Structure of micro-instabilities in tokamak plasmas: Stiff transport or plasma eruptions?
Structure of micro-instabilities in tokamak plasmas: Stiff transport or plasma eruptions?
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DOI：
10.1063/1.4861628
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发表时间：
2014-01
影响因子：
2.2
通讯作者：
D. Dickinson;C. Roach;J. Skipp;H. Wilson
中科院分区：
文献类型：
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作者：
D. Dickinson;C. Roach;J. Skipp;H. Wilson
提出了描述托卡马克等离子体中微观不稳定性的模型二维本征模方程的解，证明了模式结构的敏感性和对等离子体轮廓的稳定性。在参数空间的狭窄区域中，具有特殊的等离子体轮廓，发现了托卡马克外侧的气球的最大不稳定模式。这对应于气球模式的传统图片。然而，对于大多数剖面来说，这种模式不可能存在，相反，发现了更稳定的模式，即气球更接近等离子体的顶部或底部。如果考虑到与高阶轮廓效应相关的约束（通常被忽略），则可以发现与一维气球分析的良好定量一致性。对于临界流剪切，可能会发生从这种一般模式到更不稳定的气球模式的突然转变，这为为什么一些实验观察到小型等离子体喷发（边缘局域模式，或 ELM）而不是大型 I 型 ELM 提供了候选模型。
Solutions to a model 2D eigenmode equation describing micro-instabilities in tokamak plasmas are presented that demonstrate a sensitivity of the mode structure and stability to plasma profiles. In narrow regions of parameter space, with special plasma profiles, a maximally unstable mode is found that balloons on the outboard side of the tokamak. This corresponds to the conventional picture of a ballooning mode. However, for most profiles, this mode cannot exist, and instead, a more stable mode is found that balloons closer to the top or bottom of the plasma. Good quantitative agreement with a 1D ballooning analysis is found, provided the constraints associated with higher order profile effects, often neglected, are taken into account. A sudden transition from this general mode to the more unstable ballooning mode can occur for a critical flow shear, providing a candidate model for why some experiments observe small plasma eruptions (Edge Localised Modes, or ELMs) in place of large Type I ELMs.