Research Of Feedback Controlling Tearing Mode And Locked Mode Induced Disruption By Using Dynamic Resonant Magnetic Perturbation

The disruption is one of the biggest challenges for the future fusion device.The locked tearing mode(TM)is the main reason of the disruption.Almost all disruptions are directly triggered by the locked TMs.Hence,the disruption could be prevented via controlling the TM.Static resonant magnetic perturbation(RMP)can only suppress the high frequency(> 5 k Hz)TMs.Besides,the large static RMP could penetrate and generate a locked mode.As a result,there are significant restrictions for the TM control by static RMP.The traditional strategy,which applies the modulated RMP in the opposite phase of TM,has phase instability during the tearing mode control,which limits the applying interval of the modulated RMP.Therefore,it's important for the future fusion device to develop a new strategy of RMP for TM control and disruption prevention.This paper investigates the tearing mode control and disruption prevention by using dynamic RMP on the J-TEXT tokamak.For the low frequency tearing mode,the modulated RMP increases TM frequency significantly.For the locked mode induced disruption,the timely triggered rotating RMP maintained the mode rotation and prevent the disruption.Based on the Fitzpatrick's theory,the effects of RMP on TM are determined by the phase difference between them.Dr.Q.Hu proposes a new TM control strategy with the modulated RMP,which only applies RMP during the acceleration phase region.The simulated results show that the modulated RMP could accelerate the TM rotation and suppress the TM amplitude effectively.The modulated RMP strategy needs to turn on the RMP within a certain phase region,hence the measurement of TM phase is required in real time.A mode phase measurement system has been developed on the J-TEXT tokamak for the modulated RMP.This system measures the TM phase in real time,with a temporal resolution of 10 ?s,and provides the control signal for the RMP coils' power supplies.By applying ambipolar modulated RMP,the phase difference between tearing mode and RMP oscillates within a small phase interval,which increases the RMP efficiency from 35% to 95%compared to the unipolar modulated RMP.The ambipolar modulated RMP could accelerate the tearing mode rotation effectively,with a mode frequency increase up to 70%.Based on the statistic analysis,the increase of mode frequency is linear with the electromagnetic torque applied on the TM by the RMP,which is consistent with the theory.Besides,this paper investigates the feedback disruption control by using rotating RMP experimentally on the J-TEXT tokamak.When the plasma operates towards the low q limit,the large tearing mode was found to be locked to the error field without extra momentum injection and triggered the disruption after mode locking.This scenario is selected as the target for studying the feedback control of disruption.In order to predict the mode locking and to trigger the rotating RMP,the mode locking warning system was developed.When the rotating RMP was applied before the rapid decrease of the TM frequency,the rotating RMP could accelerate the TM rotation and maintain the mode frequency till the ramp down of plasma current.By scanning the parameters of rotating RMP,it is found that the rotating RMP with a higher frequency has a better effect on disruption control.The effectiveness of disruption control depends non-linearly on the RMP amplitude.The rotating RMP with a low amplitude has no effects on the TM rotation and the disruption.Above a certain amplitude,the rotating RMP can prevent disruption,and the effectiveness of disruption control decreases with the increase of the rotating RMP amplitude.Therefore,the higher frequency rotating RMP is,the better effectiveness of disruption control will be.In short,the RMP amplitude should be appropriate.This paper presents a systematic experimental investigation of TM control by using modulated RMP and disruption control by using rotating RMP.Those experiments are well repeatable.The modulated RMP could accelerate the tearing mode and the relationship between the parameters of modulated RMP and mode frequency are presented.Besides,rotating RMP could prevent the locked mode induced disruption and the best parameters of rotating RMP for the disruption control are suggested.This work presents an excellent strategy of disruption prevention and acts as an experimental reference for the future device.