Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Longitudinal Control of Intense Charged Particle Beams(2011) Beaudoin, Brian Louis; O'Shea, Patrick G; Kishek, Rami A; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As the accelerator frontier shifts from high energy to high intensity, accelerator facilities are demanding beams with higher quality. Applications such as Free Electron Lasers and Inertial Fusion Energy production require the minimization of both transverse emittance and longitudinal energy spread throughout the accelerator. Fluctuations in beam energy or density at the low-energy side of the accelerator, where space-charge forces dominate, may lead to larger modulations downstream and the eventual degradation of the overall beam quality. Thus it is important to understand the phenomenon that causes these modulations in space-charge dominated beams and be able to control them. This dissertation presents an experimental study on the longitudinal control of a space-charge dominated beam in the University of Maryland Electron Ring (UMER). UMER is a scaled model of a high-intensity beam system, which uses low-energy high-current electron beams to study the physics of space-charge. Using this facility, I have successfully applied longitudinal focusing to the beam edges, significantly lengthening the propagation distance of the beam to 1000 turns (>11.52 km). This is a factor of 10 greater than the original design conceived for the accelerator. At this injected current, the space-charge intensity is several times larger than the standard limit for storage rings, an encouraging result that raises the possibility of operating these machines with far more space-charge than previously assumed possible. I have also explored the transverse/longitudinal correlations that result when a beam is left to expand longitudinally under its own space-charge forces. In this situation, the beam ends develop a large correlated energy spread. Through indirect measurements, I have inferred the correlated energy profile along the bunch length. When the bunch is contained using longitudinal focusing, I have shown that errors in the applied focusing fields induce space-charge waves at the bunch edges that propagate into the middle region of the beam. In some cases, these waves sustain multiple reflections before damping away. I conclude that space-charge in an intense beam without longitudinal focusing can cause the bunch to develop a large correlated energy spread, increasing the risk that the beam is lost to the pipe walls as it requires a larger aperture. When longitudinal focusing is applied however, we are able to transport the beam over a much longer path length and reduce the correlated energy spread.Item Longitudinal Space-Charge Waves Induced by Energy Modulations(2008-11-03) Beaudoin, Brian Louis; O'Shea, Patrick G; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High intensity beams that are space-charge dominated are important for applications such as free electron lasers that require high intensity and low emittance beams. Modulations in energy or density can induce space-charge waves at low energies which could be problematic at higher energies. This thesis is a study of longitudinal space-charge waves induced by energy modulations within a highly space-charge dominated beam propagating in the University of Maryland Electron Ring (UMER). Using an induction cell, we present the first UMER experimental results on the design and application of the cell to place energy perturbations. We compare the results to one-dimensional cold fluid theory and simulation. We allow the perturbation to propagate for over 60 m so that we can get a turn by turn measurement of the experimental sound speed. In some of the turn by turn data, we obtain a 4.8% disagreement between the experimentally measured sound speed and theory.