TUNGSTEN AS TARGET MATERIAL IN FUSION DEVICES

Several experiments were conducted in ASDEX Upgrade to prove the suita bility of tungsten as a divertor target material under the conditions of a high density and low temperature divertor. The observed fluxes fr om a tungsten tile into the plasma are low, in keeping with the extrem ely low sputtering yields. In addition, the very favourable effect of 'prompt redeposition' (redeposition during the first gyration) could b e confirmed by the experiments. Cooling of the edge region by neon inj ection seems permissible, i.e. neon impurity sputtering did not increa se the eroded fluxes of tungsten. The transport and accumulation behav iour were investigated by means of the laser blow-off technique. No ac cumulation effects could be observed in ohmic discharges. In discharge s with NBI heating but without ICRH, strong accumulation can occur. Hi gh heat flux tests were performed on graphite tiles coated with plasma sprayed tungsten, which withstood a thermal load of 15 MW/m(2) lastin g 2 s as well as 1000 cycles of 10 MW/m(2) for 2 s without disabling d amage. Owing to the encouraging results, an experiment using a tungste n divertor is planned in ASDEX Upgrade.