Enhancement of Helium Exhaust During ELM suppression by Resonant Magnetic Perturbation Fields at DIII-D

Resonant magnetic perturbations (RMPs) used to suppress Edge Localized Modes (ELMs) in ITER-shaped H-mode plasmas led to enhanced global He exhaust, measured by the effective He particle confinement time τ_p*_He, in recent experiments at DIII-D. During ELM suppression, τ_p*_He decreased by 40% vs ELMy cases, and τ_p*_He/τ_E, where τ_E is energy confinement time, was reduced by ~15%. These first-time findings are important for ITER, where RMP ELM control is planned, because they suggest RMPs can replace ELM impurity flushing. A multi-reservoir particle balance model is used analyze these data. In the edge reservoir, He density measurements decay faster during ELM suppression, suggesting faster outward transport and/or reduced back-fueling after recycling. Increased He-I and He-II emission in the Scrape-off Layer (SOL) and higher neutral He pressure near the pump show that more He is retained in the SOL and neutral reservoirs, which is important for effective removal of He globally. Initial EMC3-EIRENE modeling suggests magnetic stochastization reduces the thermal force relative to the friction force, enhancing outward transport in the edge.