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650 MHz 2-cell superconducting cavities are proposed for the main ring of the Circular Electron Positron Collider (CEPC). The design, fabrication, surface treatment (buffered chemical polishing) and vertical tests of the cavities with HOM couplers were conducted. The performance of the cavity at 2 K is not affected by the HOM coupler. The maximum intrinsic quality factor of the cavity with the HOM coupler reached 3.1·10¹⁰ at 20 MV/m. The vertical test results showed that the fundamental mode external quality factor of all HOM couplers is an order of magnitude larger than quality factor of the cavity. The HOM damping results for the 650 MHz 2-cell cavity were also measured at cryogenic temperature and compared with the simulated and measured results at room temperature. Two 650 MHz 2-cell cavities jacketed have been integrated into a test cryomodule for CEPC. Another 650 MHz 2-cell cavity reached 6·10¹⁰ at 22 MV/m after nitrogen infusion. In addition, two 650 MHz 1-cell cavities reached 2.7·10¹⁰ at 35 MV/m (fine grain) and 3.6·10¹⁰ at 32 MV/m (large grain) after electro-polishing, respectively. In future, electro-polishing will be applied to 650 MHz 2-cell cavity soon., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

Aiming to high repetition rate hard X-ray facility, con-struction of Shanghai HIgh repetition rate XFEL aNd Extreme light facility (SHINE) project has been ap-proved. During the R D phase, prototypes fabrication of key components of 1.3GHz superconducting rf system have been proposed, especially 1.3 GHz 9-cell niobium cavities. Here the paper will present the progress of the fabrication status and performance of the prototypes, together with the analysis of not only the quality factor and gradient of the cavities. Consideration of HOM feed-throughs and absorbers are also reported., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

The China Spallation Neutron Source (CSNS) is de-signed to produce spallation neutrons. CSNS upgrade is planned to increase beam power by inserting a SRF linac after drift tube linac (DTL). IHEP is developing a 325MHz double spoke cavity at ¿0 of 0.5 for the CSNS SRF linac. The cavity shape was optimized to minimize Ep/Ea while keeping Bp/Ep reasonably low. Meanwhile, mechanical design was applied to check stress, Lorentz force detuning and microphonic effects, and to minimize pressure sensitivity. A new RF coupling scheme was pro-posed to avoid electrons hitting directly on ceramic win-dow. After fabrication and post processing of cavity, the cavity reached Bp of 120mT at E_{acc} = 13.8MV/m and Q₀ = 1.72·10¹⁰ under vertical test at 2K., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

Second sound is an effective way to detect the quench position on superconducting cavity. A second sound quench site detection system is under developing for the PAPS. High gradient is very important for superconducting cavity, however it may be limited by quench on the cavity high field region. Quench can be caused by various reasons. To locate the position is the key to reveal the mysteries of quench. Now we are developing the quench position detection system by RTD sensors such as Cernox and OST sensors., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

Peking University is striving for constructing a superconducting radio-frequency accelerator test facility (PKU-SETF) to provide coherent radiations [1]. A cryomodule consisting of a China made 9-cell TESLA type cavity was designed and constructed for this purpose, which is expected to provide 15-20 MeV energy gain at an operating temperature of 2K. Some technical issues in the manufacturing progress are reported, including the tungsten inert gas (TIG) welding of the LHe vessel and the superconducting cavity, the demagnetization of the vacuum vessel made of pure iron, and the manufacturing of the main power coupler., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

As part of the updated DC-SC injector, a 3.5cell cavity has been fabricated at Peking University, which includes two Coaxial High Order Mode (HOM) couplers. The effect of the HOM couplers has been studied by numerical simulation and measurement. The results are highly uniform and show that the two couplers do effectively damp the HOMs., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

Spoke cavities have been developed and have apparent advantages for high current proton accelerator based on superconductivity at low and medium energy region. As the research and the technical reserve, Peking University has started the R program of single spoke cavity (SSC). The work is proposed to do beam load experiment on the HI-13 Tandem at CIAE. The maximum kinetic energy of proton beam is 26MeV, and the frequency of the chopper for superconducting is 150MHz. It leads us to the choice of a 450MHz and β=0.2 single spoke cavity. In this paper, the RF design, mechanical study, fabrication arts, tolerance analysis, and room temperature RF test is presented., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan