Drift resonance effect on stochastic runaway electron orbit in the presence of low-order magnetic perturbations
Drift resonance effect on stochastic runaway electron orbit in the presence of low-order magnetic perturbations
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DOI：
10.1088/0029-5515/54/12/123007
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发表时间：
2014-12-01
期刊：
影响因子：
3.3
通讯作者：
Nakajima, N.
中科院分区：
文献类型：
--
作者：
Matsuyama, A.;Yagi, M.;Nakajima, N.
在主要破坏期间，感应回路电压将逃逸电子（RE）加速向高能量，在目前的托卡马克和ITER中为1- 100 MeV的量级。通过托卡马克等离子体三维轨道跟踪研究了这种高能稀土漂移轨道的随机化机制。漂移共振被证明发挥重要作用，在确定不同的电子能量的随机漂移轨道的发病，特别是在低阶扰动的情况下，具有径向全球的等离子体小半径的尺度的本征函数。由于交叉场漂移运动与径向全局模式之间的耦合引起的漂移共振在RE漂移轨道中产生次级岛结构，其中次级漂移岛的宽度显示出对相对论伽马因子γ的平方根依赖性。只有在相对论性强的稀土离子（γ>> 1）中，次级漂移岛的宽度才与磁岛的宽度相当，从而使随机阈值对稀土离子的能量变得敏感。由于超环面引起的极向不对称性，阈值变得不仅对相对振幅敏感，而且对模式之间的相位差敏感。在本文中，三维轨道跟踪计算的几个例子提出了多个环形模式数的磁扰动的分析模型，漂移共振增强和抑制的随机性被说明的两种可能性。
During major disruptions, an induced loop voltage accelerates runaway electrons (REs) towards high energy, being in the order of 1-100MeV in present tokamaks and ITER. The stochastization mechanisms of such high-energy RE drift orbits are investigated by three-dimensional (3D) orbit following in tokamak plasmas. Drift resonance is shown to play an important role in determining the onset of stochastic drift orbits for different electron energies, particularly in cases with low-order perturbations that have radially global eigenfunctions of the scale of the plasma minor radius. The drift resonance due to the coupling between the cross-field drift motion with radially global modes yields a secondary island structure in the RE drift orbit, where the width of the secondary drift islands shows a square-root dependence on the relativistic gamma factor gamma. Only for highly relativistic REs (gamma >> 1), the widths of secondary drift islands are comparable with those of magnetic islands due to the primary resonance, thus the stochastic threshold becoming sensitive to the RE energy. Because of poloidal asymmetry due to toroidicity, the threshold becomes sensitive not only to the relative amplitude but also to the phase difference between the modes. In this paper, some examples of 3D orbit-following calculations are presented for analytic models of magnetic perturbations with multiple toroidal mode numbers, for both possibilities that the drift resonance enhances and suppresses the stochastization being illustrated.