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Application of autoresonance in rapid beam extraction of synchrotrons

X. Ding1,2, S. Ruan1,2, H. Ren1, G. Wang1, R. H. Zhu1,2, J. C. Yang1,2,*, H. Zhao1,2,†, and G. D. Shen1,2,‡

  • *Contact author: yangjch@impcas.ac.cn
  • †Contact author: hezhao@impcas.ac.cn
  • ‡Contact author: shenguodong@impcas.ac.cn
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Phys. Rev. Accel. Beams 28, 100102 – Published 24 October, 2025

DOI: https://doi.org/10.1103/s85n-289k

Abstract

In recent years, ultrahigh dose rate (FLASH) radiotherapy has become a novel cancer treatment technique because of its similar tumor-killing efficacy as conventional particle therapy while significantly protecting normal tissues. However, due to the limitation of the number of particles, achieving FLASH condition in a compact heavy-ion synchrotron requires a short spill time of tens of milliseconds, which is challenging for the conventional rf-KO method. To tackle this challenge, we introduce autoresonance into the third-order resonant extraction for the first time, offering an alternative to the conventional approach of merely increasing the excitation amplitude. Resulting from a strong detuning effect, a frequency sweeping excitation with small amplitude can drive the entire beam into the autoresonant state, thus enabling rapid beam extraction within a single sweeping period. Compared with the conventional method, this innovative method requires only the addition of an octupole magnet. At the same time, conventional slow extraction rf-KO employs a repetitive multicycle frequency sweeping excitation, a specific particle resonates when the sweeping frequency aligns with its tune. In contrast to the autoresonance rf-KO, which engages the entire beam in resonance simultaneously. In this research, the autoresonance threshold of a particle in the presence of sextupole and octupole magnetic fields is analyzed, and the single particle simulation shows good agreement with the theoretical formula. Furthermore, the autoresonance-based rapid extraction process is simulated and studied, showing the possibility of millisecond scale beam extraction.

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Phys. Rev. Accel. Beams 28, 100102– Published 24 October, 2025
  • Received 3 March 2025
  • Accepted 11 September 2025
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