This study aimed to unlock the m/n = 2/1 locked mode (LM) performed in J-TEXT tokamak by using rotating resonant magnetic perturbations (RMPs), where m and n are the poloidal and toroidal mode numbers, respectively. In the experiments, to maintain the LM, mode locking occurs by using static RMPs generated by a set of saddle coils. After mode locking, another rotating RMP with frequency of several kilo-Hz is applied to drive the static LM to rotate. The unlocking of LM is realized by using rotating RMP with different frequency and amplitude. It is found that the unlocking process contains two stages, i.e. the oscillating stage and the unlocking stage. In the oscillating stage, the rotating RMP with amplitude that is not strong enough causes the LM to oscillate around its locked phase and produces magnetic fluctuation to behave as a standing wave-like structure in poloidal direction. When the amplitude of the rotating RMP is strong enough, it first causes the LM to oscillate and then transforms to mode unlocking quickly in less than 1 ms, namely the unlocking stage. Further analysis shows that the unlocking of LM is determined by the torque balance between the viscous torque and the electromagnetic torques exerted by both the static and the rotating RMP. In addition, the unlocking process is sensitive to both the amplitude and the frequency of the rotating RMP as well as the amplitude of static RMP. Nonlinear numerical modeling based on reduced MHD equations is also performed to understand the unlocking process, and numerical results qualitatively agree with the experimental ones.
本研究旨在通过旋转共振磁扰动（RMP）解锁J-TEXT托卡马克中的m/n = 2/1锁定模（LM），其中m和n分别为极向和环向模数。实验中，为维持LM，使用由一组鞍形线圈产生的静态RMP引发模锁定。模锁定后，施加频率为数千赫兹的旋转RMP以驱动静态LM旋转。通过使用不同幅度和频率的旋转RMP实现LM的解锁。研究发现，解锁过程包含两个阶段，即振荡阶段和解锁阶段。在振荡阶段，幅度不够强的旋转RMP使LM围绕其锁定相位振荡，并产生磁扰动，表现为极向方向上的驻波状结构。当旋转RMP的幅度足够强时，首先引起LM振荡，随后在不到1毫秒内迅速转变为模解锁，即解锁阶段。进一步分析表明，LM的解锁由粘性力矩与静态和旋转RMP共同施加的电磁力矩之间的力矩平衡决定。此外，解锁过程对旋转RMP的幅度和频率以及静态RMP的幅度均敏感。还进行了基于约化MHD方程的非线性数值模拟，以理解解锁过程，数值结果与实验结果定性一致。