The influence of the pre-existing islands on thermal quench and radiation asymmetries during massive gas injection on J-TEXT

Locked modes are one of the major causes of disruptions in tokamak. The disruption mitigation system, like massive gas injection (MGI), is expected to be deployed with a non-rotating modes. A series of plasmas were penetrated with different phases m/n=2/1 resonant magnetic perturbation (RMP) were terminated by massive gas injection of helium in J-TEXT tokamak. The results show that the phase of the 2/1 mode relative to the MGI valve can influence the gas penetration progress. Thus, the thermal quench (TQ) onset and duration will be influenced: the core TQ duration can be delayed when the o-point is aligned with the MGI valve and reduced when x-point is aligned with the MGI valve. The radiation asymmetries have also been analyzed with AXUV arrays. The experimental results have been compared with the 3D extended MHD code NIMROD. The simulation results indicate that the pre-existing 2/1 mode can influence the parallel impurity spreading and the energy loss.