[PEPPo] Accurate Modelling of Intrabeam Scattering and its Impact on Photoinjectors for Free-Electron Lasers

[Jay Benesch]

https://arxiv.org/abs/2510.02058

effects significant at a few pC per bunch per figure 3

Accurate Modelling of Intrabeam Scattering and its Impact on 
Photoinjectors for Free-Electron Lasers

Thomas Geoffrey Lucas, Paolo Craievich, Eduard Prat, Sven Reiche, Erion 
Gjonaj

Intrabeam scattering (IBS) is a fundamental effect that can limit the 
performance of high-brightness electron machines, yet it has so far been 
neglected in standard modelling of RF photoinjectors. Recent 
measurements at SwissFEL reveal that the slice energy spread (SES) in 
the injector is significantly underestimated by conventional tracking 
codes. In this work, we present a dedicated Monte Carlo simulation model 
that accurately predicts the IBS-induced SES growth in the photoinjector 
of an X-ray free-electron laser. The simulations are benchmarked against 
SES measurements at the SwissFEL as well as theoretically supported by a 
new analytical model. The results demonstrate that IBS-induced SES 
growth occurs throughout the injector, most prominently in the electron 
source, and must be taken into account when assessing photoinjector 
performance. We further show that while the 5D brightness is largely 
conserved, the 6D brightness undergoes notable degradation with 
propagation, underscoring the need to include IBS in the accurate design 
and optimization of photoinjectors.