Comportement du deutérium dans les matériaux d’intérêt pour la fusion thermonucléaire

Elodie Bernard 1
1 LEEL - UMR 3685 - Laboratoire d'Etudes des Eléments Légers
NIMBE UMR 3685 - Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Energie (ex SIS2M)
Abstract : Plasma-wall interactions play an important part while choosing materials for the first wall in future fusion reactors. Moreover, the use of tritium as a fuel will impose safety limits regarding the total amount present in the tokamak. Previous analyses of first-wall samples exposed to fusion plasma highlighted an in-bulk migration of deuterium (used as an analog to tritium) in carbon materials. Despite its limited value, this retention is problematic: contrary to co-deposited layers, it seems very unlikely to recover easily the deuterium retained in such a way. Because of the difficult access to in situ samples, most published studies on the subject were carried out using post-mortem sample analysis.In order to access to the dynamic of the phenomenon and come apart potential element redistribution during storage, we set up a bench intended for simultaneous low energy ion implantation, reproducing the deuterium interaction with first-wall materials, and high energy microbeam analysis. Nuclear reaction analysis performed at the micrometric scale (µNRA) allows characterizing deuterium repartition profiles in situ. This analysis technique was checked to be non-perturbative.We observed from the experimental data set that the material surface (depth 0-1 µm) displays a high and nearly constant deuterium content, with a uniform distribution. On the contrary, in-bulk deuterium (1-11 µm) localizes in preferential trapping sites related to the material microstructure. In-bulk deuterium inventory seems to increase with the incident fluence, in spite of the wide data scattering attributed to the structure variation of studied regions. Deuterium saturation at the surface as well as in-depth migration is instantaneous; in-vacuum storage leads only to a small deuterium global desorption.Observations made via µNRA were combined with results from other characterization techniques. X-ray µtomography allowed identifying porosities as the preferential trapping sites for in-depth deuterium retention. Raman µspectrometry disclosed the formation of an amorphous layer at the surface, very thin (~30 nm) and deuterium saturated, following deuterium irradiation.At last, we confronted the experimental characterization obtained with existing models for deuterium behaviour in carbon materials and proposed a simple and original one. Considering that in-depth retention is due to deuterium implantation and Coulombian diffusion at the open porosity surfaces, it allows reproducing qualitatively the observed experimental profiles.
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Elodie Bernard. Comportement du deutérium dans les matériaux d’intérêt pour la fusion thermonucléaire. Autre [cond-mat.other]. Université Paris Sud - Paris XI, 2012. Français. ⟨NNT : 2012PA112250⟩. ⟨tel-00879145⟩

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