The nonlinear evolution of the m/n = 2/1 double tearing mode (DTM) is investigated by the toroidal resistive magnetohydrodynamic code CLT. It is found that the m/n = 2/1 DTM can lead to either a core pressure crash or an off-axis pressure crash. Unlike the core pressure crash, the plasma pressure at the magnetic axis remains almost unchanged during the off-axis pressure crash. The pressure crash only occurs in the annular region during the off-axis crash, and the on-axis plasma pressure slowly reduces after the crash, which is consistent with TFTR observations. A series of simulations are carried out to investigate the influence of the radial position of the inner resonant surface r 1, the magnetic shear at the inner resonance surface, and the spatial separation between the two resonant surfaces on nonlinear behaviors of DTMs. We find that r 1 plays a dominant role in the nonlinear DTM behaviors. It is more likely for the DTM to lead to the core pressure crash with a smaller r 1. It is also found that the magnetic shear at the inner resonant surface and the spatial separation between the two resonant surfaces can also largely influence the nonlinear evolution of the DTM. A simple theoretical formula of the transition criterion between the two pressure crashes is proposed, which agrees well with the simulation results.

中文翻译：

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与 m/n = 2/1 双撕裂模式非线性演化相关的离轴压力碰撞

m/n = 2/1 双撕裂模式 (DTM) 的非线性演化由环形电阻磁流体动力学代码 CLT 研究。发现 m/n = 2/1 DTM 会导致核心压力崩溃或离轴压力崩溃。与核心压力崩溃不同，在离轴压力崩溃期间，磁轴处的等离子体压力几乎保持不变。离轴碰撞时压力碰撞仅发生在环形区域，碰撞后轴上等离子体压力缓慢降低，这与TFTR观测结果一致。进行了一系列仿真以研究内谐振表面的径向位置 r 1 、内谐振表面的磁剪切以及两个谐振表面之间的空间分离对 DTM 非线性行为的影响。我们发现 r 1 在非线性 DTM 行为中起主导作用。r 1 较小时，DTM 更有可能导致核心压力崩溃。 还发现内共振表面的磁剪切和两个共振表面之间的空间分离也可以在很大程度上影响非线性演化DTM。提出了两种压力碰撞之间过渡判据的简单理论公式，与仿真结果吻合较好。