Measurements of radial profiles of He2+ transport coefficients on the TFTR tokamak

Measurements of the spatial structure of the transport coefficients of He2+ on the Tokamak Fusion Test Reactor is reported. He2+ profiles were measured using charge-exchange spectroscopy after a helium puff into corotating L-mode plasmas. Modeling shows that the He2+ diffusivity is about 10 m2/s near the plasma edge and drops to below 1 m2/s inside of the q=1 surface. The convective velocity ranges from 13 m/s near q=1 to 2040 m/s near the edge. The helium diffusivity is on the order of the ion momentum and thermal diffusivity and is greater than the electron thermal diffusivity.