The effects of elastic scattering in neutral atom transport

Neutral atom elastic collisions are one of the dominant interactions in the edge of a high recycling diverted plasma. Starting from the quantum interatomic potentials, the scattering functions are derived for H on H⁺, H on H₂, and He on H₂ in the energy range of 0.1-1000 eV following classical scattering theory and an impact parameter formulation. Potentials for both the gerade and ungerade electronic wavefunctions were included. An algorithm for the addition of these reactions to the DEGAS [J. Comput. Phys. 46, 309 (1982)] code is presented and used to simulate three test problems: (1) the transport of neutral atoms through a dilute edge plasma, (2) the penetration of neutral atoms into a dense plasma from a divertor plate, and (3) the transmittance of neutral atoms through a pump duct. In all three cases the inclusion of elastic scattering has a significant influence on the neutral atom density, temperature, and flux to the walls.