High electrical fields are needed inside the accelerating cavities of particle accelerators in order to accelerate the particles to higher energies in shorter distances. But high electrical fields will lead to electrical breakdowns. The electrical breakdowns are events in which the insulating proprieties of a typically electrically insulating medium are weakened due to the presence of high electrical fields. One of the best insulating mediums is the ultra high vacuum because there are no molecules that will ionize and that will conduct the electricity. But even in vacuum, there will be electrical breakdowns. They are called vacuum arc breakdowns. The conducting medium in this case is given by the ions and the electrons emitted from the metal surface of the electrodes that create the high electrical fields.  It has been observed that applying repeatedly high electrical fields on the surface of the electrodes reduces the number of breakdowns. This process is called conditioning. One explanation is that the large electric fields create dislocations near the surface of the metal that reduce the probability of having new vacuum arc breakdowns. These dislocations should also increase the electrical resistivity of the metal near its surface. To test if new dislocations are formed during conditioning, precise measurements of the surface resistivity are needed. These measurements will be made with radio pulses in the GHz range. In this range of frequencies, the electromagnetic fields penetrate only a few microns inside the surface of the metal and it will be possible to measure only the resistivity of the metal near its surface. The surface resistivity data is encoded in the quality factor (Q-factor) of a resonant cavity. This parameter describes how fast the energy is dissipated inside the cavity. A larger surface resistivity leads to a larger dissipation of energy in the walls of the cavity and to a lower Q-factor. It is advantageous to perform the measurements in cryogenic conditions because the increase in resistivity due to the formation of dislocations is much more pronounced at very low temperatures. The measurements are planned for the discharge system available in FREIA laboratory, that consists of two electrodes, separated by a small gap (60 µm), and placed inside a cryostat cooled with liquid helium. In this thesis, I describe the algorithms used to extract the Q-factor from experimental data and the results of some experiments done using the electrodes and test cavities. Small changes in resistivity (less than 0.6%), induced by temperature changes, were measured. The final chapter explores the results of the 3D EM simulations, where the electrode system in the cryogenic setup in FREIA laboratory is modified to act as a resonant cavity.

Att få en fördjupad bild av energiförlusten när joner med olika initialenergier interagerar med diverse material kan lägga grunden till viktig forskning inom till exempel materialvetenskap och strålbehandling. Det här projektet gick ut på att utföra flygtidsmätningar för att bestämma energiförlust för accelererade jod och vanadinjoner med energier mellan 4 och 44 MeV vid passage genom tunna fristående filmer av aluminium och titan. För att framställa tunna filmer sputtras material på en saltbelagd glasskiva som därefter sänks ner i vatten så saltet löses upp och filmen kan fiskas upp på en hållare. I en accelerator bombarderas folierna med joner och flygtiden mäts i en flygtidsdetektor. Skillnaden mellan de flygtider som mätts med och utan en folie kan sedan kalibreras om till energiförlust. Vid analys av filmernas tjocklek visade sig, framförallt för titanfilmerna, föroreningar och ojämnheter bidra till felkällor och påverka resultatet. Resultatet följer tidigare forskning väl vilket ger metoden merit men med vissa avvikelser som antas bero på felanpassad mätdata.

<p>Presentation held over Zoom.</p>

The future experimental programs both at FNAL and at CERN will have a strong focus on the search for new physics at the intensity frontier. In order to provide beams of unprecedented intensities to the various experiments at these labs, the booster accelerators in which the beams originate must perform far beyond their original design specifications. The optical properties of the booster accelerator lattices will need to be carefully controlled in order to deliver these high-intensity proton beams. This thesis presents the results of linear optics measurements made with unprecedented precision in the FNAL Booster and the CERN PS Booster using LOCO and K-modulation techniques. In the FNAL Booster, corrections to the observed optics distortions were also successfully implemented. The implications of these results for future high-intensity operations are discussed. / text

High intensity proton synchrotrons provide beams for several types of facility around the world, including spallation neutron sources and high energy physics experiments. The defining feature of these particle accelerators, that of intense beams, is tightly coupled to what limits the intensity, which is the controlled loss of beam particles. Many different factors contribute to beam loss. Beam will be lost on injection to a synchrotron and may be lost on extraction or in transfer lines. Non-linearities in the accelerator lattice can introduce driving terms for resonant beam behaviour. Collective effects between the beam particles and with the beam environment modify the single particle behaviour considerably. High intensity loss that occurs in the transverse plane, due to space charge and image fields, was investigated. The rapid cycling synchrotron at the ISIS Spallation Neutron Source in the UK was the focus for all of the work. The ISIS Synchrotron has many particular features which were described. One such feature is the conformal rectangular vacuum vessel, which takes the shape of the design beam envelope with certain modifications. This vacuum vessel has a complex effect on beam image fields. Numerical tools to study the space charge and image fields at ISIS were created and reported. The tools included two Poisson solvers to study space charge and images which were benchmarked against commercially available algorithms. A two dimensional particle-in-cell tracking code was created using the space charge solvers in combination with either a smooth focusing lattice model or one which generated Twiss matrices. A variety of diagnostic tools were available. A survey of existing analyses for pencil beams in parallel plate and rectangular geometry was made. Results from the analysis were then compared with two dimensional simulations with round uniform beams in rectangular geometry. Differences and extensions to the analysis were summarised. Coefficients for higher order image terms were defined and tabulated. The two dimensional nature of the image field was discussed and values for the coefficients for certain higher order terms identified in the plane orthogonal to the beam offset. Solutions for closed orbits produced with single and harmonic kicks at low and high intensity were discussed and simulated. A model was proposed which included the higher order image coefficients produced by the closed orbits. A single particle model was then explored which obtained resonance conditions from the closed orbits and image coefficients. The effect of self-consistent coherent motion on the results was discussed. Particle-in-cell beam tracking simulations were used to explore the results of this analysis numerically. Image resonances were found and described for a variety of simulation parameters starting with a smooth focusing lattice and uniform density beam, then progressing to more realistic cases including waterbag beams, alternating gradient lattices and conformal vacuum vessels. Image resonances described by the models were reported as were others that needed further explanation. Their possible impact for ISIS was discussed. New experiments with coasting beams at ISIS were carried out to explore the relationship between tune and beam loss at low intensity. Such experiments are a vital first step to understanding high intensity behaviour. It was shown that ISIS has existing lattice nonlinearities (some known, some unknown) which will need to be taken into account for high intensity experiments and simulations. Finally this work was put into context by examing specific transverse space charge effects for a proposed ISIS upgrade and including ideas developed throughout the thesis. Estimates were made of the strength of space charge effects and emittance scaling using conventional methods. The particle tracking tools developed for the thesis were then used to study beam behaviour with lattice gradient errors, the effects of closed orbits and changes to the working point. The transverse calculations and simulations suggested that the upgrade was feasible.

The ARIEL electron linac is a 0.3MW accelerator that will drive the production of rare isotopes in TRIUMF's new ARIEL facility. A planned upgrade will allow a second beam to be accelerated in the linac simultaneously, driving a Free Electron Laser while operating as an energy recovery linac. To not disrupt beam delivery to the ARIEL facility, an RF beam separator is required to separate the interleaved beams after they exit the accelerating cavities. A 650MHz superconducting RF deflecting mode cavity has been designed, built, and tested for providing the required 0.3MV transverse deflecting voltage to separate the interleaved beams. The cavity operates in a TE-like mode, and has been optimized through the use of simulation tools for high shunt impedance with minimal longitudinal footprint. The design process and details about the resulting electromagnetic and mechanical design are presented, covering the cavity's RF performance, coupling to the operating and higher order modes, multipacting susceptibility, and the physical design. The low power dissipation on the cavity walls at the required deflecting field allows for the cavity to be fabricated using non-conventional techniques. These include fabricating from bulk, low purity niobium and the use of TIG welding for joining the cavity parts. A method for TIG welding niobium is developed that achieves minimal degradation in purity of the weld joint while using widely available fabrication equipment. Applying these methods to the fabrication of the separator cavity makes this the first SRF cavity to be built at TRIUMF. The results of cryogenic RF tests of the separator cavity at temperatures down to 2K are presented. At the operating temperature of 4.2K, the cavity achieves a quality factor of 4e8 at the design deflecting voltage of 0.3MV. A maximum deflecting voltage of 0.82MV is reached at 4.2K, with peak surface fields of 26MV/m and 33mT. The cavity's performance exceeds the goal deflecting voltage and quality factor required for operation. / Graduate

The Large Hadron Electron Collider (LHeC) is a proposal for a TeV scale, 10^33 cm^−2 s^−1 luminosity electron-proton collider at CERN. In the proposal, an electron accelerator collides a beam of electrons with one of the Large Hadron Collider (LHC) proton beams at one LHC interaction point (IP). At the time of writing, the project has been approved as part of the CERN mid-term plan. The LHeC project is planned for the 2020s, around the time of the High Luminosity LHC (HL-LHC) upgrade. The LHeC thus depends upon the success of the HL-LHC project, which plans to deliver p-p luminosity of L=5×10^34 cm^−2 s^−1. Unique challenges are presented by the LHeC, particularly by the interaction region (IR) and long straight section (LSS), and constraints must be considered from beam, particle and detector physics and engineering. This thesis presents the study and design of a complete collision insertion solution for a ring-ring LHeC. This provides a solution at a conceptual level to the problem of delivering TeV scale e−p collisions at L∼10^33 cm^−2 s^−1 for the first time, with detector coverage within 1 degree of the beam. This high acceptance, high luminosity solution substantially increases the value of the project, allowing high statistics across an unprecedented kinematic range. Further studies are presented into optimising the optical flexibility of the LHC LSSs, and into the effects of fringe fields in the HL-LHC large aperture quadrupoles. Modifications are proposed which maximise LSS flexibility, and fringe effects are found to be significant but manageable.

ESS neutrino Super Beam (ESSnuSB) is a project that aim to create ahigh energy beam of neutrinos and anti-neutrinos to study thephenomenon neutrino oscillation and learn more about symmetryviolations in quantum mechanics. To create the neutrino beam, negativeHydrogen ions must be transported from the ESS linear accelerator at2.5 GeV, to a proton accumulation ring. This is done through a transferline, that shall direct the ion beam while preserve the beam as much aspossible. In thisproject, there was an attempt at finding a design for this transferline. Preferably, the line consists of a long main line of FODO cellsand two matching sections at each end. A simulation of the beam wasdone that gives the progression beta and dispersion functions,statistical measurements of the particle distribution, through a partof the transfer line. A design for the main line was found. For tuningthe quadrupole magnets, an iterative method using the system's responsematrix was used. However, it could not match more than four parametersat the time, while six was required for complete matching. Because ofthis, it is not able to match thedispersion.

Particle accelerators are indispensable tools for probing matter at the smallest scales and the improvements of such tools depend on the progress and understanding of accelerator physics. The Compact Linear Collider (CLIC) is a proposed, linear electron–­positron collider on the TeV-scale, based at CERN. In such a large accelerator complex, diagnostics and alignment of the beam are crucial in order to maintain beam quality and luminosity. In this thesis we have utilized the nonlinear fields from the octupole component of the radio-frequency fields in the CLIC accelerating structures for beam-based diagnostics. We have investigated methods where the nonlinear position shifts of the beam are used to measure the strength of the octupole component and can also be used for alignment. Furthermore, from the changes in transverse beam profile, due to the nonlinear octupole field, we determine the full transverse beam matrix, which characterizes the transverse distribution of the beam. In circular accelerators, nonlinear fields result in nonlinear beam dynamics, which often becomes the limiting factor for long-term stability. In theoretical studies and simulations we investigate optimum configurations for octupole magnets that compensate amplitude-dependent tune-shifts but avoid driving fourth-order resonances and setups of sextupole magnets to control individual resonance driving terms in an optimal way.

This thesis describes the design of novel magnetic lattices for the transport line and gantry of a charged particle therapy complex. The designs use non-scaling Fixed Field Alternating Gradient (ns-FFAG) magnets and were made as part of the PAMELA project. The main contributions in this thesis are the near-perfect FFAG dispersion suppression design process and the designs of the transport line and the gantry lattices. The primary challenge when designing an FFAG gantry is that particles with different momenta take up different lateral positions within the magnets. This is called dispersion and causes problems at three points: the entrance to the gantry, which must be rotated without distortion of the beam; at the end of the gantry where reduced dispersion is required for entry to the scanning system; and a third of the way through the gantry, where a switch in curvature of the magnets is required. Due to their non-linear fields, dispersion suppression in conventional FFAGs is never perfect. However, as this thesis shows, a solution can be found through manipulation of the field components, meaning near-perfect dispersion suppression can be achieved using ns-FFAG magnets (although at a cost of irregular optics). The design process for an FFAG dispersion suppressor shown in this thesis is a novel solution to a previously unsolved problem. Other challenges in the gantry lattice design, such as height and the control of the optics, are tackled and a final gantry design presented and discussed. The starting point for the transport line is a straight FFAG lattice design. This is optimised and matched to a 45o bend. Fixed field solutions to the problem of extracting to the treatment room are discussed, but a time variable field solution is decided on for practical and patient safety reasons. A matching scheme into the gantry room is then designed and presented.