The toroidal dispersal of gas puffed impurities

A series of experiments has been performed on the DITE tokamak in which helium and methane have been puffed from the tip of an instrumented probe limiter immersed in the edge of a helium plasma. The spatial distributions of He I, He II, C I, C II and C III have been obtained with a CCD camera using interference filters. The intensity distributions for He I, C I and C II are very localised while in the cases of He II and C III, streaming along field lines has been observed. The toroidal distributions are in approximate agreement with a parallel transport model that includes ionisation, heating and diffusion.