Plasma turbulence response to topology changes in the tokamak edge

等离子体湍流对托卡马克边缘拓扑变化的响应

• 批准号: 2117173
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2117173
• 关键词: Plasma; turbulence; response; topology; changes

The performance of nuclear fusion experiments depends sensitively on the ionized gas (=plasma) next to the wall of the device. This region is characterised by a change in the topology of the magnetic field lines. In the hot plasma region where fusion reactions happen, known as core, magnetic-field lines cover surfaces ergodically and never come into contact with the wall, whereas in the region near the wall, known as Scrape-Off-Layer (SOL), magnetic-field lines encounter the wall after spanning a finite length. This change in the topology of the magnetic-field lines has important effects on the response of the plasma to perturbations and hence on the turbulence that transports energy away from the hot plasma region. As a first step, the student will develop a kinetic model to describe the plasma near the wall. The density and the temperature of the plasma will be treated as normalization variables, and they will be evolved in time independently from the rest of the distribution function. Thanks to this separation between density, temperature and the rest of the distribution function, the model will connect smoothly with the fluid treatments used for the SOL and with kinetic treatments used for the core, where turbulence is a small perturbation to a mostly quiescent plasma.Once the model is developed, the student will derive fluid equations with hot ions. Even though ions are usually hotter than electrons, many fluid models for the SOL assume that ions are very cold to simplify the equations. The new fluid equations will be appropriate for both core and SOL, and they will be compared to existing SOL models. These equations will be implemented numerically to study the evolution of plasma quantities as the plasma flows from the core to the wall. The student will focus on the electric field because it is determined very differently in the SOL and in the core. In the SOL, the electric field is mostly determined by the potential at the wall, whereas in the core the electric field is determined by turbulent momentum transport.

核聚变实验的性能敏感地依赖于设备壁附近的电离气体（等离子体）。该区域的特征在于磁场线的拓扑结构的变化。在聚变反应发生的热等离子体区域（称为核心），磁场线各态历经地覆盖表面，并且永远不会与壁接触，而在靠近壁的区域（称为刮除层（SOL）），磁场线在跨越有限长度后遇到壁。磁场线的拓扑结构的这种变化对等离子体对扰动的响应具有重要影响，因此对将能量从热等离子体区域传输出去的湍流具有重要影响。作为第一步，学生将建立一个动力学模型来描述壁附近的等离子体。等离子体的密度和温度将被视为归一化变量，它们将独立于分布函数的其余部分随时间演化。由于密度、温度和分布函数的其余部分之间的分离，该模型将与用于SOL的流体处理以及用于核心的动力学处理顺利连接，其中湍流是对大部分静止等离子体的小扰动。模型开发完成后，学生将推导出热离子的流体方程。尽管离子通常比电子热，但许多SOL的流体模型假设离子非常冷以简化方程。新的流体方程将适用于堆芯和SOL，并且将与现有的SOL模型进行比较。这些方程将被实施数值研究的等离子体量的演变等离子体从核心到壁。学生将专注于电场，因为它在SOL和核心中的确定方式非常不同。在SOL中，电场主要由壁处的电势决定，而在核心中，电场由湍流动量输运决定。