We present a noninterferometric method for measuring the transverse electron beam size at the European XFEL based on synchrotron radiation intensity autocorrelation. The technique enables cell-by-cell diagnostics along the SASE1 undulator using existing hardware: a commissioning monochromator and a spatial x-ray detector. We extend the results of A. Trebushinin et al., companion paper, First observation of synchrotron radiation spikes for transverse electron beam size measurements at a free-electron laser, Phys. Rev. Lett. 135, 215001 (2025). focusing on data analysis procedures and technical implementation. Our method allows for extraction of the beam size from noisy measured intensity distributions with a signal-to-noise ratio as low as 0.9 and is capable of distinguishing between the projected and slice sizes. To validate our approach, we introduced a mismatch in the magnetic lattice, inducing a controlled sinusoidal variation in the beam size along the undulator. The corresponding modulation was clearly reproduced in the electron beam size values extracted from the autocorrelation measurements. This method offers a practical solution for transverse electron beam size diagnostics in high-energy linacs, with direct application to the operation and tuning of free-electron laser facilities.
Trebushinin et al. (Wed,) studied this question.