Suppression of runaway current by electrode biasing and limiter biasing on J-TEXT

The avoidance of runaway electrons(REs) generated during plasma disruption is of great concern for the safe operation of tokamak devices.Experimental study on the suppression of runaway current by electrode biasing(EB) and limiter biasing(LB) has been performed on the J-TEXT tokamak,which could be an alternative way to suppress the runaway current.The experimental results show that the higher the voltage value,the smaller the runaway current in both EB and LB experiments.The runaway current can be completely suppressed at an electrode biased voltage of +450 V and a limiter biased voltage of +300 V.The comparison of the energy spectra during the runaway plateau phase shows that the maximum energy max(E_(RE)) and radiation temperature T_(HXR)hard x-rays(HXRs)are significantly reduced after the application of +200 V limiter biased voltage.The electric field generated by the biased voltage may be the key factor to suppress the runaway current,and the measured radial electric field increases obviously after the voltage is applied.This may result in an increase in the loss of REs to realize the suppression of runaway current.

Development of the pellet injection system on the J-TEXT tokamak

Pellet injection is an attractive technology for core-fueling and magnetohydrodynamic study in magnetic-conflnement fusion devices like tokamaks and stellarators.It can inject solid hydrogen/deuterium pellets into the plasma with deeper density deposition compared with other fueling methods,such as gas pufflng.A three-barrel H_(2)pellet injection system was installed on the J-TEXT tokamak and experiments were carried out.The pellets are formed in three barrels cooled by a cryocooler and compressor system at around 9 K,and are 0.8 mm/1 mm diameter and 0.8 mm length.The pellet is launched by helium propellant gas and injected from the lowfleld side of the plasma.The normal range of pellet speed is 210–310 m s^(-1)for different propellant gas pressures.Due to the three-barrel structure,the number of injected pellets can be adjusted between one and three.Pellets can be launched sequentially with arbitrary time intervals,which enables flexible applications.The results of the experiments show that pellet fueling efflciency can reach 50%.The energy conflnement time increased by about 7.5–10 ms after pellet injection.