Neste trabalho investiga-se, inicialmente, o comportamento de um amplificador klystron de múltiplas cavidades segundo uma análise a pequenos sinais linear considerando o efeito de carga espacial para, na seqüência, apresentar uma análise do dispositivo utilizando um modelo não-linear a grandes sinais. Na primeira investigação apresenta-se, a partir da teoria dos modos normais, expressões que descrevem o balanço de potência complexo em uma cavidade excitada por um feixe de elétrons. Na seqüência, utiliza-se um modelo linearizado a pequenos sinais para desenvolver uma expressão para a densidade de corrente de convecção ao longo do tubo de deriva acoplado a múltiplas cavidades reentrantes, em função do campo elétrico produzido nos gaps de interação das cavidades. Estas expressões formam a base para a determinação do ganho de voltagem e de ganho de potência de um amplificador klystron de múltiplas cavidades, além da determinação de uma expressão para a largura de banda, sob a hipótese de cavidades idênticas e igualmente espaçadas. O código desenvolvido é validado utilizando-se os parâmetros de um amplificador klystron de 4 cavidades, com corrente d.c. de 525 mA, voltagem d.c. de 6 kV e freqüência de 1,849 MHz, quando se obteve um ganho de 70 dB. Na análise a grandes sinais, o modelo matemático utiliza o formalismo lagrangiano para resolver a dinâmica das partículas, descritas conforme o modelo de discos com raio finito, em uma análise unidimensional, considerando os efeitos não-lineares devido aos campos de carga espacial. O código é validado usando os dados de um amplificador klystron comercial Varian. Dentre outros, os gráficos da velocidade e da densidade do feixe de elétrons, da corrente harmônica, do ganho por cavidade, da conversão AM/AM, da compressão de ganho e da energia do sistema são mostrados e discutidos. Além disso, apresentou-se também um método para a determinação da freqüência de ressonância 0 f , para o fator de qualidade Q e para a razão (R Q) em cavidades cilíndricas reentrantes, de relevância para o projeto de amplificadores klystron de múltiplas cavidades, utilizando a técnica do casamento de admitância do gap de interação entre a cavidade e o tubo de deriva. Um dos resultados mais significativos é o da corrente harmônica fundamental, que resultou 60% maior do que a corrente d.c. considerando um dispositivo com 4 cavidades. / This work investigates, initially, a klystron amplifier with multiple cavities using a small signal analysis considering the space charge effects for, in sequence, provide an analysis of the device using a model for large signals. In the first investigation is presented, from the normal modes theory according to J. Slater, expressions that describe the complex balance of power in a cavity excited by an electron beam. Subsequently, it uses a linearized model for small signals to develop an expression for the convection current density along the drift tube coupled to multiple reentrant cavities, depending on the electric field produced in the interaction gaps of the cavities. These expressions form the basis for determining the voltage gain and power gain of an amplifier klystron to multiple cavities, and determination of an expression for the bandwidth, under the hypothesis of identical and equally spaced cavities. The developed code is validated using the parameters of a klystron amplifier, four cavities, with dc current 525 mA, dc voltage of 6 kV, and frequency of 1.849 GHz, when it obtained a gain of 70 dB. In the large signal analysis, the mathematical model uses the lagrangian formalism to solve the dynamics of particles, described as the model disk with finite radius in a one-dimensional analysis, considering the nonlinear effects due to space charge fields. The code is validated using data from a commercial Varian klystron amplifier of 1.848 GHz. Among others, the graphs of velocity and density of the electron beam, the harmonic current, the gain per cavity, the conversion AM/AM compression gain and energy of the system are shown and discussed. Moreover, it is presented a method for determining the resonant frequency 0 f , for the quality factor Q and the (R Q) at reentrant cylindrical cavities, of relevance for the design of a klystron amplifier of multiple cavities, using the admittance matching technique in the gap of interaction between the cavity and drift tube. One of the more significant is the fundamental harmonic current, which resulted 60% higher than the dc current considering a device with four cavities.

Neste trabalho investiga-se, inicialmente, o comportamento de um amplificador klystron de múltiplas cavidades segundo uma análise a pequenos sinais linear considerando o efeito de carga espacial para, na seqüência, apresentar uma análise do dispositivo utilizando um modelo não-linear a grandes sinais. Na primeira investigação apresenta-se, a partir da teoria dos modos normais, expressões que descrevem o balanço de potência complexo em uma cavidade excitada por um feixe de elétrons. Na seqüência, utiliza-se um modelo linearizado a pequenos sinais para desenvolver uma expressão para a densidade de corrente de convecção ao longo do tubo de deriva acoplado a múltiplas cavidades reentrantes, em função do campo elétrico produzido nos gaps de interação das cavidades. Estas expressões formam a base para a determinação do ganho de voltagem e de ganho de potência de um amplificador klystron de múltiplas cavidades, além da determinação de uma expressão para a largura de banda, sob a hipótese de cavidades idênticas e igualmente espaçadas. O código desenvolvido é validado utilizando-se os parâmetros de um amplificador klystron de 4 cavidades, com corrente d.c. de 525 mA, voltagem d.c. de 6 kV e freqüência de 1,849 MHz, quando se obteve um ganho de 70 dB. Na análise a grandes sinais, o modelo matemático utiliza o formalismo lagrangiano para resolver a dinâmica das partículas, descritas conforme o modelo de discos com raio finito, em uma análise unidimensional, considerando os efeitos não-lineares devido aos campos de carga espacial. O código é validado usando os dados de um amplificador klystron comercial Varian. Dentre outros, os gráficos da velocidade e da densidade do feixe de elétrons, da corrente harmônica, do ganho por cavidade, da conversão AM/AM, da compressão de ganho e da energia do sistema são mostrados e discutidos. Além disso, apresentou-se também um método para a determinação da freqüência de ressonância 0 f , para o fator de qualidade Q e para a razão (R Q) em cavidades cilíndricas reentrantes, de relevância para o projeto de amplificadores klystron de múltiplas cavidades, utilizando a técnica do casamento de admitância do gap de interação entre a cavidade e o tubo de deriva. Um dos resultados mais significativos é o da corrente harmônica fundamental, que resultou 60% maior do que a corrente d.c. considerando um dispositivo com 4 cavidades. / This work investigates, initially, a klystron amplifier with multiple cavities using a small signal analysis considering the space charge effects for, in sequence, provide an analysis of the device using a model for large signals. In the first investigation is presented, from the normal modes theory according to J. Slater, expressions that describe the complex balance of power in a cavity excited by an electron beam. Subsequently, it uses a linearized model for small signals to develop an expression for the convection current density along the drift tube coupled to multiple reentrant cavities, depending on the electric field produced in the interaction gaps of the cavities. These expressions form the basis for determining the voltage gain and power gain of an amplifier klystron to multiple cavities, and determination of an expression for the bandwidth, under the hypothesis of identical and equally spaced cavities. The developed code is validated using the parameters of a klystron amplifier, four cavities, with dc current 525 mA, dc voltage of 6 kV, and frequency of 1.849 GHz, when it obtained a gain of 70 dB. In the large signal analysis, the mathematical model uses the lagrangian formalism to solve the dynamics of particles, described as the model disk with finite radius in a one-dimensional analysis, considering the nonlinear effects due to space charge fields. The code is validated using data from a commercial Varian klystron amplifier of 1.848 GHz. Among others, the graphs of velocity and density of the electron beam, the harmonic current, the gain per cavity, the conversion AM/AM compression gain and energy of the system are shown and discussed. Moreover, it is presented a method for determining the resonant frequency 0 f , for the quality factor Q and the (R Q) at reentrant cylindrical cavities, of relevance for the design of a klystron amplifier of multiple cavities, using the admittance matching technique in the gap of interaction between the cavity and drift tube. One of the more significant is the fundamental harmonic current, which resulted 60% higher than the dc current considering a device with four cavities.

Les klystrons sont des tubes électroniques dans lesquels un ou plusieurs faisceaux d'électrons sont modulés afin de d'amplifier un signal radiofréquence. Pour ce faire, des cavités passives constituant la ligne d’interaction du klystron échangent de l’énergie électromagnétique avec le faisceau. Il en résulte une modification périodique de la vitesse des électrons, qui sont regroupés en paquets. A la fin de la ligne d’interaction, cette énergie est partiellement transmise à un circuit radiofréquence externe. Afin d’améliorer les performances des klystrons et d’augmenter leur rendement énergétique, une nouvelle architecture, inspirée des RFQ (Radio-Frequency Quadrupole), a été proposée. Il s’agit d’utiliser un nombre plus important de cavités, faiblement couplées au faisceau, et permettant la mise en paquets des électrons de façon très progressive et économe en énergie. Dans l’optique de tester cette nouvelle architecture, le point de départ de ce projet a été la modification de la ligne d’interaction d’un klystron existant. Les éléments d’origines ont été modélisés avec différents programmes de simulation (AJ-Disk, Klys2D et MAGIC2D). Plusieurs architectures ont été ensuite simulées avec ces programmes, afin d’améliorer le rendement énergétique de ce klystron. Une fois que les paramètres électromagnétiques des cavités ont été déterminés, il a été nécessaire de concevoir les pièces constituant cette nouvelle ligne. Le développement de ce nouveau klystron a imposé la création d’un système d’accord des cavités en fréquence, et d’une méthode de titanage, afin d’empêcher la création de phénomène de multipactor. Pour ce faire, deux séries de prototypes ont été conçues, fabriquées et testées. Cette étape a également permis la vérification des méthodes de brasage prévues avec les pièces finales. Les différents éléments de la ligne d’interaction ont été réalisés par un partenaire industriel extérieur au projet. Ces pièces ont été ensuite assemblées à Thales Electron Devices Vélizy, avant que le nouveau klystron soit testé sur un banc dédié. / Klystrons are vacuum tubes that amplifiy microwave signals with the modulation of its beam electrons velocities. The electron beam and the klystron cavities exchange electromagnetic energy. This energy exchanges accelerate or decelerate electrons, and create bunches. The electromagnetic energy carried by these bunches is transferred to an external radio-frequency circuit in the last cavity. In the frame of the improvement of klystrons efficiency, a new design inspired by RFQ (Radio-Frequency Quadrupole) had been proposed. With more cavities, poorly-coupled with the beam, the electron bunching is expected to be smoother and more efficient. The purpose of this project was the test of this new design by replacing the interaction line of an existing klystron. This klystron was simulated with several codes such as AJ-Disk, Klys2D and MAGIC2D. We then used this simulation software to try new designs to improve this klystron efficiency. Once we chose the new cavities electromagnetic properties, we designed the interaction line parts.This klystron development involved the design of a new tuning system for the cavities frequencies, and a new titanium deposition method, in order to prevent multipactor effect. This step needed the design and the fabrication of two series of cavities prototypes to test our new parts and methods. The brazing method was also checked with these cavities. The final interaction line parts were fabricated by a subcontractor, and then assembled and brazed at Thales Electron Devices Vélizy. This new klystron was finally tested on a dedicated conditioning and testing bench.

Les propriétés électriques des matériaux sont des données indispensables dans les phases de conception de circuits micro-ondes. Ainsi, de nombreuses méthodes ont été mises au point en s’appuyant sur des mesures de paramètres «S», pour les systèmes de transmission-réflexion, ou de fréquences de résonance, pour les méthodes résonantes. Chacune d’entre elles présente des caractéristiques adaptées à un type de géométrie d’échantillon, à une bande de fréquence d’analyse, à une précision des résultats souhaitée... Dans tous les cas, les dimensions de l’échantillon doivent être au moins de l’ordre de grandeur de la longueur d’onde et donc, les caractérisations deviennent impossibles aux basses fréquences pour des échantillons de petites tailles. Un autre inconvénient de ces méthodes est qu’il est obligatoire de connaître parfaitement l’épaisseur de l’échantillon pour déterminer avec précision les caractéristiques électriques du matériau. L’objectif de ce travail de thèse a donc consisté à mettre au point une nouvelle méthode de caractérisation en s’appuyant sur une cavité de géométrie particulière. Celle-ci permet des mesures basses fréquences pour des dimensions très inférieures à la longueur d’onde. Avec un système de couplage original, nous avons pu également obtenir une réponse en transmission particulière, caractérisée par une fréquence de résonance et une fréquence d’antirésonance. Par rapport aux méthodes classiques qui ne travaillent que sur la fréquence de résonance, cette double information permet de déterminer à la fois la permittivité du milieu mais également l’épaisseur de l’échantillon. / The electrical properties of the materials are essential data in the design phases of microwave circuits. Thus, many methods have been developed based on "S" parameter measurements, for transmission-reflection systems, or resonance frequencies, for resonant methods. Each of them has characteristics adapted to a type of the samplegeometry, to the frequency band of analysis, to a desired precision of the results... In all the cases, the dimensions of the sample must be at least of the order of the wavelength and therefore the characterizations become impossible at low frequencies for samples of small sizes. Another disadvantage of these methods is that it is mandatory to know perfectly the thickness of the sample to accurately determine the electrical characteristics of the material. The objective of this thesis work was therefore to develop a new method of characterization based on a cavity of particular geometry. This allows low frequency measurements for dimensions much smaller than the wavelength. With an original coupling system, we have also been able to obtain a particular transmission response, characterized by a resonance frequency and an antiresonance frequency. Compared to conventional methods that only work on the resonant frequency, this double information makes it possible to determine both the permittivity of the medium but also the thickness of the sample.

La consommation d'énergie est au centre de nos préoccupations. Quelle qu'en soit la raison, économique, écologique, ou politique, ce problème est aujourd'hui au coeur de notresociété.L'objectif de cette thèse est de proposer un moyen de réduire le coût énergétique de composants spécifiques: les klystrons et les klystrodes, appelées aussi IOTs pour Inductive Output Tubes. Ces composants sont des amplificateurs utilisés comme source de haute puissance RF (Radio-Fréquence). Ces tubes existent sous plusieurs formes mais l'état de l'art, en matière de consommation d'énergie, sont les tubes multi-faisceaux. Nous nous fixons donc comme objectif d'améliorer ces klystrons et IOTs multi-faisceaux : les MBKs et MBIOTs. Cette thèse s'inscrit dans le contexte d'amélioration des accélérateurs de particules, par le biais d'une meilleure production des ondes radiofréquence; plus particulièrement en améliorant le rendement des tubes. Améliorer le rendement signifie simplement diminuer l'écart entre l'énergie fournie pour générer les ondes radios et l'énergie effectivement produite etutilisée dans les accélérateurs. Afin d’atteindre cet objectif, la thèse décrit une nouvelle méthode d’analyse des données des simulations (le diagramme de dispersion de vitesse), explique les étapes de conception d’un tube, et approfondit théoriquement la dynamique des électrons et les structures liées au haut rendement. / Nowadays, energy consumption is a capital issue. It is a central problematic in our society for economical, ecological or politicalreasons.The aim of this thesis is to study ways to lower energical costs of specific components : klystrons and klystrodes, also known as IOTs (Inductive Output Tubes). Those components are amplifiers which are used as RF (Radio Frequency) sources in particle accelerators.Various forms of those tubes exist, however themulti-beam tubes are the state of the art regarding energy consumption. Thus, we focus on enhancing the efficiency of multi-beam klystrons and IOTs : the MBKs and MBIOTs.As a result, this thesis is part of the effort to decrease the costs of particle accelerators, by better producing RF waves; and more specifically enhancing the efficiency of tubes.This simply means lowering the gap between the energy needed to produce RF waves and the energy used in accelerators.In order to fulfill this task, the thesis describes a new method to analyse simulated data (the velocity dispersion diagram), explains the steps to develop a tube, and study theoretically beam dynamics and structures in order to reach high efficiency.

Resonant cavity controlled klystron frequency stabilization circuits and quartz-crystal oscillator frequency stabilization circuits were investigated for reflex klystrons operating at frequencies in the X-band range. The crystal oscillator circuit employed achieved better than 2 parts in 10 in frequency stability. A test of the functional properties of the frequency standard was made using the Stark effect in molecules.