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.

Submitted by Rosa Assis (rosa_assis@yahoo.com.br) on 2017-03-24T18:15:07Z No. of bitstreams: 2 Wellington Luiz da Cruz.pdf: 6031617 bytes, checksum: 7a15565e2d3fcf871e0c5c9b319f81f9 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Paola Damato (repositorio@mackenzie.br) on 2017-04-03T13:21:37Z (GMT) No. of bitstreams: 2 Wellington Luiz da Cruz.pdf: 6031617 bytes, checksum: 7a15565e2d3fcf871e0c5c9b319f81f9 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-04-03T13:21:37Z (GMT). No. of bitstreams: 2 Wellington Luiz da Cruz.pdf: 6031617 bytes, checksum: 7a15565e2d3fcf871e0c5c9b319f81f9 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-02-20 / Recent observations of solar flares at high-frequencies have provided evidence of a new spectral component with fluxes increasing with frequency in the sub-THz to THz range. This new component occurs simultaneously but is separated from the well-known microwave spectral component that maximizes at frequencies of a few to tens of GHz. The aim of this work is to study in detail a mechanism recently suggested to describe the double spectrum observed in solar flares based on the physical process known as microbunching instability, which occurs with high-energy electron beams in laboratory accelerators. Such a process is responsible for the production of synchrotron radiation with a double spectrum similar to that observed in solar flares, showing a broadband coherent synchrotron radiation component (CSR) and a distinct incoherent synchrotron radiation component (ISR) with maximum at higher frequencies. / Observações recentes de explosões solares em altas freqüências têm fornecido evidências de um nova componente espectral com fluxos crescentes com a freqüência na faixa de sub-THz a THz. Essa nova componente ocorre simultaneamente mas é separada da bem conhecida componente espectral em microondas que maximiza em freqüências da ordem de dezenas de GHz. O objetivo deste trabalho é estudar em detalhe um mecanismo recentemente proposto para descrever o duplo-espectro observado em explosões solares, baseado no processo físico conhecido como microbunching instability que ocorre com feixes de elétrons de alta-energia em aceleradores de laboratório. Esse processo é responsável pela produção de radiação síncrotron com duplo-espectro semelhante ao observado em explosões solares, exibindo uma componente coerente de banda larga (Coherent Synchrotron Radiation - CSR) e uma componente incoerente distinta (Incoherent Synchrotron Radiation - ISR) com máximo em freqüências maiores.

Um die zu erwartenden Eigenschaften einer ERLbasierten Synchrotronstrahlungsquelle zu untersuchen, baut das Helmholtz Zentrum Berlin die Testanlage bERLinPro. Die Strahlenergie in diesem Testbeschleuniger beträgt Ekin = 50MeV bei einem Strom von 100 mA. Solch ein hochstromiger Elektronenstrahl im mittleren Bereich der kinetischen Energie ist Raumladungskräften unterworfen. Raumladungskräfte sind eine Quelle von Microbunching Instabilität, die zu einer Dichtemodulation in einer Elektronenverteilung führen kann. Eine solch modulierte Verteilung kann z.B. beim Durchgang durch einen Dipol kohärente, hochbrillante Synchrotronstrahlung emittieren, also Strahlung mit längeren Wellenlängen als die Verteilung. Im Rahmen dieser Arbeit wird sowohl das Auftreten, als auch die Einsatzmöglichkeit von Microbunching Instabilität in bERLinPro untersucht. Es ist geplant, bERLinPro bei zwei verschiedenen Betriebsarten (normaler Betriebsmodus und KurzPulsModus) zu betreiben. Im Rahmen dieser Arbeit wurden zum ersten Mal nummerische Simulationen des Testbeschleunigers von dessen Anfang bis dessen Ende durchgeführt, die sowohl von analytischen Rechnungen unterstützt als auch mit ihnen verglichen wurden. Ausführlich werden sowohl der Simulationscode, das Programm zur Nachbearbeitung der nummerischen Untersuchungen als auch ein SigmamatrixTrackingSkript beschrieben. Dieses dient als Basis für analytische Rechnungen, dass zusätzlich auch Impedanz Berechnungen und Gain Rechnungen beinhalten. Für den KurzPulsModus können nur analytische Rechnungen betrachtet werden, denn das entsprechende Design der Maschine, wie auch die Anpassung der Phase im Linearbeschleuniger, sind Gegenstand aktueller Untersuchungen. / To investigate the expected properties of an ERLbased synchrotron light source, the Helmholtz Zentrum Berlin (HZB) is building the test facility bERLinPro. The beam energy of the test facility amounts to Ekin = 50MeV at a current of 100 mA. Such a high current electron beam with a medium bunch energy underlies space charge forces. These are a source of microbunching instability which can lead to a density modulation of the electron distribution in the electron bunch. These modulated bunches can emit highbrilliance coherent synchrotron radiation; radiation with wavelengths longer than the bunch, i.e. by passing a dipole. In the framework of this thesis both the occurence and the possible application of microbunching instability are investigated in bERLinPro. Planes are to run bERLinPro in two different operation modes: Standard operation mode and short pulse mode. In the context of this thesis, numerical start-to-end simulations for standard operation mode have been carried out for the first time. Both were compared and supported with analytical calculations. Elaborated descriptions of simulation codes and postprocessing tools for numerical investigation are described, as well as a sigma matrix tracking script as basis for analytical investigation, including impedance and gain calculations. Since current investigations include lattice design and linac phase adjustments for the short pulse mode, only analytical calculation could be considered for this operation mode.

La spectroscopie par transformée de Fourier est l’outil multiplexe de mesure de spectres à haute résolution le plus utilisé dans l’infrarouge. Son extension au domaine Térahertz se révèle de grand intérêt pour la spectroscopie de molécules présentes dans le milieu interstellaire, mais se heurte à différents obstacles : en particulier, aucune source large bande n'est suffisamment intense et stable pour ces applications. Cette thèse présente des développements instrumentaux basés sur l’exploitation du rayonnement synchrotron cohérent (CSR) sur la ligne AILES du synchrotron SOLEIL, optimisée pour l'infrarouge lointain. Les conditions de production du CSR sont étudiées pour les besoins des analyses spectroscopiques à haute résolution ; les performances de cette source sont caractérisées et comparées à celles du rayonnement incohérent. La mise en place d'un système de double détection permet une correction de l'effet des instabilités de la source et une augmentation conséquente du rapport signal-sur-bruit. Ces développements sont appliqués à la mesure de spectres de rotation pure ; une modélisation améliorée du spectre dans l'état fondamental de la molécule de propynal a ainsi pu être faite, prouvant la complémentarité de la source étudiée vis-à-vis des sources micro-onde ou infrarouge classiques. / Fourier Transform spectroscopy is the most used multiplex tool for high-resolution measurements in the infrared range. Its extension to the Terahertz domain is of great interest for spectroscopic studies of interstellar molecules. This application is however hampered by the lack of dedicated, broadband sources with a sufficient intensity and stability. In this work, Coherent Synchrotron Radiation (CSR) was used as a source for molecular spectroscopy at high resolution on the AILES infrared and Terahertz beamline of SOLEIL synchrotron. The beamline being optimized for far-infrared, we could characterize the properties of CSR and compare them to the incoherent synchrotron radiation. A double detection system allowed to correct the effect of the source-related instabilities, hence to significantly increase the signal-to-noise ratio. Pure rotational spectra were measured using these developments. The case of the propynal molecule, for which a refined set of rotational and centrifugal distortion constants was calculated, proves the complementarity between CSR and the classical microwave or infrared sources.

La spectroscopie par transformée de Fourier est l'outil multiplexe de mesure de spectres à haute résolution le plus utilisé dans l'infrarouge. Son extension au domaine Térahertz se révèle de grand intérêt pour la spectroscopie de molécules présentes dans le milieu interstellaire, mais se heurte à différents obstacles : en particulier, aucune source large bande n'est suffisamment intense et stable pour ces applications. Cette thèse présente des développements instrumentaux basés sur l'exploitation du rayonnement synchrotron cohérent (CSR) sur la ligne AILES du synchrotron SOLEIL, optimisée pour l'infrarouge lointain. Les conditions de production du CSR sont étudiées pour les besoins des analyses spectroscopiques à haute résolution ; les performances de cette source sont caractérisées et comparées à celles du rayonnement incohérent. La mise en place d'un système de double détection permet une correction de l'effet des instabilités de la source et une augmentation conséquente du rapport signal-sur-bruit. Ces développements sont appliqués à la mesure de spectres de rotation pure ; une modélisation améliorée du spectre dans l'état fondamental de la molécule de propynal a ainsi pu être faite, prouvant la complémentarité de la source étudiée vis-à-vis des sources micro-onde ou infrarouge classiques.