Light impurity production in tokamaks
The different erosion processes of carbon materials are summarised with emphasis on conditions relevant to plasma surface interactions. New results on the chemical erosion and radiation enhanced sublimation of boron-carbon layers are presented. The chemical hydrocarbon formation produced by the interaction of the TEXTOR scrape-off plasma with a carbon target is investigated up to temperatures of 1500K using a sniffer probe. The chemical interaction of the plasma with the carbon walls in TEXTOR is also analysed by measuring the hydrocarbon and CO and CO(2) partial pressures built up on the surrounding walls during the discharges. The recycling of oxygen impurities in an all carbon surrounding occurs predominantly in the form of CO and CO(2) molecules and the analysis of both neutral pressures during the discharges is used as an additional diagnostic for the oxygen impurity situation in TEXTOR. These data are discussed in view of spectroscopic measurements on the influx of carbon and oxygen atoms from the walls and impurity line radiation. CD-band spectroscopy is employed to identify the hydrocarbon chemical carbon erosion. Present understanding of the oxygen impurity recycling and the oxygen sources are described. Particle induced release of CO molecules from the entire first wall is believed to be the dominant influx process of oxygen in the SOL of plasmas with carbon facing materials. The effect on the light impurity behaviour of coating the TEXTOR first wall with a boron-carbon film (B/C=1) is shown.
Bibliographic Reference: Article: Plasma Physics and Controlled Fusion, Vol. 31 (1989) No. 10, pp. 1685-1698, IOP Publishing Ltd. and Pergamon Press
Record Number: 199010663 / Last updated on: 1994-12-01
Original language: en
Available languages: en