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Starting with carbonised walls as a reference condition, the TEXTOR vessel was first flushed with reactive diborane gas (B(2)H(6)), and then the inner plasma facing surface was boronised with a-C/B:H. After the introduction of the boron into the machine a drastic decrease of the oxygen contamination of the plasma was observed. However, the amount of oxygen collected on graphite targets in the scrape-off layer (SOL) increased. This behaviour is explained with gettering of the oxygen ions by the boron. The oxygen forms stable oxides with the boron due to energetic ion deposition keeping the plasma contamination low. The observations also allow the quantification of two other contributory terms: sticking of oxygen ions and the oxygen absorption by uptake from air. For the external analysis, the graphite targets were studied by ion beam analysis (O, B, D metals). XPS investigations showed the bonding state between oxygen and boron.

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Authors: WIENHOLD P, Forschungszentrum Jülich GmbH, Institut für Plasmaphysik (DE);VON SEGGERN J, Forschungszentrum Jülich GmbH, Institut für Plasmaphysik (DE);RUBEL M, MSI, Stockholm (SE);GUDOWSKA I, MSI, Stockholm (SE);KÜNZLI H, University of Basel, Institute of Physics (CH)
Bibliographic Reference: Article: Vacuum, Vol. 43 (1992) No. 5-7, pp. 745-748
Record Number: 199310249 / Last updated on: 1994-11-29
Original language: en
Available languages: en