Long term observations of materials deposited on wall samples in ASDEX

• Published in: Journal of nuclear materials 1982-01, Vol.111, p.173-176
• Main Authors: Staib, P., Kukral, H., Glock, E., Staudenmaier, G.
• Format: Article
• Language: English
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/0022-3115(82)90204-5

Protective glasses are mounted inside the vacuum vessel in front of the observation windows used for H α-measurements. These glass discs are positioned near the wall surface and are routinely replaced at each major opening of the vessel, namely after several months of operation of ASDEX. Comprehensive surface analyses are performed using a scanning electron microscope combined with Auger, SIMS and X-ray microanalysis techniques. The lateral as well as the depth distributions of deposited materials are measured. The observations based on large number of samples (about 30) distributed all over the vacuum vessel, are the following: — deposits in the main plasma chamber consist of thin layers of stainless steel (i.e. Fe, Cr, Ni) and of titanium. These layers are completely oxidized and have been successively deposited during the major phases of the machine operation (limiter, divertor, titanium gettering). Many stainless-steel particles are observed. These are molten droplets projected and stuck on the glass surface. Their dimensions range from a few μm to about 100 μm. Very tiny titanium particles are also observed spread over the surface. — Deposits on samples exposed in the upper divertor chamber are covered with a uniform titanium layer. It is heavily oxidized over its thickness of ~ 10 nm. No droplets are observed in the upper divertor chamber, but many are found in the lower chamber.