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Neutron production with a 10 kW HiCANS based on SATELIT, a CEA-Saclay target with liquid lithium
No full textInternational audienceHigh-Current Accelerator-driven Neutron Sources (HiCANS) are currently under development across Europe to address the shortage of medium-scale neutron sources, as many research nuclear reactors have been decommissioned over the past several years. At CEA-Saclay, a HiCANS has been developed utilizing the IPHI accelerator, which delivers a 3 MeV proton beam with a current of up to 100 mA, and the CEA-Saclay liquid lithium target named SATELIT. In 2024-2025, a successful experimental campaign was conducted, during which a 10 kW proton beam was directed at the liquid lithium target for nearly 100 h to generate neutrons via the 7Li(p,n)7Be nuclear reaction. Throughout the experimental campaign, a total deposited beam power of 840~kW.h was accumulated, including two continuous operational days exceeding 11 h each. A polyethylene moderator coupled with SATELIT enabled the extraction of a thermal neutron beam, with a flux measured at 1.4 m from the extraction point exceeding n.cm.s, which is sufficient for numerous neutron applications. The next step for the long-term operation of this facility involves developing strategies to mitigate the radiological concerns associated with the accumulation of 7Be within the system. Overall, this work demonstrates that such facilities can play a significant role in the future of medium-scale neutron sources in Europe
Beyond Stage IV: Quasar and Galaxy Clustering and the Fundamental Physics of the 2040s
No full textInternational audienceStage IV galaxy surveys (DESI, 4MOST, MOONS, Euclid) are establishing precision constraints on cosmological parameters through baryon acoustic oscillations and redshift-space distortions, yet fundamental questions on neutrino masses, inflationary physics, and the nature of gravity remain beyond their reach. We present a science case for next-generation wide-field spectroscopic surveys targeting with simultaneous observations of thousands of galaxies, quasars, and emission-line galaxies. Such surveys would deliver transformative advances: (i) cosmological constraints on absolute neutrino masses (), three times more stringent than Stage IV, enabling resolution of the neutrino mass hierarchy; (ii) detection of primordial non-Gaussianity at the level of , probing multi-field inflation; (iii) measurements of structure growth spanning cosmic time to constrain dark energy and test gravitational modifications. Achieving these goals requires revolutionary advances in spectroscopic multiplexing ( simultaneous spectra), sub- redshift precision at scale, and field-level inference techniques exploiting higher-order clustering statistics. We demonstrate that the proposed Wide-field Spectroscopic Telescope concept provides a technically feasible and scientifically compelling path to unlock the physics of neutrinos, inflation, and gravity that will remain inaccessible to Stage IV surveys
Leptonic and Hadronic Models of High-energy Nebula Around V4641 Sgr
No full textInternational audienceA prominent, 200-pc-scale high-energy nebula surrounding the microquasar V4641~Sgr is the brightest known gamma-ray source in the Southern sky at . In this paper, we develop self-consistent leptonic, hadronic, and leptohadronic models that reproduce both the observed spectrum and morphology of the source. Purely leptonic models are energetically more favorable yet they require rather specific morphological assumptions. The gamma-ray morphology of the source can be better explained within a hadronic scenario based on the identification of cold gas structures spatially correlated with the observed gamma-ray emission. However, a purely hadronic model for the source emission requires a substantial energy reservoir in protons and fails to reproduce the extended X-ray emission recently detected by XRISM. We show that emission including a combination of leptonic and hadronic components can reproduce both the spectral and morphological properties of the source. We provide predictions for the X-ray and neutrino spectra of~the~nebula that can discriminate the hadronic and leptonic contributions to the overall source signal
Joint cosmological fits to DESI-DR1 full-shape clustering and weak gravitational lensing in configuration space
No full textInternational audienceWe present a joint -pt cosmological analysis of auto- and cross-correlations between the Dark Energy Spectroscopic Instrument Data Release 1 (DESI-DR1) Bright Galaxy Survey (BGS) and Luminous Red Galaxy (LRG) samples and overlapping shear measurements from the KiDS-1000, DES-Y3 and HSC-Y3 weak lensing surveys. We perform our analysis in configuration space and, in addition to the cosmic shear correlation functions for each weak lensing dataset, we fit the tangential shear of the weak lensing source galaxies around DESI lens galaxies. Finally, we make use of the anisotropic BGS and LRG clustering information by fitting the full shape of the two-point correlation function multipoles measured over the full DESI-DR1 footprint, presenting the first full-shape analysis of DESI measurements in configuration space. We find that the addition of weak lensing information serves to improve, with respect to the clustering-only case, the measurements of the power spectrum amplitude parameters and by and , respectively. It also improves measurements of the linear bias of the lens galaxies by , depending on the tracer. Our results show excellent consistency, regardless of the weak lensing survey considered, and are furthermore consistent with a companion analysis that fits -pt correlations including DESI projected clustering measurements, as well as the results published by the weak lensing collaborations themselves. Our measured values for weak lensing amplitude are , , , which are below the value preferred by Planck. Finally, our clustering-only results are in good agreement with the Fourier space full-shape analysis of all DESI tracers
Du serment doctoral d'intégrité scientifique à un serment personnel : un atelier d'écriture et de réflexion sur la responsabilité et le rôle des scientifiques dans la société
No full textNous présentons un atelier de réflexion sur le serment doctoral d’intégrité scientifique et d’écriture d’un serment personnel, destiné aux doctorantes et doctorants, et plus généralement au personnel de la recherche. L’atelier est proposé depuis 2025 comme formation à l’éthique de la recherche dans quelques écoles doctorales en France. Avec un dispositif original, il permet d’examiner plusieurs aspects de la pratique et des enjeux sociaux-environnementaux de le Recherche : la responsabilité des scientifiques, l’engagement, le rôle des sciences dans l’anthropocène, la place de l’éthique et de l’intégrité dans la pratique du doctorat et des sciences en général
Algebraic hierarchical partitioning to improve H-matrix compression
No full textInternational audienceSolving large dense problems is a challenging task in many industrial applications such as computational electromagnetics. H-matrices may solve these problems efficiently while significantly reducing storage requirements. The compression rate and efficiency of H-matrices depend on the partitioning of the unknowns. This partitioning must be hierarchical and should respect geometric criteria in order to maximize compression. A fixed block size constraint is added to accommodate load balancing and performance concerns on HPC runtime systems. Numerous partitioning schemes exist, but few meet all requirements. Some geometric methods such as recursive coordinates bipartition, space-filling curves and cobblestone sorting provide acceptable results whereas algebraic graph partitioner generally do not. We propose a method to build a graph from the mesh to combine geometric and physical properties, suited to provide adapted partitions reliably. We review fitting geometric partitioning methods and compare them to our algebraic approach using relevant metrics such as compression rates before and after factorization and execution time of H-matrix assembly, factorization and solving step. We also study resulting partitions based on their volume, overlap and distance. Our contribution shows significant improvements in compression rates and execution times for complex 3D objects with multiple materials which are representative of industrial applications.</div
The Binary Fraction of Stars in the Dwarf Galaxy Ursa Minor via Dark Energy Spectroscopic Instrument
No full textInternational audienceWe utilize multi-epoch line-of-sight velocity measurements from the Milky Way Survey of the Dark Energy Spectroscopic Instrument to estimate the binary fraction for member stars in the dwarf spheroidal galaxy Ursa Minor. Our dataset comprises 670 distinct member stars, with a total of more than 2,000 observations collected over approximately one year. We constrain the binary fraction for UMi to be and , with the binary orbital parameter distributions based on solar neighborhood observation from Duquennoy & Mayor (1991) and Moe & Di Stefano (2017), respectively. Furthermore, by dividing our data into two subsamples at the median metallicity, we identify that the binary fraction for the metal-rich ([Fe/H]>-2.14) population is slightly higher than that of the metal-poor ([Fe/H]<-2.14) population. Based on the Moe & Di Stefano model, the best-constrained binary fractions for metal-rich and metal-poor populations in UMi are and , respectively. After a thorough examination, we find that this offset cannot be attributed to sample selection effects. We also divide our data into two subsamples according to their projected radius to the center of UMi, and find that the more centrally concentrated population in a denser environment has a lower binary fraction of , compared with for the subsample in more outskirts
Antiferromagnetic skyrmions in spintronics
No full textThe following chapter starts from a base of fundamental physics and from this explains the major advantages that antiferromagnetic skyrmions can provide for applications
H.E.S.S. detection and multi-wavelength study of the 1 blazar PKS 034627
No full textInternational audiencePKS 0346-27 is a Low Synchrotron Peaked (LSP) blazar at redshift 0.991. The very-high-energy (VHE, E > 100 GeV) spectra of blazars are always affected by absorption by the Extragalactic Background Light (EBL) and subsequently, no blazars have been detected in VHE -rays at redshifts exceeding 1. Extending the redshift range of VHE-detected blazars to will yield insights into the cosmological evolution of both the VHE blazar population and the EBL. This is the goal of a target-of-opportunity (ToO) programme by H.E.S.S. to observe flaring high-redshift () blazars. We report on H.E.S.S. ToO and multi-wavelength observations of the blazar PKS 034627. Along with H.E.S.S., simultaneous data from {\it Fermi}-LAT, {\it Swift} (XRT and UVOT), and ATOM have been analysed and modelled using single-zone leptonic and hadronic models. PKS~0346-27 has been detected by H.E.S.S at a significance of 6.3 during one night, on 3 November 2021, while for other nights before and after this day, upper limits on the VHE flux are determined. No evidence for intra-night -ray variability has been found. A flare in high-energy (HE, ~MeV) -rays detected by {\it Fermi}-LAT preceded the H.E.S.S. detection by 2 days. A fit with a single-zone emission model to the contemporaneous spectral energy distribution during the detection night was possible with a proton-synchrotron-dominated hadronic model, requiring a proton-kinetic-energy-dominated jet power temporarily exceeding the source's Eddington limit, although alternative (e.g. multi-zone) models can not be ruled out. A one-zone leptonic model is, in principle, also able to fit the flare-state SED, however, requiring implausible parameter choices, in particular, extreme Doppler and bulk Lorentz factors of