Exploiting the Plasma Response to Maximize Access to RMP-ELM Control in Tokamaks*

Plasma response modeling captures the optimum applied spectrum to experimentally access RMP-ELM suppression over a wide range of operating currents in EAST, and provides a hypothesis for why an optimum in triangularity is found in DIII-D and AUG. Analysis of both RMP coupling to the edge resonant surfaces and extraction of multiple eigenmodes through singular value decomposition capture the optimal spectrum for RMP-ELM control over a wide range of operating currents in EAST. This confirms that the plasma response near the pedestal top is consistent with the observed RMP-ELM control sensitivities. The 3D plasma response provides explanation for the inability to access ELM suppression at high triangularity in DIII-D, namely that the resonant coupling is reduced at high triangularity as compared to that at low triangularity. This is validated through targeted comparisons with experiments across devices. These findings indicate that the plasma shape should be taken into consideration when designing a tokamak suitable for RMP-ELM control, and that predictive plasma response calculations can be used to maximize access to RMP-ELM control in future devices by maximizing the coupling between coils and the plasma.