INSITU ANALYSIS OF THE CARBONIZATION PROCESS AND SURFACE MODIFICATION OF THE CARBON LAYER BY TOKAMAK DISCHARGES IN TEXTOR

Surface analysis has been carried out on samples exposed to carbonization, discharge cleaning and tokamak discharges with Auger Electron Spectroscopy (AES). A carbon layer of approximately 30 monolayers on an Inconel sample was neither fully removed nor contaminated during exposure to 134 tokamak discharges at the liner position. The carbon layer was also not removed with exposure to 25 discharges at 1 cm behind the main limiters. Deposition of metals and oxygen was observed on the top surface of the C-layer in this case. Deposition of carbon on silicon samples was found with a carbonized wall after exposure to tokamak discharges. From a semi-quantitative discussion of these experimental results, it has been concluded that the C-layer on the liner, on Faraday shields and on limiters have long life time, and redeposition processes contribute to maintaining the carbon layer. Removal of the carbon layer by glow-discharge cleaning has also been demonstrated.