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A major prerequisite for operating present-day tokamaks under conditions relevant to thermonuclear fusion is that the confined hydrogen plasma is almost free of impurities. These cause energy losses by radiation which increase with increasing atomic number (Z) of the impurities. The high Z contaminants are liberated predominantly by sputtering, the low Z impurities (O,C) mainly by chemical erosion. Since graphite tiles cover large fractions of the metallic first wall, it is necessary to minimise the chemical erosion of carbon. Successful conditioning techniques, such as carbonisation and boronisation, are described. In particular, boronisation has almost completely suppressed the metal liberation and has decreased drastically the oxygen contamination of the plasma due to the high getter efficiency of the boron. After a short review of the development of the methods used at the Jülich tokamak TEXTOR, a more detailed discussion of the technique, the properties of the protective coatings and their interaction with the plasma is presented. The problem of hydrogen isotope control in such layers and hence in the plasma is addressed.

Additional information

Authors: ESSER H G, Institut für Plasmaphysik, Kernforschungsanlage Jülich GmbH, Jülich (DE)
Bibliographic Reference: Article: Proceedings of the 10th International Symposium on Plasma Chemistry, Vol. 1 (1991) 3.1 i 1
Record Number: 199210240 / Last updated on: 1994-12-02
Original language: en
Available languages: en