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In addition to discharge cleaning techniques, gettering of tokamaks has been used since 1975 as a powerful tool for controlling the impurity influx into fusion plasmas. Initially, high-Z metals such as Ti and Cr, evaporated onto the walls of the fusion devices, were used. After the introduction of carbon as a low-Z plasma facing material for the large tokamaks, new techniques were developed to optimise the low-Z aspects of wall materials. These were the boronisation technique and the evaporation of Be in conjunction with the use of Be limiters. The different gettering techniques and the observed results are reviewed, focussing on a comparison of the tokamak performance achieved with boronisation and with the use of beryllium. It is shown that in all cases of gettering, the most important mechanism for the improved machine performance is the control of the oxygen impurity influx. Very similar results are found for the impurity control potential. The added benefit of boronisation and Be gettering arises from the low-Z of the materials. Both techniques essentially lead to the same machine performance and are suitable for use in future devices.

Additional information

Authors: WINTER J, Institut für Plasmaphysik, Kernforschungsanlage Jülich GmbH, Jülich (DE)
Bibliographic Reference: Report: Jül-2371 EN (1990) 61 pp.
Availability: Available from Zentralbibliothek der Kernforschungsanlage Jülich GmbH, Postfach 1913, 5170 Jülich (DE)
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