J. Plasma Fusion Res. SERIES, Vol.4 (2001) 106-110 Electric Field Measurement and Limiter Experiment on LHD

Transition from the ion root to the electron root in neutral beam heated plasmas was observed in the Large Helical Device for the first time. The measured values of the radial electric field were found to agree well with those estimated by neoclassical theory. The pedestal configuration, which is characterized by a high edge temperature gradient, was observed in LHD plasma, resulting in the improvement of the energy confinement. A radially movable limiter was inserted into the pedestal region. The pedestal configuration was still observed at the edge region bounded by the limiter without changing its width and gradient, and no confinement degradation was observed. Keywords: radial electric field, electric field transition from the ion root to the electron root, radially movable limiter, pedestal configuration 1. lntroduction The Large Helical Device (LHD) [1-4] is the largest superconducting heliotron type device with I