Nitrogen retention mechanisms in tokamaks with beryllium and tungsten plasma-facing surfaces

M. Oberkofler (Corresponding Author), G. Meisl, Antti Hakola, A. Drenik, D. Alegre, S. Brezinsek, R. Craven, T. Dittmar, T. Keenan, S. G. Romanelli, R. Smith, D. Douai, A. Herrmann, K. Krieger, U. Kruezi, G. Liang, Ch Linsmeier, M. Mozetic, V. Rohde

    Research output: Contribution to journalArticleScientificpeer-review

    14 Citations (Scopus)

    Abstract

    Global gas balance experiments at ASDEX Upgrade (AUG) and JET have shown that a considerable fraction of nitrogen injected for radiative cooling is not recovered as N2 upon regeneration of the liquid helium cryo pump. The most probable loss channels are ion implantation into plasma-facing materials, co-deposition and ammonia formation. These three mechanisms are investigated in laboratory and tokamak experiments and by numerical simulations. Laboratory experiments have shown that implantation of nitrogen ions into beryllium and tungsten leads to the formation of surface nitrides, which may decompose under thermal loads. On beryllium the presence of nitrogen at the surface has been seen to reduce the sputtering yield. On tungsten surfaces it has been observed that the presence of nitrogen can increase hydrogen retention. The global nitrogen retention in AUG by implantation into the tungsten surfaces saturates. At JET the steady state nitrogen retention is increased by co-deposition with beryllium. The tokamak experiments are interpreted in detail by simulations of the global migration with WallDYN. Mass spectrometry of the exhaust gas of AUG and JET has revealed the conversion of nitrogen to ammonia at percent-levels. Conclusions are drawn on the potential implications of nitrogen seeding on the operation of a reactor in a deuterium-tritium mix.

    Original languageEnglish
    Article number014077
    JournalPhysica Scripta
    Volume2016
    Issue numberT167
    DOIs
    Publication statusPublished - 25 Jan 2016
    MoE publication typeA1 Journal article-refereed

    Fingerprint

    beryllium
    Nitrogen
    tungsten
    Plasma
    nitrogen
    Implantation
    Ammonia
    ammonia
    implantation
    Experiment
    exhaust gases
    Ion Implantation
    nitrogen ions
    inoculation
    Sputtering
    tritium
    Nitrides
    regeneration
    liquid helium
    Mass Spectrometry

    Keywords

    • ammonia
    • AUG
    • ITER
    • JET
    • nitride
    • nitrogen seeding

    Cite this

    Oberkofler, M., Meisl, G., Hakola, A., Drenik, A., Alegre, D., Brezinsek, S., ... Rohde, V. (2016). Nitrogen retention mechanisms in tokamaks with beryllium and tungsten plasma-facing surfaces. Physica Scripta, 2016(T167), [014077]. https://doi.org/10.1088/0031-8949/T167/1/014077
    Oberkofler, M. ; Meisl, G. ; Hakola, Antti ; Drenik, A. ; Alegre, D. ; Brezinsek, S. ; Craven, R. ; Dittmar, T. ; Keenan, T. ; Romanelli, S. G. ; Smith, R. ; Douai, D. ; Herrmann, A. ; Krieger, K. ; Kruezi, U. ; Liang, G. ; Linsmeier, Ch ; Mozetic, M. ; Rohde, V. / Nitrogen retention mechanisms in tokamaks with beryllium and tungsten plasma-facing surfaces. In: Physica Scripta. 2016 ; Vol. 2016, No. T167.
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    abstract = "Global gas balance experiments at ASDEX Upgrade (AUG) and JET have shown that a considerable fraction of nitrogen injected for radiative cooling is not recovered as N2 upon regeneration of the liquid helium cryo pump. The most probable loss channels are ion implantation into plasma-facing materials, co-deposition and ammonia formation. These three mechanisms are investigated in laboratory and tokamak experiments and by numerical simulations. Laboratory experiments have shown that implantation of nitrogen ions into beryllium and tungsten leads to the formation of surface nitrides, which may decompose under thermal loads. On beryllium the presence of nitrogen at the surface has been seen to reduce the sputtering yield. On tungsten surfaces it has been observed that the presence of nitrogen can increase hydrogen retention. The global nitrogen retention in AUG by implantation into the tungsten surfaces saturates. At JET the steady state nitrogen retention is increased by co-deposition with beryllium. The tokamak experiments are interpreted in detail by simulations of the global migration with WallDYN. Mass spectrometry of the exhaust gas of AUG and JET has revealed the conversion of nitrogen to ammonia at percent-levels. Conclusions are drawn on the potential implications of nitrogen seeding on the operation of a reactor in a deuterium-tritium mix.",
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    Oberkofler, M, Meisl, G, Hakola, A, Drenik, A, Alegre, D, Brezinsek, S, Craven, R, Dittmar, T, Keenan, T, Romanelli, SG, Smith, R, Douai, D, Herrmann, A, Krieger, K, Kruezi, U, Liang, G, Linsmeier, C, Mozetic, M & Rohde, V 2016, 'Nitrogen retention mechanisms in tokamaks with beryllium and tungsten plasma-facing surfaces', Physica Scripta, vol. 2016, no. T167, 014077. https://doi.org/10.1088/0031-8949/T167/1/014077

    Nitrogen retention mechanisms in tokamaks with beryllium and tungsten plasma-facing surfaces. / Oberkofler, M. (Corresponding Author); Meisl, G.; Hakola, Antti; Drenik, A.; Alegre, D.; Brezinsek, S.; Craven, R.; Dittmar, T.; Keenan, T.; Romanelli, S. G.; Smith, R.; Douai, D.; Herrmann, A.; Krieger, K.; Kruezi, U.; Liang, G.; Linsmeier, Ch; Mozetic, M.; Rohde, V.

    In: Physica Scripta, Vol. 2016, No. T167, 014077, 25.01.2016.

    Research output: Contribution to journalArticleScientificpeer-review

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    AU - Oberkofler, M.

    AU - Meisl, G.

    AU - Hakola, Antti

    AU - Drenik, A.

    AU - Alegre, D.

    AU - Brezinsek, S.

    AU - Craven, R.

    AU - Dittmar, T.

    AU - Keenan, T.

    AU - Romanelli, S. G.

    AU - Smith, R.

    AU - Douai, D.

    AU - Herrmann, A.

    AU - Krieger, K.

    AU - Kruezi, U.

    AU - Liang, G.

    AU - Linsmeier, Ch

    AU - Mozetic, M.

    AU - Rohde, V.

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    KW - AUG

    KW - ITER

    KW - JET

    KW - nitride

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