Measurements of the spatial structure of the transport coefficients of ${\mathrm{He}}^{2+}$ on the Tokamak Fusion Test Reactor is reported. ${\mathrm{He}}^{2+}$ profiles were measured using charge-exchange spectroscopy after a helium puff into corotating L-mode plasmas. Modeling shows that the ${\mathrm{He}}^{2+}$ diffusivity is about 10 ${\mathrm{m}}^2$/s near the plasma edge and drops to below 1 ${\mathrm{m}}^2$/s inside of the q=1 surface. The convective velocity ranges from 1–3 m/s near q=1 to 20–40 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.

• Received 16 May 1990

DOI:https://doi.org/10.1103/PhysRevLett.65.2255