Research Of A Continues Frequency?variable Resonant Magnetic Perturbation System And Its Application On The J-TEXT Tokamak

Tearing mode(TM)instability is one of the most important magnetohydrodynamic(MHD)instabilities in tokamak fusion plasmas.It can produce magnetic island in the core of plasma,degradation the plasma confinement.It even leads to the formation of locked mode(LM)and induces major disruption,which damages the tokamak fusion device.Externally applied resonant magnetic perturbations(RMPs)has been widely applied to control the TMs.The static RMP applies a net stabilizing effect on the TM via inducing its non-uniform rotation,and then suppresses the TM completely,while larger static RMP might easily locks the TM or induced LM via the penetration of RMP field,and triggers the subsequent major disruption.The rotating RMP has also been feedback applied to control the tearing mode,but the classical feedback application requires the anti-phase between rotating RMP and TM,which leads to the well-known phase-instabilities.It is hence of great importance on how to develop new strategies for TM control and to realize these strategies both from the engineering and physical experiments point of view.In this work,the recent new TM feedback control strategies proposed based on the J-TEXT researches have been studied and analyzed.To fulfill this goal,a new continues frequency-variable(CFV)RMP system has been designed,constructed,commissioning and applied to the TM control with online frequency varying RMP field,which can realize the novel control strategies.This new RMP system consists of a newly continues frequency-variable bi-polar PS system,a newly developed control system and the existing J-TEXT RMP system and magnetic probe arrays.In this work,Firstly,a fast response bipolar-pulse PS system is designed and assembled.The key challenge of the CFV RMP system is to reverse the current polarity in a very short time for the inductive RMP coils.It is tried to use less money and space.A modified high-power inverter was designed by matching the boost capacitors and the inductance of RMP coils with the LC resonant condition,which utilizes the fast energy exchange in a resonant circuit.The main circuit of the bipolar-pulse PS was then designed,and two PS units were assembled.The output current can change the direction from the maximum to the minimum within 50?s.The frequency of the current can be varied from 1 k Hz to 8 k Hz continuously.The speed of frequency variation can be up to 500 Hz/ms in the range of 4?8 k Hz.The maximal amplitude of the current can reach 3 k A.Secondly,the control system of the CFV RMP system has been developed.The system consists of the TM detection system,which calculates the TM phase and frequency online,and the control system of the PSs.This control system can realize two TM feedback control strategies.Considering the feature of this system,a protection algorithm based on phase locked loop(PPL)has been designed and applied,which allows the safe operation at high frequency and large current.This new CFV RMP system has been applied in the physics experiment of the feedback TM control,and the new TM feedback control strategies were successfully implemented.A systematic study was carried out concerning the TM control strategy with online frequency varying RMP field.It is found that the variation of TM frequency depends on the amplitude of rotating RMP,the duration time at each frequency and the increased frequency for each frequency raise.In the best condition,f _TM can be increase from 4.5 k Hz to 7.3 k Hz.No clear stabilizing effect has been observed so far.Finally,the interaction between rotating RMP and TM in the low differential frequency region has been studied systematically.The previously studied online frequency varying RMP scenario has a challenging aspect,i.e.maintaining the differential frequency(?f=f _RMP-f _TM)at a low value,but avoiding the phase locking between TM and RMP field.In this low?f region,it is observed that the instantaneous frequency of the TM(f _TM,ins)oscillates significantly.Based on the torque balance and momentum transport equation,an analytical model has been established to describe the interaction between TM and RMP in the low?f region.The analytical expression of f _TM,ins and a new method for measuring the viscosity coefficient have been deduced.Based on the experimental data from various discharges,the viscosity coefficient is measured to be 3.3±1.7 m²/s.This work can make CFV RMP system control TM more accurately and efficiently in the future.