Effects of spatial diffusion and direct loss on burnup fractions of fast ions

Effects of spatial diffusion and of direct loss of fast ions on their burnup fractions are studied by solving a Fokker-Planck equation including a diffusive loss or a direct loss. Almost the same time evolution of the triton burnup fraction as obtained by introducing spatial diffusion can be reproduced by adjusting the loss time. However, the 14 MeV neutron emission profile in the case with spatial diffusion is broader than that with direct loss. As for the 3He burnup fraction, the difference between the cases with spatial diffusion and direct loss is found to be relatively large. The diffusive loss can become important even for 3He burnup. Effects of charge-exchange loss on the triton burnup fraction are also examined. It is found that the reduction of the burnup fraction by half of the value with no loss assumed can occur for a reasonable value of neutral density in beam injected plasmas. (author)