METAL COVERAGE OF TFR GRAPHITE TILES AND ITS EFFECTS ON THE IMPURITY CONTENT OF THE PLASMA
A number of carbon tiles of the TFR limiter and antenna protection were analyzed by PIXE, RBS, and SEM to obtain a comprehensive and quantitative picture of the metal coverage in these areas. The results show a metal coverage corresponding to more than a few hundred monolayers fairly homogeneously distributed and/or in the form of droplets (1 to 1000 gmm in diameter). Analysis of the chemical composition showed that the layer mainly consisted of Fe, Ni, Cr, and very little Ti. This indicated that the Ti Faraday shield for the ICRH antenna was not responsible for the metal contamination, in agreement with spectroscopic results. The reduction of the metal impurity content of the discharge by a factor of 3 to 10 when carbon limiters are used instead of metal ones seems to be related to the actual chemical composition of the limiter surface. Chemical sputtering of such carbon surfaces is lower than for pure carbon surfaces, whereas their hydrogen content is very high (up to 1022 D/m2).
Bibliographic Reference: JOURNAL OF NUCLEAR MATERIALS, NOS. 145-147 (1987), PP. 681-685
Record Number: 1989126005600 / Last updated on: 1988-02-01
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