Helium retention and early stages of helium-vacancy complexes formation in low energy helium-implanted tungsten

Lhuillier, Pierre-Emile; Belhabib, Taieb; Desgardin, P.; Courtois, Blandine; Sauvage, Thierry; Barthe, M.F.; Thomann, Anne-Lise; Brault, Pascal; Tessier, Yves

doi:10.1016/j.jnucmat.2012.09.001

Cited by 75 publications

(28 citation statements)

References 27 publications

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“…Second, this growth is insaturable, meaning a "single" trap site can accommodate a limitless number of He atoms 18 . Third, He thus drives the generation of vacancies and interstitials within the material [19][20][21] .…”

Section: Introductionmentioning

confidence: 99%

Diffusion and transformation kinetics of small helium clusters in bulk tungsten

2014

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The production of energy through nuclear fusion poses serious challenges related to the stability and performance of materials in extreme conditions. In particular, the constant bombardment of the walls of the reactor with high doses of He ions is known to lead to deleterous changes in their microstructures. These changes follow from the aggregation of He into bubbles that can grow and blister, potentially leading to the contamination of the plasma, or to the degradation of their mechanical properties. We computationally study the behavior of small clusters of He atoms in W in conditions relevant to fusion energy production. Using a wide range of techniques, we investigate the thermodynamics of the clusters and their kinetics in terms of diffusivity, growth, and breakup, as well as mutation into nano-bubbles. Our study provides the essential ingredients to model the early stages of He exposure leading up to the nucleation of He bubbles. arXiv:1406.6418v1 [cond-mat.mtrl-sci]

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Section: Introductionmentioning

confidence: 99%

Diffusion and transformation kinetics of small helium clusters in bulk tungsten

2014

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“…In order to better understand its swelling and embrittlement observed in special irradiation conditions, we use PAS to study the vacancy defects properties in this material. We have first shown the migration and agglomeration of single vacancy in the temperature range from 473 to 600K [9] and its interaction with helium [10]. More recently we have observed the formation of vacancy clusters in self ion irradiated W and the effect of the temperature on the size of these clusters.…”

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confidence: 97%

Positron Annihilation Spectroscopy to Characterize Irradiation Induced Vacancy Type Defects in Materials for Nuclear Fission and Fusion

Barthe

2016

EPJ Web of Conferences

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In nuclear reactors, materials are submitted to irradiations and modification of their macroscopic properties such as swelling or hardening is observed… It is of first importance to understand the origin of these evolutions and how damage at the atomic scale such as vacancy and interstitials type defects can interact with each other or with solutes and impurities to make the microstructure evolved. So the properties of defects have to be determined.Positron annihilation spectroscopy (PAS) is a well-established technique to characterize materials [1]. Due to its positive charge, positron is sensitive to the local variations of the Coulomb potential in solids. As the anti-particle of the electron, both particles can annihilate leading to the emission of gamma rays with energy depending on the momentum of the electron positron annihilated pair. The detection of these gamma rays arises original information on the defects because positron can be trapped and annihilate in localized state such as vacancies. Two different and complementary annihilation characteristics can be measured. Firstly Positron Annihilation Lifetime Spectrometer (PALS) allows to measure the positron lifetime which depends on the local electron density at the annihilation site. The second characteristic is the momentum distribution of the electron positron annihilated pairs and is obtained by measuring the energy spectrum of the gamma annihilation rays using a Doppler Broadening Spectrometer (DBS). Both characteristics give the signature of the defects and allow determining some of their properties such as their nature, concentration, chemical environment... By using slow positron accelerators which produce monokinetic positrons beams with energy varying from 0.1 to 30 keV it is possible to study the depth profile of defects in thin layers from 0.1 to about 5 µm depending on the density of materials with a resolution of the order of 0.1xdepth. 22Na source based beams [2] or user facilities taking advantages of high positrons flux available around nuclear reactor (FRMII, Garching [3]) or LINAC( as in AIST in Japan [4]) are now available to study defects in materials. PAS has numerous advantages among them, it is non-destructive and can be used for conducting as well as insulating materials crystalline or amorphous. This technique is especially useful to probe vacancy defects in metals for which it is one of the only direct characterization. The annihilation characteristics can be predicted by first principle calculations and these data when available can help to identify defects. Sensitive to the single vacancy, PAS can allow to determine the size of the vacancy clusters up to a maximum of 1 nm approximately in the concentration range from 10 15 to a few 10 18 cm -3 .In nuclear science this technique is very powerful to characterize not only damage induced by irradiation but also to determine some fundamental properties of defects that are required for modeling of the microstructural evolution of materials such as formation, migration, agglomeratio...

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“…As mentioned before, a negative S/S value is specific of He insertion in vacancy defects. It is characteristic of the filling of the W vacancies by He [15,24,25]. Thus the observed evolution with increasing fluence below the saturation step indicates that accumulation of He inside the W lattice induces the displacement of W atoms to form vacancies where He is trapped.…”

Section: Characteristics Of He Implantation In W At Kinetic Energy Ofmentioning

confidence: 93%

“…Thus the technique is particularly sensitive to the nature and concentration of vacancy defects in the sample. More details on DB-PAS could be found in [15,21].…”

Section: Positron Annihilation Spectroscopymentioning

confidence: 99%

“…The impinging ion fluences were chosen to be below and above 2.510 20 He.m -2 , fluence limit of the accumulation of He atoms within W vacancies (He-vacancy complexes) at an implantation energy of 300 eV [14,15]. The fluence is the total number of impinging ions for a given bombardment duration; it is calculated from the ion flux obtained from the measurement of the 5 ionic current at the substrate.…”

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