School of Physics - Theses
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ItemAn Optical Fibre Beam-Loss Monitor for the Australian Synchrotron( 2021)The central thread of this thesis describes the testing and commissioning of the optical fibre beam-loss monitor (oBLM) for use at the Australian Synchrotron. The four 125 m long silica fibres that form the sensitive detectors of the oBLM are installed on the Aus- tralian Synchrotron and provide complete baseline coverage of the accelerator, from the electron gun to the end of the storage ring. This configuration provided a range of testing environments in which to characterise the oBLM and investigate potential use cases. The results of these procedures demonstrated that the oBLM was able to objectively discern losses above 200 fC or approximately 10^6 electrons. The timing resolution as averaged from measurements using multiple fibres at several loss locations was determined to be 1.22 +/- 0.19 ns at FWHM across the working range of the fibres. When the oBLM is operated in time of flight mode this corresponds to a spatial resolution of 0.13 +/- 0.02 m, which is smaller than the average component spacing of lattice elements at the Australian Synchrotron and demonstrates that the oBLM is capable of attributing losses to specific errant devices. Potential and productive use cases of the oBLM were then explored and a range of operational techniques were developed, after which the oBLM was integrated into the injection efficiency monitoring and optimisation system. Where it was used, in time of flight mode, to characterise spontaneous losses along the length of the Australian Synchrotron injection and storage ring systems. The diagnostic information it provided from these measurements was employed in the tuning of the injection system and as a consequence the injection efficiency between the linac and booster ring was increased by 60 %. Based on the findings of this thesis an optimised configuration, that best enables the oBLM to address the usage scenarios identified, was created and presented in this thesis.
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ItemSpatial coherence measurement of undulator radiation using uniformly redundant arrays( 2003)Synchrotron light source are accelerating research and development and fueling innovation in a wide range of research disciplines and industries worldwide. The third-generation synchrotron radiation facilities such as Advanced Photon Source (APS), produce ultra-brilliant x-rays using insertion devices consisting mainly of undulators, which provide exciting opportunities for advanced research into materials, earth science, life science, and medicine. Using high brightness x-ray radiation with high spatial coherence, unique coherence-based experiments are now becoming possible: coherence imaging techniques such as phase contrast imaging, holography, and tomography, are under intensive development, opening up a range of new areas of investigation. At the same time some useful optical elements used in the synchrotron radiation system have been created rapidly. Crucial to the development of all these fields is some knowledge of the spatial coherence of the light produced by these sources. In other words, the characterization of spatial coherence is a high priority. The aim of this project is to develop a theoretical and experimental program to allow the measurement of the spatial coherence of synchrotron radiation. A technique to measure the spatial coherence of x-rays from undulators is presented. The essence of the coherence measurement technique is based on the interpretation of a complex diffraction pattern. We measure the spatial coherence function of a 7.9 keV x-ray beam from an undulator at a third-generation synchrotron (APS) using a sophisticated diffracting aperture known as a Uniformly Redundant Array (URA). The URA was also used to measure the spatial coherence function for soft x-rays at the APS. When a traditional Young’s double-slit experiment is used to test the degree of coherence, the separations of the two-slit have to be changed repeatedly to full map the spatial coherence function. The URA is a complex aperture consisting of many slits, (or, for a two-dimensional array, pinholes), organized such that all possible slit separations occur, and do so with exactly the same frequency. One might regard the URA as able to simultaneously perform many Young’s experiments a precisely equal number of times across the full range of slit separations permitted by the overall size of the URA. Therefore one experiment using a one-dimensional (1D) URA can perform the equivalent of multiple double-slit experiments. The diffraction theory developed in this thesis a convenient theoretical basis for interpreting this diffraction pattern.
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ItemDiagnostics and control of transverse coupled-bunch instabilities in third generation electron storage rings( 2011)The Australian Synchrotron is a newly commissioned third-generation light source situated in Melbourne, Australia. Synchrotron radiation is produced from the 216 metre circumference storage ring where 3 GeV electrons are trapped within a lattice formed by dipole bending magnets and multipole focussing magnets. The appearance of coupled-bunch instabilities form the primary limitation of modern storage rings. Instabilities enforce an upper limit on stored current and can reduce the utility of radiation production by increasing the effective emittance of the ring. Stored current limitations due to beam instabilities were discovered early in the commissioning phase of the Australian Synchrotron storage ring and were initially controlled by substantially increasing the chromaticity of the lattice from (ξx; ξy) = (2; 2) to (ξx; ξy) = (3:5; 13). Subsequent additions to the ring have resulted in an increase of the strength of destructive instabilities to the point where detrimental side-effects from chromatic corrections reduce the ability of the ring to damp instabilities. This increase in instability strength has lead to the shift from purely passive methods of instability control to the design and construction of an active transverse feedback system. This thesis describes the commissioning of a bunch-by-bunch transverse feedback system designed to combat coupled-bunch instabilities, allowing for the reduction of chromaticity within the storage ring lattice back to the initial design values (ξx; ξy) = (2; 2). Reducing the chromaticity also removes detrimental effects such as the reduction of the dynamic aperture and an increase in the lifetime of the beam. Novel methods for tuning the system and maximising the damping rate of the beam are introduced. Using these methods, the feedback system was successfully commissioned and was shown to have the stability required for user-mode storage ring operations. The bunch-by-bunch transverse feedback system can also be leveraged as a powerful diagnostic tool. New data acquisition techniques have been designed to allow for the study of different instability mechanisms as well as parameters present in the equations of motion for stored particles. These techniques and the suite of results achieved are presented.