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Abstract
Particle accelerators are machines of great importance in many scientific disciplines, including physics, chemistry, biology, and materials science. In particular, free-electron lasers (FELs) have revolutionized the study of matter at atomic and molecular scales by providing intense, ultrashort x-ray pulses. From the accelerator physics perspective, the production and transport of high-brightness, ultrashort electron bunches necessary for FEL operation remain central challenges in the development of next-generation facilities. One of the main limiting factors for electron-beam quality in FEL linear accelerators is the coherent synchrotron radiation (CSR) emitted during bunch compression. CSR induces a tail–head self-interaction within the beam via radiation emitted from the tail, which distorts the beam distribution in phase space and consequently degrades its quality. Therefore, understanding the CSR-induced effects on the beam phase-space distribution is essential for the optimal operation of present and future facilities. However, experimental studies of CSR effects generally rely on measurements of one- or two-dimensional projections of the full six-dimensional phase space distribution, which limits the observation of the intricate beam structures produced by CSR.
This dissertation presents the first experimental measurement of the six-dimensional phase space distribution of a beam influenced by CSR, conducted at the Argonne Wakefield Accelerator Facility (AWA). To enable this measurement, the generative phase space reconstruction method (GPSR) has been developed, which allows six-dimensional phase space reconstructions with as few as 20 two-dimensional measurements of the transverse beam profile. This work also describes the implementation of differentiable beam dynamics simulations as a core component of the GPSR method. The experimental results suggest the presence of CSR effects for a 1 mm-long, 1 nC beam at the AWA reverse chicane section, and the methodological advancements presented here lay the foundation for experimental studies of CSR effects using GPSR.