UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

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 given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    DEVELOPMENT OF AN ADAPTIVE MASKING METHOD TO IMAGE BEAM HALO
    (2011) Zhang, Hao; O'Shea, Patrick G; Fiorito, Ralph B; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Beam halo is a common phenomenon in most intense particle beams and is associated with many bad effects. Halo is very hard to characterize because of its low intensity, which requires a measurement system with high dynamic range (≥105). Here, we have developed a technique that employs a digital micro-mirror array to produce an image of the halo of an electron beam with an enhanced dynamic range. Light produced by the beam intercepting a phosphor screen is first imaged onto the array; an adaptive mask is created and applied to filter out the beam core; and the result is re-imaged onto a CCD camera. In this thesis, we describe the optics used, the masking operation and preliminary results of experiments we have performed to study beam halo at the University of Maryland Electron Ring.
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    Beam halo creation and propagation in the University of Maryland Electron Ring
    (2009) Papadopoulos, Christos F.; O'Shea, Patrick G; Kishek, Rami A; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In this thesis we discuss the phenomenon of halo creation in charged particle beams. For this, we combine analytical, numerical and experimental work, which focuses on the University of Maryland Electron Ring, but is applicable to a wide range of accelerators in the same intensity regime. We find that the details of the beam distribution do not affect the structure of the halo, but are nonetheless important as they determine the number of particles in the halo and whether the latter can be regenerated. Furthermore, we show that the halo in configuration and velocity space comprises of the same particles, a prediction that has great importance for halo removal and diagnostics. In particular, we show that even in the case of ideal halo removal in phase space, the complicated internal dynamics of the beam core lead to halo regeneration. Following on previous work, we also construct a theoretical particle-core model for a skew quadrupole focusing channel, and compare the results to PIC simulations as well as measurements on UMER. The agreement between these three approaches is satisfactory, within the constraints of each case.