Pedestal, SOL and divertor plasma properties in DIII-D RMP ELM-suppressed discharges at ITER relevant edge collisionality

Large Type-I edge localized modes (ELMs) were completely suppressed by applying edge resonant magnetic perturbations (RMPs) in DIII-D H-mode plasmas with the same low pedestal collisionality (νe∗∼0.1) as in ITER. The RMP suppressed ELMs by reducing the edge pressure gradient through a reduction in the pedestal density gradient. Divertor emission profiles showed increases in toroidally localized Dα and carbon ion emission and carbon emission throughout both divertor legs. The lowest density ELM-suppressed discharges showed elevated levels of carbon in the core plasma. The data and boundary simulations indicate that the divertor strikepoints make a transition from a high recycling regime during the ELMing phase to a sheath-limited regime during ELM suppression in the lowest density plasmas. ELM suppression during scans of RMP amplitude, injected power and density suggests a possible optimum combination of these actuators for ELM control, without elevated impurity levels, that is extrapolatable to ITER.