Observation of the bifurcation of tearing modes due to supersonic gas injected into the J-TEXT plasmas

Abstract The influence on the magnetohydrodynamic (MHD) behaviors due to the gas injected by Super-sonic Molecular Beam Injection (SMBI) has been observed on J-TEXT tokamak. The change of local electron temperature and density due to the injected supersonic gas triggers relaxation instability, and then the relaxation could bifurcate into two different types of tearing modes' behaviors. One is tearing mode with single m / n = 2 / 1 helicity, another is tearing modes with different helicities ( m / n = 2 / 1 , 3/2). The mechanism which is responsible for the bifurcation is closely related to changes of the pressure due to gas injection.