Title: STUDY OF COHERENT SYNCHROTRON RADIATION EFFECTS USING GENERATIVE PHASE SPACE RECONSTRUCTION

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’s 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.