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World's first 1.3 GHz cryomodule containing eight 9-cell superconducting radio-frequency (RF) cavities treated by medium-temperature furnace baking (mid-T bake) was developed, assembled and tested at IHEP for the Dalian Advanced Light Source (DALS) and CEPC R&D. The 9-cell cavities in the cryomodule achieved an unprecedented highest average Q0 of 3.8E10 at 16 MV/m and 3.6E10 at 21 MV/m in the horizontal test. The cryomodule can operate stably up to a total CW RF voltage greater than 191 MV, with an average cavity CW accelerating gradient of more than 23 MV/m. The results significantly exceed the specifications of CEPC, DALS and the other high repetition rate free electron laser facilities (LCLS-II, LCLS-II-HE, SHINE, S3FEL). There is evidence that the mid-T bake cavity may not require fast cool-down or long processing time in the cryomodule. This paper reviews the cryomodule performance and discusses some important issues in cryomodule assembly and testing., Comment: 5 pages, 6 figures

Superconducting cavities with low RF frequencies and heavy damping of higher order modes (HOM) are desired for the main accelerator of High Energy Photon Source (HEPS), a 6 GeV synchrotron light source promising ultralow emittance currently under construction in Beijing. A compact 166.6 MHz superconducting cavity was proposed adopting a quarter-wave beta=1 geometry. Based on the successful development of a proof-of-principle cavity, a HOM-damped 166.6 MHz compact superconducting cavity was subsequently designed. A ferrite damper was installed on the beam pipe to reduce HOM impedance below the stringent threshold of coupled-bunch instabilities. Being compact, RF field heating on the cavity vacuum seal was carefully examined against quenching the NbTi flange. The cavity was later dressed with a helium vessel and the tuning mechanism was also realized. Excellent RF and mechanical properties were eventually achieved. Finally, the two-cavity string was designed to ensure smooth transitions among components and proper shielding of synchrotron light. This paper presents a complete design of a fully dressed HOM-damped low-frequency beta=1 superconducting cavity for HEPS., Comment: Presented at the 2021 International Conference on Radio Frequency Superconducting Conference (SRF 2021), Jun 28th - Jul 2nd, 2021

The 10 MeV accelerator-driven subcritical system (ADS) Injector-I test stand at Institute of High Energy Physics (IHEP) is a testing facility dedicated to demonstrate one of the two injector design schemes [Injector Scheme-I, which works at 325 MHz], for the ADS project in China. The Injector adopted a four vane copper structure RFQ with output energy of 3.2 MeV and a superconducting (SC) section accommodating fourteen \b{eta}g=0.12 single spoke cavities, fourteen SC solenoids and fourteen cold BPMs. The ion source was installed since April of 2014, periods of commissioning are regularly scheduled between installation phases of the rest of the injector. Continuous wave (CW) beam was shooting through the injector and 10 MeV CW proton beam with average beam current around 2 mA was obtained recently. This contribution describe the results achieved so far and the difficulties encountered in CW commissioning., Comment: 11 pages,27 figures

RF power coupler is a key component of the superconducting accelerating system in Chinese ADS proton linac injector I, which is used to transmit 15kW RF power from the power source to the superconducting HWR cavity. According to the requirement of working frequency, power level, transmission capability and cooling condition, the physics design of coupler has been finished, which includes RF structure optimization, thermal simulation, thermal stress analysis and so on. Based on this design, the prototype of HWR coupler has been fabricated, and then has passed the high power test successfully.

Power couplers, used in China-ADS proton linac injector I, are required to transfer 6kW RF power to the superconducting Spoke cavities. At present, first two couplers of coaxial design have been fabricated and accomplished high power test at IHEP. The test results indicated that couplers of this design are qualified to deliver 10kW RF power in continuous travelling wave mode. This paper described the coupler's room temperature test procedures and results, discussed the original high power test terminated due to serious out-gassing and after some modifications. In the final test, the couplers smoothly exceeded the design power level., Comment: 3 pages,6 figures