crucial role in determining the performance of a magnetic confinement fusion reactor. Turbulence in the edge likely sets the height of the pedestal that forms in high-confinement-mode discharges, and the associated transport sets the heat load to the vessel walls. Plasma dynamics in the edge and SOL are particularly challenging to model and to simulate due to, e.g., the presence of open field lines, neutral particles, extreme changes in magnetic geometry and large-amplitude fluctuations. As part of the ongoing ExCALIBUR/Neptune project, a group of researchers at Oxford - in collaboration with UKAEA colleagues - have created a novel, moment-based drift kinetic code to study the dynamics in the edge and SOL. The fundamental aim of the code is to solve efficiently a self-consistent version of the drift- and/or gyro-kinetic equation, while enabling a straightforward connection to fluid codes in the far SOL and delta-f gyrokinetic codes in the core. To our knowledge, all current codes are either prohibitively expensive for routine physics studies, use a simplified fluid treatment (possibly with a reduction in the number of dimensions considered) or use an inconsistent kinetic treatment. The moment-kinetic approach that we are pursuing should allow for a self-consistent kinetic treatment where required without undue numerical expense. At the moment the code solves only for either parallel dynamics (with or without the moment kinetic approach) or for a homogeneous, helical magnetic field (with only standard drift kinetics). Both versions of the code assume a simplified response for electrons that corresponds to a Boltzmann statistical equilibrium.Our proposal is for a PhD student based at Oxford to carry forward the code development; to continue with more advanced verification, validation and performance benchmarks; and to ultimately use the code to do fundamental physics studies. Key aspects of code development that could be explored include an extension to treat kinetic electrons, addition of collisions amongst charged particles, extension to 3D (non-helical) geometry, treatment of the separatrix region that ties together open and closed field line regions, addition of more sophisticated wall boundary conditions and a scheme for transitioning from drift kinetic to gyrokinetic or fluid models within a single simulation. There are a lot of avenues to explore, and which ones are addressed by the student will depend on the state of the code once the student gets up to speed, what will be seen as the most novel and timely contribution, which provides the most direct path to physics results and the relevance of the targeted physics to reactor design studies.This project falls within the EPSRC "Plasma and Lasers" and "UK Magnetic Fusion Research Programme" research areas.