Effect of 2/1 tearing mode on radiation asymmetry during disruptions on J-TEXT

•Radiation asymmetry calculates the radiation information of four positions, each of which is about 90° apart, covering the whole tokamak.•There are more pre-existing locking mode phases in the experiment.•Two disruption mitigation systems, MGI and SPI, were used in the experiment and compared with each other.•The possible explanation of the effect of pre-existing locking mode phase on radiation asymmetry is found and verified from the perspective of radiation energy. Plasma disruption in the tokamak is a huge threat to the safe operation of ITER, which will cause serious damage to the tokamak device. At present, massive impurity injection is the main disruption mitigation method, include massive gas injection (MGI) and shattered pellet injection (SPI) which can dissipate most of the internal thermal energy via radiation. However, radiation asymmetry will still cause damage to the device when it results the concentration of radiation in a small area. It has been observed on many devices that n = 1 mode has a strong influence on radiation asymmetry. In this paper, the experimental results of radiation asymmetry on J-TEXT tokamak have been introduced, and there is a close to sine function relationship between toroidal peaking factor (TPF) and the phase of 2/1 tearing mode. It is found that when the injection position is aligned with the X-point of the pre-existing magnetic island, TPF has the maximum value, and while the injection position is between the X-point and the O-point, TPF has the minimum value. This will be helpful for the study of disruption mitigation of future large devices.