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Design, fabrication, and tuning studies of the low beta high-gradient S-band traveling wave cryogenic copper cavity at the Institute of Modern Physics

Peng Yu1,2, Min Yang1, Quantang Zhao1,2,*, Xiaoxiao Yuan1, Chihao Ni1,2, Lejian Zhang1,2, Jiao Xu1,2, Yao Yang1,2, Zimin Zhang1,2 et al.

Liangting Sun1,2 and Hongwei Zhao1,2

  • *Contact author: zhaoquantang@impcas.ac.cn
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Phys. Rev. Accel. Beams 29, 061602 – Published 23 June, 2026

DOI: https://doi.org/10.1103/ndky-79h9

Abstract

The high-frequency, high-gradient, low-β accelerator structure is a key technology enabling compact ion linacs for hadron therapy, garnering significant interest in cancer treatment research. Currently, multiple institutions globally are advancing this technology. However, the achievable accelerating gradient remains limited to approximately 50  MV/m due to radio-frequency (rf) breakdown (BD) limitations. To enable higher accelerating gradients, researchers at the Institute of Modern Physics, Chinese Academy of Sciences, have proposed and designed a low-β high-gradient cryogenic copper cavity targeting a theoretical accelerating gradient of 60  MV/m with a specified breakdown rate (BDR≤10−6  bpp/m). This paper details the design, fabrication, and tuning methodology of a β=0.3 cryogenic traveling-wave high-gradient accelerating structure. Cell tests were performed to verify the cryogenic performance of the cavity. Upon cooling from room temperature to 77 K, the cavity’s quality factor (Q) increased by a factor of 2.9, while its resonant frequency shifted upward by 9.85 MHz. Subsequently, a 15-cell cryogenic traveling-wave structure was fabricated and tuned to meet stringent design specifications. The conduction cooling methodology was experimentally validated, achieving a stable cavity temperature of 77±0.3  K within 5 h. This work establishes a framework for tuning cryogenic traveling-wave copper cavities and implementing conduction cooling in high-gradient systems.

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Phys. Rev. Accel. Beams 29, 061602– Published 23 June, 2026
  • Received 11 November 2025
  • Accepted 21 May 2026
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