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Purpose <p>The BEPCII upgrade project necessitates two new final focus superconducting magnets on both sides of interaction point to achieve a high luminosity at higher beam energy. Each superconducting magnet consists of a quadrupole magnet for final focusing the beam and an anti-solenoid for canceling the magnetic field of Detector solenoid. Compared with the BEPCII magnet, the magnetic field gradient of new superconducting quadrupole (SCQ) increases from 18.7 to 25&#xa0;T/m. The field harmonics of SCQ are required to be less than 3 × 10<sup>–4</sup>.</p> Methods <p>Use line current approximation and field simulation by OPERA, the magnetic design of serpentine coil of SCQ is determined, and the calculated field harmonics are less than 0.5 × 10<sup>–4</sup>. According to the theoretical trajectory of each turn conductor, the SCQ coil is wound layer by layer using direct winding technology. Room temperature magnetic field measurement and cryogenic vertical test at 4.2&#xa0;K are used to check the field quality and validate the magnet fabrication process.</p> Results <p>Cryogenic horizontal test at 4.5&#xa0;K shows that the magnetic field performance of SCQ and anti-solenoid of the two magnets meets the design requirements. The measured field harmonics of SCQ are less than 2 × 10<sup>–4</sup> corresponding to the nominal field gradient 25&#xa0;T/m. The measured magnetic field distribution of anti-solenoid is consistent with field simulation result.</p> Conclusion <p>Two new final focus superconducting magnets have been successfully developed for BEPCII upgrade project. They were installed in upgraded BEPCII interaction region at the end of 2024, and have maintained stable operation under the Detector solenoid field without any quench since May 2025.</p>

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Final focus superconducting magnets for BEPCII upgrade project

  • 期刊论文

  • 发表日期：

    2026年7月4日

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  • Yingshun Zhu,
  • Xiangchen Yang,
  • Yingzhi Wu,
  • Wan Chen,
  • Jianxin Zhou,
  • Mei Yang,
  • Xiaojuan Bian,
  • Jieru Geng,
  • Chuang Shen,
  • Zilin Chen,
  • Zhuo Zhang,
  • Quanling Peng,
  • Ran Liang,
  • Fusan Chen,
  • Yafeng Wu,
  • Baogui Yin,
  • Jinliu Su,
  • Jintao Li,
  • Bin Chen,
  • Xiaoling Guo,
  • Fengli Long,
  • Ruixiong Han,
  • Miaofu Xu,
  • Penghui Li,
  • Shaopeng Li,
  • Lingling Men,
  • Huiping Geng,
  • Rui Ge,
  • Chenghui Yu

摘要

Purpose

The BEPCII upgrade project necessitates two new final focus superconducting magnets on both sides of interaction point to achieve a high luminosity at higher beam energy. Each superconducting magnet consists of a quadrupole magnet for final focusing the beam and an anti-solenoid for canceling the magnetic field of Detector solenoid. Compared with the BEPCII magnet, the magnetic field gradient of new superconducting quadrupole (SCQ) increases from 18.7 to 25 T/m. The field harmonics of SCQ are required to be less than 3 × 10–4.

Methods

Use line current approximation and field simulation by OPERA, the magnetic design of serpentine coil of SCQ is determined, and the calculated field harmonics are less than 0.5 × 10–4. According to the theoretical trajectory of each turn conductor, the SCQ coil is wound layer by layer using direct winding technology. Room temperature magnetic field measurement and cryogenic vertical test at 4.2 K are used to check the field quality and validate the magnet fabrication process.

Results

Cryogenic horizontal test at 4.5 K shows that the magnetic field performance of SCQ and anti-solenoid of the two magnets meets the design requirements. The measured field harmonics of SCQ are less than 2 × 10–4 corresponding to the nominal field gradient 25 T/m. The measured magnetic field distribution of anti-solenoid is consistent with field simulation result.

Conclusion

Two new final focus superconducting magnets have been successfully developed for BEPCII upgrade project. They were installed in upgraded BEPCII interaction region at the end of 2024, and have maintained stable operation under the Detector solenoid field without any quench since May 2025.