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Prospects for the production and detection of Breit-Wheeler tunneling positrons in Experiment 320 at the FACET-II accelerator
No full textInternational audienceThe SLAC Experiment 320 collides 10 TW-class laser pulses with the high-quality, 10 GeV electron beam from the FACET-II RF LINAC. This setup is expected to produce a sizable number of pairs via nonlinear Breit-Wheeler mechanism in the strong-field tunneling regime, with an estimated yield of ~0.01-0.1 pairs per collision. This small signal rate typically comes along with large backgrounds originating, e.g., from dumping the high-charge primary beam, secondaries induced by the beam halo, as well as photons and low-energy electrons produced in the electron-laser collision itself. These backgrounds may reach densities of O(100) charged particles per cm^2 (and even more neutral particles) at the surface of the sensing elements, making it a tremendous challenge for an unambiguous detection of single particles. In this work, we demonstrate how detectors and methods adapted from high-energy physics experiments, can enable this measurement. The solution presented is based on a highly granular, multi-layer, radiation-hard pixel detector paired with powerful particle-tracking algorithms. Using a detailed simulation of the existing experimental setup, we show how the false-positive rate due to background processes can be reduced by more than an order of magnitude relative to the expected signal after full reconstruction. Furthermore, we show that the high spatial tracking resolution achievable (<10 microns) allows for positron momentum measurements with a resolution of <2%, enabling spectral characterization of the nonlinear Breit-Wheeler process. Based on our extensive simulation, with a conservatively large background assumption, we show that it is possible to measure single Breit-Wheeler positrons in the coming data taking campaign of E320. That would be the first statistically significant observation and characterization of this elusive process in the (deep) tunneling regime
Electrically-driven antiferroelectric-ferroelectric phase transition in PbZrO3 thin films studied by in situ synchrotron X-ray diffraction
No full textInternational audienceElectric-field-induced phase transitions are the most important characteristics of antiferroelectric materials furnishing them with rich functional properties. While they are actively studied for their potential applications such as high-strain transducers or electrocaloric devices, the applied electric field needed to reach the polar phase makes structural studies throughout the full transition of uttermost importance. Here, the evolution of both structure and strain in antiferroelectric PbZrO3 thin films was investigated by in situ synchrotron X-ray diffraction during electrical actuation up to 700 kV/cm applied DC electric field. The ferroelectric phase, characterized by its polar order and resulting piezoelectric activity, was found to nucleate at an electric field of 200 kV/cm and to disappear below 160 kV/cm, showing a hysteretic behavior. The variation of the different Bragg peaks widths of antiferroelectric and ferroelectric phases revealed the variation of strain distributions in the thin film where antiferroelectric and polar regions coexist during the phase transformation. In addition, the effective longitudinal piezoelectric coefficient of the ferroelectric phase itself, which remains not accessible by classical macroscopic interferometric measurements, was determined for the first time and reaches a value of 67 pm/V, quite significant for a thin film clamped on a substrate. These findings provide a clearer understanding of the dynamics of the electric-field-induced phase transition in antiferroelectric PbZrO3 thin film
Affiliative behaviours regulate allostasis development and shape biobehavioural trajectories in horses
No full textInternational audienceSocial interactions shape both the physiological and behavioural development of offspring, and poor care/early caregiver loss is known to promote adverse outcomes during infancy in both animals and humans. How affiliative behaviours impact the future development of offspring remains an open question. Here, we used Equus caballus (domestic horse) as a model to investigate this question. By coupling magnetic resonance imaging, longitudinal biobehavioural assessments and advanced multivariate statistical modelling, we found that prolonged maternal presence during infancy promotes the maturation of brain regions involved in both social behaviour (anterior cingulate cortex and retrosplenial cortex) and physiological regulation (hypothalamus and amygdala). Additionally, offspring benefiting from a prolonged maternal presence showed higher default mode network connectivity, improved social competences and feeding behaviours, and higher concentrations of circulating lipids (triglyceride and cholesterol). The findings of the present study underscore the salient role of social interactions in the development of allostatic regulation in offspring
Low-uncertainty measurement of the 239Pu(n,f) cross section at n_TOF in a very broad energy range from 0.02 eV up to 10 MeV
No full textInternational audienceThe 239Pu(n,f) cross section was measured with uncertainties below 4 % from 20 meV up to 10 MeV of neutron energy at CERN’s n_TOF facility using a novel fission fragment detector with a 185.59 m flight path. Measured cross section was normalized to 1059(6) eV · b in the 9–20 eV energy range, and is consistent within uncertainties with the standard thermal value and the IAEA reference 239Pu(n,f) cross section. Experimental key values include the integral ratio I3/I1=41.20(42) defined by Duran et al. 2024 and the spectrum averaged cross section in 252Cf(sf) reference neutron field of 1802(40) mb
Rapport sur les services climatiques réussis dans le monde et leurs critères de succès: Livrable commun au Projet ciblé TRACCS-PC1-DIALOG (D5.3) et au Projet Ciblé TRACCS-PC3-DEMOCLIMA (D1)
No full textLes enjeux socio-économiques liés aux effets du réchauffement climatique sont tels qu’une demande croissante d’informations climatiques adaptées pour la mise en place de stratégies d’atténuation et/ou d’adaptation est clairement exprimée par les secteurs économiques (e.g. agriculture, énergie, tourisme, infrastructures terrestres ou maritimes, etc…) et par les territoires/régions qui mesurent pleinement leursvulnérabilités. En réponse à ces demandes, de nombreux projets de recherche nationaux (e.g., la "Convention relative à l’attribution d’un appui financier au bénéfice des services climatiques", signée entre le Ministère de la Transition Écologique et Solidaire (MTES) et le CNRS en mars 2017, ou le développement du portail DRIAS), européens (e.g., le programme ERA4CS « European Research Area for Climate Services » du JPI Climate, ou encore Copernicus) ou internationaux (e.g., les outils développés par la NASA, le GIEC…) ont permis le financement de « services climatiques ». Plusieurs acteurs opérationnels nationaux et européens développent et mettent à disposition des « services climatiques » via des plateformes souvent libres d’accès et enfin, apparaissent sur le marché des bureaux d’études dont l’activité commerciale vise le développement de « services climatiques » à la carte et adaptés aux demandes des clients.L’offre pour les « services climatiques » est donc aujourd’hui multiforme par l’information fournie (données climatiques « simples », indicateurs, outils d’aide à la décision) et par son mode de développement. Face à cette diversité, les enjeux sont de documenter et comprendre le paysage des services climatiques actuels, de faire ressortir les besoins, et de se munir de moyens pour caractériser la réussite des services climatiques, pour évaluer l'existant et guider le développement de nouveaux projets. Menée conjointement par les projets ciblés DIALOG (PC1) et DEMOCLIMA (PC3) du PEPR TRACCS, cette étude vise quatre objectifs :i) Documenter le paysage actuel des services climatiques (section 2) en France et dans le monde (identifiés par la communauté TRACCS) en les présentant par usages et cibles ;ii) Identifier des besoins non satisfaits vis-à-vis des services climatiques (section 4) ;iii) Identifier un ensemble de critères de réussite d'un service climatique pour les évaluer (section 5) ;iv) Proposer des bonnes pratiques pour atteindre ces critères de réussite (section 6); ces éléments guideront les choix des futurs démonstrateurs qui seront conçus et développés au sein de DEMOCLIMA.Notre travail repose en grande partie sur le recueil de dires d'acteurs des "services climatiques", dans une approche "bottom-up"
Influence of printing orientation of Inconel 718 specimens on LEFM parameters analyzed via DVC
No full textInternational audienceLaser powder bed fusion (LPBF) is an additive manufacturing technique that enables for the production of metallic parts with complex geometries, and the possibility of locally adapting mesostructures. This study aims at determining the influence of hatch angle and build orientation on Linear Elastic Fracture Mechanics (LEFM) parameters of specimens obtained by LPBF. In the present work, the mechanical response of mini CT specimens made of Inconel 718 alloy obtained by LPBF were studied when subjected to in-situ tensile loading. The LEFM parameters of the different specimens were extracted from displacement fields measured with Digital Volume Correlation (DVC) using Williams' fields. The crack front and Stress Intensity Factors (SIF) profiles of the different experiments were analyzed. The extracted LEFM parameters for the different specimens displayed significant differences in Young's Modulus and fracture toughness due to variations in build orientation
Local cubic spline interpolation for Vlasov-type equations on a multi-patch geometry
No full textInternational audienceWe present a semi-Lagrangian method for the numerical resolution of Vlasov-type equations on multi-patch meshes. Following N. Crouseilles et al. [A parallel Vlasov solver based on local cubic spline interpolation on patches. Journal of Computational Physics (2009)], we employ a local cubic spline interpolation with Hermite boundary conditions between the patches. The derivative reconstruction is adapted to cope with non-uniform meshes as well as non-conforming situations. In the conforming case, there are no longer any constraints on the number of points for each patch; however, a small global system must now be solved. In that case, the local spline representations coincide with the corresponding global spline reconstruction. Alternatively, we can choose not to apply the global system and the derivatives can be approximated. The influence of the most distant points diminishes as the number of points per patch increases. For uniform per patch configurations, a study of the explicit and asymptotic behavior of this influence has been led. The method is validated using a two-dimensional guiding-center model with an O-point. All the numerical results are carried out in the Gyselalib++ library
Mitigating Nonlinear Systematics in Weak Lensing Surveys II: Stability and Diagnostics with Intrinsic Alignment
No full textInternational audienceThe Bernardeau-Nishimichi-Taruya (BNT) transform provides a powerful framework for analysing tomographic cosmic shear data by improving the localization of shear correlations in physical scale. It operates by performing a linear combination of the shear data vector in -space, yielding a transformed vector that is better localized in both redshift and -space. BNT is particularly useful for estimating cosmological parameters while minimizing the impact of poorly understood nonlinear physics, without discarding large amounts of information as is typically done with simple scale cuts. In our previous work, we showed that BNT outperforms traditional weak-lensing analyses; however, that study did not include intrinsic alignments (IA). In the present work, we assess the robustness of our BNT-based -cut framework in the presence of realistic IA models. We consider two cases: (i) when the assumed IA model used in sampling is close to, but not identical to, the true one, and (ii) when the assumed IA model is significantly biased compared to the true one. In the first case, the -cut framework yields precise and unbiased constraints even with limited knowledge of large-scale modes. Using Euclid-like mock data and a stringent -cut of for all tomographic bins, we found that BNT can constrain with a precision better than 2% while non-BNT has lost all constraining power. In the second case, the BNT transform serves as a powerful diagnostic tool, revealing internal inconsistencies in -space and redshift-space both exceeding 5 when the functional form of the sampling and fiducial IA models differ fundamentally
Tritium retention in the ITER/DEMO actively cooled tungsten monoblock in the presence of neutron-induced defects
No full textInternational audienceTritium retention in ITER like divertor monoblock is simulated with FESTIM adding trapping induced by neutron damage in the tungsten armor. The simulated scenario is a 10 MWm−2 heat flux representing an exposure near the strike line during an ITER attached plasma. The tungsten armor is damaged with rate from 5 dpa/fpy to 100 dpa/fpy in the range of expected DEMO damaging rates. It is observed that the temperature field affects the distribution of the neutron-induced traps with a significant annealing of them in the hottest part of the monoblock, which affects the resulting tritium distribution. The tritium retention is 28 times higher in the damaged monoblock compared to undamaged monoblock after a dpa level of 0.64 dpa with a high dpa rate of 100 dpa/fpy, which is an extreme damage rate for ITER or DEMO. The damaged layer slows down the tritium permeation toward the coolant, acting as a temporary permeation barrier until all the damaged-induced traps are filled. This effect is more effective with higher dpa rates as two extreme regimes exists for the growth of the tritium inventory: (i) limited by the tritium migration (low dpa rates) (ii) limited by the neutron-induced trap creation (high dpa rates)
Excitation energy of fission fragments within nuclear time-dependent density functional theory
No full textInternational audienceThe number and properties of the neutrons and photons emitted in nuclear fission are directly related to the excitation energy of the fission fragments when they are formed at scission. Though not observable experimentally because of the extremely short time scales, the excitation energy of fission fragments can be predicted by microscopic theory based on time-dependent density functional theory (TDDFT). Initial results on the value of the total kinetic energy of fission reactions were very promising, but could not probe all possible fragmentations. In this work, we perform large-scale TDDFT calculations in Pu enabled by the development of a new TDDFT solver. We obtain TDDFT trajectories covering nearly all possible fragmentations. We find that the total kinetic energy is close to experimental values only for the most likely fission while it is severely underestimated at both small and large asymmetries. This conclusion seems rather independent of the parameterization of the energy functional, both in its particle-hole and particle-particle channels