ABSTRACT The multi-disciplinary accelerator based facilities at iThemba LABS are used intensively for nuclear physics experiments, radiotherapy and the production of radioisotopes. To increase the beam intensity for radioisotope production and to improve the beam quality of the 66 MeV proton beam, a double-gap horizontal half-wave flat-topping resonator has been developed for the separated-sector cyclotron to operate at the associated fixed frequency. This type of flattopping resonator has never before been implemented in a cyclotron and this study is the first to show that it can be done, featuring a special characteristic not offered by other types. The resonator is reviewed against the other types of resonators that are already in use at other institutes around the world. The flat-topping voltage of the selected type has a sinusoidal half-wave distribution along a radial line in each of its acceleration gaps with the nodal points located on the injection and extraction orbits. The flat-topping voltage therefore progressively increases from zero at both of the two most critical orbits in a cyclotron to a maximum at about halfway between them. As a result will this resonator, apart from its basic function to reduce the energy spread in the beam, not decrease the orbit separation at the injection and extraction orbits in the cyclotron, as is the case with other types of flat-topping resonators. This advantageous feature implies that the beam pattern in the cyclotron is not affected in the regions of the delicate injection and extraction components and therefore will these components or the operational control of the beam not require any modification to accommodate the resonator. In order to design a resonator that will meet our requirements, the theory of the beam dynamics and resonator characteristics were studied to ascertain the expected improvement in beam quality and beam intensity when a flat-topping resonator is implemented with the cyclotron. All resonator types were considered and studied in terms of their power dissipation, voltage distribution, harmonic number, space requirements and influence on the beam. The horizontal half-wave resonator type, with two acceleration gaps, was selected as the most suitable for our application, because of its preferred electromagnetic characteristics and its geometric shape that permits the installation inside an existing vacuum chamber through an existing flange. Initially a half-scale resonator model was build to test the feasibility of such a resonator and also to verify the calculation methods. Transmission line methods and numerical field analysis in 3D were applied to determine the resonator characteristics. In the former method a computer program, POISSON, was used to calculate curvilinear squares on sections through a triangular-shaped transmission line and in the latter method a commercial computer program, SOPRANO, was used. SOPRANO is part of an internationally acclaimed suite of programs and the acquired knowledge and skill to use this state-of-the-art software for the studying and designing of such and other electromagnetic devices also put the institute amongst the front-runners in the world. The calculated characteristics of the half- and full-scale resonator models, the study of the different electromagnetic modes that resonate in close proximity to the required frequency, the heat transport modelling and the theory and implementation of the coupling and tuning devices are all in good agreement with their respective measured results and are reported in this document. This study lead the way to have the first-ever double-gap horizontal half-wave flat-topping resonator in a cyclotron successfully commissioned at iThemba LABS and the first tests with beam report very stable operation. Accelerator physicists now have another option to utilize for the establishing of flat-topped acceleration voltages.

Es centres de rayonnement synchrotron sont des accélérateurs de particules qui génèrentun faisceau de lumière bien intense et collimaté en courbant la trajectoire d'un faisceau d´électronrelativiste. Le champ le plus simple utilisé pour courber la trajectoire d'un électron est unchamps magnétique constant généré par un dipôle. Des rayonnements plus intense peuventêtre émis dans une insertion. Une insertion est composée d'une séries de dipôle de polaritésinverses. Les insertions comprennent en général deux types : onduleurs et wigglers. Leswigglers sont très importants pour une source de rayonnement synchrotron. Ils peuvent êtreutilisé pour objectives différents, comme moduler le structure temporel de paquets d´électron,la production de faisceau de photon de haut énergie et réduire la taille transverse de faisceau.Ce travail est consacré pour l´étude de deux wigglers différent pour deux objective différents :le wiggler W164 et wiggler Robinson. Le W164 a étéconstruit pour la production des impulsionsde courte durée (femtosecond ) en utilisant le principe de femtoslicing. Dans le principede femtoslicing, si un faisceau d´électron se propage avec un faisceau de laser de durée defemtosecond dans le wiggler, ce dernier fait le rôle d'un modulateur qui extrait un “ slice “du paquet de durée de femtosecond qui émet à son tour un rayonnement X de durée de femtosecond.En plus, W164 fait un autre rôle d' une source rayonnement de photon des hautsénergies pour une autre ligne de lumière. La deuxième partie de ce travail est dédiée à l´étude d'unwiggler Robinson pour réduire l´emittance horizontal. L'effet Robinson à été étudié et observéexpérimentalement à SOLEIL avant la construction de wiggler. Les résultats sont présentés.Un pré-design a été aussi proposé. / Synchrotron light sources are particle accelerators that generate intense and highly collimatedradiation by bending the trajectory of a relativistic electron beam. The most commonsimple field used to deflect a relativistic electron beam trajectory is a constant magnetic fieldgenerated by bending magnet. More intense radiation can produced through insertion devices.An insertion device is made by combining short bending magnets of opposite polarities. Theyinclude in general two types: undulators and wigglers. Wigglers play an important role ina synchrotron radiation source, since they can be employed for different objectives such asmodulating the time structure of the electron bunch, generating high energy photons, andreducing the transverse beam size. This work studies two different wigglers for different purposes:W164 and Robinson wiggler. The wiggler W164 was constructed for the production offemtosecond light pulses based on the femtoslicing principle. Femtoslicing implies that if anelectron beam co-propagates through the wiggler with a femtosecond laser pulse, the wiggleracts on the electron beam as a modulator and extracts a femtosecond slice of the bunch thatcreates in turn a femtosecond X-ray pulse. Moreover, the W164 plays another role of being ahigh energy photon source for another beamline. The second topic studied here is reducing thehorizontal emittance by using Robinson wiggler. Robinson effect was studied and observedexperimentally at SOLEIL before the wiggler construction. A preliminary wiggler design isproposed

Im Jahre 1958, schlug Kenneth W. Robinson die Nutzung eines Korrektormagneten vor um den entdämpften radialen Betatronoszillationen im Cambridge electron accelerator entgegen zu wirken. Dieser Korrektormagnet sollte aus kurzen, alternierenden Dipolen mit einem starken Gradienten bestehen, sodass die Verluste durch Synchrotronstrahlung mit zunehmendem Trajektorienradius abnehmen. Diese Transversal-Gradienten-Wiggler werden auch "Robinson Wiggler" (RW) genannt. Die Metrology Light Source (MLS), welche Eigentum der Physikalisch-Technischen Bundesanstalt (PTB) ist und vom Helmholtz-Zentrum Berlin (HZB) entworfen und betrieben wird, ist ein Elektronen-Synchrotron, optimiert für die Produktion von Synchrotronstrahlung im Spektralbereich zwischen THz und EUV. Da die MLS eine gerampte Maschine ist, nimmt der gespeicherte Elektronenstrom mit der Zeit ab und die Strahllebensdauer ist von Bedeutung für die Nutzer der Synchrotronstrahlung. Es wird vorgeschlagen einen RW bei der MLS zu installieren um die Strahllebensdauer zu erhöhen. Mit RW wäre es möglich, Dämpfung aus der longitudinalen in die horizontale Ebene zu verschieben sodass sich die Energiebreite um einen Faktor 3 erhöht und die Emittanz sich um ungefähr einen Faktor 2 reduziert. Die Länge der Elektronenpakete wird dadurch stärker verlängert als die mittlere horizontale Paketbreite reduziert wird. So nimmt die Elektronendichte im Paket ab und die Verlustrate sinkt. Dies hat zu Folge dass sich die Lebensdauer verbessert und die Aktivierung von Komponenten reduziert wird. Mit erhöhter Energiebreite und verringerter Emittanz, wird der Beitrag der Dispersion zur horizontalen Quellgröße stärker. Durch geeignete Wahl der Magnetoptik kann die Brillianz am Quellpunkt erhöht werden bei gleichzeitiger Verbesserung der Lebensdauer. Simulationen zeigen dass die Lebensdauer an der MLS durch die Installation eines solchen RW um einen Faktor 2.3 ansteigt, was einem Zugewinn an integriertem Photonenfluss von 30 % entspricht. / In 1958, Kenneth W. Robinson proposed the usage of a magnetic correction device to reduce the antidamping of radial betatron oscillations in the Cambridge electron accelerator. The essence of this correction device are short, alternating dipoles with a strong gradient, such that the radiation loss decreases with increasing radius of trajectory. These transverse gradient wigglers are also called "Robinson Wigglers" (RW). The Metrology Light Source (MLS), owned by the Physikalisch-Technische Bundesanstalt (PTB) and designed and operated by Helmholtz-Zentrum Berlin (HZB), is an electron synchrotron, optimized for the production of synchrotron radiation in the THz to the EUV spectral region. Being a ramped machine, Top-Up operation is not possible. With a decaying beam current, the lifetime of the stored beam is of importance for the user community, for reasons of temporal stability and integrated photon flux. It is proposed to install a RW at the MLS in order to improve the beam lifetime. With a RW, it is possible to transfer damping from the longitundinal to the horizontal plane in a way, that the energy spread increases by a factor of 3 and the emittance reduces by a factor of 2. Doing so, the bunch length is increased by a larger fraction than the average bunch width is decreased. Thereby the electron density is reduced which results in a lower loss rate of electrons. This improves the beam lifetime and reduces induced radioactivity of accelerator components and shielding. With an increased energy spread and a reduced emittance, the contribution of the dispersion to source size becomes more important. By carefully choosing the magnet optics, the brilliance at the source point can be improved simultaneously to increasing the lifetime. Simulations indicate that a RW is able to increase the lifetime in the standard user operation mode at the MLS by a factor of 2.3, corresponding to an increase in photon flux for one standard user run of approximately 30 %.

Dizertační práce se zabývá problematikou výpočtu vlivu coulombovských interakcí částic na parametry emitovaného elektronového svazku v blízkosti Schottkyho a studené katody. Práce poskytuje základní předhled o problematice, popisuje vytvořené modely emisních zdrojů a metodu simulace Monte Carlo. Představuje novou metodu generování vstupních dat, která klade větší důraz na přesnou simulaci emisního procesu. Pozornost je zde věnována zejména vlivu interakcí na energiovou šířku, velikost virtuálního zdroje a jas katody v závislosti na velikosti poloměru hrotu a emisním proudu. Sledováním vývoje energiové šířky bylo zjištěno, že naprostá většina interakcí se odehrává v prostoru do několika mikrometrů od hrotu katody. Závislost spočtené celkové energiové šířky na úhlové intenzitě je ve shodě s dostupnými experimentálními daty. Spočtené energiové rozšíření vlivem coulombovských interakcí bylo srovnáno s hodnotami vypočtenými pomocí vzorců založených na analytických přiblíženích. Bylo zjištěno, že některé z nich přijatelně předpovídají trendy ale nemohou být použity pro kvantitativní odhad.