Experimental comparison of recycling and pumping changes during resonant magnetic perturbation experiments at low and high collisionality in DIII-D

Abstract

Resonant magnetic perturbations (RMPs) have been shown to successfully suppress edge localized modes (ELMs) in the DIII-D tokamak. A previous study of target plate conditions highlighted differences in RMP discharges between low and high electron collisionality, ν e ∗ , operation in DIII-D. This paper reports on a systematic study of the electron density pump-out associated with the turn-on of the RMP over a wide range of operating conditions in DIII-D, including shapes and collisionalities similar to those anticipated in ITER. It is shown that the pump-out magnitude, Δ n e, has an upper envelope that is inversely proportional to the pedestal ν e ∗ . The particle decay times, which are calculated based on global D 2 particle balances, show an increase as the pedestal ν e ∗ is increased. Both results are suggestive that the underlying physics mechanism is an increase in edge particle transport and/or that wall depletion is playing a role in the pump-out magnitude.