European Spallation Source

Résumé

L'ESS (pour European Spallation Source en anglais, soit en français source européenne de spallation) est le nom d'une future installation de recherche scientifique sur la matière utilisant des techniques de dispersion des neutrons. La construction à Lund, en Suède, a commencé le 30 juin 2014, avec des prévisions de mise en service en 2019 et une installation entièrement opérationnelle en 2025. En 2016, le Comité directeur de l'ESS rassemble 16 pays partenaires. La future installation est composée d'un accélérateur linéaire dans lequel des protons sont accélérés et projetés sur une cible en tungstène. Ces deux sous-ensembles constituent la source de neutrons thermiques et froids. Avec ce procédé, des émissions intenses de bouffées de neutrons sont conduites dans des lignes de guidage et de tri jusqu'aux stations d'expérimentation où sont menées des recherches avancées sur la matière dans les domaines de l'énergie, les télécommunications, la fabrication, les transports, les technologie

Source officielle

https://fr.wikipedia.org/wiki/European_Spallation_Source

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NNeutron and X-ray scattering are some of the most powerful and versatile experimental methods to study the structure and dynamics of materials on the atomic scale. This course covers basic theory, instrumentation and scientific applications of these experimental methods.

This lecture gives an introduction to Solid State Physics, namely to their crystal and electronic structure, their magnetic properties, as well as to their thermal and electric conductance. The level is that of the book by Ashcroft & Mermin. The lecture is for Physics Students in their 3rd year

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The neutron Time-Of-Flight (n_TOF) facility at the European Laboratory for Particle Physics (CERN) is a pulsed white-spectrum neutron spallation source producing neutrons for two experimental areas: EAR1, located 185 m downstream of the spallation target, and EAR2, located 20 m above the target. The facility is based on a lead target impacted by a high-intensity 20 GeV/c proton beam. It is designed to study neutron-nucleus interactions for neutron kinetic energies from a few meV to several GeV, with applications in nuclear astrophysics, nuclear technology, and medical research. The facility is undergoing a major upgrade in 2019-2020, which will include the installation of the new third-generation target. The second-generation target consists in a water-cooled lead cylinder, while the new target will be cooled by nitrogen to avoid erosion-corrosion phenomena and contamination of the cooling water with radioactive lead spallation products. The new design will be optimized also for the vertical flight path. The operation of the new spallation target will start in 2021. This paper presents an overview on the evolution of the design and on the related R&D activities (including beam irradiation tests) carried out to ensure the best performance for both experimental areas and avoid the contamination issues of the previous targets.

IOS PRESS2020

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Embrittlement induced by the synergistic effects of radiation damage and helium in structural steels

Kun Wang

Ferritic/martensitic steels are candidate materials for fusion reactor structural components, liquid metal containers of spallation neutron sources, and accelerator driven systems, with good radiation resistance and thermo-mechanical properties. However, embrittlement resulting from the combined effects of radiation induced displacement damage (measured in dpa = displacement per atom) and transmutation products, especially helium gas, is one of the key issues. Four different steels were selected for mechanical and microstructural studies to understand the mechanisms of embrittlement induced by the combined effects of displacement damage and helium after irradiation in SINQ, the Swiss spallation source. The irradiations conditions were in the range: 10.7 ¿ 20.4 dpa with 850-1750 appm He at 160-300 °C. The evolution of the mechanical properties after irradiation was investigated by tensile and hardness tests. Radiation-induced defect clusters and helium bubbles were quantified by transmission electron microscopy (TEM). Emphasis was put on the deformation mechanisms under the different observed fracture mode, (ductile, quasi-cleavage and intergranular), whose occurrence depends on the irradiation conditions (dpa, He content and irradiation temperature). The tensile stress-strain curves and the scanning electron microscopy images of fracture surfaces showed distinct fracture mechanisms under different irradiation and test conditions. The tensile tests showed a yielding stress increase and loss of ductility of irradiated specimens. Hardness was measured on the specimens before tensile testing. The hardness results demonstrated an increasing trend with irradiation dose and helium content. TEM observations were done for all irradiated fractured specimens. Small defect clusters were observed in the 12.3 dpa specimen, but large defect clusters with loop-shape were very few. In the specimens of 17.2, 17.7 and 20.4 dpa, many large dislocation loops were detected besides small clusters. In addition, helium bubbles were observed in all specimens. The average size of defect clusters increased from 4.2 nm to 11.8 nm with dose increasing from 12.3 dpa to 20.4 dpa, whereas the number density did not change significantly. Meanwhile, the average size of visible helium bubbles increased from 1.03 nm to 1.93 nm. The microstructures in deformed area of irradiated specimens were observed and defect free channels with {110} and {112} slip planes were found in some specimens, indicating plastic flow localization. The average width of the channels is about 100 nm. Regarding the brittle samples, the TEM-lamella were extracted directly below intergranular fracture surfaces or cleavage surfaces by focused ion beam. Strikingly, deformation twinning was observed as the main feature in three irradiated specimens at high dose. Only twins with {112} planes were observed in all of these samples. The average thickness of twins is about 34 nm. Twins started from a fracture surface became gradually thinner with distance away from the fracture surface and stopped in the matrix finally. Features such as twin-precipitates interaction, twin-grain boundary and/or lath boundary interaction were observed. Twinning bands were seen to be arrested by grain boundaries or large precipitates, but could penetrate martensitic lath boundaries. Unlike the case of defect free channels, inside twins small defect-clusters, dislocation loops and dense small helium bubbles were observed.

EPFL2015

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Continuous Angular Multiple Energy Analysis Spectrometer Report on Instrument Concept and Scientific Case

Paul Gregory Freeman

Abstract This work unit proposes to construct a cold indirect geometry time of flight spectrometer for performing inelastic neutron scattering experiments optimized for optimal efficiency in the horizontal scattering plane at the European Spallation Source. A horizontal geometry is chosen for compatibility with performing neutron scattering experiments under extreme conditions. The instrument concept is called the Continuous Angular Multiple Energy Analysis Spectrometer, CAMEA. In this report we will outline the science case for CAMEA, highlighting the science that could be performed on CAMEA, the demand for an instrument of this type, aswell as identifying the current and future technology in neutron scattering that can be utilized. The basic concept of CAMEA is to maximize neutron count rates for scattering in the horizontal plane, with a quasi-continuous angular coverage of the scattered neutrons. High neutron detection efficiency will be obtained by using banks of concentric analysers placed behind each other, analysing different neutron energies of the scattered neutrons. Optimization of a horizontal scattering geometry has been chosen to be compatible with extreme sample environments and the ability to perform inelastic neutrons scattering studies. We will highlight how this provides a generation of advancement in inelastic neutron scattering under extreme environments, and what new possibilities for scientific studies CAMEA enables in inelastic neutron scattering.

2014

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Embrittlement induced by the synergistic effects of radiation damage and helium in structural steels

Kun Wang

EPFL2015