U-Net-based surrogate modeling for attosecond X-ray free-electron lasers

Abstract: Attosecond X-ray pulse generation in modern X-ray free-electron lasers relies on strongly compressed, precisely tailored electron bunches, making accurate diagnostics and control of the longitudinal phase space (LPS) essential. In the self-chirping scheme, collective effects in the linac generate a strong energy chirp that is converted into high peak current through pre-undulator compression, enabling isolated attosecond pulse generation. Reliable operation of this scheme depends on precise LPS control and fast diagnostics. In this work, we present a U-Net-based neural network surrogate that predicts two-dimensional LPS distributions directly from accelerator settings. The model exhibits excellent agreement with start-to-end simulation results. These results demonstrate the potential of neural network surrogates to facilitate real-time tuning and control in attosecond X-ray pulse generation.