Interaction of candidate plasma facing materials with tokamak plasma in COMPASS

Jiří Matějíček, Vladimír Weinzettl, Anna Macková, Petr Malinský, Vladimír Havránek, Diana Naydenkova, Veronika Klevarová, Per Petersson, Pawel Gasior, Antti Hakola, Marek Rubel, Elzbieta Fortuna, Jukka Kolehmainen, Sanna Tervakangas

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    Abstract

    The interaction of tokamak plasma with several materials considered for the plasma facing components of future fusion devices was studied in a small-size COMPASS tokamak. These included mainly tungsten as the prime candidate and chromium steel as an alternative whose suitability was to be assessed. For the experiments, thin coatings of tungsten, P92 steel and nickel on graphite substrates were prepared by arc-discharge sputtering. The samples were exposed to hydrogen and deuterium plasma discharges in the COMPASS tokamak in two modes: a) short exposure (several discharges) on a manipulator in the proximity of the separatrix, close to the central column, and b) long exposure (several months) at the central column, aligned with the other graphite tiles. During the discharges, standard plasma diagnostics were used and a local emission of spectral lines in the visible near ultraviolet regions, corresponding to the material erosion, was monitored. Before and after the plasma exposures, the sample surfaces were observed using scanning electron microscopy, the coatings thickness was measured using Rutherford backscattering spectroscopy, and the concentration profiles of hydrogen and deuterium were measured by elastic recoil detection analysis. The uniformity of the coatings and their thickness was verified before the exposure. After the exposure, no reduction of the thickness was observed, indicating the absence of ‘global’ erosion. Erosion was observed only in isolated spots, and attributed to unipolar arcing. Slightly larger erosion was found on the steel coatings compared to the tungsten ones. Incorporation of deuterium in a thin surface layer was observed, in dependence on the exposure mode. Additionally, boron enrichment of the long-exposure samples was observed, as a result of the tokamak chamber boronization.

    Original languageEnglish
    Pages (from-to)102-119
    Number of pages18
    JournalJournal of Nuclear Materials
    Volume493
    DOIs
    Publication statusPublished - 1 Sep 2017
    MoE publication typeA1 Journal article-refereed

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  • Cite this

    Matějíček, J., Weinzettl, V., Macková, A., Malinský, P., Havránek, V., Naydenkova, D., Klevarová, V., Petersson, P., Gasior, P., Hakola, A., Rubel, M., Fortuna, E., Kolehmainen, J., & Tervakangas, S. (2017). Interaction of candidate plasma facing materials with tokamak plasma in COMPASS. Journal of Nuclear Materials, 493, 102-119. https://doi.org/10.1016/j.jnucmat.2017.06.009