Particle Exhaust from Plasma Discharges with an Expanded-Boundary Divertor

Measurements of the divertor-region plasma characteristics and argon exhaust efficiencies of the expanded-boundary divertor are reported. High plasma and neutral-hydrogen densities (\ensuremath{\sim}${10}^{14}$/${\mathrm{cm}}^{\ensuremath{-}3}$) are observed in the divertor region, and the exhaust efficiency for injected argon exceeds 95%. A simple model based on electron heat conduction parallel to the diverted field lines and frictional force due to proton-argon collisions in the divertor region accurately describes the experimental observations.