Interaction of charge exchange neutrals with the main chamber walls of plasma machines

Abstract

The fluxes and energy distributions of the charge exchange (CX) neutrals as measured at specific locationsat the tokamak ASDEX Upgrade (AUG) and the stellarator W7-AS at Garching are discussed as a function of the dischargeconditions. For the evaluation of the plasma-wall interaction, knowledge of the energetic neutral fluxes andtheir energy and angular distributions at all poloidal and toroidal locations are required. For AUG these are obtainedfrom B2-EIRENE computer simulations, taking the experimental results into account. The CX fluxes and the shapes ofthe spectra vary greatly around a poloidal cross-section. This has a strong effect on the wall erosion bysputtering and hydrogen isotope implantation into the vessel walls. The sputtering of the actual carbon wall, andthe effect on possible wall materials, such as tungsten, beryllium, TiC and SiC, are discussed. The depthdistribution of the CX neutrals implanted into the walls is calculated for two cases using the TRIMSP code.Saturation, release by glow discharges and permanent retention of the implanted hydrogen isotopes are discussed.This is important for the expected tritium content of the vessel walls of a future D-T fusion device.