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Design study of a high-brightness high-repetition rate thermionic injector for free-electron laser application: The architecture

Vitaliy Goryashko1,2,*, Kazuaki Togawa1,†, Peter Salén2, and Anatoliy Opanasenko2,1

  • *Contact author: vitaliy.goryashko@physics.uu.se, vitgor06@gmail.com
  • †Contact author: togawa@spring8.or.jp
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Phys. Rev. Accel. Beams 28, 091601 – Published 11 September, 2025

DOI: https://doi.org/10.1103/b7sd-jvxq

Abstract

SACLA is the world’s most compact hard x-ray free-electron laser and has been successfully and reliably operated for over a decade. To meet increasing user demands, an upgrade of the SACLA linear accelerator is planned in order to achieve a kHz-level repetition rate and enhanced beam brightness. A key component of this upgrade is a new injector, based on the existing pulsed dc gun with a thermionic cathode, which has demonstrated high beam quality, excellent stability, and simple maintenance. In this work, we present an in-depth beam dynamics study of a highly promising new SACLA injector architecture. Multistage velocity bunching, combined with one stage of magnetic compression and careful control of emittance growth, allows for up to 3 orders of magnitude of bunch compression while keeping the emittance growth at the submicron level. Our optimization approach utilizes a genetic algorithm coupled to 3D space-charge-dominated beam tracking to refine beam performance and identify optimal injector parameters. Thus, we demonstrate that the proposed injector can deliver electron beams with bunch durations and emittances comparable to those produced by the state-of-the-art C-band injector based on an rf photocathode gun [A. Giribono et al., Phys. Rev. Accel. Beams 26, 083402 (2023)]. Additionally, our extensive beam dynamics analysis of the dc electron gun (see part 2) provides valuable insights applicable to low-voltage continuous-wave very high frequency guns and superconducting radio-frequency guns.

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Design study of a high-brightness high-repetition rate thermionic injector for free-electron laser application. II. Gun technology

Vitaliy Goryashko, Kazuaki Togawa, and Anatoliy Opanasenko
Phys. Rev. Accel. Beams 28, 110101 (2025)

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Phys. Rev. Accel. Beams 28, 091601– Published 11 September, 2025
  • Received 16 March 2025
  • Accepted 28 July 2025
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