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Radiation Induced Conductivity (RIC) is the change in conductivity of a material due to bombardment from incident high energy radiation. RIC has consistently been found to follow a standard power law relation, 𝜎𝑅𝐼𝐶(𝑇) = 𝑘𝑅𝐼𝐶(𝑇)Ḋ∆(𝑇), between conductivity, 𝜎𝑅𝐼𝐶 and adsorbed dose rate, Ḋ. 𝑘𝑅𝐼𝐶(𝑇) and ∆(𝑇) are material dependent parameters. Previous RIC models were developed in the 𝑇 → 0 limit. Now expanded models are developed in the low temperature limit (within a few 𝑘𝐵𝑇 of the effective Fermi level) by approximating the Fermi-Dirac equation within a few 𝑘𝐵𝑇 of the effective Fermi level. Derivations are based on seven density of states (DOS) models for highly disordered insulating materials: three monotonically decreasing models within the bandgap (exponential, power law, and linear) and two symmetric peaked models within the bandgap (Gaussian and delta function), plus a limiting case with a uniform DOS for each type. In addition, temperature dependent RIC data is compiled from literature for five polymeric materials used commonly in spacecraft: KaptonTM (polyimide or PI), polyethylenes (PE, low density polyethylene or LDPE, high density polyethylene or HDPE), TeflonTM (polytetrafluoroethylene or PTFE), MylarTM (polyethylene terephthalate or PET), and fluorinated ethylene propylene (FEP). Comparisons are made between compiled data from the literature and Utah State University RIC data, along with pertinent discussion of the results with a focus on the relevance of structural phase transition temperatures on measured RIC values. The second part of this work addresses the serious dearth of pertinent RIC data available needed to make critical design decisions for spacecraft, namely for the current NASA Europa Clipper and Lander missions.

Successful spacecraft design and charging mitigation techniques require precise and accurate knowledge of charge deposition profiles. This paper compares models of charge deposition and transport using a venerable deep dielectric charging code, AF-NUMIT3, with direct measurements of charge profiles via pulsed electroacoustic (PEA) measurements. Eight different simulations were performed for comparison to PEA experiments of samples irradiated by 50 keV or 80 keV monoenergetic electrons in vacuum and at room temperature. Two materials, polyether-ether ketone (PEEK) and polytetrafluoroethylene (PTFE), were chosen for their very low conductivities so that minimal charge migration would occur between irradiation and PEA measurements. PEEK was found to have low acoustic attenuation, while PTFE has high acoustic attenuation through the sample thicknesses of 125 μm and 250 μm for each material. The measurements were directly compared to AF-NUMIT3 simulations to validate aspects of the code and to investigate the importance of various simulation options, as well as to characterize the PEA instrumentation, measurement methods, and signal processing used. The measurement and simulation values for magnitude of charge deposition, penetration depth, and charge deposition spatial profiles are largely in agreement, though spatial and temporal distributions in incident electron flux and effects of radiation induced conductivity (RIC) and delayed RIC during the deposition process complicate the process. This work provides an experimental validation of the AF-NUMIT3 deep dielectric charging code and insight into the accuracy and precision of the PEA method.

Various oxides and SiC have been proposed as candidate materials for electrical insulation coatings and inserts to suppress the magnetohydrodynamic (MHD) pressure drop in liquid metal fusion blanket systems. From the early stage of the MHD insulator development, the magnitudes of the radiation-induced conductivities (RICs), i.e., increases in conductivities by radiation excitation, have been evaluated on bulk and coated specimens by using several radiation sources. While the insulating performances of the oxide coated and SiC plate specimens are inferior to those of high quality and purity bulk materials due to cracks, pits, sintering additives, etc., the results indicate that the RIC phenomenon would not prevent the MHD insulators from achieving the required performances (10−3–10−2 S/m for coatings, 102 S/m for inserts) at the first wall of the blanket (500–700 °C, several kGy/s). The recent design investigation of blanket modules for DEMO reactor conditions provides more precise information for prediction of the performances in reactors and conditions to be simulated in the future irradiation damage studies. In the case of the coatings, the suppression of recoiled Li from the liquid metal breeder/coolant might be an issue to be considered in the development.

In space environment, satellites have to cope with strong level of energetic particles (electrons, protons), which can lead to an accumulation of electrical charges on devices and insulators. The implantation of these charges in the materials can generate the initiation of electrostatic discharges and electric arcs. These discharges are potentially dangerous and can create electromagnetic disturbances, power losses or even lead to the destruction of some onboard system. To overcome these possible risks, it is necessary to have a good prediction of the charging materials behaviour under space irradiation. It is therefore essential to have a good understanding, from a microscopic/macroscopic point of view, electron/material interactions, charge transport processes and ageing mechanisms. Indeed, high energy irradiation irreversibly degrades the chemical structure of the material, which affects its electrical behaviour during the space mission. High-energy electronic irradiation on polymeric materials leads to a specific evolution of surface potential due to what is called: Radiation Induced Conductivity (RIC). This RIC is described through models developed at ONERA and based on band theory models applied to imperfect insulator materials to predict these charge and ionization effects. However, some physical mechanisms are not taken into account in these models, and more specifically: energy transfer processes and ageing effects. To highlight these mechanisms and for the extraction of physical parameters related to the models, new experimental techniques must be developed at ONERA: in particular the Thermally Stimulated Current (TSC) and Cathodoluminescence (CL) measurement techniques. Thermally Stimulated Current measurements allowed characterization of the the energy levels and energetic distributions of traps present in different families of space-used polymers (polyimides, fluoropolymers and polyaryletherketones). Important physical parameters for predictive models, such as activation energy distribution profiles, detrapping times as well as densities of traps have thus been extracted using different analysis methods. The effect of aging under high radiation dose was also studied, demonstrating a modification of the band structure associated with the creation of deeper traps levels. Cathodoluminescence measurements have made it possible to observe radiative energy transitions on different space-used polymers. The comparison of CL spectra between polymers with similar chemical structures allowed us to have a first approach on the origin of the different contributions involved. To support these results, a parametric study (temperature, dose) was achieved to propose qualitative models and reaction processes at the origin of luminescence.The objective of this PhD study was therefore to characterize and model the physical mechanisms governing the charge potential of different space-used polymers and to highlight the aging mechanisms. The experimental data derived from these studies have been added into existing charge transport models in order to have a better description of the charging/discharging behavior of materials under space irradiation in both pristine and aged condition.; En environnement spatial, les satellites doivent faire face à des radiations de particules énergétiques (électrons, ions) de forte intensité, pouvant conduire à une accumulation de charges électriques sur les dispositifs et isolants. L’implantation de ces charges au sein des matériaux, peut initier l’amorçage de décharges électrostatiques et d’arcs électriques. Ces décharges potentiellement dangereuses peuvent générer des perturbations électromagnétiques, des pertes de puissance, voir conduire à la destruction de sous-systèmes embarqués. Pour pallier à ces risques éventuels, il est nécessaire d’avoir une bonne prédiction du comportement en charge des matériaux sous irradiation spatiale. Il est donc primordial de bien comprendre, d’un point de vue microscopique/macroscopique, les interactions électrons/matériaux, les processus de transport de charges ainsi que les mécanismes de vieillissement. En effet, l’irradiation de haute énergie dégrade de manière irréversible la structure chimique du matériau, ce qui affecte son comportement électrique au cours de la mission spatiale. L’irradiation électronique de haute énergie sur des matériaux polymères conduit à une évolution particulière du potentiel de surface due à ce que l’on appelle : la conductivité induite sous irradiation (RIC en anglais : Radiation Induced Conductivity). Cette RIC est décrite au travers de modèles développés à l’ONERA et basés sur la théorie des bandes appliquée aux matériaux isolants imparfaits pour prédire les effets de charge et d’ionisation. Cependant, certains mécanismes physiques ne sont pas pris en compte dans ces modèles, et plus particulièrement : les processus de transfert énergétique et les effets de vieillissement. Pour mettre en évidence ces mécanismes et pour l’extraction de paramètres physiques liés aux modèles de nouvelles techniques expérimentales doivent être développées à l’ONERA : il s’agit en particulier de la technique de mesure courant thermostimulé (CTS) et de la cathodoluminescence (CL).Les mesures de courant thermostimulé ont permis de caractériser les niveaux et distributions énergétiques de pièges présents dans différentes familles de polymères à usage spatial (polyimides, fluoropolymères et polyaryléthercétones). Des paramètres physiques importants pour les modèles prédictifs, tels que les énergies d’activation, les temps de dépiégeage ainsi que les densités de pièges ont ainsi pu être extraits via différentes méthodes d’analyse. L’effet du vieillissement sous forte dose radiative a également été étudié, démontrant une modification de la structure de bande associée à la création de niveaux de pièges plus profonds. Les mesures de cathodoluminescence ont rendu possible la mise en évidence de transitions énergétiques radiatives sur différents polymères à usage spatial. La comparaison des spectres CL entre des polymères de structures chimiques proches a permis d’avoir une première approche sur l’origine des différentes contributions mises en jeu. Pour conforter ces résultats, une étude paramétrique (température, dose) a été réalisée afin de proposer des modèles qualitatifs et des schémas réactionnels sur les processus à l’origine de la luminescence.Ce travail de doctorat a donc pour objectif de caractériser et de modéliser les mécanismes physiques gouvernant le potentiel de charge de différents matériaux polymères à usage spatial et de mettre en évidence les mécanismes de vieillissement. Les données expérimentales déduites de ces études ont parallèlement alimenté des modèles existants de transport de charges afin d’avoir une meilleure description du comportement en charge/décharge des matériaux sous irradiation spatial à l’état neuf et vieilli.

In space environment, satellites have to cope with strong level of energetic particles (electrons, protons), which can lead to an accumulation of electrical charges on devices and insulators. The implantation of these charges in the materials can generate the initiation of electrostatic discharges and electric arcs. These discharges are potentially dangerous and can create electromagnetic disturbances, power losses or even lead to the destruction of some onboard system. To overcome these possible risks, it is necessary to have a good prediction of the charging materials behaviour under space irradiation. It is therefore essential to have a good understanding, from a microscopic/macroscopic point of view, electron/material interactions, charge transport processes and ageing mechanisms. Indeed, high energy irradiation irreversibly degrades the chemical structure of the material, which affects its electrical behaviour during the space mission. High-energy electronic irradiation on polymeric materials leads to a specific evolution of surface potential due to what is called: Radiation Induced Conductivity (RIC). This RIC is described through models developed at ONERA and based on band theory models applied to imperfect insulator materials to predict these charge and ionization effects. However, some physical mechanisms are not taken into account in these models, and more specifically: energy transfer processes and ageing effects. To highlight these mechanisms and for the extraction of physical parameters related to the models, new experimental techniques must be developed at ONERA: in particular the Thermally Stimulated Current (TSC) and Cathodoluminescence (CL) measurement techniques. Thermally Stimulated Current measurements allowed characterization of the the energy levels and energetic distributions of traps present in different families of space-used polymers (polyimides, fluoropolymers and polyaryletherketones). Important physical parameters for predictive models, such as activation energy distribution profiles, detrapping times as well as densities of traps have thus been extracted using different analysis methods. The effect of aging under high radiation dose was also studied, demonstrating a modification of the band structure associated with the creation of deeper traps levels. Cathodoluminescence measurements have made it possible to observe radiative energy transitions on different space-used polymers. The comparison of CL spectra between polymers with similar chemical structures allowed us to have a first approach on the origin of the different contributions involved. To support these results, a parametric study (temperature, dose) was achieved to propose qualitative models and reaction processes at the origin of luminescence.The objective of this PhD study was therefore to characterize and model the physical mechanisms governing the charge potential of different space-used polymers and to highlight the aging mechanisms. The experimental data derived from these studies have been added into existing charge transport models in order to have a better description of the charging/discharging behavior of materials under space irradiation in both pristine and aged condition., En environnement spatial, les satellites doivent faire face à des radiations de particules énergétiques (électrons, ions) de forte intensité, pouvant conduire à une accumulation de charges électriques sur les dispositifs et isolants. L’implantation de ces charges au sein des matériaux, peut initier l’amorçage de décharges électrostatiques et d’arcs électriques. Ces décharges potentiellement dangereuses peuvent générer des perturbations électromagnétiques, des pertes de puissance, voir conduire à la destruction de sous-systèmes embarqués. Pour pallier à ces risques éventuels, il est nécessaire d’avoir une bonne prédiction du comportement en charge des matériaux sous irradiation spatiale. Il est donc primordial de bien comprendre, d’un point de vue microscopique/macroscopique, les interactions électrons/matériaux, les processus de transport de charges ainsi que les mécanismes de vieillissement. En effet, l’irradiation de haute énergie dégrade de manière irréversible la structure chimique du matériau, ce qui affecte son comportement électrique au cours de la mission spatiale. L’irradiation électronique de haute énergie sur des matériaux polymères conduit à une évolution particulière du potentiel de surface due à ce que l’on appelle : la conductivité induite sous irradiation (RIC en anglais : Radiation Induced Conductivity). Cette RIC est décrite au travers de modèles développés à l’ONERA et basés sur la théorie des bandes appliquée aux matériaux isolants imparfaits pour prédire les effets de charge et d’ionisation. Cependant, certains mécanismes physiques ne sont pas pris en compte dans ces modèles, et plus particulièrement : les processus de transfert énergétique et les effets de vieillissement. Pour mettre en évidence ces mécanismes et pour l’extraction de paramètres physiques liés aux modèles de nouvelles techniques expérimentales doivent être développées à l’ONERA : il s’agit en particulier de la technique de mesure courant thermostimulé (CTS) et de la cathodoluminescence (CL).Les mesures de courant thermostimulé ont permis de caractériser les niveaux et distributions énergétiques de pièges présents dans différentes familles de polymères à usage spatial (polyimides, fluoropolymères et polyaryléthercétones). Des paramètres physiques importants pour les modèles prédictifs, tels que les énergies d’activation, les temps de dépiégeage ainsi que les densités de pièges ont ainsi pu être extraits via différentes méthodes d’analyse. L’effet du vieillissement sous forte dose radiative a également été étudié, démontrant une modification de la structure de bande associée à la création de niveaux de pièges plus profonds. Les mesures de cathodoluminescence ont rendu possible la mise en évidence de transitions énergétiques radiatives sur différents polymères à usage spatial. La comparaison des spectres CL entre des polymères de structures chimiques proches a permis d’avoir une première approche sur l’origine des différentes contributions mises en jeu. Pour conforter ces résultats, une étude paramétrique (température, dose) a été réalisée afin de proposer des modèles qualitatifs et des schémas réactionnels sur les processus à l’origine de la luminescence.Ce travail de doctorat a donc pour objectif de caractériser et de modéliser les mécanismes physiques gouvernant le potentiel de charge de différents matériaux polymères à usage spatial et de mettre en évidence les mécanismes de vieillissement. Les données expérimentales déduites de ces études ont parallèlement alimenté des modèles existants de transport de charges afin d’avoir une meilleure description du comportement en charge/décharge des matériaux sous irradiation spatial à l’état neuf et vieilli.

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The electrical properties of thin films of poly(arylene ether ketone) copolymers (co-PAEKs) with a fraction of phthalide-containing units of 3, 5, and 50 mol% in the main chain were investigated by using radiation-induced conductivity (RIC) measurements. Transient current signals and current-voltage (I-V) characteristics were obtained by exposing 20 &divide, 25 &mu, m thick films of the co-PAEKs to monoenergetic electron pulses with energy ranging from 3 to 50 keV in an electric field ranging from 5 to 40 V/&mu, m. The Rose-Fowler-Vaisberg semi-empirical model based on a multiple trapping formalism was used for an analysis of the RIC data, and the parameters of the highly dispersive charge carrier transport were evaluated. The analysis revealed that charge carriers moved in isolation from each other, and the applied electric fields were below the threshold field triggering the switching effect (a reversible high-to-low resistivity transition) in the co-PAEK films. It was also found that the co-PAEK films, due to the super-linear I-V characteristics, are highly resistant to electrostatic discharges arising from the effects of ionizing radiation. This property is important for the development of protective coatings for electronic devices.

液体リチウム冷却ブランケット用に開発が進められているセラミック電気絶縁被覆の候補材料Er２O３，Y２O３，CaZrO３に対して，10－３ Gy/s から約600 Gy/s の幅広い線量率範囲および室温から650 ℃の温度範囲における照射実験を実施し，候補材料の放射線誘起伝導（RIC：Radiation Induced Conductivity）現象による絶縁性能の低下は，核融合炉の高放射線・高温環境下において，要求絶縁性能の達成を妨げる要因とならないことを明らかにした．

Dielectric materials used on satellites are subject to radiative and thermal extreme stresses which may lead to disturbances on board instrumentation. The application efficiency can then decrease significantly due to charging and aging effects of used ceramics. With the aim to understand and predict these phenomena, the mechanisms investigation of charges transport and electrical aging on these ceramics is of high importance. The scientific approach of this study was to define a protocol and an experimental method which allows characterising the electrical and physico-chemical behaviours of raw boron nitride and coated with a thin coating of alumina. For this purpose, a parametric study was performed in the irradiation chamber, named CEDRE (at ONERA Toulouse) in order to assess the influence of some parameters such as, incident energy, primary electron flux, temperature, ionising dose, on charging, relaxation and electrical aging kinetics of these industrial ceramics. This study demonstrated that it is possible to greatly limit the dielectrics charging thanks to the use of a ceramic coating and suitable annealing thermal treatment. Indeed, the high secondary electron emission of alumina and the increase of surface conductivity generated by the annealing thermal treatment partly govern the low surface potential of coated boron nitride. Some alumina coating were subsequently elaborated through PVD–RF and then characterised in the irradiation chamber in order to identify the preparation parameters which allow optimising the electrical properties of system. It was shown that the optimisation of the roughness and the coating thickness limits the surface potential of ceramics. An experimental study was conducted in the frame of an international collaboration with the Materials Physics Group of the Utah State University (Logan, USA), in order to investigate the influence of nature and densities of electron defects on the electrical properties of different ceramics. The cathodoluminescence method was used and brought to light the origin of total conductivity difference between materials, raw, coated and annealed. A new method to measure the surface potential under continuous electron irradiation was developed and then validated. A partial discharges mechanism was identified on surface of annealed samples with this optimised device. Ageing processes of the irradiated materials was also studied in the irradiation chamber to reproduce the observed degradation in orbit over the long time. It was demonstrated that the charging of annealed coated materials is noticeable when the sample receive a critical ionising dose. Several physico-chemical characterisations were thus performed at CIRIMAT in order to study the evolution of structural and chemical properties of ceramics. This evolution was correlated with that of electrical properties after deterioration under critical electron irradiation. The contamination and deterioration mechanisms of coated ceramics are responsible of the electrical aging observed experimentally. Finally, these thorough experimental characterisations allowed the development of physical model for the description of the different mechanisms involved on irradiated ceramics and coating.; Les matériaux diélectriques utilisés au sein des applications internes aux satellites sont soumis à des contraintes radiatives et thermiques extrêmes qui peuvent conduire à des perturbations sur l'instrumentation embarquée. Le rendement des applications électroniques diminue ainsi en raison des effets de charge et de dégradation des céramiques utilisées. Dans le but de comprendre et de prédire ces phénomènes, l’étude des mécanismes de transport de charges et de vieillissement électrique sur ces matériaux est primordiale. La démarche de cette étude a alors consisté à définir un protocole et une méthode expérimentale qui permettent d’étudier hors application, les comportements électriques et physico-chimiques sous irradiation électronique, du nitrure de bore brut et revêtu d’une couche mince d’alumine.Pour cela, une étude paramétrique a été réalisée dans l’enceinte d’irradiation CEDRE (ONERA Toulouse), afin d’évaluer l’influence de l’énergie incidente, du flux d’électrons primaires, de la température et de la dose, sur les cinétiques de charge, de relaxation et de vieillissement électrique des céramiques industrielles. Il a été démontré qu'il était possible de limiter fortement la charge de ces céramiques par l'application d'un dépôt d'alumine et par un traitement thermique adéquat. En effet, le rendement d’émission secondaire élevé de l’alumine et l’augmentation de la conductivité de surface, engendrée par le recuit, contribuent à la limitation du potentiel de surface du matériau. Des dépôts d’alumine ont ensuite été élaborés par PVD-RF puis caractérisés en chambre d’irradiation afin de cibler les paramètres d’élaboration qui permettent d’optimiser les propriétés électriques du système. Il a été montré que l’optimisation de la rugosité et de l’épaisseur des dépôts limite le potentiel de surface des matériaux. Une étude amont a été menée dans le cadre d'une collaboration internationale avec le Groupe de Physique des Matériaux de l'Université d’Etat de l’Utah (Logan, USA), afin d’étudier l’influence de la nature et de la population des pièges électroniques sur les propriétés électriques des différentes céramiques. La technique de cathodoluminescence a été utilisée et a ainsi permis d’expliquer la différence de conductivité apparente entre les matériaux bruts, revêtus et recuits. Une nouvelle méthode de mesure de potentiel de charge sous irradiation continue (méthode REPA) a été mise au point puis validée. Des mécanismes de décharge partielle ont été identifiés en surface des échantillons recuits grâce au dispositif optimisé qui a été développé.Une étude de dégradation accélérée des matériaux a ensuite été réalisée en laboratoire dans le but de reproduire la détérioration observée en orbite sur le long terme. Il a été déterminé que la charge des matériaux revêtus et recuits s’amorce après avoir reçu une dose ionisante critique. Des caractérisations physico-chimiques ont donc été effectuées au CIRIMAT afin d’étudier l’évolution des propriétés structurales et chimiques des céramiques. Cette évolution a été corrélée à celle des propriétés électriques après détérioration sous irradiation électronique critique. Les mécanismes de contamination et de détérioration des dépôts de céramiques, responsables de leur vieillissement électrique, ont été mis en évidence.Enfin, ces caractérisations expérimentales approfondies ont servi de base au développement d'un modèle physique qui rend compte des différents mécanismes mis en jeu sur les céramiques et dépôts irradiés.

Dielectric materials used on satellites are subject to radiative and thermal extreme stresses which may lead to disturbances on board instrumentation. The application efficiency can then decrease significantly due to charging and aging effects of used ceramics. With the aim to understand and predict these phenomena, the mechanisms investigation of charges transport and electrical aging on these ceramics is of high importance. The scientific approach of this study was to define a protocol and an experimental method which allows characterising the electrical and physico-chemical behaviours of raw boron nitride and coated with a thin coating of alumina. For this purpose, a parametric study was performed in the irradiation chamber, named CEDRE (at ONERA Toulouse) in order to assess the influence of some parameters such as, incident energy, primary electron flux, temperature, ionising dose, on charging, relaxation and electrical aging kinetics of these industrial ceramics. This study demonstrated that it is possible to greatly limit the dielectrics charging thanks to the use of a ceramic coating and suitable annealing thermal treatment. Indeed, the high secondary electron emission of alumina and the increase of surface conductivity generated by the annealing thermal treatment partly govern the low surface potential of coated boron nitride. Some alumina coating were subsequently elaborated through PVD–RF and then characterised in the irradiation chamber in order to identify the preparation parameters which allow optimising the electrical properties of system. It was shown that the optimisation of the roughness and the coating thickness limits the surface potential of ceramics. An experimental study was conducted in the frame of an international collaboration with the Materials Physics Group of the Utah State University (Logan, USA), in order to investigate the influence of nature and densities of electron defects on the electrical properties of different ceramics. The cathodoluminescence method was used and brought to light the origin of total conductivity difference between materials, raw, coated and annealed. A new method to measure the surface potential under continuous electron irradiation was developed and then validated. A partial discharges mechanism was identified on surface of annealed samples with this optimised device. Ageing processes of the irradiated materials was also studied in the irradiation chamber to reproduce the observed degradation in orbit over the long time. It was demonstrated that the charging of annealed coated materials is noticeable when the sample receive a critical ionising dose. Several physico-chemical characterisations were thus performed at CIRIMAT in order to study the evolution of structural and chemical properties of ceramics. This evolution was correlated with that of electrical properties after deterioration under critical electron irradiation. The contamination and deterioration mechanisms of coated ceramics are responsible of the electrical aging observed experimentally. Finally, these thorough experimental characterisations allowed the development of physical model for the description of the different mechanisms involved on irradiated ceramics and coating., Les matériaux diélectriques utilisés au sein des applications internes aux satellites sont soumis à des contraintes radiatives et thermiques extrêmes qui peuvent conduire à des perturbations sur l'instrumentation embarquée. Le rendement des applications électroniques diminue ainsi en raison des effets de charge et de dégradation des céramiques utilisées. Dans le but de comprendre et de prédire ces phénomènes, l’étude des mécanismes de transport de charges et de vieillissement électrique sur ces matériaux est primordiale. La démarche de cette étude a alors consisté à définir un protocole et une méthode expérimentale qui permettent d’étudier hors application, les comportements électriques et physico-chimiques sous irradiation électronique, du nitrure de bore brut et revêtu d’une couche mince d’alumine.Pour cela, une étude paramétrique a été réalisée dans l’enceinte d’irradiation CEDRE (ONERA Toulouse), afin d’évaluer l’influence de l’énergie incidente, du flux d’électrons primaires, de la température et de la dose, sur les cinétiques de charge, de relaxation et de vieillissement électrique des céramiques industrielles. Il a été démontré qu'il était possible de limiter fortement la charge de ces céramiques par l'application d'un dépôt d'alumine et par un traitement thermique adéquat. En effet, le rendement d’émission secondaire élevé de l’alumine et l’augmentation de la conductivité de surface, engendrée par le recuit, contribuent à la limitation du potentiel de surface du matériau. Des dépôts d’alumine ont ensuite été élaborés par PVD-RF puis caractérisés en chambre d’irradiation afin de cibler les paramètres d’élaboration qui permettent d’optimiser les propriétés électriques du système. Il a été montré que l’optimisation de la rugosité et de l’épaisseur des dépôts limite le potentiel de surface des matériaux. Une étude amont a été menée dans le cadre d'une collaboration internationale avec le Groupe de Physique des Matériaux de l'Université d’Etat de l’Utah (Logan, USA), afin d’étudier l’influence de la nature et de la population des pièges électroniques sur les propriétés électriques des différentes céramiques. La technique de cathodoluminescence a été utilisée et a ainsi permis d’expliquer la différence de conductivité apparente entre les matériaux bruts, revêtus et recuits. Une nouvelle méthode de mesure de potentiel de charge sous irradiation continue (méthode REPA) a été mise au point puis validée. Des mécanismes de décharge partielle ont été identifiés en surface des échantillons recuits grâce au dispositif optimisé qui a été développé.Une étude de dégradation accélérée des matériaux a ensuite été réalisée en laboratoire dans le but de reproduire la détérioration observée en orbite sur le long terme. Il a été déterminé que la charge des matériaux revêtus et recuits s’amorce après avoir reçu une dose ionisante critique. Des caractérisations physico-chimiques ont donc été effectuées au CIRIMAT afin d’étudier l’évolution des propriétés structurales et chimiques des céramiques. Cette évolution a été corrélée à celle des propriétés électriques après détérioration sous irradiation électronique critique. Les mécanismes de contamination et de détérioration des dépôts de céramiques, responsables de leur vieillissement électrique, ont été mis en évidence.Enfin, ces caractérisations expérimentales approfondies ont servi de base au développement d'un modèle physique qui rend compte des différents mécanismes mis en jeu sur les céramiques et dépôts irradiés.

International audience; Prediction of charging behaviour of space used materials often raise the issue on the definition of the applied electron energy spectrum used for irradiation under representative conditions. Radiation induced conductivity (RIC) can not be discarded for a proper qualification of these materials.But RIC level is significantly dependent upon radiation dose and dose rate. We have been able to demonstrate that the applied energy spectra lead to strong and hazardous charging levels, when radiation history is not regarded. However, charging effect is strongly smoothed by radiation history of the material. We have been able therefore to reveal in this study that a good electric qualification of space materials under electron irradiation requires the definition of realistic electron energy spectrum and implies to take into account radiation history in space.

International audience; Dedicated experimental facilities have been developed at ONERA and CNES (Toulouse, France) for the electrical qualification of space used materials and the extraction of the different physical parameters steering their charging behaviour under electron irradiation. These facilities allow working in a large energy range between few eV up to several MeV, a large temperature range (down to -150°C and up to 600°C depending on the facility) and at high vacuum level. This paper aims at presenting the technical characteristics of these different facilities.

International audience; Polymers are widely used on spacecraft for different specific functions : thermal and electrical insulation, mechanical support, adhesion... These polymers are highly sensitive to radiation met in space. Their electric properties is especially significantly altered leading to very specific behaviour in term of charge transport and discharge processes. Different dedicated facilities have been developed at ONERA, with CNES support, for the characterisation of space used materials in representative conditions. Thanks to the use of these different facilities, it has indeed been demonstrated that radiation induced conductivity of space polymers strongly affects the charging surface potential and depends on several parameters (radiation dose rate, total radiation dose, temperature and on the induced electric field) through complex physical mechanisms that are described in this paper. The sensitivity of polymers on these different parameters strongly depends upon polymer trap distribution and molecular configuration. Experimental as well as numerical results shall be presented in this paper, coupled with the different experimental techniques developed and applied in this work.

International audience; This paper presents a numerical estimation of spacecraft surface charging that combines the effects of both spacecraft material properties and severe environments, often called worst-cases. A series of simulations with the SPIS-GEO tool (Spacecraft Plasma Interaction Software) is analysed in order to determine if a worst-case environment can be extracted from the literature. The simulation especially focuses on the conductivity parameters, especially radiation induced. It is found hardly feasible to define a single and global worst-case, applicable to all situations.

Thisstudy measures Radiation Induced Conductivity (RIC) of Low Density Polyethylene(LDPE) over temperatures ranging from ~110 K to ~350 K. RIC occurswhen incident ionizing radiation deposits energy and excites electrons intothe conduction band of insulators. Conductivity was measured when avoltage was applied across vacuum-baked, thin film LDPE polymer samplesin a parallel plate geometry. RIC was calculated as thedifference in sample conductivity under no incident radiation and underan incident ~4 MeV electron beam at low incident fluxes of10−4–10−1 Gr/sec. The steady-state RIC was found to agree well withthe standard power law relation, RIC = kRIC· between conductivity, andadsorbed dose rate, . Both the proportionality constant, kRIC, andthe power, , were found to be temperature dependant above~250 K, with behavior consistent with photoconductivity models developed for localizedtrap states in disordered semiconductors. Below ~250 K, kRIC and exhibited little change. The observed difference in temperature dependence mightbe related to a structural phase transition seen at T~256 Kin prior studies of mechanical and thermodynamic properties of LDPE. ©2009 American Institute of Physics