Research On MGI Disruption Mitigation And Runaway Current Generation Under Electron Cyclotron Resonance Heating On The J-TEXT Tokamak

Disruption could cause serious damage to large tokamak(like ITER).By plasma rapid shutdown(such as massive impurities injection)will increase the proportion of thermal radiation,so the damage caused by disruption can be mitigated.Massive Gas Injection(MGI)can well mitigate the harm of heat and electromagnetic force load.However,most of MGI disruption mitigation and runaway current experiments are under the condition of constant plasma electron temperature(T_e),and less attention has been paid to the influence of rising electron temperature on the interaction between impurity and plasma during disruption.In order to understand the mechanism of the radiation evolution of impurities and the generation of runway electron(RE)current during disruption,this article relies on the Electron Cyclotron Resonance Heating(ECRH)system on J-TEXT tokamak,to conduct an experimental study on the disruption mitigation and the generation of RE current,accumulate research experience and provide reference for the simulation and device operation of ITER tokamak.This article is based on J-TEXT tokamak to carry out experiment on the disruption mitigation of MGI(He,Ne,Ar).By fixing the MGI valve voltage and changing the ECRH power,the radiation and mixing efficiency of impurities are studied.In Pre-Thermal Quench(Pre-TQ)stage,it is found that when the power of ECRH is higher,the longer duration it takes for the impurities to reach the core from the plasma edge,and the speed of cold front decreases.In Thermal Quench(TQ)stage,it is found that the radiation power and ionization of impurities are significantly increased with the application of ECRH,and TQ duration is reduced to about half of the reference discharge.In Current Quench(CQ)stage,there is no significant difference on CQ duration and CQ rate.In addition,by calculation,it is found that when the ECRH power is 400 k W,the radiation of impurities is more uniform compared with the reference discharge,the Toroidal radiation asymmetry Peaking Factor(TPF)decreases to about 75%of the reference discharge,and the impurity mixing efficiency increases by 50%at the point of 80%CQ.In this article,the generation of runaway current during disruption is further studied by using the ECRH system,and the elevation of the runaway current during disruption is realized.It is found that the conversion efficiency of runaway current increases with the application of ECRH.When the power of ECRH is 400 k W,T_e is about 1.42 ke V,the conversion efficiency of runaway current increases about 35%.The experimental analysis shows that,during the TQ process,the collision rate of the suprathermal electrons generated by ECRH is lower,and the shortened TQ duration reduces the probability of the suprathermal electrons being decelerated by impurity,resulting in a large number of hot-tail RE seeds after the TQ phase.In this article,with the increase of ECRH power,more RE electrons in the low energy are generated during TQ is observed by the off-axis ECE chord,which confirmed that the increase of hot-tail RE electrons is effective.During CQ,an increase in the number of runaway electron seeds acts as an avalanche multiplier,resulting in a large number of runaway electrons produced in the avalanche process,resulting in an elevation of runaway current.