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

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 trigger a relaxation instability, and then the relaxation could bifurcate into two different types of tearing modes' behaviors. One is the tearing mode with single m/n$=$2/1 helicity (m and n are poloidal and toroidal mode numbers, respectively), another is the tearing modes with different helicities (m/n$=$2/1, 3/2). The mechanism responsible for the bifurcation is closely related to changes of the pressure, and lately the plasma current density profile, due to the gas injection.