Comparative Simulations of the Plasma Response to RMPs During ELM-Crash Mitigated and Suppressed Phases in KSTAR

Full text: Control of the edge localized modes (ELMs) is one of the most critical issues for a ITER and the future tokamak fusion reactors. In order to develop a predictive model of the access to ELM-crash suppressed states, it is essential to understand first the underlying physics mechanism of ELM-crash-suppression. This paper reports comparative simulation results for particular KSTAR experimental shot, where both of the ELM mitigated and suppressed phases were observed sequentially and separated distinctly in time with low-n resonant magnetic perturbations (RMPs) in KSTAR. We have observed that toroidal (ω_t) and E x B (ω_ExB) rotation frequencies are increased, while electron pressure gradient and the associated electron diamagnetic rotation frequency (ω_*e) reduced near the pedestal top through the transition from mitigation to suppression of ELMs. This results in a small outward shift in the zero-crossing of the electron perpendicular rotation (ω_⊥e ∼ 0) and ω_⊥e becomes even smaller inside the pedestal. Correspondingly, two-fluid linear plasma response modelling with the resistive MHD code M3D-C1 indicates that resonant tearing response is increased significantly near the pedestal top, which is well correlated to the observed onset of ELM-crash suppression. This result is similar to the recent ECEI observation of perpendicular flow changes at the onset of ELM-crash suppression in KSTAR. It remains unclear how the RMP-driven transport (with associated kinetic effects) bring out such changes to the rotation profiles and we plan to study that with XGC0 and XGC1 codes. Detailed results will be presented. (author)