Tuner design and testing of HWR010 copper niobium composite RF superconducting cavity

<bold>Background</bold>The frequency stability of superconducting cavities is essential for the stable operation of superconducting proton linear accelerators in accelerator-driven subcritical systems.<bold>Purpose</bold>This study aims to develop a helium-driven mechanical frequency tuner for the HWR010 copper-niobium composite superconducting cavity to compensate for frequency detuning caused by helium pressure fluctuations, Lorentz force, beam loading effects, and microphonics.<bold>Method</bold>First, ANSYS software was employed to design a helium-driven mechanical frequency tuner and analyze its mechanical response during tuning with consideration of the high mechanical rigidity and large RF volume of the HWR010 copper-niobium cavity. Second, a control system using both pressure regulation and pulse-width modulation (PWM) was developed to achieve precise frequency control with a closed-loop feedback mechanism for stable operation in cryogenic temperatures, vacuum, and radiation environments. Finally, comprehensive testing of the tuner was conducted at both room temperature and cryogenic temperature (4 K) to verify its performance characteristics, including tuning range, resolution, and control accuracy.<bold>Results</bold>The test results demonstrate that the tuner achieves a tuning sensitivity of 65 kHz/0.1 MPa, a total tuning range of 130 kHz, and a tuning resolution of 2 Hz/step, which is significantly better than the design requirement of 5 Hz/step. The measured helium pressure control accuracy is less than 5 Pa, and the tuning system showes excellent repeatability with minimal hysteresis during repeated inflation and deflation cycles. The mechanical simulation results correlate well with the experimental data, confirming that all components operate within their elastic limits under 3 MPa working pressure.<bold>Conclusions</bold>The developed helium-driven frequency tuner in this study successfully meets the high-precision and fast-response requirements for frequency tuning of the HWR010 copper-niobium composite superconducting cavity. With its tuning range of 130 kHz, frequency resolution of less than 5 Hz, and stable operation in cryogenic environments, the tuner effectively ensures the frequency stability of the superconducting cavity and satisfies the frequency tuning requirements for various superconducting cavities in the superconducting proton linear accelerator of the China Initiative Accelerator Driven System (CiADS).