X-ray broadband Ni/SiC multilayers: improvement with W barrier layers

International audienceWe present an experimental study and performance improvement of periodic and aperiodic Ni/SiC multilayer coatings. Periodic Ni/SiC multilayer mirrors have been coated and characterized by grazing incidence X-ray reflectometry at 8.048 keV (Cu Kα radiation) and by measurements at 3 keV and 5 keV on synchrotron radiation facilities. An interdiffusion effect is found between Ni and SiC layers. A two-material model, NixSiy/SiC, using a silicide instead of Ni, was used to fit the measurements. The addition of 0.6 nm W barrier layers at the interfaces allows a significant reduction of the interdiffusion between Ni and SiC. In order to obtain a specific reflectivity profile in the 2 – 8 keV energy range, we have designed and coated aperiodic multilayer mirrors by using Ni/SiC with and without W barrier layers. The experimental reflectivity profiles as a function of the photon energy were measured on a synchrotron radiation facility in both cases. Adding W barrier layers in Ni/SiC multilayers provides a better precision on the layer thicknesses and a very good agreement between the experimental data and the targeted spectral profile

Characterization of subnanometric layers by grazing incidence X-ray reflectometry

International audienceWe present a method to characterize subnanometric layers based on grazing incidence X-ray reflectometry. For this purpose, we propose to use a “Fabry–Pérot” type multilayer structure in order to improve the sensitivity of the measurement to the layer thickness. For our study, this structure consists of a thin layer of scandium inserted between two periodic chromium (Cr)/scandium (Sc) multilayers. We describe the principle and estimate the sensitivity of the method by simulation. Experiments were performed on two optimized Fabry–Pérot structures with 0.6 and 1.2 nm Sc layer thicknesses using a laboratory grazing incidence reflectometer at 8.048 keV (Cu Kα radiation). Fitting of experimental data allows determining the Sc layer thickness. Finally, the structural parameters used in the fit were confirmed by measurements at 3 keV on the hard X-ray branch of the synchrotron SOLEIL Metrology and Tests beamline

Premiers diagnostics X pour le LMJ

Nous décrivons les premiers diagnostics X développés actuellement pour le LMJ. Ceux-ci sont principalement dédiés à la qualification de l’installation (mesure de tache focale, contrôle du pointage et de l’équilibrage des faisceaux), mais également au diagnostic de la cavité, du transfert radiatif (mesure de rendement de conversion X), au diagnostic de l’hydrodynamique (expériences de radiographie d’instabilités hydrodynamiques) et à l’imagerie de microballons DT. Ce premier lot de diagnostics comprend deux systèmes de multi imagerie X bidimensionnelle associés à un tube obturateur et un système d’imagerie monodimensionnelle avec une caméra à balayage de fente. Ces trois systèmes d’imagerie X appelés « imageurs X » mesurent le rayonnement dans le domaine [500 eV–15 keV]. Un diagnostic de spectrométrie X large bande fonctionnant dans le domaine [30 eV–20 keV] est également développé. Le design des diagnostics prend en compte les problématiques de vulnérabilité aux produits de tirs, de durcissement aux X-durs, gammas et neutrons, de contamination au tritium. Les contraintes liées à l’exploitation sont également considérées puisque l’intervention humaine au sein des diagnostics doit être limitée au cours d’une campagne d’expériences. Les concepts retenus pour ces diagnostics sont présentés, de même que la caractérisation d’une première maquette de microscope de multi imagerie X

CVD diamond detector with interdigitated electrode pattern for time-of-flight energy-loss measurements of low-energy ion bunches

International audienceIon stopping experiments in plasma for beam energies of few hundred keV per nucleon are of great interest to benchmark the stopping-power models in the context of inertial confinement fusion and high-energy-density physics research. For this purpose, a specific ion detector on chemical-vapor-deposition diamond basis has been developed for precise time-of-flight measurements of the ion energy loss. The electrode structure is interdigitated for maximizing its sensitivity to low-energy ions, and it has a finger width of 100 μm and a spacing of 500 μm. A short single α-particle response is obtained, with signals as narrow as 700 ps at full width at half maximum. The detector has been tested with α-particle bunches at a 500 keV per nucleon energy, showing an excellent time-of-flight resolution down to 20 ps. In this way, beam energy resolutions from 0.4 keV to a few keV have been obtained in an experimental configuration using a 100 μg/cm2 thick carbon foil as an energy-loss target and a 2 m time-of-flight distance. This allows a highly precise beam energy measurement of δE/E ≈ 0.04%–0.2% and a resolution on the energy loss of 0.6%–2.5% for a fine testing of stopping-power models

Simultaneous X-ray and XUV absorption measurements in nickel laser-produced plasma close to LTE

International audienceWe present an experiment performed in 2016 at the LULI2000 laser facility in which X-ray and XUV absorption structures of nickel hot plasmas were measured simultaneously. Such experiments may provide stringent tests of the accuracy of plasma atomic-physics codes used to the modeling of plasmas close to local thermodynamic equilibrium. The experimental setup relies on a symmetric heating of the sample foil by two gold hohlraums in order to reduce the spatial gradients. The plasma conditions are characterized by temperatures between 10 and 20 eV and densities of the order of 10$^{−3}$ g/cm $^3$-10$^{−2}$ g/cm$^3$. For the X-ray part, we investigate the 2p-3d and 2p-4d transitions, and for the XUV part, we recorded the $\Delta$n = 0 (n = 3) transitions, which present a high sensitivity to plasma temperature. These latter transitions are of particular interest because, in mid-Z plasmas, they dominate the Planck and Rosseland mean opacities. Measured spectra are compared to calculations performed using the hybrid opacity code SCO-RCG and the Flexible Atomic Code (FAC). The influence of a spectator electron on the calculated spectra is analyzed using the latter code

Decline in antibiotic resistance and changes in the serotype distribution of [i]Streptococcus pneumoniae[/i] isolates from children with acute otitis media; a 2001-2011 survey by the French Pneumococcal Network

Streptococcus pneumoniae is an important cause of acute otitis media (AOM). The aim of this study was to evaluate trends in antibiotic resistance and circulating serotypes of pneumococci isolated from middle ear fluid of French children with AOM during the period 2001-2011, before and after the introduction of the PCV-7 (2003) and PCV-13 (2010) vaccines. Between 2001 and 2011 the French pneumococcal surveillance network analysed the antibiotic susceptibility of 6683 S. pneumoniae isolated from children with AOM, of which 1569 were serotyped. We observed a significant overall increase in antibiotic susceptibility. Respective resistance (I+R) rates in 2001 and 2011 were 76.9% and 57.3% for penicillin, 43.0% and 29.8% for amoxicillin, and 28.6% and 13.0% for cefotaxime. We also found a marked reduction in vaccine serotypes after PCV-7 implementation, from 63.0% in 2001 to 13.2% in 2011, while the incidence of the additional six serotypes included in PCV-13 increased during the same period, with a particularly high proportion of 19A isolates. The proportion of some non-PCV-13 serotypes also increased between 2001 and 2011, especially 15A and 23A. Before PCV-7 implementation, most (70.8%) penicillin non-susceptible pneumococci belonged to PCV-7 serotypes, whereas in 2011, 56.8% of penicillin non-susceptible pneumococci belonged to serotype 19A. Between 2001 and 2011, antibiotic resistance among pneumococci responsible for AOM in France fell markedly, and PCV-7 serotypes were replaced by non-PCV-7 serotypes, especially 19A. We are continuing to assess the impact of PCV-13, introduced in France in 2010, on pneumococcal serotype circulation and antibiotic resistance