Recent gaseous divertor experiments in DIII-D

The expected heat loads at the divertor plates for next generation tokamaks raise concern from the standpoints of both mechanical integrity and erosion rate. The peak heat flux anticipated for the present International Thermonuclear Experimental Reactor (ITER) design are predicted to be as high as ∼20MW/m2. High peak heat fluxes can be reduced to more manageable levels by increasing the radiated power in the divertor, which has the additional benefit of reducing divertor plasma temperature and sheath potential, thereby lowering the ion impact energy. Neutral deuterium gas injection into or near the divertor has been suggested as one means of reducing heat flux via radiation and/or momentum transfer and ionization collisions with the neutral gas; this method is often referred to as the 'gaseous divertor'. In this paper we report on experiments in which the gaseous divertor approach was used to reduce the heat flux on the divertor tiles of the DIII-D tokamak during ELMing H-mode discharges. (author) 7 refs., 4 figs