Role of divertor geometry on detachment and core plasma performance in JT60U

Experimental results related to the divertor geometry such as divertor plasma detachment, neutral transport and plasma energy confinement, were compared in the open and W-shaped divertors. The ion flux near the outer strike point was larger than in the open divertor, and the electron temperature at the target, T-c(div), was reduced. Divertor detachment and x-point MARFEs occurred at (n) over bar(e) 10-20% lower than that for the open divertor. Although the leakage of neutrals from the divertor to the main chamber decreased, a neutral source in the main chamber due to an interaction of the outer scrape-off layer (SOL) plasma to the baffle plates became dominant above the baffle. Degradation in the enhancement factor of the energy confinement was observed similarly in the open and W-shaped diverters. The neutral density inside the separatrix was estimated to be a factor of 2-3 smaller, which did not affect the energy confinement. (C) 1999 Elsevier Science B.V. All rights reserved.