Plasma turbulence in transport barriers of magnetic confinement fusion devices

磁约束聚变装置输运势垒中的等离子体湍流

• 批准号: 1734486
• 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: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1734486
• 关键词: Plasma; turbulence; transport; barriers; magnetic

Magnetic confinement fusion is based on the fact that charged particles are bound to magnetic field lines if the strength of the magnetic field is sufficiently large. Confinement is, however, not perfect because the plasma gradients in fusion devices drive fluctuations in the electric and magnetic fields that cause particle and energy leakage. These fluctuations are known as plasma turbulence. Due to plasma turbulence, the external power input to maintain a fusion plasma is far greater than naïve theoretical estimations suggest. As a result, plasma turbulence imposes a severe limit on the minimum size and prize of a fusion power plant. It has been experimentally observed that regions of reduced turbulent fluctuations appear naturally in the most promising concept for a fusion reactor, the tokamak. In these regions, known as transport barriers, the gradients of the plasma parameters have to become very large to drive sufficient turbulence to evacuate the particles and energy injected into the plasma. The gradients are sufficiently large that even though transport barriers tend to be thin, the overall plasma performance is greatly improved.The mechanism behind transport barriers is poorly understood. It is believed that plasma flow is an important ingredient because differential rotation can shear turbulent structures. The objective of this DPhil project is to determine when the flow shear can form transport barriers. The student will use the plasma turbulence code GS2, maintained and developed at the University of Oxford and the Culham Centre for Fusion Energy. First, the student will study the effect of flow on turbulence. The study will be done for large plasma gradients, since the turbulence suppression must be effective even for the large gradients present in transport barriers. Previous turbulent simulations show that turbulence driven by very large plasma gradients is difficult to suppress. For this reason, it will be important to consider the magnetic field line geometry, and in particular the magnetic shear (the derivative of the pitch-angle of the magnetic field line). The magnetic shear in conjunction with the flow may explain the suppression observed in experiments. In addition to the simulations, the student will have the data collected by the Doppler Backscattering Diagnostic (DBS) in JET and MAST.After studying the effect of flow of turbulence, the student will use a model recently developed at the University of Oxford to determine whether the necessary flow for suppression can be driven by the plasma turbulence. If this is possible, the student will develop a self-consistent model for the transport barrier. If not, the student will study alternative mechanisms for flow generation (plasma-wall interaction, collisions with neutrals...).This project falls within the EPSRC Plasma and Lasers research area.

磁性限制融合是基于以下事实：如果磁场的强度足够大，则带电的颗粒与磁场线结合。但是，限制并不完美，因为融合设备中的血浆梯度驱动导致粒子和能量泄漏的电场中的波动。这些波动称为血浆湍流。由于血浆湍流，维持融合等离子体的外部功率输入远大于幼稚的理论估计。结果，血浆湍流不可能严重限制融合发电厂的最小尺寸和奖励。经过实验观察到，减少湍流波动的区域自然出现在融合反应堆Tokamak的最有望的概念中。在这些区域（称为传输障碍物）中，等离子体参数的梯度必须变得非常大，以驱动足够的湍流，以疏散注入等离子体的颗粒和能量。梯度足够大，即使传输屏障往往很薄，但总体血浆性能也大大提高。传输障碍背后的机制知之甚少。据信，血浆流是重要的成分，因为差异旋转可以剪切湍流结构。该DPHIL项目的目的是确定流动剪切何时可以形成传输屏障。学生将使用牛津大学和库勒姆融合能源中心维护和开发的等离子湍流代码GS2。首先，学生将研究流动对湍流的影响。该研究将针对大型血浆梯度进行，因为即使对于传输壁垒中存在的大梯度，湍流抑制也必须有效。以前的湍流模拟表明，由非常大的血浆梯度驱动的湍流很难抑制。因此，考虑磁场线的几何形状，尤其是磁性剪切（磁场线的螺距角度）将很重要。与流相结合的磁剪切可能解释了在实验中观察到的抑制。除了模拟外，学生还将在射流和桅杆中由多普勒反向诊断（DBS）收集的数据。在研究湍流的影响后，学生将使用最近在牛津大学开发的模型来确定是否可以通过血浆湍流来驱动必要的抑制作用。如果可能的话，学生将为运输壁垒开发自洽的模型。如果没有，学生将研究流量产生的替代机制（等离子壁相互作用，与中性碰撞...）。该项目属于EPSRC等离子体和激光研究区域。