Tritium transport and influx, and helium ash measurements on TFTR during DT operation

The evolution of the tritium density profile is inferred from 14.1 MeV t(d,n)α and 2.5 MeV d(d,n)3He neutron emissivity profiles measured in a deuterium neutral beam heated plasmas into which a small amount of tritium gas has been puffed. For the first time, hydrogenic ion transport coefficients in the form of a diffusivity and convective velocity are determined. The particle diffusivities of tritium and 4He, and the deuterium thermal diffusivity are of similar magnitude, and thus are consistent with theoretically calculated ExB drift transport. The first measurements of helium ash have been made using charge exchange recombination spectroscopy. The measured radial ash profile shape is consistent with that predicted from simulations that include calculations of the central alpha ash source and thermal ash transport. This suggests that ash transport in the plasma core will not be a fundamental limiting factor in determining helium exhaust rates in a reactor. The authors also report the first spectroscopic measurements of tritium Balmer-alpha emission, which provided a measure of tritium influx from the limiter. Tritium influx persists in discharges subsequent to tritium neutral beam injection, decaying with an initial decay of 7.5 discharges, and followed by a long term decay on the order of 400 discharges. Tritium transport and influx, and helium ash transport are important issues for profile control, retention, and ash removal in future reactors like ITER. (author). 35 refs, 6 figs