Observations of edge radial electric field transition in LHD plasmas

Transition phenomena of the radial electric field are investigated using charge exchange spectroscopy with an improved time resolution in large helical device (LHD). The critical density, where the radial electric field changes from a positive to negative value, is observed to be higher in the outward shifted configuration because of a large ripple loss than that in the inward shifted configurations, which qualitatively agrees with the predictions of neoclassical theory.This article was due to appear in volume 45, issue 12A of Plasma Physics and Controlled Fusion. To access this special issue please follow this link www.iop.org/EJ/toc/0741-3335/45/12A.