Research Of A New Tokamak Plasma Disrutption Mitigation Method Based On Poloidal Magnetic Energy Transfer

Quick dissipation of plasma thermal energy and poloidal magnetic energy inside vacuum vessel(VV)during disruption often leads to damage to the tokamak device in form of of heat load,electromagnetic force and runaway current.The magnitude of plasma disruption damage increases as the energy dissipated inside VV during disruption,which increases as the plasma parameters.The plasma disruption damage might threat the safety operation and lifetime of International Thermonuclear Experimental Reactor(ITER)and the future fusion devices due to their large plasma thermal energy and poloidal magnetic energy.Therefore,it is necessary to mitigate the plasma disruption damage.Among the existed plasma disruption mitigation methods,the most effective one is impurity injection.Although the impurity injection can mitigate the disruption damage of ITER in theory,there still remains several challenge to overcome,such as the asymmetrical heat radiation caused by impurity injection and the mitigation of runaway current.This paper provides a new plasma disruption mitigation method based on transference of plasma poloidal magnetic energy,which is shorted for magnetic energy transfer.This method can transfer part of the poloidal magnetic energy out of VV during disruption by a couple of magnetic energy transfer coils(MET coils)that are inductively coupled with the plasma.Thus,this method can reduce the energy dissipated inside VV and mitigate the plasma damage.The MET coils are connected with a switch and a resistance load.The switch is triggered only in the disruption phase and is used to conduct the MET coils.During the normal discharge the switch is not triggered and the MET coils are open circuits that have no adverse effect on normal discharge.This method is studied in J-TEXT tokamak,which can provide reference for ITER and the future fusion devices.The main contents of this paper are introduced as following.First of all,the J-TEXT dissipation principle of the poloidal magnetic energy during disruption is analyzed,which can establish foundation to the study of magnetic energy transfer.The structure and parameter of J-TEXT is introduced,the electromagnetic coupling between plasma,poloidal coils and VV is anslyzed,the magnitude and distribution of pre-disruption and post-disruption poloidal magnetic energy is calculated by the finite element software ANSYS,and the analyzation result is verified in the experiment.About 80-100%of the pre-disruption magnetic energy is dissipated inside VV during disruption in J-TEXT.Then,the new plasma disruption mitigation method based on magnetic energy transfer is studied.An analyzation model of magnetic energy transfer is built,a typical magnetic energy transfer process is analyzed,the magnetic energy transfer efficiency is calculated,and the analyzation results are verified in the experiments.It is found that the magnetic energy transfer efficiency is dependent on the coupling coefficient between the plasma and the MET coils,which depends on the irrelative position In J-TEXT the Bias coils are used as MET coils,and the magnetic energy transfer efficiency reached 25.3%,and only 65.9%of the pre-disruption magnetic energy is dissipated inside VV during disruption in J-TEXT.At last,mitigation effects of magnetic energy transfer on runaway current is studied.During disruption a co-current with the plasma is induced in the MET coils as the plasma current decreases,which can reduce the toroidal electric field and mitigate the runaway current.In experiment the mitigation effect of runaway current is observed.The study result in J-TEXT proves that the magnetic energy transfer can reduced the poloidal magnetic energy dissipated inside VV and mitigate the runaway current during disruption.The principle of magnetic energy transfer and impurity injection is different and can co-work to get better disruption mitigation effects.