Particle trapping in carbon walls during ICRH heating in Tore Supra

The role of high-energy charge exchange (CX) particles during radio-frequen cy (RF) heating is examined in an attempt to develop a predictive model for wall saturation and desaturation processes. Tore Supra discharges in which an apparent saturated wall, previously obtained through a succession of oh mic discharges, was transformed into a pumping wall with the application of RF heating are analyzed. Direct measurements show the increased mean energ y of the CX spectrum upon application of RF heating. This leads to deeper C X neutrals penetration reaching the remaining a:C-D unsaturated layer and r estoring the wall pumping efficiency. The conversion from a saturated to a pumping state with the application of RF heating, and the time scales for s aturation during the ohmic and the heating phases, are reasonably well expl ained by several existing models. The deeper particle wall penetration obse rved during RF plasma experiments points to a potential mechanism which can increase tritium trapping in a fusion reactor. (C) 2001 Elsevier Science B .V. All rights reserved.