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，在该系统中，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特性，因此是任何未来反应堆设计的核心。如下图所示，在某些条件下，湍流波动可以组织成大规模的纬向流。这些流动可以通过剪切来调节湍流，并被认为是等离子体向高约束模式(H模式)转变的关键因素，高约束模式是目前ITER反应堆的主要操作场景。纯粹的带状流动没有频率，在实验室很难观察到。托卡马克的环向曲率会产生附加的纬向流压缩模式，称为测地线声学模式(GAM)。这种模式以实频振荡，可以深入了解湍流和纬向流之间的非线性相互作用和反馈。GAM频率取决于离子和电子温度、旋转和等离子体形状。这一建议解决了湍流、GAMS和非振荡纬向流之间的相互作用。该项目的主要兴趣领域包括GAM的径向结构，了解沿磁力线的电子传输如何影响GAM的耗散，以及快速等离子体旋转对该模式的影响。实用方面将探索使用观察到的GAM特征来推断电子和离子温度比的可能性，这在目前的诊断中是不可用的。与CCFE主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实用技能相结合，如高级数据分析和使用高性能计算资源进行数值模拟。用于描述纬向流的数学技术非常丰富和通用，与控制木星大气、洋流和托卡马克等离子体中的流的方程相同。

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.