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Multi-port cavity model and low-level RF systems design for VHF gun

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Abstract

Very high frequency (VHF) photocathode guns have excellent performance and are being increasingly selected as electron sources for high-repetition-rate X-ray free-electron lasers. As a highly loaded quality factor cavity, the VHF gun requires high stability in the amplitude and phase of the cavity field. However, the gun is microwave powered by two solid-state power sources through two separate power couplers. The input difference between the two power couplers will influence the stability of the cavity field. To systematically study this influence and obtain measurement formulae, a multi-port VHF gun LCR circuit model is built and analyzed. During the warm-up condition, the cavity structure will be deformed due to the large-scale change in the cavity temperature. Then, the deformation will result in cavity resonant frequency changes. To prevent the mechanic tuner from suffering damages due to the frequent and long-distance movement for correcting the cavity resonant frequency, a self-excited loop (SEL) control system is considered for changing the loop phase and make the loop frequency follow the resonant frequency. In this study, a steady-state model of the VHF gun cavity is built for obtaining the optimal input coupler coefficient and the stability requirement of the forward voltage. Then, the generator-driven resonator and SEL control system, which combine with the VHF multi-port modeling, are modeled and simulated. The simulated results show that the SEL system can perfectly operate in the process of condition and warm-up.

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Acknowledgements

The authors are very grateful to Dr. Qiu Feng from KEK for his assistance in the self-excited loop modeling and simulations.

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Authors and Affiliations

  1. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201800, China

    Kui Liu, Cheng Wang & Ming-Hua Zhao

  2. University of Chinese Academy of Sciences, Beijing, 100049, China

    Kui Liu & Cheng Wang

  3. Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201204, China

    Lin Li & Qiang Gu

Authors
  1. Kui Liu
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  2. Lin Li
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  3. Cheng Wang
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  4. Qiang Gu
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  5. Ming-Hua Zhao
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Correspondence to Qiang Gu or Ming-Hua Zhao.

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Liu, K., Li, L., Wang, C. et al. Multi-port cavity model and low-level RF systems design for VHF gun. NUCL SCI TECH 31, 8 (2020). https://doi.org/10.1007/s41365-019-0711-2

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  • DOI: https://doi.org/10.1007/s41365-019-0711-2

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