Oscillatory zonal flows and their interaction with turbulence in magnetically confined plasmas

核聚变磁约束等离子体是一种非平衡驱动系统，其中微观不稳定性从温度和密度梯度中提取能量，驱动湍流波动。湍流输运强烈影响全球等离子体约束性能，因此是任何未来反应堆设计的核心。在某些条件下，湍流波动可以组织成大规模的带状流动，如下图所示。这些流动可以通过剪切来调节湍流，并且被认为是等离子体向高约束模式（H-mode）转变的关键因素，而高约束模式（H-mode）是目前ITER反应堆的主要运行场景。托卡马克的环形曲率诱导了被称为测地声学模（GAM）的带状流的附加压缩模。该模式以真实的频率振荡，可以深入了解湍流和带状流之间的非线性相互作用和反馈。GAM的频率取决于离子和电子的温度、等离子体的旋转和形状。该项目的主要兴趣领域包括GAM的径向结构，了解电子传输沿着磁场线如何影响GAM的耗散，以及快速等离子体旋转对这种模式的影响。实践方面将探讨使用所观察到的GAM功能来推断电子和离子温度的比例，这是不提供的MAST与当前的诊断的可能性。与CCFE MAST团队的密切合作对该项目至关重要。该项目将令人兴奋的核聚变物理与先进的数据分析和使用高性能计算资源进行数值模拟等实用技能相结合。用于描述纬向流的数学技术非常丰富和通用，在赤道大气、洋流和托卡马克等离子体中，都有相同的方程。

Nuclear FusionMagnetically confined plasmas are out of equilibrium driven systems in which micro-instabilities extract energy from temperature and density gradients, driving turbulent fluctuations. Turbulent transport strongly impacts on global plasma confinement properties and thus is in the core of any future reactor design. Under certain conditions turbulent fluctuations can organise into large-scale zonal flows, as shown in the figure below. These flows can regulate turbulence by shearing and are believed to be a key factor in plasma transition to high-confinement mode (H-mode), currently the main operating scenario for the ITER reactor.Pure zonal flows have no frequency and are difficult to observe in the laboratory. The toroidal curvature of a tokamak induces additional compressional mode of zonal flows known as the Geodesic Acoustic Mode (GAM). This mode oscillates with real frequency and can give an insight into the non-linear interactions and feedback between the turbulence and zonal flows. The GAM frequency is dependent on the ion and electron temperatures, rotation and shaping of the plasma.This proposal addresses interaction between turbulence, GAMs and non-oscillatory zonal flows. Main areas of interest for this project include radial structure of GAM, understanding how electron transport along the magnetic field lines influences dissipation of GAMs and what is the impact of fast plasma rotation on this mode. Practical aspects will explore a possibility of using observed GAM features to infer the ratio of electron and ion temperature, which are not available on MAST with current diagnostics. Close collaboration with CCFE MAST team is essential for the project.The project combines exciting physics of nuclear fusion with practical skills such as advanced data analysis and the use of high performance computational resources for numerical simulations. The mathematical techniques used to describe zonal flows are very rich and generic, with the same equations governing flows in the Jupiters atmosphere, ocean currents and in tokamak plasmas.