Plasma-based accelerators offer the potential to achieve accelerating gradients orders of magnitude higher than are typical in conventional accelerators. A Plasma Accelerator Research Station has been proposed using the CLARA accelerator at Daresbury Laboratory. In this thesis, theory and the results of particle-in-cell simulations are presented investigating experiments that could be conducted using CLARA as well as the preceding VELA and CLARA Front End. Plasma wakefield acceleration was found to be viable with both CLARA and CLARA Front End, with accelerating gradients of GV/m and 100 MV/m scale respectively. Drive-witness and tailored bunch structures based on the CLARA bunch were also investigated. Plasma focus- ing of the VELA and CLARA Front End bunches was studied in simulations, showing that substantial focusing gradient could be achieved using a passive plasma lens. A plasma beam dump scheme using varying plasma density is also presented. This scheme allows the performance of a passive plasma beam dump to be maintained as the bunch is decelerated and has some advantages over a previously proposed method.

J.R. Terrall, J.C. Slater. / "May 31, 1948." / Bibliography: p. 4. / Army Signal Corps Contract No. W-36-039 sc-100 Project No. 8-102B-0. Dept. of the Army Project No. 3-99-10-022.

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Plasma-based accelerators aim to efficiently generate relativistic electrons by exciting plasma waves using a laser or particle beam driver, and "surfing" electrons on the resulting wakefields. In the blowout regime of such wakefield acceleration techniques, the intense laser radiation pressure or beam fields expel all of the plasma electrons transversely, forming a region completely devoid of electrons ("bubble") that co-propagates behind the driver. Injection, where initially quiescent background plasma electrons become trapped inside of the plasma bubble, can be caused by a variety of mechanisms such as bubble expansion, field ionization or collision between pump and injector pulses. This work will present a study of the injection phenomenon through analytic modeling and particle-in-cell (PIC) simulations. First, an idealized model of a slowly expanding spherical bubble propagating at relativistic speeds is used to demonstrate the importance of the bubble's structural dynamics in self-injection. This physical picture of injection is verified though a reduced PIC approach which makes possible the modeling of problem sizes intractable to first-principles codes. A more realistic analytic model which takes into account the effects of the detailed structure of the fields surrounding the bubble in the injection process is also derived. Bubble expansion rates sufficient to cause injection are characterized. A new mechanism for generation of quasi-monoenergetic electron beams through field ionization induced injection is presented, and simulation results are compared to recent experimental results. Finally, a technique for frequency-domain holographic imaging of the evolving bubble is analyzed using PIC as well as a novel simulation method for laser probe beam propagation. / text

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

The report detailing the Hardware Accelerator for the JPEG encoder is organized into three sections. First, it will review the processes of the Joint Photographic Experts Group (JPEG) encoding and decoding standard. Second, it will review three different implementations of the discrete cosine transform in hardware. This is a very computationally intensive element of the JPEG encoding process and the analysis of these designs covers the benefits and costs of the various approaches for the Field Programmable Gate Array (FPGA) and Application Specific Integrated Circuit (ASIC) implementations. Finally, it will discuss this specific hardware accelerator design for a color state transformation for the standard JPEG encoder. An eight by eight matrix of Red, Green, Blue (RGB) values is passed into the FPGA as well as calculated in software. The Y Cr Cb results from that of the hardware accelerator implementation are compared with the software implementation for computational accuracy and the differences in computation time are sampled for a comparison. There is a clear 38% improvement in speed from the hardware accelerator. / text

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The BEAMnrc and DOSXYZnrc codes from EGSnrc Monte Carlo (MC) system are considered to be the gold standards for simulating radiotherapy linear accelerators and resulting dose depositions (Rogers, Faddegon et al. 1995). The aim of this project was to setup the EGSnrc system for the simulation of the linear accelerator (linac) head and a Scanning Liquid Ionisation Chamber (SLIC) Electronic Portal Imaging Device (EPID) for calculations of transmitted dose in the EPID. The project was divided into two parts. The head of a 6 MV Varian 600C/D photon linac was first simulated by BEAMnrc. The modelling parameters such as the electron beam energy and the Full Width at Half Maximum (FWHM) of the electron spatial distribution were adjusted until the absorbed dose profiles and the Percentage Depth Dose (PDD) curves, in general agreed better than the measured profiles and PDDs by 2%. The X-ray beam obtained from the modelled linac head was used for the simulation of the transmitted dose in the EPID in the second part of the project. The EPID was simulated by DOSXYZnrc based on the information obtained from Spezi and Lewis 2002 (Spezi and Lewis 2002), who also modelled the Varian SLIC EPID (MK2 Portal Vision system, Varian Inc., Palo Alto, CA, USA). The comparisons between the measured and the simulated transmitted doses were carried out for three different phantom setups consisting of an open field, homogeneous water equivalent phantom and a humanoid phantom (RANDO). These phantom setups were designed so that the accuracy of the MC method for simulating absorbed dose in air, homogeneous and inhomogeneous phantoms could be assessed. In addition, the simulated transmitted dose in an EPID was also compared with values obtained from the Pinnacle treatment planning system (v6.2b, Phillips Medical Systems). In the process of selecting the electron beam energy and FWHM, it was confirmed (Sheikh-Bagheri and Rogers 2002; Keall, Siebers et al. 2003) that the variation of the electron beam FWHM and energy influenced the beam profiles strongly. The PDD was influenced by the electron beam energy less strongly. The increase in the energy led to the increase in the depth of maximum dose. However, the effect could not be observed until the energy change of 0.2 MeV was made. Based on the analysis of the results, it was found that the combination of FWHM and energy of 1.3 mm and 5.7 MeV provided the best match between the measured and MC simulated beam profiles and PDDs. It can be concluded that an accuracy of 1.5% can be achieved in the simulation of the linac head using Monte Carlo method. In the comparison between the Monte Carlo and the measured transmitted dose maps, agreements of 2% were found for both the open field and homogeneous water equivalent phantom setups. The same agreements were also found for the comparison between Monte Carlo and Pinnacle transmitted dose maps for these setups. In the setup where the humanoid phantom RANDO was introduced in between the radiation field and the EPID, a general agreement of about 5% found for the comparison between Monte Carlo and measured transmitted dose maps. Pinnacle and measured transmitted dose map was also compared for this setup and the same agreement was found. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1352973 / Thesis (M.Sc.) - University of Adelaide, School of Chemistry and Physics, 2009

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.