EFFECTS OF RADIAL DIFFUSION ON TRITON BURN UP

A detailed investigation is made of the effect of finite confinement time and radial diffusion on the burn up of fusion produced 1 MeV tritons in hot deuterium plasmas. Explicit expressions are obtained for the concomitant reduction in total triton burn up and applications to JET and TFTR burn up measurements indicate diffusion constants D congruent-to 0.1-0.2 m2/s for the fast tritons if the reduction is due to radial diffusion. The time dependence and the width of the emission profile of the 14 MeV neutrons from the triton burn up are also analyzed. Recent measurements of 14 MeV emission profiles on JET indicate a much smaller diffusion constant, viz. D << 0.1 m2/s. This implies that the observed finite confinement time of the tritons should not be due to radial diffusion and that the diffusion constant of the fast tritons should be very small.