Simulations and experimental activities on electron diagnostics for EuPRAXIA@SPARC_LAB

The development of advanced beam diagnostics is essential in next-generation high-brightness accelerator facilities, including free-electron lasers and plasma-based accelerators. The EuPRAXIA@SPARC_LAB facility, currently under construction at INFN-LNF, will demonstrate a high-brightness plasma-driven accelerator capable of delivering beams suitable for a freeelectron laser. In this context, this thesis presents dedicated beam dynamics studies aimed at characterizing and determining the resolution limits of the diagnostic systems foreseen for EuPRAXIA@SPARC_LAB. The work evaluates the performance of diagnostics at three representative energies — low (118 MeV), medium (400 MeV), and high (1 GeV) — through dedicated beam dynamics simulations. Particular attention is devoted to the PolariX Transverse Deflection Structure (PolariX TDS), an X-band cavity with variable polarization developed by PSI, CERN, and DESY. Its capability to continuously rotate the streaking field in the transverse plane allows the same device to perform longitudinal diagnostics in orthogonal planes. This unique flexibility also enables tomographic reconstruction of the longitudinal and transverse phase-space distributions. The work presents theoretical activities, including RF studies and beam dynamics simulations of the PolariX TDS, such as the validation of 3D field maps and the RF design of the 50-cell structure for the low-energy section. In addition, dedicated simulations were performed to evaluate the measurement resolution for emittance, energy, and bunch length across the EuPRAXIA diagnostic sections. Finally, experimental results from the SwissFEL Athos beamline demonstrate the feasibility of 3D and 5D beam tomography using the PolariX TDS, performed on realistic high-brightness beams and intended for future implementation at both SwissFEL and EuPRAXIA. The outcomes of this research establish the achievable resolution of the EuPRAXIA diagnostic systems and validate the integration of the PolariX TDS concept as a key enabling technology for next-generation compact FEL facilities.