Μία από τις βασικότερες διαγνωστικές μεθόδους για το πλάσμα είναι αυτή των ηλεκτροστατικών καθετήρων. Η μέθοδος αυτή συνίσταται στην εμβάπτιση ενός καθετήρα σε περιβάλλον πλάσματος, την πόλωση του σε διάφορες τάσεις, τόσο αρνητικές όσο και θετικές, και την μέτρηση του συλλεγόμενου ρεύματος. Από τη μορφή της καμπύλης τάσης- ρεύματος εξάγονται πολύ σημαντικές πληροφορίες για το πλάσμα. Στην παρούσα εργασία παρουσιάζονται, πρώτον, η ανάπτυξη ενός αυτοματοποιημένου συστήματος –κατασκευασμένου εξολοκλήρου από απλά ηλεκτρονικά εξαρτήματα- για την πόλωση του καθετήρα και την καταγραφή των απαραίτητων δεδομένων και δεύτερον, η κατασκευή μίας πειραματικής διάταξης για την παραγωγή επαγωγικού πλάσματος ραδιοσυχνοτήτων (13.56 MHz), στην οποία έγινε δοκιμή της σωστής λειτουργίας της συσκευής. / One of the most fundamental techniques for plasma characterization is the use of electrostatic probes. This method involves the insertion of a small metallic electrode into the plasma, the biasing of this electrode to various voltages, both negative and positive, and the measurement of the collected current. From the voltage–current characteristic curve one can calculate important parameters of the plasma. This work is devoted to: a) the development of a fully automated system (made entirely with modern electronic parts) for probe biasing and current data acquisition on a personal computer, and b) the construction of an experimental setup for the generation of inductively coupled plasmas (13.56 MHz), where the aforementioned system is tested.

Os estudos sobre o plasma na região da borda de máquinas tokamak têm se intensificado nos últimos anos em decorrência da constatação de que o comportamento do plasma na região central da máquina é bastante influenciado por processos que ocorrem na borda da coluna. Neste trabalho feito um estudo experimental das propriedades de transporte do plasma na região da sombra do limitador do TBR-l, um tokamak de pequeno porte em operação no Instituto de Física da Universidade de São Paulo. São também determinados os tempos de confinamento globais de partículas e energia. Três foram os diagnósticos usados neste trabalho. Inicialmente, é abordada a utilização de sondas de Langmuir para a obtenção de perfis radiais e temporais da temperatura de elétrons, densidade e potencial de plasma; descreve-se também o arranjo experimental usado para este diagnóstico. A seguir, discute-se o projeto e a construção de uma sonda sensível a íons associada a um sistema eletrônico que permitiu a determinação simultânea das temperaturas locais de íons e elétrons. Finalmente, é discutido o dimensionamento e a implantação de um interferômetro de microondas para medidas de densidade de elétrons na região central da coluna de plasma do TBR-1; o sistema opera em 65 GHz e toda a eletrônica associada foi projetada e construída em nosso Laboratório. Os resultados obtidos com as sondas foram analisados com o ajuda de um modelo não colisional de transporte de partículas e energia para a região da sombra do limitador de máquinas tokamak. A partir dos decaimentos radiais da termperatura de elétrons (\'lâmbda IND. e\' \'APROXIMADAMENTE IGUAL A\' 2,6cm) e da densidade (\'lâmbda IND. n\' \'APROXIMADAMENTE IGUAL A\' 1,4cm), bem como do fator de transmissão de energia para os elétrons (\'delta IND. e\' \'APROXIMADAMENTE IGUAL A\' 4), determinou-se o coeficiente de difusão perpendicular ao campo magnético (\'D IND. 1\' \'APROXIMADAMENTE IGUAL A\' 6 \'m POT. 2\'\'s POT. -1\') e a difusividade térmica dos elétrons (\'qui POT. e IND. 1\' \'APROXIMADAMENTE IGUAL A\' 8 \'m POT. 2\'\'s POT. -1\'), resultados que indicam valores próximos aos previstos pelo modelo de Bohm. As medidas das temperaturas de íons e elétrons mostram um claro desacoplamento térmico entre íons e elétrons (\'T IND. i\'/\'T IND. e\' \'APROXIMADAMENTE IGUAL A\' 2). As medidas de densidade obtidas no centro da coluna, em conjunto com as obtidas na borda, permitiram a determinação dos tempos de confinamento globais de partículas (\'tau IND. p\'\'APROXIMADAMENTE IGUAL A\' 1,8 x \'10 POT. -3\'s) e de energia (\'tau IND. E\'\'APROXIMADAMENTE IGUAL A\' 1,2 x \'10 POT. -4\'s). Os resultados foram comparados com os previstos por várias leis de escala. / The study of the plasma edge in Tokamak machines has increased in recent last years, since the recognition that the behavior of the plasma core is influenced by the Physical processes that occur in the edge region. This work develops an experimental stud) of plasma transport properties in the shadow region of TBR-l limiter. TBR-l is a small Tokamak in operation in the Physics Institute of São Paulo University. We have also determined the global confinement time of particles and energy. We have used three diagnostics: a Langmuir probe, an ion sensitive probe, and a microwave interferometer. Initially we discuss the use of Langmuir probes in Tokamak machines to obtain temporal and radial profiles of electron temperature, plasma density and potential; we show also the experimental arrangement used in the TBR-l for this diagnostic. Then, we discuss the design and construction of an ion sensitive probe associated with an electronic system, that was used to obtain, simultaneously, local ion and electron temperature. Finally we discuss a microwave interferometry system that has been built for the TBR-1. The microwave generator is a reflex Klystron (f = 65 GHz), and with the interferometer we obtained electron density time profiles of the center of TBR-l plasma column. All the electronics associated with the interferometer were designed and built in our laboratory. The results obtained with the probes are discussed with the help of a collisionless model for Tokamak scrape-off plasma. With the radial e-foldings of electron temperature (e 2.6 cm) and density (n 1.4 cm), and the sheath electron transmission coefficient (e 4) we have determined the cross-field diffusion coefficient (D1 6 m2s-1) and the electron cross-field thermal diffusivity (e1 8 m2s-1). These results indicate values near those predicted by the Bohm model. The measurements of electron and ion temperature shows a clear thermal decoupling between ions and electrons (T1/Te 2). The measurements of plasma parameters in the center of the plasma column, with that obtained with the probes permitted the determination of the particle (p 1.8 x 10-3s) and energy (e 1.2 x10-4s) global confinement times. These results were compared with those predicted by scaling laws.

The 'high-pressure' atmospheric (TIG) arc plasma is studied by means of a multi-Langmuir probe system. In order to determine the appropriate regime of operation, definitions of the plasma parameters for the description of the argon arc are considered and evaluations are presented. A description of the probe basic techniques is followed by an in-depth discussion of the different regimes of probe operation. The emphasis is put on atmospheric and flowing (arc) regimes. Probe sheath theories are compared and “Nonidealities” like cooling due to plasma-probe motion and probe emission mechanisms are then described. The extensive literature review reveals that the existing probe theories are inappropriate for a use in the TIG arc, because of ‘high’ pressure (atmospheric), broad range of ionization across the arc, flowing conditions, and ultimately, to the uncertainty about onset of Local Thermodynamical Equilibrium. The Langmuir probe system is built to operate in floating and biased conditions. The present work represents the first extensive investigation of electrostatic probes in arcs where the experimental difficulties and the primary observed quantities are presented in great detail. Analysis methodologies are introduced and experimental results are presented towards a unified picture of the resulting arc structure by comparison with data from emission spectroscopy. Results from different measurements are presented and comparison is made with data on TIG arcs present in literature. Probe obtained temperatures are lower than the values obtained from emission spectroscopy and this ‘cooling’ is attributed to electron-ion recombination. However, it is believed that probes can access temperatures regions not attainable by emission spectroscopy. Only axial electric potential and electric field are obtained because of the equipotential-probe requirement. Estimations of the sheath voltage and extension are obtained and a qualitative picture of the ion and electron current densities within the arc is given.

Os estudos sobre o plasma na região da borda de máquinas tokamak têm se intensificado nos últimos anos em decorrência da constatação de que o comportamento do plasma na região central da máquina é bastante influenciado por processos que ocorrem na borda da coluna. Neste trabalho feito um estudo experimental das propriedades de transporte do plasma na região da sombra do limitador do TBR-l, um tokamak de pequeno porte em operação no Instituto de Física da Universidade de São Paulo. São também determinados os tempos de confinamento globais de partículas e energia. Três foram os diagnósticos usados neste trabalho. Inicialmente, é abordada a utilização de sondas de Langmuir para a obtenção de perfis radiais e temporais da temperatura de elétrons, densidade e potencial de plasma; descreve-se também o arranjo experimental usado para este diagnóstico. A seguir, discute-se o projeto e a construção de uma sonda sensível a íons associada a um sistema eletrônico que permitiu a determinação simultânea das temperaturas locais de íons e elétrons. Finalmente, é discutido o dimensionamento e a implantação de um interferômetro de microondas para medidas de densidade de elétrons na região central da coluna de plasma do TBR-1; o sistema opera em 65 GHz e toda a eletrônica associada foi projetada e construída em nosso Laboratório. Os resultados obtidos com as sondas foram analisados com o ajuda de um modelo não colisional de transporte de partículas e energia para a região da sombra do limitador de máquinas tokamak. A partir dos decaimentos radiais da termperatura de elétrons (\'lâmbda IND. e\' \'APROXIMADAMENTE IGUAL A\' 2,6cm) e da densidade (\'lâmbda IND. n\' \'APROXIMADAMENTE IGUAL A\' 1,4cm), bem como do fator de transmissão de energia para os elétrons (\'delta IND. e\' \'APROXIMADAMENTE IGUAL A\' 4), determinou-se o coeficiente de difusão perpendicular ao campo magnético (\'D IND. 1\' \'APROXIMADAMENTE IGUAL A\' 6 \'m POT. 2\'\'s POT. -1\') e a difusividade térmica dos elétrons (\'qui POT. e IND. 1\' \'APROXIMADAMENTE IGUAL A\' 8 \'m POT. 2\'\'s POT. -1\'), resultados que indicam valores próximos aos previstos pelo modelo de Bohm. As medidas das temperaturas de íons e elétrons mostram um claro desacoplamento térmico entre íons e elétrons (\'T IND. i\'/\'T IND. e\' \'APROXIMADAMENTE IGUAL A\' 2). As medidas de densidade obtidas no centro da coluna, em conjunto com as obtidas na borda, permitiram a determinação dos tempos de confinamento globais de partículas (\'tau IND. p\'\'APROXIMADAMENTE IGUAL A\' 1,8 x \'10 POT. -3\'s) e de energia (\'tau IND. E\'\'APROXIMADAMENTE IGUAL A\' 1,2 x \'10 POT. -4\'s). Os resultados foram comparados com os previstos por várias leis de escala. / The study of the plasma edge in Tokamak machines has increased in recent last years, since the recognition that the behavior of the plasma core is influenced by the Physical processes that occur in the edge region. This work develops an experimental stud) of plasma transport properties in the shadow region of TBR-l limiter. TBR-l is a small Tokamak in operation in the Physics Institute of São Paulo University. We have also determined the global confinement time of particles and energy. We have used three diagnostics: a Langmuir probe, an ion sensitive probe, and a microwave interferometer. Initially we discuss the use of Langmuir probes in Tokamak machines to obtain temporal and radial profiles of electron temperature, plasma density and potential; we show also the experimental arrangement used in the TBR-l for this diagnostic. Then, we discuss the design and construction of an ion sensitive probe associated with an electronic system, that was used to obtain, simultaneously, local ion and electron temperature. Finally we discuss a microwave interferometry system that has been built for the TBR-1. The microwave generator is a reflex Klystron (f = 65 GHz), and with the interferometer we obtained electron density time profiles of the center of TBR-l plasma column. All the electronics associated with the interferometer were designed and built in our laboratory. The results obtained with the probes are discussed with the help of a collisionless model for Tokamak scrape-off plasma. With the radial e-foldings of electron temperature (e 2.6 cm) and density (n 1.4 cm), and the sheath electron transmission coefficient (e 4) we have determined the cross-field diffusion coefficient (D1 6 m2s-1) and the electron cross-field thermal diffusivity (e1 8 m2s-1). These results indicate values near those predicted by the Bohm model. The measurements of electron and ion temperature shows a clear thermal decoupling between ions and electrons (T1/Te 2). The measurements of plasma parameters in the center of the plasma column, with that obtained with the probes permitted the determination of the particle (p 1.8 x 10-3s) and energy (e 1.2 x10-4s) global confinement times. These results were compared with those predicted by scaling laws.

Dans un propulseur à courant de Hall, la création des ions et leur accélération sont régis par le même phénomène physique. L'idée du propulseur de Hall double étage (DSHT) est de découpler l'ionisation du gaz (poussée) et l'accélération des ions (ISP), de sorte à rendre le système davantage versatile. Les travaux menés durant cette thèse visent à démontrer, grâce à des essais expérimentaux, la pertinence et la faisabilité d'un tel concept. Dans un premier temps, un prototype de DSHT, baptisé ID-HALL, a été conçu et assemblé. Il est constitué d'une source inductive magnétisée insérée dans un tube en céramique et d'un étage d'accélération identique à une barrière magnétique de propulseur simple étage. La source inductive a été optimisée de sorte à réduire le couplage capacitif et à maximiser l'efficacité du transfert de puissance par ajout de pièces en ferrite et diminution de la fréquence RF d'excitation. Dans un deuxième temps, la source inductive du propulseur a été caractérisée indépendamment du propulseur en argon et xénon pour différentes pressions. Le dispositif expérimental a permis notamment de tracer une cartographie 2D de la densité et de la température. Enfin, le propulseur a été monté dans son caisson et des mesures préliminaires (caractéristiques courant-tension, mesures par sonde RPA) ont été menées. En parallèle, des simulations utilisant un modèle hybride 2D ont été effectuées en mode simple et double étage. Elles mettent en évidence un fonctionnement versatile du moteur pour des tensions inférieures à 150 V. A terme, on visera à démontrer que la densité de courant et l'énergie des ions peuvent être, dans certaines conditions, significativement découplées. / In Hall thrusters, the same physical phenomenon is used both to generate the plasma and to accelerate ions. Furthermore, only a single operating point is experimentally observed. The double stage Hall thruster (DSHT) design could allow a separate control of ionization (thrust) and ions acceleration (ISP) to make the system more versatile. The work carried out during this PhD aims to experimentally demonstrate the relevance and the feasibility of this concept. Firstly, a new design of DSHT, called ID-HALL, was proposed and a new prototype was built. It combines the concentric cylinder configuration of a single stage Hall thruster with a magnetized inductively coupled RF plasma source (ICP) whose coil is placed inside the inner cylinder. The ICP source was improved in terms of power coupling efficiency by adding ferrite parts and by decreasing the heating RF frequency. The ICP source used in the ID-HALL thruster was then characterized independently of the thruster using argon and xenon and varying pressure. The experimental setup has allowed to measure the spatial variations of the electron density and temperature. Finally, the thruster was mounted in its vacuum chamber and preliminary measures (voltage-current characteristics, RPA measurements) were led. At the same time, simulations using a two-dimensional hybrid model were performed in single and double stage. A versatile operation for voltages lower than 150 V was highlighted. An emphasis will be given to demonstrate that the current density (given by the ion flux probe) and the ions energy (given by the RPA) might be significantly decoupled.

Title: Anomalous diffusion of plasma in tokamak edge region Author: Jakub Seidl Tutoring institution: Institute of Plasma Physics AS CR, v.v.i. Supervisor: Doc. Ing. Ladislav Krlín, DrSc., IPP AS CR Consultant: RNDr. Radomír Pánek, Ph.D., IPP AS CR Abstract: This work provides brief introduction to the topic of plasma turbu- lence in tokamak edge region and several aspects of anomalous plasma diffusion are discussed. We use numerical code ESEL to model interchange turbulence and investigate properties of turbulent structures in different regimes of parallel trans- port. Means of experimental verification of the results are discussed. Results of the modelling are then used to interpret unexpected results experimentally obtained by electrostatic ball-pen probes on tokamak ASDEX Upgrade, mainly appearance of a 'bump' in power spectra of measured plasma potential. Next, we explain be- haviour of cross-correlation function of density signals measured by two spatially separated Langmuir probes in the vicinity of magnetic separatrix and we point out an ambiguity in interpretation of results of vorticity measurement made by set of floating Langmuir probes. In the last part, transport of plasma impurities by electrostatic turbulent potential is modelled. We identify reversal of radial particle velocity for particles with...

All satellites need a propulsion system for orbit correction maneuvers. Electric Hall effect thrusters are an interesting technology for space applications. The big advantage compared to chemical propulsion devices is the higher specific impulse Isp, a higher ejection speed and thus a substantial gain in terms of propellant consumption. In a Hall effect thruster the ions are created and accelerated in a low pressure discharge plasma in a magnetic field. The first part of the work concerns scaling laws for Hall effect thrusters. A semi-empirical scaling model based on analytical laws and relying on simplifying assumptions is developed. This scaling model can be used to extrapolate existing thruster technologies in order to meet new mission requirements. In a second part, the influence of the channel width on the thruster performance level is investigated. It has been demonstrated that enlarging the channel width of a low power Hall effect thruster leads to an increase in thruster efficiency. Finally, electron properties are measured by means of electrostatic probes in the plume of different Hall effect thrusters. Experimental data on electron properties is of great interest for the validation of numerical plume models that are essential for the integration of the thruster on the satellite. Time-averaged and timeresolved measurements of the electron properties have been carried out for different operating conditions of the thruster. A fast-moving probe system has been developed in order to perform measurements of the electron properties close to the thruster exit plane.

Cette thèse porte sur l'étude expérimentale de la production d’ions négatifs (H-) par des sources multi-dipolaires microondes (2.45 GHz) fonctionnant à la Résonance Cyclotron des Electrons (RCE). Les sources H- sont nécessaires aux accélérateurs de haute énergie et surtout pour les systèmes d’injection de neutres à haute énergie pour le chauffage des plasmas de fusion. Pour cette étude, deux sources (Prometheus I et ROSAE III) ont été conçues, fabriquées et étudiées. Ces deux sources sont munies de réseaux 2D des sources multi-dipolaires. Il est prouvé que la formation des ions négatifs dans ces sources d'ions, est dû à un mécanisme de production en volume : l'attachement dissociatif des électrons de faible énergie sur des molécules ro-vibrationallement excitées. Contrairement aux sources impliquant des réactions de surface, la production en volume a l’avantage de fonctionner sans césium. Une étude détaillée des principes fondamentaux de la production de H- est réalisée, et les voies possibles pour d'optimisation sont explorées au moyen de : sondes électrostatiques, photodetachment laser, spectroscopie d'émission optique dans la région spectrale du visible et de l'ultraviolet du vide et finalement par spectroscopie d'absorption et de fluorescence induite dans la région spectral de l'ultraviolet du vide en utilisant radiation synchrotron dans un montage expérimental spécial (SCHEME). Analytiquement:La source "Prometheus I" est d'abord étudiée en détails, dans une large gamme de conditions expérimentales (par exemple, pression, puissance, position des zones RCE). Cette étude souligne l’efficacité de production des ions H- en volume, et dévoile une fenêtre de fonctionnement optimal et des voies d'optimisation pour atteindre de plus fortes densités d'ions H-. La contribution du processus d'attachement dissociatif et de l'ionisation résonnante des neutres, à la production H- pour cette source ont été évaluée et la prépondérance de la première finalement confirmée par un modèle rendant compte du bilan des créations et pertes d’espèces.En raison de l'importance des molécules ro-vibrationnallement excitées lors du processus d'attachement dissociatif, l'étude se concentre sur leurs réactions de formation. Deux réactions de formation sont étudiées par des expériences dédiées : la désorption recombinative des atomes d'hydrogène à la surface de divers matériaux ("ROSAE III" et "SCHEME") et l'excitation par impact d'électrons à travers les états singulets temporaires ("Prometheus I"). L'étude de la désorption recombinative a été appréhendée de deux façons différentes. Avec la source ROSAE III, l'impact indirect du processus pour la production d'ions négatifs, à travers la formation de molécules ro-vibrationnellement excitées, a été évaluée dans les plasmas RCE. Dans la deuxième approche, la source "SCHEME" a été conçue pour l'étude de la désorption recombinative des atomes en utilisant le rayonnement synchrotron. La formation des états vibrationnels suite à l’excitation des états singulets, dans la source "Prometheus I" a été étudiée par des mesures d'émission de l'ultraviolet du vide.Une étude qui combine la spectroscopie d'émission de l'ultraviolet du vide, le photodétachement et la caractérisation de la cinétique des électrons par sondes électrostatiques, a permis l'identification des facteurs qui limitent la production d'ions négatifs dans le plasma RCE de "Prometheus I". Des perspectives pour surmonter ces limitations sont finalement proposées. / The present PhD thesis is devoted to the experimental study of hydrogen negative ion (H-) production in microwave-driven (2.45 GHz) multi-dipolar Electron Cyclotron Resonance (ECR) plasma sources. H- sources are required in high-energy accelerators and more importantly in neutral beam injection systems for fusion plasma heating. Towards this directions, two sources (namely, "Prometheus I" and "ROSAE III") are designed, fabricated and studied. Both sources are driven by 2D networks of dipolar ECR elementary sources. It is proven that, negative ion formation in these ion sources is governed by the volume production mechanism, which mostly refers to the dissociative attachment of low energy electrons to vibrationally excited molecules. Contrary to the so called surface sources, volume production sources have the advantage of cesium-free operation. Extended experimental study on fundamental principles of H- production is realized, and possible ways for potential source optimization are tested by means of: electrostatic probes, laser photodetachment, optical emission spectroscopy, both in the visible and vacuum ultra-violet spectral range and finally, vacuum-ultraviolet absorption and induced fluorescence spectroscopy using synchrotron radiation in a specially designed setup ("SCHEME"). Analytically:The source "Prometheus I" is initially studied in detail (EEDF, H- density, optical emission spectra etc), under a wide range of experimental conditions (e.g., pressure, power, ECR-zone location), proving its efficiency for H- volume production, and unveiling optimum operational window and paths for obtaining higher H- densities. The contribution of the dissociative attachment process and neutral resonant ionization to H- production in this source, is evaluated, and the dominance of the former is finally confirmed by an equilibrium model.Due to the importance of the ro-vibrationally excited molecules to the dissociative attachment process, the study is focused on their formation reactions. Two formation reactions are considered by adequately adapted experiments: the recombinative desorption of hydrogen atoms on the surface of various materials (ROSAE III and SCHEME) and the electron impact excitation through temporary singlet states (Prometheus I). The study of recombinative desorption is approached in two different ways. With the source ROSAE III, the indirect impact of the process to the production of negative ions, through the formation of ro-vibrationally excited molecules, is evaluated in ECR plasmas. In the second approach, the source SCHEME is designed for the independent investigation of the recombinative desorption of unexcited atoms using synchrotron radiation based diagnostics. The formation of vibrational states through singlet excitation in the source "Prometheus I" is studied by vacuum-ultraviolet emission measurements.A study that combined vacuum-ultraviolet emission spectroscopy, photodetachment and the characterization of electron kinetics with electrostatic probes, allowed the identification of the factors that limit negative ion production in the ECR plasma of "Prometheus I". Perspectives for overcoming these limitations are finally proposed.

Chaque satellite nécessite un système de propulsion pour des corrections d’orbite. Les propulseurs électriques à effet de Hall sont une technologie intéressante pour des applications spatiales. Le grand avantage par rapport à la propulsion chimique est une impulsion spécifique Isp plus élevée, une vitesse d’éjection plus élevée et donc un gain substantiel en termes de consommation de carburant. Dans un propulseur à effet Hall les ions sont créés et accélérés dans une décharge plasma à basse pression dans un champ magnétique. La première partie de ce travail concerne les lois d’échelle pour les propulseurs à effet Hall. Un modèle de dimensionnement semi-empirique basé sur des lois analytiques et reposant sur des hypothèses simplificatrices a été développé. Ce modèle de dimensionnement peut être utilisé pour une extrapolation des propulseurs existants afin de répondre aux exigences pour de nouvelles missions. Dans une deuxième étape, l’influence de la largeur du canal sur les performances d’un propulseur est étudiée. Il a été démontré qu’augmenter la largeur du canal conduit à une amélioration de l’efficacité du propulseur. Finalement, les propriétés électroniques ont été mesurées à l’aide de sondes électrostatiques dans la plume de différents propulseurs à effet Hall. Des données expérimentales concernant les propriétés électroniques sont très intéressantes pour la validation des modèles numériques de la plume indispensables pour l’intégration du propulseur sur le satellite. Des mesures moyennées et résolues en temps des propriétés électroniques ont été réalisées pour différents points de fonctionnement du propulseur. Un système de déplacement rapide pour les sondes a été développé afin de pouvoir faire des mesures des propriétés électroniques dans la zone proche du plan de sortie du propulseur. / All satellites need a propulsion system for orbit correction maneuvers. Electric Hall effect thrusters are an interesting technology for space applications. The big advantage compared to chemical propulsion devices is the higher specific impulse Isp, a higher ejection speed and thus a substantial gain in terms of propellant consumption. In a Hall effect thruster the ions are created and accelerated in a low pressure discharge plasma in a magnetic field. The first part of the work concerns scaling laws for Hall effect thrusters. A semi-empirical scaling model based on analytical laws and relying on simplifying assumptions is developed. This scaling model can be used to extrapolate existing thruster technologies in order to meet new mission requirements. In a second part, the influence of the channel width on the thruster performance level is investigated. It has been demonstrated that enlarging the channel width of a low power Hall effect thruster leads to an increase in thruster efficiency. Finally, electron properties are measured by means of electrostatic probes in the plume of different Hall effect thrusters. Experimental data on electron properties is of great interest for the validation of numerical plume models that are essential for the integration of the thruster on the satellite. Time-averaged and timeresolved measurements of the electron properties have been carried out for different operating conditions of the thruster. A fast-moving probe system has been developed in order to perform measurements of the electron properties close to the thruster exit plane.

La propulsion électrique est à un tournant de son histoire. La récente mise en oeuvre de satellites de télécommunication "tout-électrique" se traduit par l’ouverture d’un nouveau marché, et par une évolution des besoins opérationnels. L’identification de ces nouvelles missions nécessite l’amélioration des performances de nos moteurs. La première partie de ces travaux rapporte l’utilisation d’un outil de spectroscopie laser destiné à caractériser la distribution en vitesse des ions. Les différentes méthodes de calcul du champ électrique dans les propulseurs de Hall ont été exposées. Deux instabilités ioniques ont été observées et analysées. Les sources d’erreurs liées aux mesures par sondes électrostatiques ont été analysées, et un exemple de sonde plane étudié. Une analyse paramétrique de l’influence des paramètres de champ magnétique sur les performances des propulseurs de Hall a été conduite. Le concept de moteur "sans parois" est présenté. L’identification de ce concept constitue une avancée porteuse de promesses pour l’avenir de la propulsion électrique. / Electric propulsion is facing new challenges. Recently, the launch of "all-electric" satellites has marked the debut of a new era. Going all-electric now appears as an interesting alternative to conventional systems for telecom operators. A laser spectroscopy technique was used during this research to investigate the ion velocity distribution dynamics. The different methods for determining the electric field in Hall thrusters were exposed. Two unstable ion regimes were identified and examined. Measurement uncertainties using electrostatic probes were assessed. Planar probed have been designed and tested. A thorough investigation of the influence of the magnetic field parameters on the performance of Hall thrusters was performed. The wall-less Hall thruster design was presented, and preliminary experiments have revealed its interest for the electric propulsion community.