Numerical calculations based on nonlinear two-fluid equations have been carried out to understand the sawtooth-like crashes of electron temperature observed in Wendelstein 7-X stellarator experiments with electron cyclotron current drive (ECCD). The application of ECCD leads to non-monotonic radial profiles of the safety factor q with two q=1 surfaces in the plasma core region. Using input parameters similar to the experiment, numerical calculations show two types of crashes of the central electron temperature depending on the growth of the internal kink mode coupled to double tearing modes. When the distance between two equilibrium q=1 surfaces is sufficiently large, the internal kink mode leads to a fast radial displacement of the hot core from the center to the region of the q=1 surfaces. In agreement with experimental observation, this causes a full crash of central electron temperature in about 20-30 microseconds. When the distance between the two q=1 surfaces is not large enough, partial crashes of the central electron temperature are found. During these crashes the hot core only temporally moves outwards. Then it moves back, because the double tearing mode perturbation leads to an increase of the minimum q value about one.

中文翻译：

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在 Wendelstein 7-X 仿星器实验中观察到的电子温度碰撞的数值模拟

已经进行了基于非线性二流体方程的数值计算，以了解在使用电子回旋电流驱动 (ECCD) 的 Wendelstein 7-X 仿星器实验中观察到的锯齿状电子温度碰撞。ECCD 的应用导致在等离子体核心区域具有两个 q=1 表面的安全系数 q 的非单调径向分布。使用类似于实验的输入参数，数值计算显示了两种类型的中心电子温度碰撞，这取决于与双撕裂模式耦合的内部扭结模式的增长。当两个平衡 q=1 表面之间的距离足够大时，内部扭结模式导致热核从中心到 q=1 表面区域的快速径向位移。与实验观察一致，这会导致中心电子温度在大约 20-30 微秒内完全崩溃。当两个 q=1 表面之间的距离不够大时，会发现中心电子温度的部分崩溃。在这些碰撞过程中，热核只是暂时向外移动。然后它向后移动，因为双撕裂模式扰动导致最小 q 值增加约 1。