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  • Open Access

Fault-tolerance analysis for an injector of continuous-wave free-electron lasers

Zhen Zhang*, Yuantao Ding, and Feng Zhou

  • *Contact author: zzhang@slac.stanford.edu
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Phys. Rev. Accel. Beams 28, 090701 – Published 26 September, 2025

DOI: https://doi.org/10.1103/zz4w-tvxt

Abstract

High-repetition-rate free-electron laser (FEL) facilities such as LCLS-II rely on continuous-wave (cw) injectors to deliver high-quality electron beams to multiple undulator lines simultaneously. Ensuring injector reliability under nonideal conditions is critical for sustained user operations. In this work, we investigate the fault tolerance of a representative cw photoinjector by analyzing its performance under various degraded scenarios, including reduced gun energy, radio-frequency (rf) cavity failures, solenoid field constraints, and early-stage energy gain requirements. Using multiobjective optimization with a genetic algorithm framework (Xopt), we assess achievable beam quality—focusing on transverse emittance and bunch length—across a range of fault conditions. Our results reveal that while certain failures (e.g., buncher off) significantly impact emittance, coordinated adjustments to laser parameters, rf phases, and cavity gradients can still partially recover performance. The injector demonstrates resilience to a variety of perturbations, confirming its robustness for high-demand cw FEL operations.

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Phys. Rev. Accel. Beams 28, 090701– Published 26 September, 2025
  • Received 26 June 2025
  • Accepted 3 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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