In the J-TEXT tokamak, the penetration of resonant magnetic perturbations (RMPs) has been studied by using a set of in-vessel RMP coils. It is found that, once the RMP amplitude exceeds a critical value, the applied RMP can lead to field penetration and excitation of a large locked mode in the tearing-stable plasma. The sawtooth oscillations disappear and the confinement deteriorates significantly accompanied by tearing mode excitation. For the plasma with an initial high frequency tearing mode, the RMP can suppress the tearing mode, and field penetration followed with a further increased RMP. The relationship between the RMP penetration threshold and the electron density has been investigated for tearing-stable plasmas. It is found that the penetration threshold increases with the density and scales proportionally to in the ranges of (0.7–2.7) × 1019 m−3. Using the experimental parameters as input, the numerical modelling based on two-fluid equations gives the scaling of , which approximately agrees with the experimental density scaling.
Effect of resonant magnetic perturbations on local plasma current density gradients and neoclassical tearing modes