电阻性鱼骨模理论

THEORY OF RESISTIVE FISHBONE MODES

托卡马克等离子体中高能粒子可以激发一种称为鱼骨模的内扭曲模。现有鱼骨模理论是建立在理想磁流体近似基础上的，它预言有两支不稳定分支。对于高能粒子的比压值，ω≈〈ω（ｄＭ）〉的一支（Ｃｈｅｎ－Ｗｈｉｔｅ分支）的激发阈值较高，而ω≈ω（＊ｉ）的一支（Ｃｏｐｐｉ分支）的激发阈值很低，因而对托卡马克等离子体的加热效率及约束非常不利。不过、我们发现，电阻效应对这支模有实质性的影响。本文详细分析了电阻性鱼骨模理论，给出新的稳定性参数区结构图：Ｃｏｐｐｉ分支为一增长率很低的弱不稳定模所代替，而严格意义的稳定区不再存在。计算了增长率随高能离子比压的变化并与其它不稳定模做了对比，讨论了对未来装置中等离子体性能的影响。

A special kind of internal kink mode, the fishbone, can be excited by the energetic particles in tokamak plasma. Theoretical analysis of fishbone modes based on the ideal MHD framwork have predicted that two branches of modes exist, one is the Chen-White branch with ω≈〈ω(dm)〉, corresponding to a higher threshold in βh, the other is the Coppi's branch with ω≈ω(*i), and a much lower thresbold in βh. The latter mode should put a rathaer unfavourable restriction on heating efficiency and plasma energy confinement. However, we find that resistivity effect is essential for this mode. In this paper, a new resistive fishbone mode analysis is carried out. In the (γ(mhd), βh ) space, the stability diagram shows complicated structure, the coppi's branch is replaced by a weakly unstable mode and there is no longer closed stable region. The growth rate varies with the increase in βh, its peak value is still very small compared to other internal modes. The implications of these results to the future tokamak experiments are discussed.