Systematic simulation studies on the penetration of resonant magnetic perturbations in an Experimental Advanced Superconducting Tokamak

The penetration properties of the n = 1 resonant magnetic perturbations (RMPs) with toroidal rotation are systematically studied by the upgraded three-dimensional toroidal magnetohydrodynamic code CLTx, through both linear and nonlinear simulations. It is found that in the presence of toroidal plasma rotation, the saturation state for high resonant harmonics is obtained in linear simulations due to the mode becoming unlocked from the internal magnetic islands. In nonlinear simulations, nonlinear effects become important when the toroidal plasma rotation is not included. The zonal component resulting from the nonlinear mode coupling is necessary for the saturation of the whole system including the internal kink mode and the m /n = 2/1 tearing mode. The simulations of RMP penetration demonstrate that the mode coupling is associated with the toroidal effect rather than nonlinear effects. With a low resistivity eta(0) = 10(-9) similar to 10(-8) close to the experimental value, the single-harmonic-RMP is hard to penetrate the mode-rational surface because of the plasma screening effects, resulting in a truncation of the radial mode structure. On the other hand, the non-resonant components in the multiple-harmonic-RMP could largely reduce the effect of the plasma shielding, which leads to that the RMP is able to penetrate deeply into the central plasma region through the poloidal harmonic coupling.

Automated summary

The study shows that in a tokamak plasma, the ability of single-harmonic RMP to penetrate the mode-rational surface is limited by plasma screening effects; while in the multiple-harmonic RMP, non-resonant components can reduce plasma shielding effects, allowing the RMP to penetrate deeply into the central plasma region.