Passive control of runaway electron displacement by magnetic energy transfer in J-TEXT

Highlights: • A novel and effective control method of runaway electrons based on magnetic energy transfer is presented in this paper. • A series of experimental tests are carried out to verify the proposed method. • The different critical MET coil current can be found under different discharge parameters. • The proposed method can be also applied in the plasma displacement control when no runaway electrons are produced. -- Abstract: During disruptions runaway electrons (REs) often drift from high field side to low field side in J-TEXT. It may cause severe damage to the plasma facing components when REs strike them with high energies. In order to mitigate the damage, a novel method called magnetic energy transfer (MET) based on electromagnetic coupling is proposed. A set of extra coils with a high coupling coefficient with plasma are installed on the high field side of the device, and a toroidal current can be induced in the coils during disruptions which can transfer the plasma poloidal magnetic energy out of vacuum vessel. Flowing in the same direction as the runaway current, the induced current can attract the runaway current to high field side, control the displacement of the RE beams and prolong runaway current plateau. Experiments are carried out on J-TEXT to verify the mitigation method, and the influence of different induced current on REs horizontal displacement is studied by changing the electrical parameters of energy absorbing unit. The experiment results show that the increase rate of RE beams' horizontal displacement can be significantly slowed. The runaway current plateau can be prolonged by 4–5 ms and the control effect becomes better as the induced current in the MET coils increases. Moreover, MET also has a good effect on displacement control of plasma during disruption when no RE beams are produced.