局部反磁剪切位形下高能量粒子模的线性不稳定性分析

Linear instability analysis of energetic particle modes with locally reversed magnetic shear configuration

在HL-2A装置等离子体放电参数下,模拟研究了局部反磁剪切位形时(存在具有同一安全因子值的多个有理面时)高能量粒子(EP)激发的m/n=2/1的高能量粒子模(EPM),并给出了含有EP驱动和环耦合效应的m/n>1模式的本征值方程。通过数值求解本征值方程,计算了径向模结构,并模拟了EPM增长率和模频率对于EP比压(βh)的依赖关系。计算结果表明,局部反磁剪切位形下捕获EP可以驱动全域的EPM不稳定性,其特征类似于m/n=2/1类鱼骨模,这为相关实验提供了理论解释。通过研究EP参数对模式的影响,发现随着粒子径向分布的平化,模式趋于稳定;当束注入能量增加时,强的阿尔芬连续谱阻尼将导致不稳定性增长率的减小。

Energetic particles(EPs)excited m/n=2/1 energetic particle modes(EPMs),which is in the existence of multiple rational surfaces with the same safety factor value,are investigated for locally reversed magnetic shear configurations with HL-2A plasma parameters.The eigenvalue equation of the m/n>1 mode with effects of energetic particles driving and the toroidal coupling is given.The radial mode structure is then studied by numerically solving the eigenvalue equation.The dependence of the EPM growth rate and frequency of modes on the EP beta(βh)is simulated.Numerical results show that under the locally reversed magnetic shear configuration,the global EPM can be destabilized by trapped energetic particles with a similar characteristic as m/n=2/1 fishbone-like mode,which provides theoretical explanation for the relevant experiments.The effects of EP parameters on the mode are discussed in detail.It is found that the mode tends to be stable with the particle radial distribution flattening.And the growth rate of instability is decreased by strong Alfven continuum damping when the beam injection energy increases.