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Lhuillier P.E.,French National Center for Scientific Research | Lhuillier P.E.,University of Orleans | Belhabib T.,French National Center for Scientific Research | Belhabib T.,University of Orleans | And 11 more authors.
Journal of Nuclear Materials | Year: 2011

The behavior of tungsten under irradiation and helium implantation is a major stake of the material-related issues of fusion reactors. In this perspective the fate of helium in tungsten was studied by mean of several characterization techniques. The aim of this study is to highlight the trapping mechanisms of helium in tungsten and their correlation with implantation-induced defects. Helium was implanted into tungsten at two different energies, 0.32 and 60 keV. The helium was studied as a function of temperature by using nuclear reaction analysis. The migration propensity of helium was correlated with the release rate of helium after annealing at a given temperature. In addition, the helium trapping sites and evolution with post-implantation annealing was investigated using Doppler-Broadening Positron Annihilation Spectroscopy. It has been shown that the release, and so the migration, of helium is guided by the concentration of implantation-induced defects and the nature of the helium traps created during the implantation. © 2010 Elsevier B.V. All rights reserved. Source


Lhuillier P.E.,French National Center for Scientific Research | Lhuillier P.E.,University of Orleans | Debelle A.,French National Center for Scientific Research | Debelle A.,University of Orleans | And 10 more authors.
Journal of Nuclear Materials | Year: 2011

The behavior of helium in 3He implanted tungsten has been studied using Nuclear Reaction Analysis as a function of the post-implantation annealing temperature. Two different implantation conditions have been investigated: medium energy (60 keV), and low energy (0.3 keV), which exhibit drastically different helium release behavior. In the case of medium energy implantation, desorption starts from 1550 K and seems to be due to the dissociation of single helium-vacancy complexes (He-V1). At 1873 K the released fraction reaches 75% that suggests the presence of a second type of helium trapping site. In the case of low energy implantation, desorption is observed from 400 K (slightly above room temperature) and indicates the presence of shallow helium traps the nature of which is discussed. The released fraction of helium saturates at ∼60% at the temperature of 1473 K which could be due to helium trapping at single He-V1 complexes. © 2010 Elsevier B.V. All rights reserved. Source


Lhuillier P.E.,French National Center for Scientific Research | Lhuillier P.E.,University of Orleans | Belhabib T.,French National Center for Scientific Research | Belhabib T.,University of Orleans | And 11 more authors.
Journal of Nuclear Materials | Year: 2013

Tungsten has been selected as the material of the divertor of the ITER fusion reactor. In operation, tungsten will be submitted to high alpha particles bombardment. The consequence of helium implantation is a major issue for the reliability of tungsten components. The aim of the study was to investigate the behavior of helium implanted in tungsten at low energy and low flux. 320 eV Helium ions were introduced by plasma immersion at the flux of 2.5 × 1018 ion/m-2/s-1. The helium behavior was investigated by Nuclear Reaction Analysis and the evolution of the tungsten lattice by Positron Annihilation Spectroscopy (PAS). Helium-implanted tungsten exhibits a low retention rate (13.6% at 9.4 × 1019 He m -2) which decreases with the implantation fluence. The desorption of helium starts at low temperature (<400 K). SEM analysis after annealing over 973 K shows sparse pores probably due to bubbles opening at the surface. The creation of helium-filled defects in the near surface layer (0.5 to ∼20 nm) was followed by PAS. A low level of damages was introduced by 12 MeV proton irradiation, prior to He introduction and allowed to examine the influence of pre-existing defects on the helium trapping. The PAS results suggest that the early stage of the formation of helium-filled vacancy clusters does not require the presence of pre-existing vacancy and thus proceed from the trap mutation phenomenon. © 2012 Elsevier B.V. All rights reserved. Source

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