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Particle accelerators are machines to accelerate and store charged particle beams, such as electrons or protons, to the energy levels for various scientific applications. There are three basic types of particle accelerators: linear accelerators (linac), storage-ring (or circular) accelerators, and recirculating accelerators. The third type, also the most recent one, is designed to accelerate a particle beam in a short section of linac, circulate and then continue to accelerate it for energy boost or decelerate it for energy recovery. The modern recirculating machines possess the advantages to both accelerate and preserve the beam with high beam quality, as well as efficiently reuse the accelerating components. As modern accelerators push toward the high-brightness or high-intensity frontier by demanding particles in a highly charged bunch to concentrate in an ever-decreasing beam phase space, the interaction amongst particles via their self-generated electromagnetic fields can potentially lead to coherent instabilities of the beam and thus pose significant challenges to the machine design and operation. Microbunching instability (MBI) has been one of the most challenging issues for such high-brightness or high-intensity beam transport, as it would degrade lasing performance in the fourth-generation light sources, reduce cooling efficiency in electron cooling facilities, and eventually compromise the luminosity of colliding beams in lepton or lepton-hadron colliders. The dissertation work will focus on the MBI in modern recirculating electron accelerators. The research attempts to develop a comprehensive theoretical formulation of MBI with aspects including among various degrees of freedoms the beam itself, the beamline lattice optics, and incorporation of all relevant collective effects that the beam encounters, for example the coherent synchrotron radiation (CSR) and the longitudinal space charge (LSC) effects. This dissertation includes the following seven themes: 1) Development and generalization of MBI theory to arbitrary linear lattices and coupled beams with constant and varying energies; 2) Construction of CSR impedance models from steady state to transient state and from high to low energy regime; 3) Numerical implementation of the developed theory as a fast and numerical-noise-free Vlasov solver and benchmarking with massive particle tracking simulation; 4) Exploration of multistage cascaded amplification mechanism of CSR microbunching development; 5) Control of CSR-induced MBI in multi-bend transport or recirculation arcs; 6) Study of more aspects of microbunched structures in beam phase spaces; and 7) Study of MBI for magnetized beams and confirming the suppression of MBI for a recent cooler design for Jefferson Lab Electron Ion Collider project. / Ph. D.

<p>This thesis is concerned with <i>in-situ</i> time-, temperature- and pressure-resolved synchrotron X-ray powder diffraction investigations of a variety of inorganic compounds with twodimensional layer structures and three-dimensional framework structures. In particular, phase stability, reaction kinetics, thermal expansion and compressibility at non-ambient conditions has been studied for 1) Phosphates with composition <i>M</i><i>IV</i>(HPO₄)₂·<i>n</i>H₂O (<i>M</i><i>IV</i> = Ti, Zr); 2) Pyrophosphates and pyrovanadates with composition<i> M</i><i>IV</i>X₂O₇(<i>M</i><i>IV</i> = Ti, Zr and X = P, V); 3) Molybdates with composition ZrMo₂O₈. The results are compiled in seven published papers and two manuscripts.</p><p>Reaction kinetics for the hydrothermal synthesis of α-Ti(HPO₄)₂·H₂O and intercalation of alkane diamines in α-Zr(HPO₄)₂·H₂O was studied using time-resolved experiments. In the high-temperature transformation of γ-Ti(PO₄)(H₂PO₄)·2H₂O to TiP₂O₇ three intermediate phases, γ'-Ti(PO₄)(H₂PO₄)·(2-x)H₂O, β-Ti(PO₄)(H₂PO₄) and Ti(PO₄)(H₂P₂O₇)_0.5 were found to crystallise at 323, 373 and 748 K, respectively. A new tetragonal three-dimensional phosphate phase called τ-Zr(HPO₄)₂ was prepared, and subsequently its structure was determined and refined using the Rietveld method. In the high-temperature transformation from τ-Zr(HPO₄)₂ to cubic α-ZrP₂O₇two new orthorhombic intermediate phases were found. The first intermediate phase, ρ-Zr(HPO₄)₂, forms at 598 K, and the second phase, β-ZrP₂O₇, at 688 K. Their respective structures were solved using direct methods and refined using the Rietveld method. <i>In-situ</i> high-pressure studies of τ-Zr(HPO₄)₂revealed two new phases, tetragonal ν-Zr(HPO₄)₂and orthorhombic ω-Zr(HPO₄)₂ that crystallise at 1.1 and 8.2 GPa. The structure of ν-Zr(HPO₄)₂ was solved and refined using the Rietveld method.</p><p>The high-pressure properties of the pyrophosphates ZrP₂O₇ and TiP₂O₇, and the pyrovanadate ZrV₂O₇were studied up to 40 GPa. Both pyrophosphates display smooth compression up to the highest pressures, while ZrV₂O₇ has a phase transformation at 1.38 GPa from cubic to pseudo-tetragonal β-ZrV₂O₇ and becomes X-ray amorphous at pressures above 4 GPa.</p><p>In-situ high-pressure studies of trigonal α-ZrMo₂O₈ revealed the existence of two new phases, monoclinic δ-ZrMo₂O₈and triclinic ε-ZrMo₂O₈ that crystallises at 1.1 and 2.5 GPa, respectively. The structure of δ-ZrMo₂O₈was solved by direct methods and refined using the Rietveld method.</p>

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This work presents a spectroscopic and theoretical study of several energy materials using synchrotron-based techniques. Two classes of materials are studied: solids that have reported photocatalytic properties, and lithium compounds that are thought to form during the cycling of modern battery electrodes. An overview of synchrotron soft X-ray spectroscopic techniques is presented, along with the theory and procedures associated with performing such measurements. These measurements are compared to density functional theory (DFT) calculations, as implemented by the WIEN2k package, along with a description of the DFT method. Calculated electronic structure is shown to be a useful aid in interpreting the results of X-ray emission and X-ray near-edge absorption measurements (XES and XANES), allowing conclusions about the physical structure and properties of the materials to be reached. Two photocatalytic systems are outlined, the first of which is a solid solution of GaN and ZnO (GaN:ZnO) that exhibits an unexpected reduction in band gap. By carefully comparing common hybridized features from O, N and Zn core emission lines, a binding energy picture of the valence and conduction bands of GaN:ZnO is constructed, allowing its band gap reduction to be described as a consequence of heterojunctions between predominantly GaN and ZnO regions within the solid solution. This description attempts to resolve controversy in the literature regarding the origin of the band gap reduction, as well as to rule out a hypothesized oxynitride superlattice structure as the explanation. The second photocatalytic system studied is a carbon nitride derivative, poly(triazine imide) (PTI) that displays high crystallinity and that could be very inexpensive to produce due to its elemental abundance. Through resonant excitation, two inequivalent N sites in PTI can be probed by X-ray emission spectroscopy, indicating the material is not a conjugated polymer like other reported carbon nitrides. The band gap of the system is observed to decrease in response to disordered Li loading, an e ect that is con rmed by DFT calculation. Several potential disorder models of the Li loading of PTI are investigated with DFT force minimization in order to choose a structural candidate capable of producing calculated X-ray spectra that agree with our measurements. The presented lithium study attempts to use a modern soft X-ray absorption facility to characterize the Li surface by-products inherent to the charge-discharge cycling of a battery electrode. A survey of potential Li compounds was performed using Li K-edge XANES will be compared to DFT calculations and X-ray Raman Scattering measurements performed by collaborators in the future. Correlating measurements of the survey compounds with charge-cycled electrode measurements will be an area for future work.

This thesis describes an investigation into the performance of different schemes for generating short x-rays pulses via synchrotron radiation emission. A review is given of the methods that have been previously proposed for this task. From this review, three leading schemes are selected for in-depth investigations, each of which explores the boundary of what is presently achievable in accelerator-based light sources. The first scheme generates short x-ray pulses by operating an electron storage ring in a quasi-isochronous state using a ‘low-alpha’ lattice. High and low emittance lattices are developed, studied through simulation and then implemented on the Diamond storage ring. Beam dynamics and bunch length measurements are presented for a variety of machine conditions, and an assessment is made of the minimum practically achievable bunch length for stable user operation. Radiation pulses of 1 ps r.m.s. are demonstrated using this scheme. The second and third schemes investigate performance limits for a linac-based light source through numerical simulations. The first of these generates ultra-short pulses by passing a highly compressed electron bunch through a long undulator to radiate in the ‘single-spike’ regime. A comparison is made with theoretical predictions for the required electron bunch length to operate in this way, which highlights the need for accurate start-to-end simulations. The final scheme generates ultra-short x-ray pulses through laser manipulation of the electron bunches. The modulated electrons pass through a long undulator with tapered gap, such that only the centre of the modulated portion experiences high free-electron laser (FEL) gain. A method to enhance the FEL output from this scheme using a wavelength filter and grating-compressor is investigated. The sensitivity of the two schemes to jitter sources is determined, and it is demonstrated both schemes are capable of generating GW-level, fully coherent sub-fs soft x-ray pulses. Such pulses would open up the development of time-resolved science to new regimes.

Ces travaux de thèse rentrent dans le cadre de l’étude de la dynamique ultra rapide de l’aimantation. Tout d’abord sont présentés des aspects théoriques, puis les aspects expérimentaux de ces expériences. Pour ce faire, nous avons étudié la réponse d’alliages ferrimagnétiques à composition variables à l’aide d’un dispositif de mesure d’effet Kerr résolu en temps, puis dans une seconde partie, la dynamique de l’aimantation et de la bande de valence du gadolinium épitaxié sur tungstène. Dans ce cadre rentre une étude de l’oxydation de ce matériau, limitant dans le temps les études approfondies. Pour finir, il est mis l’accent sur un phénomène contraignant lors des études de dynamique électronique en photoémission, l’effet de charge-espace. Ceci a pour effet de générer des photoélectrons à partir de métaux, à l’aide d’un processus multiphotonique. Nous proposons dans cette partie un modèle théorique expliquant ce phénomène.Ces travaux sont inscrits dans le cadre du développement du synchrotron SOLEIL, pour permettre le développement du FEMTOSLICING, qui permettra prochainement de mesurer des dynamiques rapides résolues en éléments, à une résolution de l’ordre de la centaine de femtosecondes. / Those thesis works are included in the framework of the study of ultrafast magnetization dynamics. First of all I introduce theoretical aspects, then experimental aspects of this kind of experiments.In this aim, we have studied the answer of ferromagnetic alloys of different compositions with a bench of time resolved magneto optical Kerr effect measurement, then in a second part, the magnetization and valence band dynamics of the epitaxial Gadolinium on tungsten. In this framework, we studied the oxidization of the Gd, which limits in the time the studies. In the end, we focus on a disturbing process that happens during the study of electrons dynamics in photoemission, the space charge effect. This can generate photoelectrons from metals, with a multiphotonic process. We propose in this last part a theoretical model to explain this phenomenon.These works are included in the development of SOLEIL synchrotron facility, in order to allow the development of the FEMTOSLICING, that will next allow to perform element resolved experiments within a time resolution of a hundredth of femtoseconds.

All massive nearby galaxies, including our own, host supermassive black holes. Active galactic nuclei (AGN) are seen when such black holes accrete, and when they produce powerful jets of synchrotron-emitting plasma, they are termed radio-loud AGN. The close correlation between black hole mass and galaxy bulge mass in elliptical galaxies indicates that AGN feedback may be the key to the regulation of galaxy formation. It is thus necessary to fully understand the structure of AGN, the way that they are fuelled, and their duty cycle, in order to study the feedback processes and get a clear picture of galaxy formation. In this thesis, independent methods are developed to constrain the accretion disk and radio jet angles to the line of sight. H IX emission from a sub-sample of high-redshift quasars is measured from near-infrared spectroscopy and modelled as sums of different components, including the characteristic double-peaked profile which results from a thin, rotating accretion disk. Comparing the models using Bayesian evidence, almost all quasars were found to have infrared spectra consistent with the presence of a disk. The jet inclination angles of the same set of quasars were constrained by fitting a model, including the effect of Doppler boosting and the receding torus model for dust obscuration, to the radio \ spectral energy distribution. The fitted disk and jet angles correlate strongly, and are consistent with a model in which the radio jets are launched orthogonally to the plane of the accretion disk, as expected if the jet is powered by energy drawn from the spin of the black hole. Both disk and jet angles correlate with the observed linear source size, which is a projection effect; when deprojected using the fitted angles, the distribution of source sizes agrees with a scenario in which the sources expand into the surrounding medium at a constant rate up to ~ 1 Mpc and then shut off, probably as the nuclei become quiescent. The accretion disk angle was found to correlate weakly with the low-frequency radio luminosity, which provides direct, albeit tenuous, evidence for the receding torus model.