Plasma major disruption is one of the most critical issues to be solved for a tokamak fusion reactor. Experiments to prevent mode locking and subsequent disruptions have been carried out on J-TEXT tokamak using rotating resonant magnetic perturbations (RMPs). The tearing modes, to be locked and to lead to disruptions without applying RMPs, can be accelerated by rotating RMPs to the RMP frequency. As the result, the mode locking and subsequent disruptions are delayed or prevented. The effects of RMP amplitude and frequency on disruption prevention have been investigated.
The acceleration of the magnetic island rotation by the modulated resonant magnetic perturbation (RMP) has been studied in J-TEXT tokamak experiments. The island rotation frequency is increased by a few kilohertz for the optimized relative phase by small RMPs of the order of 10-5 of the toroidal field. The disruption is avoided via accelerating the TM by the MRMP, which indicates a possible method for avoiding mode locking in a fusion reactor. The relative phase between the magnetic island and the RMP was found to be important for changing the island rotation.
The rotating resonant magnetic perturbation (RMP) could lock the tearing mode (TM) and prevent disruption. It is found that the TM instantaneous frequency oscillates during TM locking on the RMP. In this work, the TM frequency oscillation was derived analytically based on the toroidal torque balance, which was verified experimentally. It is found that two peaks with higher frequency (2 fTM0- fRMP) and lower frequency ( fRMP) occurred in the spectrum when the window width of FFT was shorter than the TM frequency oscillating period. Those two peaks were explained analytically based on the description of TM instantaneous frequency. The independence of the temporal information and the spatial information of the TM was explained analytically and verified by the spatial structure analysis of each peaks. This work is important for mode structure identification and provides a scheme for mode coupling control.
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