EAST和CFETR托卡马克正反磁剪切位形下高能粒子驱动阿尔芬本征模的理论模拟研究

Whether strong instabilities can be excited under different magnetic shear by energetic particles, whose energies are much higher than that of the background plasma particles, are key problems to be solved for tokamak plasmas, especially burning plasmas in fusion reactors. In this project, we shall study the interactions between Alfven eigenmodes and energetic particles, which are generated by Neutral Beam Injection (NBI) and fusion reaction, on Experimental Advanced Superconducting Tokamak (EAST) and China Fusion Engineering Test Reactor (CFETR) with positive and negative magnetic shear. The eigen-analysis code will be used to study the frequency spectrum of Alfven waves. The Kinetic-MHD hybrid simulations will be taken to study the growth rate, frequency, mode structure and radial position, as well as the linear and nonlinear variations of energetic particle distribution in phase space and the corresponding transport of energetic particle and energy. On one hand, the mechanism of excitation of Alfven waves by energetic particles, including linear and nonlinear behavior will be studied. On the other hand, for the energetic particles caused by Alfven waves, both the micro changes of distribution function in phase space and the macro behaviors of loss and transport are to be investigated. The results can be compared with results from EAST experiments. The mechanisms should be helpful for interpreting or predicting to what degree the magnetic shear should be set, the long-time steady-state high-performance burning plasma can be achieved in the operation scenarios of CFETR.

托卡马克聚变堆等离子体不同磁剪切位形下，能量远高于本底热等离子体粒子的高能粒子，激发的阿尔芬本征模，是否会产生强烈的不稳定性，是燃烧等离子体能否维持长时间高约束需要考虑的重要问题。本项目采用本征值程序和混合（PIC-MHD）模拟模型，运用理论和数值模拟相结合的方法，研究EAST和CFETR托卡马克不同程度正反磁剪切位形下，中性束或聚变反应产生的高能粒子慢化之后，激发的阿尔芬本征模，全面的频谱分布、增长率、频率、模结构和位置等特征，和高能粒子相空间的分布变化及相应粒子、能量输运的线性和非线性行为。阐明高能粒子激发阿尔芬本征模特性和阿尔芬波引起的高能粒子损失、输运的机制，通过和EAST实验结果比较，揭示在什么程度的磁剪切下，能够长时间维持等离子体高约束模式，为CFETR物理和工程设计提供运行方案指导。

托卡马克等离子体不同磁剪切位形下，高能量粒子激发的阿尔芬本征模、鱼骨模等的稳定性，高能粒子的损失和输运性质，和燃烧等离子体能否维持长时间高约束运行，有密切联系。依托本项目，项目负责人开发了托卡马克阿尔芬本征分析程序，完善了混合（PIC-MHD）模拟程序。项目成员及合作者，运用理论和数值模拟相结合的方法，研究了EAST、HL-2A和CFETR托卡马克不同磁剪切位形下，高能量粒子激发的阿尔芬本征模、鱼骨模等的相关性质。具体发现有：（1）高能量粒子驱动增强，会引发阿尔芬本征模到高能量粒子模转变，及阿尔芬本征模奇偶性质的转变，这些转变的发生，对应不同的平衡磁场位型和参数区间。（2）保持安全因子剖面基本形状不变，磁轴处安全因子增大过程中，高能量粒子驱动的鱼骨模会转变为阿尔芬本征模，模式的频率会发生跳变，模结构也会发生相应变化。（3）安全因子剖面磁剪切，由正变负的过程中，靠近磁轴处的阿尔芬本征模带隙会越来越窄，阿尔芬本征模最大增长率越来越小，即反剪切位形有利于抑制阿尔芬本征模的激发。（4）EAST上阿尔芬本征模导致的磁场扰动，结合高能量离子碰撞过程，将会导致约15%的高能量离子损失。计算分析程序，尤其是自主知识产权程序，的开发和完善，将会有力促进相关领域的深入研究。一系列关于磁场位形、阿尔芬本征模性质及高能粒子损失等结果，加深了人们对高功率加热等离子体及燃烧等离子体特性的认识，为EAST和HL-2A实验理解及新的提案，CFETR物理和工程设计，提供了重要的参考和指导。