有限尺寸磁岛内电流与压强剖面改变对稳定性的影响
Stability impacts from the current and pressure profile modifications within finite sized island
AI总结：
本文利用扰动平衡方法研究有限尺寸磁岛内电流和压强剖面改变对稳定性判据的影响，揭示正螺旋电流稳定、负螺旋电流失稳，以及压强隆起或凹陷在小岛和大岛区间不同的复杂稳定效应。
摘要：
有限尺寸磁岛的稳定性（或不稳定性）可能在避免破裂或缓解破裂动力学中发挥重要作用。特别是，各种电流和压强剖面改变，例如电子回旋波引起的电流驱动和加热，或破碎弹丸注入引起的辐射冷却和电流排出，都可以施加在磁岛内部以改变其稳定性，从而改变随后的动力学过程。在本研究中，我们采用扰动平衡方法计算了磁岛内此类剖面改变所引起的模结构变化，从而得到稳定性判据 $\Delta'$ 的变化，并评估相应的准线性磁岛稳定性。结果发现，正螺旋电流扰动总是使磁岛稳定，而负螺旋电流扰动则起相反作用，这与先前的结果一致。磁岛内的压强隆起或压强凹陷对稳定性具有更复杂的影响。在小磁岛区间，其贡献是单调的，压强隆起倾向于使磁岛稳定，而压强凹陷则使磁岛失稳。不过，由于压强项在模结构二阶导数中的奇宇称贡献相互抵消，这一效应相对较弱。在大磁岛区间，由于磁岛不对称性，这种抵消被打破，压强对稳定性的贡献得以显现，且是非单调的。本文的稳定性分析有助于更准确地阐明在避免破裂或缓解破裂系统引起的剖面改变存在时磁岛的预期响应。
英文摘要：
The stability (or instability) of finite sized magnetic island could play a significant role in disruption avoidance or disruption mitigation dynamics. Especially, various current and pressure profile modifications, such as the current drive and heating caused by electron cyclotron wave, or the radiative cooling and current expulsion caused by the Shattered Pellet Injection could be applied within the island to modify its stability, thus change the ensuing dynamics. In this study, we calculate the mode structure modification caused by such profile changes within the island using the perturbed equilibrium approach, thus obtain the change of stability criterion $\gD'$ and assess the corresponding quasi-linear island stability. The positive helical current perturbation is found to always stabilize the island, while the negative one is found to do the opposite, in agreement with previous results. The pressure bump or hole within the island has a more complicated stability impact. In the small island regime, its contribution is monotonic, with pressure bump tends to stabilize the island while pressure hole destabilizes it. This effect is relatively weak, though, due to the cancellation of the pressure term's odd parity contribution in the second derivatives of the mode structure. In the large island regime, such cancellation is broken due to the island asymmetry, and the pressure contribution to stability is manifested, which is non-monotonic. The stability analysis in this paper helps to more accurately clarify the expected island response in the presence of profile modifications caused by disruption avoidance or mitigation systems.
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