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Development and high-power operation of the cw 250 kW fundamental power couplers on 166.6 MHz quarter-wave SRF cavities at the High Energy Photon Source

Tongming Huang1,2, Pei Zhang1,2,*, Qiang Ma1,2, Xinying Zhang1,2, Haiying Lin1, Qunyao Wang1,2, Dongbing Li1, Facheng Zhao1, and Fanbo Meng1

  • *Contact author: zhangpei@ihep.ac.cn
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Phys. Rev. Accel. Beams 29, 113801 – Published 10 November, 2026

DOI: https://doi.org/10.1103/rldc-9x52

Abstract

The High Energy Photon Source (HEPS), a newly commissioned 6 GeV fourth-generation synchrotron light source, employs five 166.6 MHz quarter-wave β=1 superconducting cavities in its storage ring. Each cavity requires a fundamental power coupler capable of delivering 200 kW continuous-wave power—a specification largely exceeding demonstrated limits for existing on-cell couplers in transverse electromagnetic (TEM)-type superconducting cavities. This paper presents the complete development, validation, and operation of these couplers from prototype to series production. The design resolves four competing constraints: high power handling, low cryogenic heat load, mitigation of field-emission damage, and cleanroom assembly compatibility. Overheating at the cavity-coupler interface was identified as the primary degradation mechanism during prototype testing. Consequently, Series-A and Series-B design iterations were developed to eliminate interface overheating and window frosting, respectively. These modifications reduced the maximum interface temperature from 15.4 to 10.8 K and halved the average 4.2 K heat load to 1.5 W under nominal operation. All 10 series couplers were validated via high-power testing, with five currently operating stably in the HEPS storage ring at a 150 mA beam current. This represents the highest beam-operation power level reported to date for on-cell couplers in TEM-type superconducting cavities, expanding the application of nonelliptical superconducting cavities in high-current accelerators.

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Phys. Rev. Accel. Beams 29, 113801– Published 10 November, 2026
  • Received 20 September 2026
  • Accepted 27 October 2026
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