Simulation of charge exchange neutrals interactions with gaps in first wall cladding

Angular distributions of particles impinging PFC in fusion devices with magnetic confinement are briefly discussed. It is shown that simulation of charge exchange neutrals interaction with the first wall should be made for inclined incidence of particles. Particle reflection coefficients and sputtering yields for gaps in Be, C and W first wall cladding are found with Monte Carlo computer simulations for hydrogen isotopes in the energy range ∼5-5 × 10 3 eV as well as for the flux integrated over the ITER charge exchange neutrals energy spectrum. Trapping of deuterons by the gap in the W wall increases two times (up to ∼0.6) as compared with the flat surface, while trapping in the Be gap is close to unity. The influence of isotope mass on trapping and sputtering is shown to follow data for the flat surface. Roughness of gap sidewalls taken into account slightly contributes to calculated data.