Recyling of neon at a carbon limiter

Abstract The velocity distribution of neon atoms recycling at a carbon limiter has been determined from the Doppler broadening of a NeI line at λ = 585.248 nm (3s′[1/2] J =1 −3p′[1/2] J =0 ). The measured velocity distribution matches well the radial intensity distribution from line emission (NeI, λ = 640.2 nm) of neon atoms released from the limiter. It has been found that the velocity distribution consists of two components, thermally desorbed particles at E = 0.3 eV and fast particles with an averaged energy of 15 eV. With increasing line averaged central electron density n e (corresponding to a decreasing edge temperature) the fraction of fast particles increases up to 50%, while the average velocity of fast particles decreases, as it would be expected from a reflection process. It has been tried to reproduce the observed velocity distribution by modelling the particle reflection of neon projectiles at the carbon surface with the help of the TRIM- and EIRENE- code. The calculated velocity distribution, however, shows significantly less fast particles than the measured one. Possible reasons of this discrepancy are discussed.