HELIUM TRANSPORT AND EXHAUST STUDIES OF H-MODE DISCHARGES IN THE DIII-D TOKAMAK

A collaborative program has been initiated on DIII-D to study helium ( He) transport and exhaust in H-mode plasmas. To simulate the presence of He ash in DIII-D, a 50 ms He puff is injected into a DIII-D plasma, resulting in a He concentration of approximately 15%. The time depend ence of the He density profiles in the plasma core is measured with ch arge-exchange recombination spectroscopy and the He spatial distributi on on the divertor floor is studied with an impurity monitor array. Th e dependence of core transport diffusivities as a function of edge-loc alized modes(ELM) frequency has been studied and the first demonstrati on made of He exhaust from an ELMing H-mode plasma in a diverted tokam ak. A measured value of tau(He)/tau(E) Of 14 was obtained, which is w ithin the acceptable range for a fusion reactor.