Experimental study on tuning of very-high-frequency photocathode electron gun

Jia Yanqing; Zheng Lianmin; Huang Wenhui; Tang Chuanxiang; Du Yingchao

doi:10.11884/HPLPB202537.250175

Volume 37 Issue 12

Nov. 2025

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Jia Yanqing, Zheng Lianmin, Huang Wenhui, et al. Experimental study on tuning of very-high-frequency photocathode electron gun[J]. High Power Laser and Particle Beams, 2025, 37: 124006. doi: 10.11884/HPLPB202537.250175

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Jia Yanqing, Zheng Lianmin, Huang Wenhui, et al. Experimental study on tuning of very-high-frequency photocathode electron gun[J]. High Power Laser and Particle Beams, 2025, 37: 124006. doi: 10.11884/HPLPB202537.250175

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Experimental study on tuning of very-high-frequency photocathode electron gun

doi: 10.11884/HPLPB202537.250175

Department of Engineering Physics, Tsinghua University, Beijing 100084, China

Received Date: 2025-06-17
Accepted Date: 2025-10-10
Rev Recd Date: 2025-10-10

Available Online: 2025-10-23

Publish Date: 2025-11-06

Abstract

Abstract

Background
The very-high-frequency (VHF) photocathode electron gun operates in continuous-wave mode and serves as a critical electron source for generating high-repetition-rate, high-quality electron beams. It is widely used in advanced scientific facilities such as X-ray free-electron lasers and ultrafast electron diffraction systems. However, during operation, resonant frequency shifts caused by variations in feed power and cooling water temperature can destabilize the radio-frequency (RF) field inside the cavity.
Purpose
This study aims to achieve stable amplitude and phase control of the RF field in a VHF electron gun under high-power continuous-wave operation by accurately tracking and tuning the resonant frequency of the cavity in real time.
Methods
Based on an LCR oscillator circuit model, the phase difference between the cavity-sampled microwave and the incident wave was analyzed to determine the cavity's resonant frequency. A three-step tuning strategy—comprising frequency scanning, frequency tracking, and active tuning—was implemented and applied to a VHF electron gun at Tsinghua University.
Results
Using the proposed tuning method, the electron gun maintained resonance during high-power operation, with a resonant frequency deviation controlled at an RMS value of 94.2 Hz under full power. The amplitude stability at the microwave sampling port reached an RMS value of 0.0046%, and the phase-locking accuracy achieved an RMS value of 0.0023°. These results enabled long-term, stable full-power operation of the electron gun.
Conclusions
The developed three-step active tuning method effectively ensures high amplitude and phase stability for the VHF photocathode electron gun under continuous-wave operation, providing a reliable tuning solution for high-repetition-rate accelerator-based light sources and scientific instruments.
- very high frequency,
- electron gun,
- low-level radio frequency,
- tuning

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References(19)

References

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