Search

International audience; This work presents comparisons between numerical simulations and secondary electron emission yield measurements. The impact on the secondary electron emission yield of a growing graphite layer deposited on copper substrates is analyzed. The numerical simulations confirm experimental observations showing that a very thin coating deposit, with a thickness of few nm, can affect significantly the emission yield of an irradiated material. Beyond 5 nm thickness, the surface material alone drives the secondary emission.; Ce travail présente des comparaisons entre des simulations numériques et des mesures de rendement d'émission d'électrons secondaires. L'impact sur le rendement d'émission des électrons secondaires d'une couche croissante de graphite déposée sur des substrats de cuivre est analysé. Les simulations numériques confirment les observations expérimentales montrant qu'un dépôt de revêtement très fin, d'une épaisseur de quelques nm, peut affecter de manière significative le rendement d'émission d'un matériau irradié. Au-delà de 5 nm d'épaisseur, le matériau de surface seul dirige l'émission secondaire.

Secondary electron emission often appears as a parasitic physical process in systems that either use electrons of a few hundred eV, or that can evolve in an environment where low energy electrons are present [1]. In certain cases, by an avalanche phenomenon, electrons can multiply to a level that can disturb the functioning of sensitive equipments (multipactor) [1] or lead to catastrophic effects such as corona discharges. Multipacting is an issue for space systems that undergo electrons trapped in the earth radiation belts [2]. The satellite’s power chain is particularly sensitive to this physical mechanism. In this context, the risk associated with the electron secondary emission can be mitigated by surface treatments [3] of the walls of the Radio Frequency (RF) devices. The Total Electron Emission Yield (TEY) is closely dependent to the surface state and to the nature of the coating deposited on the material. For instance, the chemical state of the surface is modified by the irradiation in a way that the TEY can be reduced. It is known that irradiations can polymerize organic molecules present at the surface of the material and fix on it a layer of graphite. Since graphite has a low emission yield, the presence of a layer of a few nanometres thick is sufficient to drive and reduce the TEY [4]. This has been shown experimentally [4], but, few numerical simulations of such behaviour have already been performed. The objective of the work presented here, is to study numerically the impact of thin carbon layers of different thicknesses, on the SEY of Ag and Cu substrates, using Monte Carlo simulations [5-[8].

The aerodynamic analysis by the exergy method is a powerful approach which allows establishing the theoretical limits of the aerodynamic performance of a given body, based on an aero-thermodynamic approach. The most used formulation is the Arntz’s method [1], which is well suited for the analysis of CFD data. This formulation was widely applied and validated for plenty of test cases but all of them were high-aspect ratio configurations. Then, the objective of this work is to study a test case with low aspect ratio: a delta wing with 74° of sweep angle, which is characterized by extreme flow features like strong vortices. It was found that the exergy formulation behaves well even under such challenging conditions. However, the related extreme flowfield allows identifying some hard points like the wake-reduced exergy analysis of the vortex breakdown, the impact of the solver setting on the final assessment, the viscous anergy generation, among other topics.

Electric Orbit Raising (EOR) for telecommunication satellites significantly reduced on-board fuel mass at the price of extended transfer durations. These relatively long transfers, which usually span a few months, cross large spans of the radiation belts, resulting in significant exposure of the spacecraft to space radiations. Since they are not very populated, the radiation environment of intermediate regions of the radiation belts is less constrained than on popular orbits such as low Earth orbit or geostationary orbit in standard environment models. In particular, there is a need for more specific models for the MeV energy range proton fluxes, responsible for solar arrays degradations, and hence critical for EOR missions. ONERA has developed a specification model of proton fluxes dedicated for EOR missions as part of the ESA ARTES program. This model can estimate the average proton fluxes between 60 keV and 20 MeV on arbitrary trajectories on the typical duration of EOR transfers. A global statistical model of the radiation belts was extracted from the Van Allen Probes RBSPICE data. For regions with no or low sampling, simulation results from the Salammbo radiation belt model were used. Special care was taken to model the temporal dynamics of the belts on the considered mission durations. A Gaussian Process model was developed, allowing to compute the distribution of the average fluxes on arbitrary mission durations analytically. Satellites trajectories can be flown in the resulting global distribution, yielding the proton flux spectrum distribution as seen by the spacecraft. We show the results of the model on a typical EOR trajectory. The obtained fluxes are compared to the standard AP8 model, the AP9 model and validated using the THEMIS satellites data. We illustrate the expected effect on solar cell degradation, where our model shows an increase of up to 20% degradation prediction compared to AP8.

The contribution of low energy particles down to ~200 eV to the dose deposited on the very near surface of materials subject to space environment is investigated by means of GEANT4 Monte Carlo simulations. The contribution to the dose, of the low energy parts of GREEN spectra ([200 eV-40 keV] for electrons, [200 eV-100 keV] for protons) are compared with calculations performed with AE8/AP8. Both GEO and LEO SPOT like orbits are studied. The dose depth profiles are estimated for silicon material. The impact on the dose calculation of different transport models is also investigated. Below 1 keV, the relevance of continuous processes is analysed for electrons by comparison with a discrete model (GEANT4/MICROELEC). This analysis is also performed for protons below 10 keV.

Les environnements radiatifs sont critiques pour l’intégrité des systèmes électroniques embarqués. Peuplés de particules plus ou moins énergétiques, ces environnements peuvent provoquer des dysfonctionnements qui, suivant les dommages occasionnés, peuvent être identifiés. Ce manuscrit porte ssentiellement sur les pannes non destructives, et plus particulièrement sur les SEU (Single Event Upset) dont les conséquences sont les basculements indésirables de certains points mémoires. Ce faisant, l’information initialement stockée peut être perdue. La thématique de la sensibilité des mémoires aux événements singuliers a pris naissance dans les années 70. Les premières erreurs observées ont été provoquées par des particules lourdes, associées à des pouvoirs ionisants élevés. Ces dernières, en traversant les dispositifs, engendrent des cascades électroniques particulièrement intenses. Aujourd’hui, les mémoires proposent des nœuds technologiques de l’ordre de la dizaine de nanomètres. Ainsi, sur les décennies qui nous séparent des premières observations des événements singuliers, les cellules mémoires ont vu leurs dimensions se comprimer drastiquement. D’un point de vue sensibilité, cela aurait pu aller dans le bon sens mais c’était sans compter sur la réduction des tensions d’alimentation qui s’est opérée dans le même temps. Ce manuscrit s’inscrit dans cette évolution et tâche d’analyser les conséquences qui ont alors émergées. Le transport des particules est une thématique commune à tant de sujets. Et la sensibilité des mémoires n’y échappe pas. D’autant que la contrition des composants nous impose maintenant une certaine rigueur : il nous revient de réaliser le transport des particules sur des échelles nanométriques. Ainsi, nous avons travaillé sur le développement et l’implémentation de nouveaux modèles physiques dans un code de transport, GEANT4. Ces travaux nous permettent de suivre les cascades électroniques jusqu’à des énergies très basses, une condition indispensable pour les autres études que nous avons menées. Des électrons aux protons, nous avons investigué l’ensemble des processus physiques potentiellement impliqués dans les déclenchements d’erreur. Plusieurs résultats inédits ont ainsi été obtenus et démontrés : le rôle des interactions Coulombiennes sur les sensibilités mesurés en environnements électrons, et celui, propre aux diffusions élastiques, dans le cas des environnements protons. Le comportement des mémoires sous ces deux types d’environnement, les dynamiques qu’ils imposent sur les courbes de sensibilité, nous ont, par la suite, guidés vers une méthode de calibration des paramètres de simulation. Cette dernière étude offre d’ailleurs un moyen de prédiction de la sensibilité des composants pour des environnements auxquels ils n’ont pas été testés. Enfin, ce manuscrit se conclura sur une dernière étude, plus proche du composant, où l’on regardera les transitoires générés par des faisceaux d’électrons sur un inverseur ultrascale Radiative environments are critical to the integrity of embedded electronic systems. These environments can cause malfunctions which, depending on the damage caused, can be identified. This manuscript focuses mainly on non-destructive failures, and more particularly on Single Event Upset (SEU) whose consequences are the undesirable switching of memory bits. In doing so, the information initially stored may be lost. The theme of the sensitivity of memories to singular events began in the 1970s. The first errors observed were caused by heavy particles, associated with high ionizing powers. The latter, by crossing the devices, generate particularly intense electronic cascades. Today, memories propose technological nodes of the order of ten nanometers. Thus, over the decades between us and the first observations of singular events, memory cells have seen their dimensions drastically compressed. From the SEU sensitivity point of view, this could have hardened the devices, but at the same time the supply voltages were reduced. This manuscript is part of this evolution and tries to analyze the consequences that emerged. The transport of particles is a common theme for many subjects. And the sensitivity of memories is one of them . Especially since the integration of memory cells now imposes constraints that we must consider: it is up to us to carry out the transport of particles on nanometric scales. Thus, we have worked on the development and implementation of new physical models in a transport code, GEANT4. This work allows us to track electronic cascades to very low energies, an essential condition for the other studies that we have conducted. From electrons to protons, we investigated all the physical processes potentially in the triggering of upsets . Several new results have thus been obtained and demonstrated: the role of Coulomb interactions on the SEU sensitivities measured in electron environments, and the specific role of the Coulomb elastic scattering in the case of proton environments. The behaviour of the memories in these two kinds of environments, the dynamics they impose on the sensitivity curves, then guided us towards a method for calibrating the simulation parameters. This last study also provides a means of predicting the sensitivity of devices for environments in which no measures are available. Finally, this manuscript will conclude with a final study, closer to the device, where we will look at the transients generated by electron beams on an ultrascale inverter

On-board electronic devices are vulnerable to the effects of space environment radiation which can cause logical errors when particle pass through the sensitive regions of the components and produce a sufficient ionization level. Historically heavy ions and protons were the first particles with these phenomena were observed. It has been demonstrated that with the increasing integration of technologies and the reduction of supply voltages, electronic devices become sensitive to the passage of "light" particles such as electrons. The aim of this work is to study in detail the mechanisms of triggering locical errors from an experimental and numerical point of view., Les microélectroniques embarquées durant les missions spatiales sont vulnérables aux environnements radiatifs. Mais avec l'intégration croissante des dispositifs et la volonté des agences à explorer des planètes comme Jupiter auxquelles sont associés des environnements particulièrement intenses, cette problématique prend un nouvel essor. En effet, en 2014, l'Université de Vanderbilt a mis en évidence la sensibilité aux SEUs (Single Event Upset) de certaines mémoires aux électrons. C'est une première : des particules légères aux faibles pouvoirs ionisants peuvent désormais être contraignantes pour les missions spatiales. Cette thèse s'inscrit dans la continuité de cette découverte, en proposant plusieurs études qui soulignent la participation de nouveaux mécanismes (et pas uniquement en environnement électrons) dans les déclenchements d'erreur.