Kinetic study of the bifurcation of resonant magnetic perturbations for edge localized mode suppression in ASDEX Upgrade

The correlation between the bifurcation of resonant magnetic perturbations (RMPs) to the unshielded state and edge localized mode (ELM) suppression in ASDEX Upgrade is studied using a kinetic plasma response model numerically and analytically. For the numerical studies, the linear kinetic Maxwell solver KiLCA for cylindrical geometry and the quasilinear transport code QL-Balance are used in combination with the ideal MHD solver GPEC to account for realistic tokamak geometry. Based on this modelling, a numerical local bifurcation criterion is introduced which estimates the effect of RMP-induced temperature plateau formation in the resonant layer. Its analytical form is derived in constant-psi approximation. The kinetic model reproduces the known gyrocenter resonance, $E_r = 0$, and the electron fluid resonance. In contrast to MHD theory, the latter is located at the zero of the perpendicular electron fluid velocity computed only with half of the electron temperature gradient. The application of the criterion to experimental data shows a correlation between bifurcation and the ELM suppression phase. Moreover, an electron density limit is found resembling the one observed in experiments.