Solution of the linear wave-particle kinetic equation for global modes of arbitrary frequency in a tokamak

M. Fitzgerald , B.N. Breizman
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Abstract

The linear response of a plasma to perturbations of arbitrary frequency and wavelength is derived for any axisymmetric magnetized toroidal plasma. An explicit transformation to action-angle coordinates is achieved using orthogonal magnetic coordinates and the Littlejohn Lagrangian, establishing the validity of this result to arbitrary order in normalized Larmor radius. The global resonance condition for compressional modes is clarified in more detail than in previous works, confirming that the poloidal orbit-average of the cyclotron frequency gives the desired result at lowest order in Larmor radius. The global plasma response to the perturbation at each resonance is captured by a poloidal and gyroaverage of the perturbing potential. A “global gyroaveraging” of the potential is a natural by-product of this analysis which takes into account the changing of the magnetic field over an orbit. The resonance condition depends on two arbitrary integers which completely separately capture the effects poloidal non-uniformity and finite Larmor radius in generating sidebands. We learn that poloidal sidebands generated for compressional modes are dominated by the change in gyrofrequency over the orbit, which is very different to shear modes where the gyrofrequency only contributes via a finite Larmor radius effect. This increases the number of bounce harmonics required to compute the linear drive, giving a more complicated resonance map. An example calculation is given comparing resonance of shear and compressional modes in a published DIII-D case.
托卡马克中任意频率全局模态线性波粒动力学方程的解
导出了任意轴对称磁化环形等离子体对任意频率和波长扰动的线性响应。利用正交磁坐标和利特尔约翰拉格朗日量实现了对作用角坐标的显式变换,建立了该结果在归一化拉莫尔半径下任意阶的有效性。与以往的研究相比,本文更详细地阐明了压缩模态的全局共振条件,证实了回旋加速器频率的极向轨道平均在拉莫尔半径的最低阶上给出了期望的结果。在每个共振中,等离子体对扰动的整体响应被摄动电位的极向和陀螺平均捕获。考虑到磁场在轨道上的变化,这种分析的自然副产品是对势的“全球陀螺平均”。共振条件取决于两个任意整数,这两个整数完全独立地捕获了极向非均匀性和有限拉莫尔半径在产生边带中的影响。我们了解到,压缩模态产生的极向侧带是由陀螺频率在轨道上的变化决定的,这与剪切模态非常不同,剪切模态的陀螺频率只通过有限的拉莫尔半径效应起作用。这增加了计算线性驱动所需的反弹谐波的数量,给出了更复杂的谐振图。在已发表的DIII-D案例中,给出了剪切模态和压缩模态共振的计算实例。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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