Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
Quasi-mono-energetic and Tunable Compton X-rays from a Laser Wakefield Accelerator
A quasi-mono-energetic x-ray source, produced by laser Compton scattering of laser wakefield accelerated electrons, is demonstrated for the first time . The peak spectral brightness of the source compares with or exceeds that of conventional, radio-frequency (RF)-based sources, but at significantly lower cost and smaller footprint. The beams are expected to have among the shortest temporal duration of any high energy x-ray source produced to date. The source was composed of a laser wakefield accelerator (LWFA) and Compton scattering undulator. The LWFA uses a laser to drive a plasma wave. Spatial and temporal properties of the drive beam were matched to the plasma resonance conditions. A near-diffraction-limited, near-transform limited and low contrast intense laser was produced using spatial and temporal phase correction and temporal gating. The high-quality laser parameters resulted in effective self-guiding over several Rayleigh lengths and stable acceleration. A dual-staged gas jet target was designed to independently control e-beam characteristics . The first stage used a He/N2 gas mixture to inject electrons, by ionization, into the accelerator. Increasing the density and nitrogen content of this jet increased the e-beam charge. The second stage used pure helium to further accelerate the injected electrons. The e-beam energy was increased, while maintaining the energy spread by increasing the density and length of the second jet. The e-beams were characterized by relatively high charge (∼20 pC), low divergence (∼10 mrad), small source size (∼1 µm), and low energy spread (<25%). The Compton undulator used a second laser pulse, split from the drive beam, to scatter from the e-beams and generate x-rays. The beam focus was spatio-temporally overlapped with the e-beam. Since the drive and scattering beams are produced by the same laser, timing jitter is reduced. Quasi-mono-energetic e-beams were used to generate x-rays with correspondingly quasi-mono-energetic spectral distributions. The x-ray beam energy was tuned from 40 keV–1 MeV. A Ross filter was designed to characterize the spectrum. Tunability of the x-ray central energy was accomplished by tuning the e-beam energy. The central energy was measured using transmission filters. The stability and source size of the x-rays were also studied.  N. D. Powers, I. Ghebregziabher, G. Golovin, C. Liu, S. Chen, S. Banerjee, J. Zhang, and D. P. Umstadter, Nat. Photonics 8, 28 (2014) URL: http://dx.doi.org/10.1038/nphoton.2013.314.
Powers, Nathan David, "Quasi-mono-energetic and Tunable Compton X-rays from a Laser Wakefield Accelerator" (2014). ETD collection for University of Nebraska - Lincoln. AAI3618804.