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Noninterferometric method for transverse electron beam size diagnostic with synchrotron radiation at a free-electron laser

Andrei Trebushinin*,†

Svitozar Serkez†

Wolfgang Freund, Giovanni Perosa, Andreas Koch, Jan Grünert, and Gianluca Geloni

Weilun Qin‡ and Sergey Tomin2

  • *Contact author: andrei.trebushinin@xfel.eu.
  • †These authors contributed equally to this work.
  • ‡Present address: Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China and Spallation Neutron Source Science Center, Dongguan 523803, China.
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Phys. Rev. Accel. Beams 28, 112801 – Published 20 November, 2025

DOI: https://doi.org/10.1103/31gl-qyk7

Abstract

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.

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Observation of Synchrotron Radiation Spikes for Transverse Electron Beam Size Measurements at a Free-Electron Laser

Andrei Trebushinin, Svitozar Serkez, Wolfgang Freund, Andreas Koch, Jan Grünert, Gianluca Geloni, Weilun Qin, and Sergey Tomin
Phys. Rev. Lett. 135, 215001 (2025)

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Phys. Rev. Accel. Beams 28, 112801– Published 20 November, 2025
  • Received 14 May 2025
  • Accepted 26 September 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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