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

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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.

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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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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T1 - Nitrogen retention mechanisms in tokamaks with beryllium and tungsten plasma-facing surfaces

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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N2 - 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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KW - ammonia

KW - AUG

KW - ITER

KW - JET

KW - nitride

KW - nitrogen seeding

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