The effect of the plasma response on peeling-ballooning modes during edge localized modes mitigated by resonant magnetic perturbations

The effects of resonant magnetic perturbation (RMP) fields on peeling-ballooning (P-B) modes are studied with the experimental equilibria of EAST based on the four-field model in BOUT++ code. As the two basic types of plasma responses, the magnetic and the transport response to RMP are considered in our simulation to reveal the roles of the plasma response during edge localized mode mitigation. On the one hand, the results show that RMP can reduce the linear growth rates of the P-B modes and the pedestal energy loss in the nonlinear process by directly coupling with the P-B modes. The magnetic response can weaken the impacts of RMPs on the P-B modes by partially screening the applied RMP fields more precisely the resonant components. On the other hand, RMP can further reduce the linear growth rates of the P-B modes and the pedestal energy loss by changing the equilibrium pressure profiles through the transport response. More detailed analysis suggests that, compared with other resonant components of RMPs, the components whose corresponding rational surfaces are located at the top of the pedestal can lead to stronger reductions in the linear growth rates of the P-B modes, and can reduce pedestal energy loss more significantly by enhancing multi-mode coupling in the nonlinear process. Finally, the multi-mode coupling increases with the strength of the resonant components, so one can change the RMP poloidal spectrum by adjusting the phase difference Delta phi between the upper and low RMP coils from 0 to 360 degrees, and hence obtain the optimal coil phase difference that leads to the strongest reductions in the linear growth rates of the P-B modes and the pedestal energy loss through maximizing the strength of resonant components, especially the resonant components whose corresponding rational surfaces are located at the top of the pedestal.