Linear colliders are an option for lepton collision at several TeV. The Compact Linear Collider (CLIC) aims at electron and positron collisions at a centre of mass energy of 3 TeV. In CLIC, the main accelerating structures are designed to operate at an X-band frequency of 12 GHz with an accelerating gradient of 100 MV/m. Two significant issues in linear accelerators that can prevent high gradient being achieved are electrical breakdown and wakefields. The baseline design for the CLIC main linacs relies on a small aperture size to reduce the breakdown probability and a strong damping scheme to suppress the wakefields. The strong damping scheme may have a higher possibility of electrical breakdown. In this thesis an alternative design for the main accelerating structures of CLIC is studied and various aspects of this design are discussed. This design is known as a Damped and Detuned Structure (DDS) which relies on moderate damping and strong detuning of the higher order modes (HOMs). The broad idea of DDS is based upon the Next Linear Collider (NLC) design. The advantages of this design are: well damped wakefields, minimised rf breakdown probability and reduced size of the structure compared to the strong damping design. Procedures necessary to minimise the rf monopole fields and enhance the wakefield suppression are discussed. The rf as well as mechanical designs of a test structure are presented. This unique design forms the basis of this research and allows both the electrical breakdown and beam dynamics constraints to be simultaneously satisfied.

Der International Linear Collider (ILC) ist ein Elektron-Positron-Beschleuniger mit einer Schwerpunktsenergie zwischen 200 und 500 GeV und einer Spitzenluminositaet von $2\cdot 10^{34}\mbox{ cm}^{-2}\mbox{s}^{-1}$. Fuer das Physikprogramm dieser Maschine ist eine exzellente paketweise Messung der Strahlenergie von grundlegender Bedeutung. Um das zu erreichen, sind am ILC verschiedene Techniken vorgesehen. Insbesondere wurden Energiespektrometer vor und nach dem $e^+/e^-$-Wechselwirkungspunkt vorgeschlagen. Die gegenwaertige Standardoption fuer das Spektrometer vor dem Wechselwirkungspunkt ist ein auf Strahllagemonitoren basierendes Magnetspektrometer. In den Jahren 2006/2007 wurde ein Prototyp eines solchen Spektrometers in der End Station A am Stanford Linear Accelerator Center (SLAC) aufgebaut, um die Leistungsfaehigkeit und Zuverlaessigkeit einer derartigen Anlage zu pruefen. Ausserdem wurde eine neue Methode zur Messung der Strahlenergie vorgeschlagen. Diese beruht auf Compton-Streuung von Laserlicht an den Strahlelektronen und erlaubt, die geforderte Energiegenauigkeit von $\Delta E_b / E_b = 10^{-4}$ zu erreichen. Erfahrungen von dem Large Electron-Positron Collider (LEP) und dem Stanford Linear Collider (SLC) zeigten, dass komplementaere Energiemessmethoden notwendig sind, um die Ergebnisse des BPM-Spektrometers zu ueberpruefen. In der vorliegenden Arbeit werden eine Uebersicht ueber das Experiment am SLAC und erste Ergebnisse praesentiert. Des Weiteren wird die neue Methode der Laser-Compton-Streuung beschrieben und wichtige Aspekte detailliert besprochen. / The International Linear Collider (ILC) is an electron-positron collider with a center-of-mass energy between 200 and 500 GeV and a peak luminosity of $2\cdot 10^{34}\mbox{cm}^{-2}\mbox{s}^{-1}$. For the physics program at this machine, an excellent bunch-by-bunch control of the beam energy is mandatory. Several techniques are foreseen to be implemented at the ILC in order to achieve this request. Energy spectrometers upstream and downstream of the electron/positron interaction point were proposed and the present default option for the upstream spectrometer is a beam position monitor based (BPM-based) spectrometer. In 2006/2007, a prototype of such a device was commissioned at the End Station A beam line at the Stanford Linear Accelerator Center (SLAC) in order to study performance and reliability. In addition, a novel method based on laser Compton backscattering has been proposed, since as proved at the Large Electron-Positron Collider (LEP) and the Stanford Linear Collider (SLC), complementary methods are necessary to cross-check the results of the BPM-based spectrometer. In this thesis, an overview of the experiment at End Station A is given, with emphasis on the performance of the magnets in the chicane and first energy resolution estimations. Also, the novel Compton backscattering method is discussed in details and found to be very promising. It has the potential to bring the beam energy resolution well below the requirement of $\Delta E_b / E_b = 10^{-4}$.

This thesis will describe the latest work from the Feedback On Nanosecond Timescales project, commonly known as FONT. The goal of the FONT project is the development of a beamline feedback system to be installed at the interaction point (IP) of a future linear collider in order to maximize the luminosity that can be achieved. The prototype FONT feedback system is beam-based, meaning that the correction is determined from direct measurement of the position of the beam, and intra-train, meaning that the correction is applied within the duration of the current bunch train. The FONT system, consisting of three stripline beam position monitors, a digital processor unit built around a Field Programmable Gate Array (FPGA) and a pair of electromagnetic kickers, is described. Recent improvements to the position measurement process are detailed and the performance of the feedback system is presented. The modification of the firmware to operate on a machine with a large number of bunch trains, such as the International Linear Collider, is described and the design is verified through the use of a laboratory test bench developed to simulate such a machine. The FONT5 digital board is proved capable of operating on a train resembling the specification for the International Linear Collider: 2820 bunches separated in time by 308 ns.

We present in this thesis a detailed analysis of Higgs boson interactions at future colliders. In particular we examine, in a model independent way, the sensitivity of an Linear Collider in probing the interaction of Higgs boson with a pair of vector bosons with/without the use of polarized initial beams and/or the information on final state fermion polarization. We devise several observables which have definite transformation properties under discrete symmetry operations to constrain the different anomalous parts of the Higgs boson interactions having the same transformation properties. We also investigate effects of initial state radiation (ISR) and beamstrahlung on probes of anomalous Higgs boson couplings at higher center of mass energies. We begin the first chapter with an introduction of the Standard Model (SM) of particle physics. We mainly focus on the Higgs sector of the SM. In this chapter we review the electroweak (EW) symmetry breaking mechanism, viz. the Higgs mechanism, responsible for generating masses of all the particles in the SM. We briefly summarize the high precision tests of the SM. We discuss constraints on the mass of the SM Higgs boson derived from theoretical considerations such as stability of the electroweak vacuum, unitarity in scattering amplitudes, perturbativity of the Higgs self-coupling and no fine-tuning in the radiative corrections in the Higgs sector. Next we present the experimental bounds on the mass of the SM Higgs boson obtained from the direct searches of the Higgs boson at LEP and from the electroweak high precision measurements. We then discuss the importance of a general model independent approach to study properties of the Higgs boson and to verify the uniqueness of the SM. In the context of low energy effective theory, this analysis can be made by using the effective Lagrangian that contains higher dimensional operators. We conclude this chapter giving examples of dimension-6 operators which can contribute to the anomalous Higgs boson interactions that we analyze in this thesis. Second chapter contains the dominant Higgs boson production processes at an collider.In a model independent analysis we consider the effects of the most general ¯ (V = W Z) vertex, consistent with Lorentz invariance, for the process where f is any light fermion. This vertex also includes the possibility of CP violation and can be written as: where ki denote the momenta of the two W’s (Z’s), ǫναβis the antisymmetric tensor with ǫ0123 = 1. Previous studies showed that the squared matrix element of the process e+e−ZH does not include all the anomalous parts of a general ZZH vertex. Also it is obvious that one cannot analyse anomalous WWH couplings using this process. Hence we consider the full process e+e−ffH to probe all the anomalous parts of the VVH vertex. We devise a general and very elegant procedure to probe these couplings at an e+e−collider. We construct various combinations by taking dot and scalar triple product of momenta of initial and final state particles. These combinations have definite transformation properties under CP and naive time reversal (T˜)transformations. Hence the corresponding observables constructed using expectation value of sign of these combinations can probe a specific part of the anomalous VVH couplings whose coefficient in the effective Lagrangian has same transformation properties. We investigate the possible sensitivity to which the anomalous VVH couplings can be probed at a Linear Collider using these observables in the process e+e−ffH for unpolarized beams [1, 2]. We consider the case of a Linear Collider, operating at center of mass energy of 500 GeV, with an integrated luminosityof 500 fb−1 and assume a Higgs boson of mass 120 GeV. We impose various kinematical cuts on different final state particles to reduce backgrounds ¯and consider the events where H decays into bb with branching ratio 0.68. We can enhance or suppress the effect of the s-channel, Z-exchange diagram by imposing cut on the ¯invariant mass of the ff system. We use b-tagging efficiency to be 70%; a value expected to be possible in the collider environment. We first consider asymmetries involving either the polar or azimuthal angular distributions. Then we combine these informations to construct combined polar-azimuthal asymmetries in order to enhance the sensitivity. We obtain strong constraints on most of the anomalous parts of the ZZH vertex using cross section and these asymmetries. The process e+eν¯ −νH has two missing ν’s in the final state. Hence their momenta are not available to construct any observables. Therefore, direct probes for T˜-odd WWH couplings viz. ℑ(bW), ℜ(˜bW), cannot be constructed and only weak, indirect bounds are possible. Further, without using polarized beams the contamination from the ZZH vertex cannot be eliminated in the determination of WWH couplings. In the third chapter we analyze use of linearly polarized e+/e−beams and/or information on final state lepton polarization in probingthe interaction of the Higgs boson with a pair of vector bosons[3, 4]. We make several combinations of different particle momenta and spins. We then define observables as expectation values of signs of these combinations for longitudinally polarized beams and/or for production of final state τ’s with a definite helicity state. Use of polarization allows us to devise more observables as compared to the unpolarized case. We list the observables for which use of polarization affords a distinct gain in sensitivity. In our analysis we divide the total luminosity of 500 fb−1 equally among different polarization states of initial state e−/e+ and take the values 80% and 60% for e−/e+ respectively, foreseen at the ILC. We construct numerical combinations of various linearly polarized cross sections to enhance the contribution of ℜ(bZ) while getting rid of ΔaZand vice versa. It is necessary to construct such combinations of cross section as ℜ(bZ), ΔaZhave same CP and T˜transformation properties and hence there are no asymmetries that can be constructed to probe them individually. With these combinations it is possible to probe both these CP-and T˜-even couplings cleanly, using linearly polarized beams. We find that longitudinal beam polarization can improve the sensitivity to CP-odd ZZH couplings viz. ℜ(˜bZ), ℑ(˜bZ), by a factor of about 6 −7. We also construct observables for final state τ’s with definite helicity. We make a plausible assumption that it should be possible to isolate events with τ’s in definite helicity state with an efficiency of 40%. With this assumption we demonstrate that the use of final state τ polarization can improve the sensitivity to the CP-even and T˜-odd ZZH coupling (ℑ(bZ)) by a factor of about 3. Moreover use of final state τ-polarization measurement along with linearly polarized beams can improve the sensitivity for one of the CP-odd ZZH couplings (ℜ(˜bZ))bya factor of about 2.Use of longitudinally polarized beams can also help to reduce the contamination in the measurement of the WWH couplings coming from the ZZH vertex contribution. We also perform χ2-analysis using the observables for different polarizations. The cross section of the t–channel diagram increases with increasing center of mass energy. Therefore, off hand it may look like that going to higher energy can increase the sensitivity to WWH couplings. Hence in this chapter we further investigate possible gain in sensitivity going to higher center of mass energies[3, 4]. We use the same observables constructed with unpolarized beams and consider various center of mass energies ranging from 300 GeV to 3 TeV. We find that it is possible to increase the bZ)byabouta factor 2 1 TeVas compared to the case of 500 GeV. In this analysis we include the effects of initial state radiation (ISR) and beamstrahlung. Both the ISR and beamstrahlung =500 GeV, the ISR can affect cross sections for s–channel processes by 10−15%.However, we observe that the effects of ISR and beamstrahlung change both the SM and anomalous contributions more beneficial for the study of anomalous V V H couplings. In the last chapter we investigate the role of transversely polarized beams to constrain the anomalous V V H couplings[5]. Using transverse spin direction of e±it is possible to devise observables which are nonzero only for transversely polarized beams. Use of transverse beam polarization allows construction of completely independent probes of both the CP-and T˜-even anomalous ZZH couplings (ΔaZ, ℜ(bZ)), leading to independent determination of all the anomalous parts of the ZZH vertex. In addition the use of transverse beam polarization can also add to the sensitivity for one of the CP-odd ZZH couplings viz. ℜ(˜bZ). Measurement of final state τ-polarization with transversely polarized beams can in fact also offer improvement on the sensitivity for ℑ(bZ) which is even under CP-and odd under T˜-transformation. Use of transverse beam polarization cannot improve the bounds on the anomalous WWH couplings as the squared matrix element of the t– channel WW–fusion diagram does not have any transverse beam polarization dependent term. A summary of the results obtained in this thesis is follows. We have developed a general procedure to construct observables with specific CP and T˜transformation properties to probe various anomalous couplings of the Higgs boson to a pair of vector bosons (V = W/Z) at an e+/e−Linear Collider. We investigate probes of these couplings in the process e+e−ffH. This process gives access to those anomalous couplings which cannot be probed using angular distribution of the Z boson in the process e+eZH. We showed that it would be possible to obtain stringent bounds on some of the parts of the anomalous ZZH vertex even without using polarized beams and/or information on polarization of final state particles. Use of longitudinal beam polarization and/or final state τ polarization can significantly enhance the sensitivity in probing most of the anomalous parts of a general ZZH vertex. Use of longitudinal beam polarization also reduces the contamination from the ZZH couplings in the determination of the ˜T-even anomalous WWH couplings (ℜ(bW), ℑ(˜bW)). However, two missing neutrinos in the final state do not allow any direct probe of the T˜-odd WWH couplings (ℑ(bW), ℜ(˜bW)).We find that use of transverse polarization of the beams is essential to construct independent probes of the two anomalous ZZH couplings, which are even under CP and T˜transformations, viz.ΔaZand ℜ(bZ).We observed that there will be no significant gain 500 GeV), but with polarized beams is preferable from the point of view of studying anomalous V V H coupling. (For mathematical equations pl see the pdf file.)

An electron-positron linear collider is an option for future large particle accelerator projects. Such a collider would focus on precision tests of the Higgs boson properties. This thesis describes three studies related to the optimisation of highly granular calorimeters and one study on the sensitivity of Higgs couplings at CLIC. Photon reconstruction algorithms were developed for highly granular calorimeters of a future linear collider detector. A sophisticated pattern recognition algorithm was implemented, which uses the topological properties of electromagnetic showers to identify photon candidates and separate them from nearby particles. It performs clustering of the energy deposits in the detector, followed by topological characterisation of the clusters, with the results being considered by a multivariate likelihood analysis. This algorithm leads to a significant improvement in the reconstruction of both single photons and multiple photons in high energy jets compared to previous reconstruction software. The reconstruction and classification of tau lepton decay products was studied. Utilising highly granular calorimeters, the high resolution of energy and invariant mass of the tau decay products enabled a high classification rate. A hypothesis test was performed for expected decay final states. A multivariate analysis was trained to classify decay final states with a machine learning method. The performance of tau decay classification is used for the electromagnetic calorimeter optimisation at the ILC or CLIC. A proof-of-principle analysis using the correlation between the polarisations of the tau pair from a boson decay as a signature to differentiate the Higgs boson from the Z boson is presented. Sensitivity of Higgs couplings at CLIC was studied using the double Higgs production process. Algorithms were developed for signal event selection. The event selection relies on the jet reconstruction and the flavour tagging. A multivariate analysis is performed to select signal events. An attempt at extracting Higgs trilinear self-coupling and quartic coupling was conducted.

Pour les accélérateurs de particules à hautes énergies, le système de verrouillage est une partie clé de la protection de la machine. Le verrouillage de la machine est l’inhibition du faisceau dès lors qu’un équipement critique tombe en panne et/ou qu’un faisceau est de faible qualité. Pour un système de verrouillage, sa sûreté de fonctionnement est la caractéristique la plus importante. Cette thèse présente le développement d’un système de verrouillage pour les collisionneurs linéaires avec une application au projet CLIC (Compact Linear Collider). Son élaboration s’appuie sur la norme d’ingénierie IEEE 1220 et se décline en quatre parties. Tout d’abord, les spécifications sont établies. Une attention particulière est portée sur la sûreté de fonctionnement, plus précisément, la fiabilité et la disponibilité du système. La deuxième étape est la proposition d’un design. Celui-ci est basé sur une analyse fonctionnelle, les interfaces du système et l’architecture du CLIC. Troisièmement, une étude de faisabilité est effectuée en appliquant les concepts dans un environnement opérationnel. Finalement, la dernière étape est la vérification matérielle. Le but est de prouver que le design proposé est capable de remplir le cahier des charges établi. / For high energy accelerators, the interlock system is a key part of the machine protection. The interlock principle is to inhibit the beam either on failure of critical equipment and/or on low beam quality evaluation. The dependability of such a system is the most critical parameter. This thesis presents the design of an dependable interlock system for linear collider with an application to the CLIC (Compact Linear Collider) project. This design process is based on the IEEE 1220 standard and is is divided in four steps. First,the specifications are established, with a focus on the dependability, more precisely the reliability and the availability of the system. The second step is the design proposal based on a functional analysis, the CLIC and interfaced systems architecture. Third, the feasibility study is performed, applying the concepts in an accelerator facility. Finally, the last step is the hardware verification. Its aim is to prove that the proposed design is able to reach the requirements.

Un défi important pour les futurs collisionneurs linéaires électron-positron est de pouvoir focaliser le faisceau à des tailles transverses de l’ordre du nanomètre au point d’interaction (IP), permettant d’atteindre la luminosité de conception. Le système délivrant les faisceaux d’e- et de e + de la sortie du Linac principal vers le point d’interaction, le Beam Delivery System (BDS), réalise les fonctions critiques requises pour atteindre l’objectif de luminosité, tel que la collimation et la focalisation du faisceau. Le faisceau est focalisé par le système de focalisation finale (FFS) tout en corrigeant les aberrations d’ordre supérieur propagées le long du système. Les effets chromatiques contribuant à l’élargissement de la taille du faisceau, sont amplifiés par la force de focalisation des deux derniers quadripôles QF1 et QD0, ou doublet final (FD), et par la longueur de la distance focale finale L* entre QD0 et l’IP. L’approche de correction de la chromaticité retenue pour les deux grands projets actuels de collisionneurs linéaires, CLIC et ILC, est fondée sur la correction locale de la chromaticité générée par le doublet final. Ce schéma est actuellement testé à l’ATF2 au KEK (Japon). Ce travail de thèse se concentre sur les problématiques liées au système de focalisation finale du projet CLIC re-optimisé avec un plus long L*, dans le cadre de la simplification de l’interface machine-détecteur (MDI), ainsi que sur le travail expérimental conduit à l’ATF2 pour l’optimisation et l’étude des optiques du système de focalisation finale à ultra-bas β* incluant les tout premiers est in situ des octupôles à l’ATF2. / The future machines considered to carry out high precision physics in the TeV energy regime are electron-positron (e+e−) linear colliders. Future linear colliders feature nanometer beam spot sizes at the Interaction Point. The Beam Delivery System (BDS) transports the e + and e− beams from the exit of the linacs to the IP by performing the critical functions required to meet the CLIC luminosity goal such as beam collimation and focusing. The beam is focused through the Final Focus System while correcting higher order transport aberrations in order to deliver the design IP beam sizes. The chromatic contributions are amplified by the focusing strength of the two last quadrupoles named QD0 and QF1, reffered to as the Final Doublet (FD), and by the length of the final focal distance L* between QD0 and the IP. The chromaticity correction approach chosen for the CLIC FFS is based on the Local chromaticity correction scheme which uses interleaved pairs of sextupole magnets in the FD region in order to locally and simultaneously correct horizontal and vertical chromaticity. The current linear collider projects, the Compact Linear Collider (CLIC) and the International Linear Collider (ILC) have FFS lattices based on the Local Chromaticity correction scheme. This scheme is being tested in the Accelerator Test Facility 2 (ATF2) at KEK (Japan). This thesis concentrates on problems related to the optimization of BDS lattices for the simplification of the CLIC Machine Detector Interface (MDI) and on the experimental work for the implementation and study of a CLIClike FFS optics for the ATF2, referred to as ultra-low β* optics.

The thesis presents phase stability studies for the Compact Linear Collider (CLIC) and focuses in particular on CLIC Drive Beam longitudinal phase stabilisation. This topic constitutes one of the main feasibility challenges for CLIC construction and is an essential component of the current CLIC stabilisation campaign. The studies are divided into two large interrelated sections: the simulation studies for the CLIC Drive Beam stability, and measurements, data analysis and simulations of the CLIC Test Facility (CTF3) Drive Beam phase errors. A dedicated software tool has been developed for a step-by-step analysis of the error propagation through the CLIC Drive Beam. It uses realistic RF potential and beam loading amplitude functions for the Drive and Main Beam accelerating structures, complete models of the recombination scheme and compressor chicane as well as of further CLIC Drive Beam modules. The tool has been tested extensively and its functionality has been verified. The phase error propagation at CLIC has been analysed and the critical phase error frequencies have been identified. The impact of planned error filtering and stabilisation systems for the Drive Beam bunch charge and longitudinal phase has been simulated and the optimal specifications for these systems, such as bandwidth and latency time, have been calculated and discussed. It has been found that a realistic feed-forward system could sufficiently reduce the longitudinal phase error of the Drive Beam, hence verifying that a satisfactory CLIC luminosity recovery system is possible to develop. Alternative designs of the Drive Beam accelerator, the recombination scheme and the phase signal distribution system have also been analysed. Measurements of the CTF3 Drive Beam phase have been performed. The source of the phase and energy errors at CTF3 has been determined. The performance of the phase feed-forward system prototype for CTF3 has been simulated. The prototype's specifications have been defined so that it will provide a sufficient test of the feed-forward correction principle. The prototype based on the defined specifications is currently in development and is to be installed at CTF3 in the second half of 2013.

Als Basis der Positronenquelle zur Erzeugung polarisierter Positronen bei einem zukuunftigen internationalen Linearkollider ist ein helikaler Undulator vorgesehen. Das E-166 Experiment testete diese Methode unter Benutzung eines ein Meter langen, kurzperiodischen, gepulsten helikalen Undulators im Final Focus Test Beam (FFTB) am SLAC. Ein 46.6 GeV Elektronenstrahl mit geringer Emittanz wurde durch diesen Undulator gefuehrt und erzeugte zirkular polarisierte Photonen mit einer Energie bis zu ungefaehr 8 MeV. Diese wiederum konvertierten in einem relativ duennen Target zu longitudinal polarisierten Positronen. Die Polarisation der Positronen wurde bei 5 verschieden Positronenergien gemessen. Zusaetzlich ist die Polarisation von Elektronen fuer einen Energiepunkt gemessen worden. Um die gemessenen Asymmetrien mit den Erwartungen vergleichen zu koennen, waren detaillierte Simulationen noetig. Dies erforderte die Erweiterung von von GEANT4 um die wichtigsten polarisationsabhaengigen Wechselwirkungen von Elektronen, Positronen und Photonen mit Materie. Die gemessene Positronpolarisation stimmt mit den Erwartungen ueberein und betraegt fuer den Energiepunkt mit der hoechsten Polarisation von 6 MeV mehr als 80 prozent. / A helical undulator based polarized positron source is forseen at a future International Linear Collider. The E-166 experiment has tested this scheme using a one meter long, short-period, pulsed helical undulator installed in the Final Focus Test Beam (FFTB) at SLAC. A low-emittance 46.6 GeV electron beam passing through this undulator generated circularly polarized photons with energies up to about 8 MeV. The generated photons of several MeV with circular polarization are then converted in a relatively thin target to generate longitudinally polarized positrons. Measurements of the positron polarization have been performed at 5 different energies of the positrons. In addition electron polarization has been determined for one energy point. For a comparison of the measured asymmetries with the expectations detailed simulations were necessary. This required upgrading GEANT4 to include the dominant polarization dependent interactions of electrons, positrons and photons in matter. The measured polarization of the positrons agrees with the expectations and is for the energy point with the highest polarization at 6 MeV about 80 percent.

Le travail développé dans cette thèse concerne un type particulier de sources de positrons utilisant le rayonnement de canalisation dans un cristal ainsi que d’autres effets cristallins observes le long des axes du cristal ; ces effets produisent un grand nombre de photons qui, à leur tour, génèrent un grand nombre de paires e+e- dans une cible amorphe. Les photons et les paires sont créés dans deux cibles différentes séparées par une certaine distance permettant l’installation d’un aimant pour dévier les particules chargées avant la cible amorphe. Une telle source est appelée source hybride de positrons ; elle a été choisie par le CERN pour le projet CLIC. Ce type de sources présente de réels avantages par rapport aux cibles conventionnelles qui ont une grande emittance ainsi qu’un niveau important de dépôt d’énergie dans la cible.Apres un rappel des phénomènes physiques qui concernent notre étude, des simulations détaillées utilisant d’une part le programme de V .Strakhovenko pour les effets cristallins et d’autre part le code GEANT4 pour la génération des positrons conduisent à une description complète pour les photons et les positrons avec, notamment, les espaces de phase longitudinal et transverse, le spectre en énergie, la distribution temporelle,.. Nous avons particulièrement insiste sur deux points : d’abord sur les dispositifs de capture des positrons -après la cible- qui sont essentiels pour avoir de bons rendements de positrons acceptes et ensuite sur la densité de l’énergie déposée dans la cible qui représente un paramètre important pour la survie des cibles. En ce qui concerne le premier point, trois dispositifs de capture ont été étudiés : le système adiabatique (AMD), le système quart d’onde (QWT) et la lentille de lithium. Pour le deuxième point qui concerne l’énergie déposée et l’échauffement de la cible, on a cherché à optimiser la densité d’énergie déposée en diminuant son maximum (PEDD) ; l’énergie moyenne déposée a aussi été optimisée en utilisant une solution spéciale pour le convertisseur : un convertisseur granulaire forme de petites sphères, comme cela avait été considéré précédemment pour les usines à neutrinos. Des résultats très prometteurs nous ont conduits à envisager la source hybride de positrons avec un convertisseur granulaire comme une solution au difficile problème d’ILC. Cette solution est étudiée moyennant une transformation des impulsions du faisceau avant la cible, comme cela avait été envisage par l’équipe du KEK. Le transport du faisceau de positrons au-delà du solénoïde a été étudié avec la première partie de l’optique quadrupolaire. / The research work carried out for this PhD is concerning a special kind of positron source using channeling radiation and other crystal effects in an axially oriented crystal to generate a high number of photons which create, subsequently, a large number of pairs in an amorphous target. Photon generation and pair creation are developing in two targets separated by some distance allowing a sweeping magnet to get off the charged particles away from the amorphous converter. Such a scheme is called an hybrid positron source and has been adopted for the CLIC baseline. This kind of sources present big advantages with respect to the conventional sources where large emittance and important heat deposition are met. After some recall on the physical phenomena of interest for our study, detailed simulations are worked out using a special program dealing with crystal effects from Prof. Strakhovenko and the GEANT4 code; these tools led to a complete description of the positron source concerning the photons from one side and the positrons, from the other side, for which the main characteristics have been determined: transverse and longitudinal phase space, energy spectrum, time distribution,…Emphasis has been put on two points: first the matching devices capturing the positrons after the target which are essential for good accepted yields and the energy deposition density which is an important question for the reliability of the targets. Concerning the former point, three matching devices have been studied and their features compared: the Adiabatic Matching Device (AMD) largely used or considered for the positron sources, the Quarter Wave Transformer (QWT) and also the Lithium lens. For the latter point, related to the energy deposition and heating of the targets, we have tried to optimize the energy deposition density lowering its maximum value (PEDD); the average heat deposition has also been optimized using special converter material in granular shape, as considered for the neutrino factories. Very promising results allowed us to consider the hybrid positron source as an alternative to the difficult case of ILC; a special scheme for the transformation of the ILC beam pulses has been used, after KEK proposition. The positron beam transport has also been studied in the first part of the positron pre-accelerator including the solenoid and the first part of the quadrupole channel.