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Title: X-ray powder diffraction as a non-destructive tool for characterising laser wakefield betatron radiation
Author: Cheung, Gavin
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2018
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Laser wakefield accelerators provide a relatively simple means of generating bright X-rays beams which are useful across many fields and industries. To achieve this, a sufficiently powerful laser is required and just a few centimetres of gas. In contrast, other bright X-ray sources, such as synchrotrons, require significantly more infrastructure and can span many hundreds of metres. This thesis looks at a novel diagnostic technique based on X-ray diffraction from a powder in order to characterise X-ray beams with large shot-to-shot variations. The mechanics behind the method, named XCERP diffraction, are presented and the results of simulations are provided as a proof of principle study. XCERP diffraction is shown to be able to retrieve details of the energy spectrum and the beam divergence in a single shot without prior knowledge of the spectral shape. A campaign at the Centre for Advanced Laser Applications in Munich focused on the first experimental demonstration of XCERP diffraction. The results reveal that an increased level of radiation shielding was required as a source of ionising radiation was found to be present whenever an electron beam was generated. This source of radiation is thought to have obscured potential X-ray diffraction. An investigation of the unknown radiation source was performed using GEANT4. From simulations of the CALA target chamber, it was found that the CCD of interest would have been subjected to both bremsstrahlung radiation and stray electrons when an electron beam is steered into a steel floor. Further simulations show potential methods of reducing the flux of particles reaching the CCD. Finally, the designs of an electron spectrometer and filter array are described in detail to measure properties of the electron bunches and betatron radiation produced during an experimental campaign at the Astra Gemini laser facility.
Supervisor: Hooker, Simon Martin Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Physics ; X-ray diffraction ; Laser wakefield acceleration