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Physical design of a high-charge beam injector for the on-axis swap-out injection scheme in an electron-positron collider

Tongning Hu*,†, Hao Hu†, Yan Wang, Yifeng Zeng, Di Lu, Kaifeng Liu, and Lanyang Zhang

Duan Gu and Xuan Li

Ailin Zhang

Youjin Yuan

Jingyu Tang‡

  • *Contact author: tongningHu@hust.edu.cn
  • †These authors contributed equally to this work.
  • ‡Contact author: jytang@ustc.edu.cn
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Phys. Rev. Accel. Beams 29, 113701 – Published 6 November, 2026

DOI: https://doi.org/10.1103/89k9-j8qk

Abstract

The Super Tau-Charm Facility (STCF), a next-generation electron-positron collider, adopts an on-axis swap-out injection scheme that demands high-charge electron bunches with exceptionally low emittance and minimal energy spread. This work presents a comprehensive and systematic beam dynamics design for the STCF electron injector. The bunching system, based on subharmonic bunchers and a traveling-wave buncher, is optimized using the nondominated sorting genetic algorithm III to efficiently explore the high-dimensional parameter space. Start-to-end simulations incorporating space-charge forces, wakefield effects, and alignment errors are performed, with beam-based alignment (BBA) applied to correct orbit deviations. The optimized injector delivers 8.5 nC bunches at 3.5 GeV with a normalized transverse emittance below 70  mm mrad and an rms energy spread below 0.5%, satisfying the stringent STCF requirements. The high transport efficiency achieved in simulations alleviates the design pressure on the electron source, while the excellent beam quality inherently suppresses beam halo effects. By integrating systematic multiobjective optimization with high-fidelity simulations, the proposed design overcomes the intrinsic limitations of thermionic cathodes while capitalizing on their proven stability, robustness, and cost-effectiveness, offering an efficient engineering solution for high-charge beam delivery in next-generation colliders.

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Phys. Rev. Accel. Beams 29, 113701– Published 6 November, 2026
  • Received 18 November 2024
  • Accepted 21 October 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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