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Extremely Dense Gamma-Ray Pulses in Electron Beam-Multifoil Collisions
No full textInternational audienceSources of high-energy photons have important applications in almost all areas of research. However, the photon flux and intensity of existing sources is strongly limited for photon energies above a few hundred keV. Here we show that a high-current ultrarelativistic electron beam interacting with multiple submicrometer-thick conducting foils can undergo strong self-focusing accompanied by efficient emission of gamma-ray synchrotron photons. Physically, self-focusing and high-energy photon emission originate from the beam interaction with the near-field transition radiation accompanying the beam-foil collision. This near field radiation is of amplitude comparable with the beam self-field, and can be strong enough that a single emitted photon can carry away a significant fraction of the emitting electron energy. After beam collision with multiple foils, femtosecond collimated electron and photon beams with number density exceeding that of a solid are obtained. The relative simplicity, unique properties, and high efficiency of this gamma-ray source open up new opportunities for both applied and fundamental research including laserless investigations of strong-field QED processes with a single electron beam
Insights into portability issues of FM3TR waveform
No full textInternational audienceThis manuscript focuses on issues related to the implementation of the Future Multiband Multiwaveform Modular Tactical Radio (FM3TR) waveform on two different SCA platforms with similar hardware but different SCA development and deployment environments. Our experimental results showed that a SCA standardization based on technologies such as CORBA, XML, IDL, is not enough to ensure the portability of the waveform. Indeed, the files generated by SCA 2.2.2 environments (ZCE, SCA Architect, http://nordiasoft.com/products/scari-software-suite/sca-architect/) may often use a specific non-standard IDL interface to generate software components. To corroborate our statement, specific examples of SCA components are considered. The portability of the waveform depends on the waveform software used by the porting team. Three classic cases can be observed during the development of a waveform according to a standard specification: The first case is related to waveform development from scratch, the second case is observed when a static library is used to carry the golden code of the waveform and the third one occurs when only platform specific codes are available to the porting process. Finally, a general discussion about portability is provided
Demonstration of a compact plasma accelerator powered by laser-accelerated electron beams
No full textInternational audienceParticle accelerators based on laser- or electron-driven plasma waves promise compact sources for relativistic electron bunches. Here, Kurz and Heinemann et al. demonstrate a hybrid two-stage configuration, combining the individual features of both accelerating schemes
Revisiting imperfect interface laws for two-dimensional elastodynamics
No full textInternational audienceWe study the interaction of in-plane elastic waves with imperfect interfaces composed of a periodic array of voids or cracks. An effective model is derived from high-order asymptotic analysis based on two-scale homogenization and matched asymptotic technique. In two-dimensional elasticity, we obtain jump conditions set on the in-plane displacements and normal stresses; the jumps involve in addition effective parameters provided by static, elementary problems being the equivalents of the cell problems in classical two-scale homogenization. The derivation of the model is conducted in the transient regime and its stability is guarantied by the positiveness of the effective interfacial energy. Spring models are envisioned as particular cases. It is shown that massless-spring models are recovered in the limit of small void thicknesses and collinear cracks. By contrast, the use of mass-spring model is justified at normal incidence, otherwise unjustified. We provide quantitative validations of our model and comparison with spring models by means of comparison with direct numerical calculations in the harmonic regime
Carnac: Algorithm Variability for Fast Swarm Verification on FPGA
No full textInternational audienceThe mapping of software verification algorithms on FPGA promise orders of magnitude faster verification. FP-GASwarm shows 900X speedup over software swarm verification. However, this approach misses important optimization opportunities and glosses over algorithmic design-space exploration.This paper introduces Carnac, a deeply pipelined swarm verification architecture, which by exposing the algorithmic variability points can realize multiple verification algorithms. Furthermore, we introduce the Mixed Young Random Frontier-Bounded (MYR_FB), a new swarm verification algorithm, found through an efficiency-based design-space exploration.Evaluated on the BEEM benchmark, the MYR_FB algorithm shows up to 144% efficiency gain over FPGASwarm on 72% of the models. The Carnac architecture runs at 400MHz on Xilinx Ultrascale+ FPGA, and can accommodate twice more verification cores than FPGASwarm. Overall the evaluation shows a 7.58X speedup over FPGASwarm, while enabling an unprecedented scalability on high-end FPGAs
Falls Detection and Prevention Systems in Home Care for Older Adults: Myth or Reality?
No full textInternational audienceThere is an exponential increase in the range of digital products and devices promoting aging in place, in particular, devices aiming at preventing or detecting falls. However, their deployment is still limited and only few studies have been carried out in population-based settings owing to the technological challenges that remain to be overcome and the barriers that are specific to the users themselves, such as the generational digital divide and acceptability factors specific to the older adult population. To date, scarce studies consider these factors. To capitalize technological progress, the future step should be to better consider these factors and to deploy, in a broader and more ecological way, these technologies designed for older adults receiving home care to assess their effectiveness in real life
Rayonnement bétatron dans l'accélération à champ de sillage du plasma piloté par faisceau et instabilités faisceau-plasma ultra-relativistes
No full textA large variety of physical processes can arise in the interaction of a relativistic particle beam with plasmas. In most of these processes the collective plasma response to the beam's charge and current can act as efficient mechanisms to transform the beam energy into large amplitude electromagnetic fields. Having a good understanding of these mechanisms allows on the one hand to develop new experimental techniques based on these fields, and on the other hand to improve the astrophysical models where similar mechanisms play an important role. This manuscript focuses on two of those processes and the programmed experiments at the FACET-II accelerator facility: plasma wakefield excitation and beam-plasma instabilities.The beam-driven plasma wakefield acceleration technique is now-a-days one of the most promising alternatives to conventional accelerators. With acceleration gradients up to four orders of magnitude larger than in an RF-cavity, this technique could significantly reduce the size and cost of high energy particle accelerators. Yet, several experimental milestones need to be achieved to demonstrate that the PWFA concept can perform at the required level of reproducibility and beam control and quality for societal, industrial and high energy physics applications. In this manuscript we propose via simulations a new non-destructive radiation-based method to diagnose beam transverse dynamics in a non-linear PWFA stage that can be detrimental for the accelerated beam quality.The beam-plasma instabilities are often studied in unbounded systems. In the ultra-relativistic limit, the so-called "oblique instability" is though to mediate the early stage of the interaction. In this manuscript the effects of the system boundaries on the oblique unstable modes are studied, namely a novel spatiotemporal theory is developed. Repercussion on experimental systems aiming to study these processes are discussed. Finally, a laser-based platform to study plasma streaming instabilities is presented together with experimental results.Une grande variété de processus physiques peut survenir dans l'interaction d'un faisceau de particules relativistes avec des plasmas. Dans la plupart de ces processus, la réponse collective du plasma à la charge et au courant du faisceau peut agir comme un mécanisme efficace pour transformer l'énergie du faisceau en champs électromagnétiques de grande amplitude. Avoir une bonne compréhension de ces mécanismes permet d'une part de développer de nouvelles techniques expérimentales basées sur ces champs, et d'autre part d'améliorer les modèles astrophysiques où des mécanismes similaires jouent un rôle important. Ce manuscrit se concentre sur deux de ces processus et les expériences programmées à l'installation de l'accélérateur FACET-II : l'excitation de l'onde de sillage plasma et les instabilités faisceau-plasma.La technique d'accélération par champ de sillage piloté par faisceau est aujourd'hui l'une des alternatives les plus prometteuses aux accélérateurs conventionnels. Avec des gradients d'accélération jusqu'à quatre ordres de grandeur plus importants que dans une cavité RF, cette technique pourrait réduire considérablement la taille et le coût des accélérateurs de particules à haute énergie. Pourtant, plusieurs étapes expérimentales doivent être franchies pour démontrer que le concept PWFA peut fonctionner au niveau requis de reproductibilité et de contrôle et qualité du faisceau pour des applications sociétales, industrielles et de physique de hautes energies. Dans ce manuscrit, nous proposons via des simulations une nouvelle méthode non destructive basée sur le rayonnement pour diagnostiquer des dynamiques transverses du faisceau dans une onde de sillage non linéaire qui sont préjudiciables à la qualité du faisceau accéléré.Les instabilités faisceau-plasma sont souvent étudiées dans des systèmes non bornés. Dans la limite ultra-relativiste, la soi-disant "instabilité oblique" est censée médier le stade précoce de l'interaction. Dans ce manuscrit, les effets des frontières du système sur les modes obliques instables sont étudiés, à savoir une nouvelle théorie spatio-temporelle est développée. Les répercussions sur les systèmes expérimentaux visant à étudier ces processus sont discutées. Enfin, une plate-forme laser pour étudier les instabilités de flux de plasma est présentée avec des résultats expérimentaux
EUREC<sup>4</sup>A
No full textThis article is part of the special issue “Elucidating the role of clouds–circulation coupling in climate:datasets from the 2020 (EUREC4A) field campaign”. It is not associated with a conference.International audienceThe science guiding the EURECA campaign and its measurements is presented. EURECA comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic – eastward andsoutheastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EURECA marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced groundbased cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EURECA explored – from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation – are presented along with an overview of EURECA’s outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplemen
Study on Non-Bragg Microwave Backscattering from Sea Surface Covered with and without Oil Film at Moderate Incidence Angles
No full textInternational audienceIn the past decades, Bragg scattering has been considered to be an important scattering mechanism of microwave backscattering from sea surfaces. However, as reported in many recent literatures, non-Bragg scattering (which is often attributed to wave breaking) also makes a significant impact on radar scattering, especially for Horizontal–Horizontal (HH) polarized radar signals. To date, we know far less about non-Bragg scattering than Bragg scattering. Herein, this paper carries out an investigation on non-Bragg scattering and its effect on radar echoes at moderate incidence angles, both for oil-free and oil-covered sea surfaces. This paper firstly presents a systematic comparison of several sea spectra commonly used for the simulation of microwave scattering from sea surfaces. It is found that none of them perform well for the description of Bragg waves. Then, the “pure” Bragg wave spectra are inverted in the framework of the two-scale model (TSM) and geophysical model functions (GMFs). The normalized radar cross sections (NRCS) related to total scattering, non-Bragg scattering, and “pure” Bragg scattering in C, X, and Ku-bands are simulated under various conditions (i.e., incidence angles, wind speeds, and wind directions). Quantitative assessments of the relative contributions of non-Bragg scattering to total scattering are conducted. We also perform a survey on the non-Bragg scattering from the oil-covered sea surface. This article provides some new insights for a better understanding of the non-Bragg microwave scattering from rough sea surfaces at moderate incidence angles
Deep Learning for RF-based Drone Detection and Identification using Welch’s Method
No full textInternational audienceRadio Frequency (RF) combined with the deep learning methods promised a solution to detect the presence of the drones. Indeed, the classical techniques (i.e. radar, vision and acoustics, etc.) suffer several drawbacks such as difficult to detect the small drones, false alarm of flying birds or balloons, the influence of the wind on the performance, etc. For an effective drones's detection, two main stages should be established: Feature extraction and feature classification. The proposed approach in this paper is based on a novel feature extraction method and an optimized deep neural network (DNN). At first, we present a novel method based on Welch to extract meaningful features from the RF signal of drones. Later on, three optimized Deep Neural Network (DNN) models are considered to classify the extracted features. The first DNN model can be used to detect the presence of the drones and contains two classes. The second DNN help us to detect and recognize the type of the drone with 4 classes: A class for each drone and the last one for the RF background activities. In the third model, 10 classes have been considered: the presence of the drone, its type, and its flight mode (i.e. Stationary, Hovering, flying with or without video recording). Our proposed approach can achieve an average accuracy higher than 94% and it significantly improves the accuracy, up to 30%, compared to existing methods