托卡马克中低频阿尔芬波动理学效应的研究

In tokamak experiments, the low-frequency Alfven waves are a major concern because they can be easily destabilized by energetic particles through wave-particle interaction and can cause the loss of the energetic particles. Due to the frequency range of this kind of Alfven waves being ordered as the thermal ion transit and the diamagnetic frequency of a typical tokamak, background plasma particle kinetic effects on the waves become crucial. Although the properties of the low-frequency Alfven waves have been investigated extensively, understanding the kinetic effects on the existence of the modes, the intrinsic connection to turblence and the long-time scale behaviors remain inadequate. In this project, we foucs on these issues through building a reduced model to develop a nonperturbative eignvalue code for both maro-scale and micro-scale regimes, which includes the wave-particle resonance, electron/ion passing trapped orbit width, ion finite Larmor radius and diamagnetic drift and adopting the models with nonlinear wave-particle resonance or the coupling between high order perturbations. The project is attribute to improve the theory of the low-frequnecy Alfven waves and understand the dynamics of the low-frequency modes as well as explain the data of the experiments with respect to energetic particles.

在托卡马克实验中，阿尔芬波的低频部分常常被高能量粒子激发，并造成芯部高能量粒子的严重损失。因而，低频阿尔芬波备受关注。由于这类阿尔芬波频率接近热离子的通行频率和反磁漂移频率，除了高能量粒子驱动，背景等离子体动理学效应对其影响不容忽视。虽然低频阿尔芬波已被广泛研究，但是动理学效应对其存在条件、与湍流的内在联系以及长时间尺度行为的影响缺少研究。该项目拟通过建立简化模型，发展一个包含了波与粒子共振作用，通行或捕获轨道效应，离子有限回旋半径效应以及反磁漂移效应，同时适用于小空间尺度的非扰动型本征值代码以及利用波与粒子非线性共振和扰动量高价耦合作用来研究低频模上述的性质。本项目具有非常重要的理论和实际意义，有助于进一步完善理论，理解低频阿尔芬波的各项物理机制，为托卡马克实验提供理论解释。

在托卡马克高功率加热实验中，阿尔芬波常常被激发，并可能造成高能量粒子的严重损失。为了研究阿尔芬波行为，行之有效的办法之一：根据阿尔芬波vorticity方程，发展一个包含了波与快粒子共振作用，同时适用于有限通行或捕获轨道宽度、有限离子有限回旋半径等小空间尺度的动理学阿尔芬波物理的非扰动型本征值代码。本课题基于回旋动理学理论/漂移动理学理论，利用阿尔芬波本征值代码，着重研究阿尔芬波的基本性质和激发机制，从而为托卡马克快粒子物理实验和将来的燃烧等离子体实验提供参考。资助以来，本项目结合阿尔芬波实验观测，开展了数值模拟计算，得到了HL－2A中向下扫频的阿尔芬本征模；同时结合代码对阿尔芬波物理机制进行了研究，发现磁流体压缩效应有利于反剪切阿尔芬本征模的存在和建立，理解了代码计算得到的向下扫频的阿尔芬本征模的物理，验证了其结构宽度与离子拉摩半径的平方根呈正比的标度关系。另外，结合代码发展需求，开展阿尔芬波动理学压缩效应模型的研究，推导出了包含有限通行轨道宽度的动理学势能，初步用于fishbone研究，并可推广至阿尔芬波动理学压缩项。