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The graphite used for the limiter of the tokamak reactor produces carbon-containing molecular impurities as a result of the interactions with the edge plasma. The behaviour of these molecular impurities has been studied using emission spectroscopy. The present study includes : (1) finding molecular bands and atomic lines in the visible spectral range which can be used for the study of the molecular impurities, (2) studying the breakup processes of the molecular impurities on their way from the source into the plasma, (3) developing a spectroscopic diagnostic method for the absolute measurement of the molecular impurity flux resulting from graphite erosion. Carbon-containing molecules such as CH(4), C(2)H(2), C(2)H(4), CO and CO(2) were injected into the tokamak-boundary-like plasma generated by PISCES-A. The breakup processes of these gases were studied by observing the spatial profiles of the emission of the molecules and their radicals for different plasma conditions. For the absolute measurement of the eroded molecular impurity flux, the photon efficiency of the lines and bands was found by measuring the absolute number of emitted photons and injected gas molecules. The chemical sputtering yield of graphite by hydrogen plasma showed good agreement with results obtained by weight loss measurements.

Additional information

Authors: RA Y, University of California, Los Angeles (US);HIROOKA Y, University of California, Los Angeles (US);LEUNG W K, University of California, Los Angeles (US);CONN R W, University of California, Los Angeles (US);POSPIESZCZYK A, Institut für Plasmaphysik, Kernforschungsanlage Jülich GmbH, Jülich (DE)
Bibliographic Reference: Paper presented: 36th National Symposium of American Vacuum Society, Boston (US), Aug. 1989
Availability: Available from (1) as Paper EN 35581 ORA
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