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Redeposition of eroded carbon on the walls of fusion devices together with the D-T plasma forms amorphous, hydrogenated carbon films with D-T concentrations ranging from deposition conditions. The trapping of large amounts of hydrogen isotopes in these so-called deposited layers may represent a potential safety hazard during D-T operation because large amounts of tritium will be retained in these layers. To erode carbon films and deplete the T concentration an experimental investigation was performed using O(2), D(2), H(2), H(2)O and O(2)/H(2), electron cyclotron resonance low-pressure discharges. Real-time in-situ ellipsometry was applied to measure the optical response of the layers during deposition and erosion. This allows a precise determination of the optical constants and film thickness. From these data the deposition and erosion rates are calculated. The dependence of the erosion rates on substrate temperature, applied ion energy, gas composition and discharge pressure for two different types of a -C:H films was measured.

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Authors: JACOB W, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE);LANDKAMMER B, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE);WU C H, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE)
Bibliographic Reference: Article: Journal of Nuclear Materials, 266-269 (1999), 552-556
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