Beam diagnostics of a C-band photocathode RF gun

Huang Weiling; Yang Renjun; Li Fang; Liu Renhong; Lu Zhijun; Qiu Ruiyang; Yang Tao; Jiang Shimin; Chen Weiwen; Zeng Lei; Yang Rui; Ma Na; Wang Yigang; Xu Zhihong; Li Xiao

doi:10.11884/HPLPB202638.250340

Volume 38 Issue 4

Mar. 2026

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Article Navigation > High Power Laser and Particle Beams > 2026 > 38(4): 044002

Huang Weiling, Yang Renjun, Li Fang, et al. Beam diagnostics of a C-band photocathode RF gun[J]. High Power Laser and Particle Beams, 2026, 38: 044002. doi: 10.11884/HPLPB202638.250340

Citation:

Huang Weiling, Yang Renjun, Li Fang, et al. Beam diagnostics of a C-band photocathode RF gun[J]. High Power Laser and Particle Beams, 2026, 38: 044002. doi: 10.11884/HPLPB202638.250340

Huang Weiling, Yang Renjun, Li Fang, et al. Beam diagnostics of a C-band photocathode RF gun[J]. High Power Laser and Particle Beams, 2026, 38: 044002. doi: 10.11884/HPLPB202638.250340

Citation:

Huang Weiling, Yang Renjun, Li Fang, et al. Beam diagnostics of a C-band photocathode RF gun[J]. High Power Laser and Particle Beams, 2026, 38: 044002. doi: 10.11884/HPLPB202638.250340

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Beam diagnostics of a C-band photocathode RF gun

doi: 10.11884/HPLPB202638.250340

Huang Weiling^{1, 2
,},
Yang Renjun^{1, 2
,
,},
Li Fang^{1, 2},
Liu Renhong^{1, 2},
Lu Zhijun^{1, 2},
Qiu Ruiyang^{1, 2},
Yang Tao⁴,
Jiang Shimin^{1, 2},
Chen Weiwen^{1, 3},
Zeng Lei^{1, 2},
Yang Rui²,
Ma Na^{1, 2},
Wang Yigang^{1, 2},
Xu Zhihong^{1, 2},
Li Xiao^{1, 2}

1.
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
2.
Spallation Neutron Source Science Center, Dongguan 523803, China
3.
University of Chinese Academy of Sciences, Beijing 100049, China
4.
Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China

Received Date: 2025-10-12
Accepted Date: 2026-02-12
Rev Recd Date: 2026-02-11

Available Online: 2026-03-19

Publish Date: 2026-03-20

Abstract

Abstract

Background
The C-band photocathode radio frequency (RF) electron gun, with an ultra-high accelerating gradient exceeding 150 MV/m, is a key technology for generating high-brightness electron beams in fourth-generation light sources. However, its output beam features picosecond-scale ultrashort pulses, a wide charge dynamic range of 50 pC to 2500 pC, and an ultra-low transverse emittance of 0.18 mm·mrad@100 pC. Existing measurement methods developed for L/S-band systems can hardly meet the stringent requirements on measurement accuracy and bandwidth for such beams.
Purpose
This study aims to develop a high-precision beam measurement system adapted to the characteristics of the C-band electron gun, based on the test platform of the South Advanced Light Source (SAPS).
Methods
Firstly, a flange-mounted active integrating charge transformer (Active-ICT) was independently developed to address the challenge of narrow-pulse charge measurement, and a cross-calibration method based on a set of commercial high-sensitivity ICT and terminator was proposed, achieving a measurement linearity better than ±1% full scale (FS). Secondly, to mitigate the significant influence of space charge force in ultra-low emittance measurement, the slit parameters and drift length of the double-slit emittance meter were optimized via Astra simulation, confining the systematic error within 10% in the emittance range of 0.15～0.25 mm·mrad. Thirdly, an optical path combining double-slit collimation and a sector dipole magnet was designed to suppress noise floor interference in energy spread measurement.
Results
Preliminary beam experiments were conducted with the established system. The results show that the measured photocurrent and dark current are in good agreement with Faraday cup measurements, and the beam energy curves obtained under different accelerating gradients are highly consistent with beam dynamics simulation results, verifying the reliability and measurement accuracy of the system.
Conclusions
This work solves the key beam diagnostics technical bottlenecks in the commissioning of domestic C-band photocathode RF electron guns, and provides core technical support for the engineering development of similar high-gradient injectors.
- photocathode electron gun,
- beam diagnostics and measurement,
- bunch charge measurement,
- beam spread measurement,
- double-slit emittance meter

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References(17)

References

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