Brookes, Emily; Kamps, Thorsten: Achieving diverse beam modes with modelling and optimisation for the versatile SRF gun at SEALab. In: Ming-Chyuan Lin ... [Ed.] : Proceedings of the 16th International Particle Accelerator Conference : IPAC'25 : Taipeh, Taiwan, 1-6 June 2025Geneve: JACoW, 2025. - ISBN 978-3-95450-248-6, p. WEPS043/2337-2340
10.18429/JACoW-IPAC2025-WEPS043
Open Accesn Version
Abstract:
The SEALab facility in Berlin is home to an R&D superconducting radio-frequency (SRF)photoinjector and electron diagnostics beamline. Designed to support multiple varied applications - ranging from Energy Recovery Linac (ERL) to Ultrafast Electron Diffraction (UED) and Electron-Beam Water Treatment (EBWT) - the photoinjector requires flexible, high-precision tuning to support these diverse beam modes. These applications span over three orders of magnitude in bunch charge, emittance, and current, alongside picosecond to sub-picosecond pulse lengths. This makes the accelerator setup and tuning a significant challenge. With the world’s first beam achieved at a SRF photoinjector from a Na-K-Sb cathode, a suite of analytical and computer-aided models have been developed to support understanding of the beam dynamics in the injector, even where no observations are possible through virtual diagnostics, and to support the commissioning process. These models include a firstorder analytical model based on equations of motion, particle tracking simulations with the ASTRA code, and a machinelearning surrogate model trained for achievable operation ranges during commissioning. These models are coupled with a Multi-Objective Bayesian Optimisation (MOBO) algorithm to enable rapid tuning across multiple beam modes. This combination of surrogate modelling and optimization algorithm reduces optimisation timescales from hundreds of hours to minutes, allowing near-real-time tuning for the accelerator. This paper presents the modelling framework, its validation, and its application to photoinjector multi-mode optimisation.