Plasma response to m/n = 3/1 resonant magnetic perturbation at J-TEXT Tokamak

The influence of resonant magnetic perturbations (RMPs) with a large m/n = 3/1 component on electron density has been studied at J-TEXT tokamak by using externally applied static and rotating RMPs, where m and n are the poloidal and toroidal mode number, respectively. The detailed time evolution of electron density profile, measured by the polarimeter-interferometer, shows that the electron density n _e first increases (decreases) inside (around/outside) of the 3/1 rational surface (RS), and it is increased globally later together with enhanced edge recycling. Associated with field penetration, the toroidal rotation around the 3/1 RS is accelerated in the co-I _p direction and the poloidal rotation is changed from the electron to ion diamagnetic drift direction. Spontaneous unlocking-penetration circles occur after field penetration if the RMPs amplitude is not strong enough. For sufficiently strong RMPs, the 2/1 locked mode is also triggered due to mode coupling, and the global density is increased. The field penetration threshold is found to be linearly proportional to n _eL (line-integrated density) at the 3/1 RS but to (n _eL)^0.73 for n _e at the plasma core. In addition, for rotating RMPs with a large 3/1 component, field penetration causes a global increase in electron density.