Des sources Radio Fréquence au faisceau de particules : optimisation du transfert de puissance RF pour les cavités accélératrices

Radiofrequency cavities are a fundamental element of particle accelerators, since theytransfer the radiofrequency energy generated by power sources to a particle beam. This dissertation presents my contribution to the design, fabrication, preparation and operation of such cavities, destined to some of the main today and future acceleratorprojects in the world. The development of superconducting cavities for ESS, with elliptical shape, and for IFMIF/DONES, with half wave resonator shape, is detailed. I give a focus on the mitigation of radiofrequency losses in niobium, due to the surrounding magnetic eld trapping in the material. My contribution to the power transfer optimization also resulted in studies on high eciency klystrons, used as radiofrequency power source for cavities, with the design, fabrication and test of aklystron based on the kladistron principle. Finally, I present the work carried out on diagnostic tools, essential for cavity operation and for R&D further development.Les cavités radiofréquence sont un élé-ment fondamental des accélérateurs de particules,puisqu'elles transfèrent l'énergie radiofréquencegénérée par les sources d'énergie à un faisceau departicules. Ce mémoire présente ma contribution àla conception, à la fabrication, à la préparation et àl'exploitation de telles cavités, destinées à certainsdes principaux projets d'accélérateurs actuels et futursdans le monde. Le développement de cavitéssupraconductrices pour ESS, de forme elliptique,et pour IFMIF/DONES, de forme résonateur demi onde,est détaillé. Je décris également mon travailsur l'atténuation des pertes radiofréquences dans leniobium, dues au piégeage du champ magnétiqueenvironnant dans le matériau. Ma contribution àl'optimisation du transfert de puissance a égalementdonné lieu à des études sur les klystrons àhaut rendement, utilisés comme source d'énergieradiofréquence pour les cavités, avec la conception,la fabrication et le test d'un klystron basésur le principe du kladistron. Enfin, je présente lestravaux réalisés sur les outils de diagnostic, essentielspour le fonctionnement des cavités et pour ledéveloppement futur de la R&D

Injection d'harmonique dans un Tube à Ondes Progressives : amélioration de la puissance de sortie

président du jury : Fabrice DoveilTraveling Wave Tubes (TWT) are amplifiers for microwave signals. Nonlinearity occurs for high input powers, and compromises their performances. The overall aim of this Ph.D thesis is to improve the linearity of the tubes ; we present a method where the second harmonic (2F) is injected simultaneously with the fundamental signal (F).A theoretical study of the nonlinearity of TWT identifies the "inertial saturation", as an essential aspect of output power saturation. The possibility of improving linearity in TWT is explained with analytical models and numerical simulations, and then validated with experimental measurements on industrial tubes.This work envisages to allows industrial applications to improve the efficiency of TWTs.Les Tubes à Ondes Progressives (TOP), utilisés pour amplifier des signaux hyperfréquences, présentent un comportement non-linéaire pour des puissances d'entrée élevées, ce qui limite leurs performances. Ce travail vise à améliorer la linéarité des TOP, et propose une solution consistant à injecter, en plus d'une l'onde fondamentale F, sa seconde harmonique 2F, afin d'améliorer la puissance de sortie.Une étude théorique approfondie de la non-linéarité dans les TOP a identifié la "saturation inertielle", comme un aspect essentiel de la saturation de la puissance de sortie. La possibilité d'améliorer la linéarité des TOP par injection d'harmonique a été étudiée à l'aide de modèles analytiques et de simulations numériques, puis validée par des mesures sur des tubes industriels. Ce travail a ouvert des perspectives pour des applications industrielles qui amélioreront le rendement des TOP

AMR Sensors Studies and Development for Cavities Tests Magnetometry at CEA

International audienceStudying flux expulsion during superconducting cavities test increases the need for exhaustive magnetometric cartography. The use of Anistropic Magneto Resistance (AMR) sensors, much cheaper than commercial fluxgates, allows the use of tens of sensors simultaneously. Such sensors are developed and sold for room temperature application but are resistant to cryogenic temperatures. However, they need proper calibration, which is more difficult at cryogenic temperature. Actually, this calibration uses the flip of the magnetization of the anisotropic ferromagnetic element, which coercitive field is increased at low temperature. We will present the development of method and software carried out at CEA for the use of such sensors, as well as the preliminary design of a rotating magnetometric device destined to elliptical cavities

Klystron efficiency optimization based on a genetic algorithm

This paper presents a method based on a genetic algorithm optimization to design a high efficient klystron, operating in the X band. First, the genetic algorithm is used to optimize the bunching circuit and then to optimize the geometry of the output cavity. Finally the output cavity is integrated to the bunching circuit and the achieved efficiency is about 70%

Beam Dynamics Studies For the IFMIF-DONES SRF-Linac

International audienceThe DONES (DEMO oriented neutron source) project is aimed at constructing a DEMO of IFMIF to provide sufficient material damage [1]. In the SRF-Linac of this project, losses can cause harmful material activation and must be maintained much less than 1W/m. It's a challenge to keep losses at such a low level with high beam power and high space charge. This paper presents two designs of the DONES SRF-Linac, one with 4 cryomodules and another with 5 cryomodules. The design details to reduce the losses and the multi-particle simulation results will be shown. The errors studies for these results will also be discussed

Beam Dynamics Errors Studies for the IFMIF-DONES SRF-LINAC

International audienceThe goal of the IFMIF-DONES (International Fusion Materials Irradiation Facility-DEMO Oriented Neutron Source) project is to build an irradiation facility that will provide a sufficient neutron flux to study and characterize structure materials foreseen for future fusion power plant. In order to accelerate the required 125mA/40 MeV continuous deuteron beam from 5 MeV to 40 MeV, a superconducting radio-frequency (SRF) linac, housed in five cryomodules, is proposed. The design is based on two beta families (β=0.11 and β=0.17) of half-wave resonators (HWR) at 175MHz. The transverse focusing is achieved using one solenoid coil per focusing period. This paper presents the extensive multiparticle beam dynamics simulations that have been performed to adapt the beam along the SRF-linac in such a high space charge regime. As one of the constraints of the IFMIF linac is a low level of beam losses, specific optimizations have been done to minimize the beam occupancy in the line (halo). A Monte Carlo error analysis has also been carried out to study the effects of misalignments or field imperfections (static errors) and also vibrations or power supplies ripple (dynamic errors). The results of these errors studies are presented and discussed

Photonic band structures for bi-dimensional metallic mesa gratings

International audienc

High-Efficiency Klystron Design for the CLIC Project

The CLIC project requests new type of RF sources for the high power conditioning of the accelerating cavities. We are working on the development of a new kind of high-efficiency klystron to fulfill this need. This work is performed under the EuCARD-2 European program and involves theoretical and experimental study of a brand new klystron concept

Fabrication and test of a 5 GHz kladistron

A 5 GHz klystron of type “kladistron” has been designed and realized. It was adapted from the TH2166 from Thales, where the interaction line was transformed from 6 to 16 cavities. This klystron was fabricated and tested at Thales. The results of these tests are presented and discussed in this paper

Preliminary Design of the IFMIF-DONES Superconducting Linac

International audienceThe linear accelerator for the DONES facility (DEMO oriented neutron source) will serve as a neutron source for the assessment of materials damage in future fusion reactors. The DONES accelerator, which is based on the design of LIPac (Linear IFMIF Prototype Accelerator, which is under construction in Rokkasho, Japan) will accelerate deuterons from 100 keV up to 40 MeV at full CW current of 125 mA. This paper will present the preliminary design of the superconducting linac which is based on five cryomodules