RECYCLING OF NEON AT A CARBON LIMITER

The velocity distribution of neon atoms recycling at a carbon limiter has been determined from the Doppler broadening of a NeI line at lambd a = 585.248 nm (3s'[1/2](J=1)-3p'[1/2](J=0)). The measured velocity di stribution matches well the radial intensity distribution from line em ission (NeI, lambda = 640.2 nm) of neon atoms released from the limite r. It has been found that the velocity distribution consists of two co mponents, thermally desorbed particles at E = 0.3 eV and fast particle s with an averaged energy of 15 eV. With increasing line averaged cent ral electron density (n) over bar(e) (corresponding to a decreasing ed ge temperature) the fraction of fast particles increases up to 50%, wh ile the average velocity of fast particles decreases, as it would be e xpected 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 si gnificantly less fast particles than the measured one. Possible reason s of this discrepancy are discussed.