A numerical modeling for the dynamics of an edge-localized mode (ELM) crash in the spherical tokamak is proposed with a consecutive scenario which is initiated by the spontaneous growth of the ballooning mode instability by means of a three-dimensional nonlinear magnetohydrodynamic simulation. The simulation result shows a two-step relaxation process which is induced by the intermediate-n ballooning instability followed by the m/n=1/1 internal kink mode, where m and n represent the poloidal and toroidal mode numbers, respectively. By comparing with the experimental observations, we have found that the simulation result can reproduce several characteristic features of the so-called type-I ELM in an appropriate time scale:(1) relation to the ballooning instability, (2) intermediate-n precursors, (3) low-n structure on the crash, (4) formation and separation of the filament, and (5) considerable amount of loss of plasma. Furthermore, the model is verified by examining the effect of diamagnetic stabilization and comparing the nonlinear behavior with that of the peeling modes. The ion diamagnetic drift terms are found to stabilize some specific components linearly; nevertheless they are not so effective in the nonlinear dynamics such as the filament formation and the amount of loss. For the peeling mode case, no prominent filament structure is formed in contrast to the ballooning case.
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机译:提出了一种球形托卡马克边缘局部模式(ELM)碰撞动力学的数值模型,并通过三维非线性磁流体动力学模拟,通过气球模式不稳定性的自发增长来启动连续场景。仿真结果显示了两步松弛过程,该过程是由中间n个气球膨胀不稳定性继之以m / n = 1/1内部扭结模式引起的,其中m和n分别表示多倍体模态和环形模态数。通过与实验观察结果进行比较,我们发现仿真结果可以在适当的时间范围内重现所谓的I型ELM的几个特征:(1)与膨胀不稳定性有关,(2)中n个前体,(3)碰撞时的低n结构,(4)灯丝的形成和分离,以及(5)大量的等离子体损失。此外,通过检查抗磁稳定作用并将非线性行为与剥离模式进行比较,从而验证了该模型。发现离子反磁性漂移项可以线性稳定某些特定组分;但是,它们在非线性动力学(例如长丝形成和损耗量)方面不是很有效。对于剥离模式情况,与膨胀情况相反,没有形成明显的细丝结构。
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