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Modeling of hydrogen isotopes retention in plasma-facing components of magnetic fusion reactor

par Caroline CHAMPENOIS - publié le

séminaire général

vendredi 19 decembre, à 14:00, service 322 du campus Saint-Jérôme

Jerome Guterl,
UCSD, La Jolla, USA

Résumé (J. Guterl, R.D. Smirnov, S.I. Krasheninnikov) :
Plasma-material interactions may strongly influence plasma performance and life-time of future magnetic fusion devices. Retention and recycling of hydrogen isotopes in plasma-facing components (PFCs) may indeed lead to dynamics plasma-material interactions and significant accumulation of tritium in material [1]. Understanding the multifaceted physics of hydrogen retention in PFCs is thus crucial, but remains challenging due to the wide spectrum of retention processes on PFC surface (erosion, co-deposition, etc.) and in PFC bulk (trap sites, bubbles, etc.) induced by long-time exposure of PFCs to high flux of energy and particles[2].
We revisit in this talk some aspects of reaction-diffusion models used to describe hydrogen retention in metallic PFCs. We first focus on analysis of thermal desorption spectroscopy (TDS) considering only one type of defects (traps) in material and neglecting surface effects. We show that solute hydrogen concentration in retention region usually remains in equilibrium during TDS. In this regime, analytic description of thermal desorption spectra indicates that trapping of solute hydrogen during TDS cannot be ignored. Main features of thermal desorption are then analytically described and refined interpretation of Arrhenius plots is proposed. We also highlight the use of tails and skewness of thermal desorption spectra to estimate activation energy of diffusion and to determine whether surface effects affect hydrogen release or not during TDS.
Hydrogen retention induced by large number of traps is addressed in the second part. Modeling of TDS with large number of traps (n>3) is presented for the first time, and is illustrated with several experimental thermal desorption spectra which are consistently reproduced using several traps with a fixed broad spectrum of detrapping energies. Values of detrapping energies are shown to be in agreement with values predicted by DFT models [3] when several hydrogen atoms are trapped in one material vacancy. Possible applications of retention modeling with large numbers of traps are discussed.

[1] J. Roth and K. Schmid, Phys. Scr., 014031 (2011)
[2] R.A. Causey, J. Nucl. Mater. 300 (2002) 91
[3] Y. Ferro et al, 2014 Joint ICTP-IAEA Conference

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