A SINGLE RAY APPROXIMATION FOR ALPHA-PARTICLE TRANSPORT

We report the development of a one-ray approximation for the numerical transport of 3.5 MeV alpha particles generated in DT fusion reactions . Similar in spirit to techniques used in photon transport, this metho d provides respectable accuracy at potentially large savings in time a nd storage when compared to multigroup diffusion, S-n, or Monte Carlo techniques. The approximation works in a restricted, but large, class of plasmas, those in which scattering of the alpha's and bending of th eir trajectories by magnetic fields can be neglected. Test cases in pl anar, cylindrical, and spherical geometry are presented. In another ca lculation it is demonstrated that the achievement of ignition in an im ploding Z pinch may depend sensitively on the degree to which a magnet ic field confines the alpha particles in the dense central core. (C) 1 995 Academic Press. Inc.