ION BACKSCATTERING AND SPUTTERING OF PLASMA-IRRADIATED CARBON AND TUNGSTEN SURFACES IN AN OBLIQUE MAGNETIC-FIELD

A Monte Carlo simulation model which combines ion backscattering and s puttering of solids with transport of emitted particles in the scrape- off layer plasma is developed for the study of the plasma-wail interac tion in magnetic confinement fusion devices. The emphasis is put on th e precise understanding of ionization and redeposition processes of ba ckscattered and sputtered particles. In the model, Maxwellian ion-soli d interaction, ionization of backscattered and sputtered neutral parti cles in the plasma, and gyromotion of the ionized particles in an obli que magnetic field are included. The heavier masses (lower charge stat es and lower energies) the particles have, the more they are redeposit ed. Due to impact of carbon ions on carbon and tungsten, therefore, le ss backscattered carbon is redeposited, whereas most of the sputtered tungsten atoms are redeposited. The redeposition causes substantially lower effective sputtering yields and a decrease in low-energy compone nt of the sputtered atoms.