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Linac Coherent Light Source II injector commissioning and early operational experience

F. Zhou*, G. Adhikari, A. Brachmann, D. Cesar, W. Colocho, Y. Ding, D. Dowell, G. Just, D. Kennedy et al.

D. Magana, A. Osman, R. Roussel, N. Sudar, T. Vecchione, Z. Zhang, and C. Zimmer

  • *Contact author: zhoufeng@slac.stanford.edu
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Phys. Rev. Accel. Beams 29, 104501 – Published 15 October, 2026

DOI: https://doi.org/10.1103/1wk3-p29y

Abstract

The Linac Coherent Light Source II (LCLS-II) is designed to generate 4 GeV electron bunches at an up-to-1-MHz-high repetition rate to drive x-ray free electron lasers. It has been in user operation since 2023 and has progressively ramped up the beam repetition rate to 93 kHz to date. The LCLS-II 1-MeV electron source was successfully commissioned between 2018 and 2020. The full-scale LCLS-II injector, operating above 75 MeV, began commissioning in 2022 and transitioned to operations a few months later. The LCLS-II injector has demonstrated the ability to deliver a high-brightness, low-emittance electron beam at high repetition rates, meeting key performance targets. However, several operational challenges have emerged during commissioning and early user operations. These include substantial gun dark current, the dependence of bunch charge generation and free-electron laser pulse intensity on the beam repetition rate, the formation of cathode quantum efficiency craters and bumps, significant emittance growth through the laser heater chicane, beam breakup, and the presence of beam halos. This paper presents recent progress in addressing these challenges, along with injector emittance measurements and optimizations, and the first demonstration of operating a laser heater undulator at the third-harmonic resonance.

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Phys. Rev. Accel. Beams 29, 104501– Published 15 October, 2026
  • Received 25 June 2026
  • Accepted 11 September 2026
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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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