Resonant Magnetic Perturbation Thresholds for ELM Suppression

This large database study of RMP ELM suppression thresholds in the AUG, DIII-D, EAST, and KSTAR tokamaks details the key aspects of various resonant magnetic perturbation (RMP) metrics and the distribution of their empirical values at the threshold of edge localized mode (ELM) suppression. The database contains data at the time of transition from ELMing to ELM suppressed states where a clear threshold is identified and calculates MHD metrics quantifying the RMP magnitude at that point. The threshold distributions are compared for 5 common metrics: (1) the island overlap width, (2) pedestal top Chirikov overlap, (3) peeling edge displacement, (4) pedestal top resonant drive, and (5) edge dominant mode overlap. The distributions, the dependence on RMP coil currents, and the sensitivities of a given metric to equilibrium reconstruction details are compared. Two relatively new metrics, one utilizing a threshold from the non-linear Modified Rutherford Equation evaluated at the pedestal top and one utilizing the SLAYER code to calculate the linear tearing threshold from torque balance, offer possible paths to extrapolation of the RMP threshold beyond the existing database parameter space.