CEA Gramat

A compact, frequency-tunable, and efficient relativistic magnetron (RM) featuring a reducing coaxial section (RCS) and tilted tuners was developed and experimentally tested. The study validates numerical predictions through experiments, focusing on sustained oscillations, power efficiency, and frequency tuning. Four cathode configurations were tested. The solid cathode with reduced diameter yielding the best results: up to 34% efficiency, 450-MW average output power, and 1.55-GW peak power at 430 kV. A tuning bandwidth of 16% was achieved between 1.8 and 2.12 GHz. Plasma effects were investigated via improved particle-in-cell (PIC) simulations using a dispersive Drude model, identifying plasma as the main source of observed RF instabilities and pulse shortening.

La collaboration, constitutive de l'ducation inclusive, suppose l'interrelation entre les expertises dans un but commun (UNESCO, 2021).Sur cette voie, la cration de rseaux d'coles et de communauts d'apprentissage favoriserait le dveloppement professionnel collectif et l'agir ensemble (Conseil suprieur de l'ducation, 2017 ; UNESCO, 2021).Pour surmonter les contraintes individuelles, organisationnelles et contextuelles susceptibles d'entraver ces ambitions, des recherches ont montr l'intrt des mesures de soutien et d'accompagnement (Curchod-Ruedi, et al., 2013 ; Maillot & Merini, 2021).Au Qubec, le dveloppement de l'agir collectif dans une perspective inclusive entre en contradiction avec le cloisonnement des champs d'expertise professionnelle, qui se trouve au fondement d'un ensemble de cadres d'organisation du travail (Conseil suprieur de l'ducation, 2017 ; Tardif & LeVasseur, 2010). Une dmarche de recherche-action a t mene auprs de membres du personnel de centres de services scolaires de la province pour dvelopper des aptitudes de collaboration interprofessionnelle et interorganisationnelle dans une perspective inclusive. partir de la thorie du leadership transformatif et de la notion d'agir ensemble (Blanger, et al., 2018 ;Glinas-Proulx & Shields, 2016), les rsultats mettent en lumire quatre constats et six dfis qui se rapportent aux leviers et freins qui conditionnent le dveloppement de ce type de collaboration.Les constats permettent d'approfondir les enjeux de confiance, respect et communication qui fondent la collaboration ; les dfis prcisent les difficults relatives la division du travail et aux rapports de pouvoir.

Abstract Cooling fractures found within impact melt deposits have been manually mapped within several craters on the Moon and Mercury, as their distribution can indicate which heat‐loss processes were most significant in the periods after impact. However, due to the discovery of melt deposits in Lunar impact craters with sub‐km diameters, it is unlikely that the complete mapping of these impact melt fractures (IMFs) on the Moon will be achievable without automation. As such, we have trained a DeepLabV3 semantic segmentation deep convolutional neural network, called IMFMapper, to detect IMFs within Lunar Reconnaissance Orbiter Narrow Angle Camera (LROC NAC) satellite imagery. As a means of maximizing the size of the training data set, “weak” pixel‐level labels were generated by buffering line annotations. In testing upon the IMFs found within Ohm crater, IMFMapper achieved an average ‐score of 69.3%. IMFMapper has also been deployed to map IMFs within the previously surveyed Crookes crater, where we have found new candidate melt deposits within the crater's western and southern walls. In addition, IMFMapper has produced the first map of IMFs within Schomberger A crater, in which IMFs may act as permanently shadowed regions due to the crater's proximity to the Lunar South Pole. The successful mapping of IMFs in Schomberger A also signifies IMFMapper's robustness to extreme solar incidence angles. We also demonstrate that IMFMapper could be implemented for automated mapping of IMFs on Mercury upon the commencement of BepiColombo's science operations.

CEA Gramat is the French national reference center for the study of electromagnetic directed energy weapons (EM DEW). Conducted researches focus on the vulnerability of electronic systems to electromagnetic aggression, and the development of technological proofs of concept to produce these vulnerabilities, with the aim of designing demonstrators for EM DEW. The subject consists in the design of a new high power microwave (HPM) source and its antenna operating in Ka-band, compatible with the compact PFN Marx generator employed at CEA Gramat. First, a state of the Art permitted to sort the tube types in function of the required characteristics (impedance near 100Ω, input voltage of 380 kV, center frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\approx 30 \text{GHz}$</tex>, output power <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\min =100 \text{MW}$</tex>). Best candidates are the TM02 BWO and the RLO. However, considering the low input impedance of the RLO, the study is conducted on the TM02 BWO. A particular attention has been paid to the reflectors that adopt a trapezoidal shape in order to lower RF breakdown. The BWO is designed with an output EM mode converter in order to cut undesired TM02 and only transmit TM01. To verify the design of the tube, the prototype is simulated with three solvers Particle In Cells (PIC), transient and Eigenmode. Today, the best results obtained in simulation are 175 MW at 30 GHz for a pulse duration of 50 ns.

This paper outlines the design of a focused planewave illumination bench for studying the electromagnetic susceptibility of electronic systems. The bench consists of a horn antenna and a dielectric lens used to focus plane wave in the Xband at 10 GHz.

Abstract Shock‐to‐Detonation Transition (SDT) of heterogeneous high explosives results from processes occurring at the microstructural level. Thus, mesoscale modeling is expected to allow a better comprehension of the SDT. Recent experimental evidence suggested that hotspots mainly developed on the surface of the energetic crystals, which are then consumed by the propagation of a deflagration front. In the present study, mesoscale simulations of the SDT of pressed HMX were performed. The reactive model employed consisted of igniting the surface of the crystals after the shock passage, and reconstructing the burn front propagation, using a modified Youngs’ method. In this reactive model, the velocity of the deflagration front was modeled by a pressure‐dependent law, as suggested by the literature. The simulations showed that the Single Curve Initiation principle remained valid. The parameter deflagration velocity times the surface to volume ratio was found to enable the equivalence between microstructures. This approach provides a new framework to study the SDT of heterogeneous explosives, by considering how the combustion of energetic crystals participate to the shock acceleration and transition into a detonation. This paper serves as a proof of concept, applied to the pressed HMX.

For many years, modern defense and security applications have driven the development of compact pulsed power generators to produce high-power electromagnetic waves. Usually, such generators fill a volume of at least a few tens of liters. This article aims to present the development and tests of an ultra-compact ultra-wideband (UWB) radiating electromagnetic pulse source for electromagnetic stress testing and therefore vulnerability studies of electronic devices. The pulse source named source Bande Ultra Large Ultra Compacte (French acronym, BULUC) is autonomous and fills a volume of only 2.5 L ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$260\times 195\times50$ </tex-math></inline-formula> mm, without antenna). BULUC is composed of a set of batteries, a software-driven high-voltage dc supply, a ten-stage Marx generator, a bipolar pulse forming line (B-PFL), and an external UWB Vivaldi antenna. The Marx generator produces 135 kV, 20 ns rise time pulses at a working pulse repetition frequency (PRF) of 20 Hz during 10 s. Then the pressurized B-PFL generates a peak-to-peak signal of 135 kV with a transition time of 260 ps for a bi-pulse duration of 1 ns. This signal feeds a planar Vivaldi antenna which can radiate a 90 kV/m peak-to-peak electric field at 1 m (+50/−40 kV/m). The figure of merit (FOM: the maximum value of far-field peak electric field strength multiplied by the distance considering the fact that in the far-field region, the electric field variation is expected to be proportional to 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$r$ </tex-math></inline-formula> ) is about 50 kV.