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 dependence of the He density profiles in the plasma core is measured with charge-exchange recombination spectroscopy and the He spatial distribution on the divertor floor is studied with an impurity monitor array. The dependence of core transport diffusivities as a function of edge-localized modes (ELM) frequency has been studied and the first demonstration made of He exhaust from an ELMing H-mode plasma in a diverted tokamak. A measured value of tau *_He/ tau _E of 14 was obtained, which is within the acceptable range for a fusion reactor.