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Speaker: MaryKate Duncan on Beam Instability Thresholds 

Title: Multiscale Electron Microscopy of Defects in Nb-Based Superconducting Materials

Abstract: Niobium-based superconductors underpin technologies ranging from particle accelerators to quantum information devices, yet their performance is often limited by nanoscale defects, interfacial disorder, and localstrain. In this talk, I will demonstrate how advanced, multimodal electron microscopy enables a unified,multiscale understanding of these limitations by directly linking structure and composition to superconducting behavior.

For Nb₃Sn, I will show how different growth methods produce distinct defect populations using Focused Ion Beam–Scanning Electron Microscope (FIB-SEM) and spectroscopic imaging. Next, by combining 4D-STEMwith quantitative Energy Dispersive X-Ray Spectroscopy (EDX), I establish direct correlations between local composition and lattice distortions, and introduce a three-dimensional strain mapping approach thatreveals a strain-stabilized tetragonal phase at room temperature. Furthermore, at the atomic scale, multislice electron ptychography (MEP) visualizes point defects and resolves intermediate configurations in defect formation pathways that are not accessible to conventional approaches.

For superconducting thin films used in quantum devices, I examine interfacial disorder associated with dielectric loss. I will show how capping layers suppress oxide formation, and how MEP enables three-dimensional characterization of nanocrystalline oxide layers.

This multiscale characterization demonstrates how next-generation electron microscopy can uncover the structural origins of performance-limiting defects and guide the design of improved superconducting materials.

Speaker: Michael Van Duinen on Patent Law

Speaker: MaryKate Duncan on Beam Instability Thresholds 

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.