Integration of RMP ELM control with divertor detachment in the DIII-D tokamak*

Dedicated experiments in the DIII-D tokamak have been performed to explore the compatibility of ELM control by n=3 resonant magnetic perturbations (RMPs) with divertor detachment seeded by impurities in the closed divertor configuration. Simultaneous RMP ELM mitigation and divertor detachment have been achieved in the DIII-D ITER-similar shape plasma with H_98y2~1.2, q₉₅~3.5, β_N~2, energy loss per ELM decreased from 5% to 0.5%, and the peak heat flux decreased by 6 and 4 times during the intra- and inter-ELM respectively. In contrast to low collisionality plasma, during high collisionality detachment, n=3 RMP with up-down phase difference of △Φ_UL=180° is found to produce stronger magnetic response at the pedestal-top and cause stronger ELM mitigation than for △Φ_UL=0. The RMP is first found to facilitate divertor detachment by decreasing the detachment onset line-averaged density by up to 30% but increasing the scrape-off layer density by up to 80%. This is consistent with predictions for ITER but opposite to open divertor results where the RMP increases the divertor detachment density. Lobe structures are consistently observed during attached and detached conditions from line radiation imaging. They are found to enhance particle transport and result in higher upstream density in the near-SOL region based on EMC3-Eirene simulations. Linear calculations by GPEC show that the magnetic response to the RMP decreases by up to 70% during detachment due to the strongly degraded pedestal bootstrap current and the resulting weaker edge kink response. Analysis indicates that full RMP ELM suppression with divertor detachment is challenging for DIII-D due to the decreased plasma response in high collisionality plasmas, but it is predicted to be less challenging for ITER where detachment will be achieved with low pedestal collisionality.