Experimental Research Of Tokamak Plasma Disruption Mitigation Based On Poloidal Magnetic Energy Transfer

Plasma disruption is one of the main factors that seriously threaten the safe and stable operation of the tokamak devices.The quick and complete loss of plasma thermal energy and poloidal magnetic energy inside vacuum vessel(VV)during disruption often lead to heat load,electromagnetic force and runaway current,which can cause damage to plasma facing components and inner structures of tokamaks.Therefore,it's an urgent problem for the fusion devices to effectively mitigate the disruption damage.Although impurity injection is widely used to mitigate disruption,there are still some problems to be solved,such as the reduction of the total energy dissipated in VV,the asymmetrical heat radiation and complete suppression of runaway current.From the perspective of reducing the energy dissipated in VV during the disruption,a new method based on magnetic energy transfer(MET)is proposed in J-TEXT.It has realized the goal of transferring part of the poloidal magnetic energy out of VV by a couple of magnetic energy transfer coils that are inductively coupled with the plasma.Based on the MET system,this paper continues to explore the disruption mitigation effects of MET.The main contents are introduced as following:Firstly,the exploratory experiments are carried out,which find that MET can reduce loop voltage,suppress runaway current,and control the horizontal displacement of runaway.The results of experiment show that MET can reduce the loop voltage by 35.3% when the plasma current quench rate is increased by 50.7%.The effects of MET on plasma current quench rate and loop voltage is analyzed by establishing transformer model among the energy transfer coils,plasma,and OH coils based on the principle of MET.The results show that MET can effectively suppress the runaway current by reducing the loop voltage.Joint experiments with MGI system are carried out to explore the gas injection range of suppressing the runaway current when using MET.MET can still suppress runaway current when ECRH can enhance runaway current.The experiments also find that MET can control the horizontal displacement of the runaway electron beams and prolong runaway current plateau.When there is no runaway current existing,the range of energy transfer coil current for effectively controlling the plasma horizontal displacement is explored under different discharge parameters.Secondly,an active MET based on the discharge of the capacitors is proposed.Through theoretical analysis and experimental research,the mechanism of the new method to improve the disruption mitigation effect is revealed.The model of active MET is established to analyze the working process of active MET.The influence of pulse capacitors' parameters on magnetic energy transfer efficiency is analyzed.The active MET system is designed and built.The relevant experiments are carried out.The experimental results verify the theoretical analysis,which show that the active MET can improve the magnetic energy transfer efficiency up to43.3% and the reduction of the loop voltage can reach 43.7%,which are 71.1% and 23.8%higher than the MET.Combined with the characteristics of the new system,the experiments of dissipating runaway current is carried out by active MET system,which achieves runaway current dissipation rate up to 7.7 MA/s.Finally,the application of MET in air-core tokamak devices is carried out.The application suggestions are given.Taking EAST tokamak as a research subject,based on the finite element method and partial element equivalent circuit method,the induced eddy current on VV during disruption is analyzed.The distribution and evolution of poloidal magnetic energy during disruption are studied.76.9% of the total poloidal magnetic energy is dissipated inside VV and23.1% of the total poloidal magnetic energy is consumed by the wall of VV in the form of eddy current loss.The model of three-winding transformer with VV,plasma and the magnetic energy transfer coils is established to analyze the evolution law of the magnetic energy transfer coil current.The shielding effect of VV on magnetic energy transfer coil is found.The influence of the parameters of coils and VV on magnetic energy transfer efficiency is studied.The guidance of applying magnetic energy transfer method in air-core tokamak is given.It's important to study new disruption mitigation methods for the safe and stable operation of the tokamak devices.In J-TEXT,MET can reduce the total energy dissipated in VV,reduce loop voltage,suppress runaway current,and control the horizontal displacement of runaway.With upgrading of the MET system,the active MET can improve the effects on disruption mitigation and conduct the experiments of dissipating runaway current.As an effective method of disruption mitigation,it will have reference value for future fusion devices.