AI 中文总结
本研究采用JOREK代码的混合模型，探究逃逸电子束的有限轨道宽度效应，发现其对撕裂模的稳定作用主导额外模式耦合，可显著改变逃逸电子束的磁流体动力学稳定性与非线性动力学。
AI 中文摘要
在托卡马克等离子体破裂期间，欧姆电流可能被非感应逃逸电子（RE）电流取代，影响电阻不稳定性。以往研究表明，在线性阶段，与仅存在欧姆电流的情况相比，逃逸电子的存在对撕裂模（TM）具有去稳定作用，这在非线性阶段体现为更大的饱和振幅。这些结果基于逃逸电子漂移轨道与磁通量面零偏差的假设，对应低能极限情况。本研究通过探究不同能量逃逸电子束中线性与非线性撕裂模动力学，研究该动力学效应的重要性，明确有限轨道宽度（FOW）效应的清晰图像。我们在3D非线性磁流体动力学（MHD）代码JOREK中使用混合流体-动力学模型，采用全粒子蒙特卡洛方法动力学处理逃逸电子，与MHD模式动力学自洽相互作用。研究显示，逃逸电子的存在从多方面改变不稳定性特征：第一，漂移轨道相对于磁通量面的主径向位移对平衡电流产生m=1扰动，引入(m,n)不稳定性与(m±1,n)边带之间的额外模式耦合；第二，逃逸电子能量升高对MHD模式具有稳定作用，因为漂移轨道位移使逃逸电子无法在有理磁通量面上支撑窄电流片，这抵消了低能极限下逃逸电子对撕裂模的去稳定作用。在所研究的场景中，稳定作用主导额外模式耦合，随逃逸电子能量升高减少随机磁区的发展，从而降低径向粒子输运。总体而言，有限轨道宽度效应可显著改变逃逸电子束的MHD稳定性与非线性动力学。
英文摘要
During tokamak disruptions, the Ohmic current may be replaced by a non-inductive runaway electron (RE) current, affecting resistive stability. Previous studies suggest that, in the linear phase, the presence of REs acts destabilizing for tearing modes (TM) compared to a scenario with Ohmic current. In the non-linear regime, this translates to larger saturation amplitudes. These results are based on the assumption of zero drift-orbit deviation from the magnetic flux surfaces corresponding to the low-energy limit. This work investigates the importance of this kinetic effect by studying the linear and non-linear TM dynamics in RE beams with different RE energies, providing a clear picture of finite-orbit-width (FOW) effects. We use a hybrid fluid-kinetic model in the 3D non-linear magnetohydrodynamic (MHD) code JOREK, treating REs kinetically with a full-f Monte Carlo approach in self-consistent interaction with the MHD mode dynamics. The study shows that the presence of REs modifies the characteristics of the instability in several ways. First, we find that the major-radial displacement of drift orbits from flux surfaces induces an $m=1$ perturbation to the equilibrium current, introducing additional mode coupling between $(m,n)$ instabilities and the $(m\pm1,n)$ sidebands. Second, we find that increasing RE energy has a stabilizing effect on the MHD modes because REs cannot support narrow current sheets on rational flux surfaces owing to the drift-orbit displacement. This counteracts the destabilizing effect that REs have on TMs in the low-energy limit. For the scenario investigated, the stabilizing effect dominates over the additional mode coupling, reducing the development of stochastic magnetic regions with increasing RE energy and thereby lowering radial particle transport. Overall, we find that FOW effects can substantially alter the MHD stability and non-linear dynamics of RE beams.
Comments19 pages, 11 figures
