Active microphonics noise suppression based on DOB control in 166.6-MHz superconducting cavities for HEPS



Superconducting 166.6-MHz cavities will be used to accelerate electron beams in high-energy photon source (HEPS). The radio-frequency (RF) fields inside these cavities have to be controlled better than 0.03% (rms error) for the amplitude and 0.03\(^\circ \) (rms error) for the phase. Adopting a quarter-wave geometry with \(\beta =1\), the 166.6-MHz cavity has two intrinsic mechanical modes at \(\sim \) 100 Hz observed in both simulations and cryogenic tests. If coupled to external vibrations, these microphonics modes shall stress the existing proportional–integral (PI) feedback controller and inevitably deteriorate the field stabilities. Therefore, additional noise suppression may be required.


A digital low-level RF system previously in-house developed was connected to a 166.6-MHz dressed cavity at room temperature in the laboratory. Piezo-tuners were used to “knock” on the cavity at various frequencies to excite cavity vibrations, and microphonics spectrum was subsequently measured. A disturbance observer (DOB)-based algorithm was adopted and integrated into the existing feedback controller. The performance of PI controller, DOB controller and a combination of PI and DOB controller was compared. The limitation of the DOB controller was also examined.

Results and conclusions

The PI controller was proved to be insufficient in suppressing large cavity microphonics during the tests. By adding the DOB controller, the excellent field stabilities can be restored. Optimized loop parameters were obtained. The simple first-order filter was adequate thanks to the robustness of the DOB controller. This constitutes a first laboratory demonstration of the active microphonics noise suppression in the 166.6-MHz RF cavity for HEPS.

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  1. 1.

    Y. Jiao, G. Xu, X.-H. Cui, Z. Duan, Y.-Y. Guo, P. He, D.-H. Ji, J.-Y. Li, X.-Y. Li, C. Meng, Y.-M. Peng, S.-K. Tian, J.-Q. Wang, N. Wang, Y.-Y. Wei, H.-S. Xu, F. Yan, C.-H. Yu, Y.-L. Zhao, Q. Qin, The HEPS project. J. Synchrotron Radiat. 25(6), 1611–1618 (2018).

    Article  Google Scholar 

  2. 2.

    Y. Jiao, F. Chen, P. He, C. Li, J. Li, Q. Qin, H. Qu, J. Wan, J. Wang, G. Xu, Modification and optimization of the storage ring lattice of the High Energy Photon Source. Radiat. Detect. Technol. Methods (2020).

    Article  Google Scholar 

  3. 3.

    P. Zhang, X. Hao, T. Huang, Z. Li, H. Lin, F. Meng, Z. Mi, Y. Sun, G. Wang, Q. Wang, X. Zhang, Superconducting RF system for the HEPS storage ring. J. Phys. Conf. Ser. 874, 012091 (2017).

    Article  Google Scholar 

  4. 4.

    P. Zhang, X. Zhang, Z. Li, J. Dai, L. Guo, H. Lin, Q. Ma, T. Huang, Z. Mi, Q. Wang, F. Meng, Development and vertical tests of a 166.6 MHz proof-of-principle superconducting quarter-wave beta = 1 cavity. Rev. Sci. Instrum. 90(8), 084705 (2019).

    Article  ADS  Google Scholar 

  5. 5.

    X. Zhang, P. Zhang, Z. Li, J. Dai, X. Hao, Q. Ma, T. Huang, H. Lin, Z. Mi, Q. Wang, F. Meng, The mechanical design, fabrication and tests of a 166.6 MHz quarter-wave beta=1 proof-of-principle superconducting cavity for HEPS. Nucl. Instrum. Methods Phys. Res. Sect. A Accel. Spectrom. Detect. Assoc. Equip. 947, 162770 (2019).

    Article  Google Scholar 

  6. 6.

    X. Zhang, P. Zhang, Z. Li, Q. Wang, H. Lin, Z. Mi, Q. Ma, W. Pan, J. Dai, T. Huang, R. Han, R. Ge, L. Sun, F. Meng, D. Li, Design and mechanical performance of a dressed 166.6 MHz \(\beta =1\) proof-of-principle superconducting cavity in horizontal tests. IEEE Trans. Appl. Superconduct. 30(8), 1–8 (2020).

    Article  Google Scholar 

  7. 7.

    T. Huang, P. Zhang, Q. Ma, H. Lin, Q. Wang, W. Pan, F. Bing, K. Gu, L. Guo, Development of fundamental power couplers for 166.6 MHz superconducting quarter-wave beta = 1 proof-of-principle cavities. Rev. Sci. Instrum. 91(6), 063301 (2020).

    Article  ADS  Google Scholar 

  8. 8.

    T. Huang, P. Zhang, Z. Li, X. Zhang, H. Lin, Q. Ma, F. Meng, W. Pan, Development of fundamental power couplers for 166.6 MHz superconducting quarter-wave beta = 1 proof-of-principle cavities. Nucl. Sci. Tech. 31(9), 87 (2020).

    Article  Google Scholar 

  9. 9.

    Q. Wang, J. Dai, T. Huang, D. Li, H. Lin, Z. Mi, P. Zhang, Development of a 166.6 MHz digital LLRF system for HEPS-TF project, in Proceedings of the SRF’19, no. 19 in International Conference on RF Superconductivity (JACoW Publishing, Geneva, 2019), pp. 1073–1077.

  10. 10.

    D. Li, P. Zhang, Q. Wang, H. Lin, Development of a high-performance RF front end for HEPS 166.6 MHz low-level RF system. Radiat. Detect. Technol. Methods 4, 84–91 (2020).

    Article  Google Scholar 

  11. 11.

    H. Padamsee, J. Knobloch, T. Hays, RF Superconductivity for Accelerators, 2nd edn. (Wiley-VCH, Weinheim, 2008)

    Google Scholar 

  12. 12.

    K. Ohishi, M. Nakao, K. Ohnishi, K. Miyachi, Microprocessor-controlled DC motor for load-insensitive position servo system. IEEE Trans. Ind. Electron. IE 34(1), 44–49 (1987).

    Article  Google Scholar 

  13. 13.

    T. Umeno, Y. Hori, Robust speed control of DC servomotors using modern two degrees-of-freedom controller design. IEEE Trans. Ind. Electron. 38(5), 363–368 (1991).

    Article  Google Scholar 

  14. 14.

    F. Qiu, S. Michizono, T. Miura, T. Matsumoto, M. Omet, B.W. Sigit, Application of disturbance observer-based control in low-level radio-frequency system in a compact energy recovery linac at KEK. Phys. Rev. ST Accel. Beams 18, 092801 (2015).

    Article  ADS  Google Scholar 

  15. 15.

    T. Schilcher, RF applications in digital signal processing, in CAS—CERN Accelerator School: Digital Signal Processing, Sigtuna, Sweden, 31 May–9 June 2007 (CERN, Geneva) (2007), pp. 249–283. Accessed Dec 2020

  16. 16.

    Experimental Physics and Industrial Control System, v3.15. Accessed Dec 2020

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This work was supported by high-energy photon source (HEPS), a major national science and technology infrastructure in China. Funding was also received from the Chinese Academy of Sciences.

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Correspondence to Pei Zhang.

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Li, D., Wang, Q., Zhang, P. et al. Active microphonics noise suppression based on DOB control in 166.6-MHz superconducting cavities for HEPS. Radiat Detect Technol Methods (2021).

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  • Microphonics
  • Disturbance observer
  • Feedback loop
  • Low-level RF
  • Superconducting cavity
  • High Energy Photon Source