New recycling model for light ions and atoms

Recent theoretical studies and experimental results suggest a revision of light-ion reflection models used in simulation codes. Surface impenetrability leads to large reflection coefficients for hydrogen isotopes incident below 5–20 eV. Adsorption below 5–10 eV also depends on saturation of the surfaces. An effective surface roughness is included for all energy regimes. The fraction of nonreflected particles reemitted as molecules depends on the previous exposure of the surface and the incident flux. Simple models of these processes are collected in a form usable in neutral transport codes. The relevance of such models to tokamak design and interpreting divertor tokamak data is discussed and illustrated by numerical computation.