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166.6-MHz superconducting cavities have been chosen for the High Energy Photon Source (HEPS) as the main accelerating structures to provide 900 kW of beam power and 5.4 MV of accelerating voltage. A proof-of-principle cavity adopting the quarter-wave beta = 1 geometry was previously developed. Excellent performance was achieved in vertical tests at cryogenic temperatures. The cavity was later welded with a helium jacket, dressed with a power coupler and other ancillaries, and high-power tested in a test cryomodule. Performance degradation was observed and analyzed. Evidence from temperature sensor readout and heat loss measurement results suggested an overheating in the cavity–coupler interface region causing a "thermal runaway" and eventually quenching the cavity at its design voltage. Electromagnetic-fluid-thermal coupled simulation has thus been conducted, and the hypothesis was nicely validated. Finally, solutions were proposed including an elongated niobium extension tube at the coupler port and an optimized helium gas cooling of the power coupler's outer conductor. These modifications have been subsequently applied on the 166.6-MHz higher-order-mode damped superconducting cavities for the HEPS. Heat loss at 4.2 K contributed by the power coupler can be largely reduced with a modest gas cooling scheme. Similar design approaches can also be applied to other non-elliptical superconducting structures with on-cavity high-power coupler mountings. [ABSTRACT FROM AUTHOR]

The Chinese Accelerator Driven Sub-critical system (C-ADS) Injector-I is designed and constructed by the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences (CAS) in Beijing, China. The test cryomodule (TCM), housing two 325 MHz spoke cavities and two solenoids and operating at 2 K, has been designed, assembled and commissioned since the beginning of 2012. The C-ADS Injector-I linac with the TCM successfully accelerated the proton beam to 3.68 MeV with the peak current of 10.1 mA in pulse mode. It is the world's first prototype of spoke cavity cryomodule with beam, and is an important step in the qualification of the cryomodule before series productions. This paper describes the detail of the design, operation and thermal performances of the prototype cryomodule. The analysis takes into account the heat loads of the main components (support posts, multilayer insulation and cavities) at various cryogenic temperature levels. The estimated heat loads of the cryomodule have been compared with the available experimental measurements, and the cryogenic deformations by simulation is verified by the experimental measurements by the wire position monitors (WPMs). The operation experiences including the cool down, alignment and heat load measurement are reported. • The 325 MHz spoke cavity prototype cryomodule has been designed, assembled and commissioned. • The thermal performance of the bottom-supported cryomodule has been proved firstly worldwide. • The cryomodule can be in a stable operation at 2 K and 31 mbar with beam. • The operation experiences including the cool down, alignment and measurement of heat loads are reported. • The linac with cryomodule had been accelerated successfully to 3.68 MeV@10.1 mA in pulse mode. [ABSTRACT FROM AUTHOR]

• The 325 MHz spoke cavity cryomodules have been designed, fabricated and commissioned. • The bottom-supported cryomodules have been put into operation. • The thermal performances analysis and experimental measurements were compared. • The cryomodules are in a stable operation at 2 K and 31 mbar with beam commissioning. • The accelerating cryomodules successfully reached to 10 MeV in pulse and CW mode. The Chinese Accelerator Driven Sub-critical system (C-ADS) is an important strategic research that is based on a high energy proton beam for nuclear waste transmutation. To meet the requirements of stability and reliability of the lower energy part, two identical Injectors are operated in parallel. The Injector-I is designed and constructed by the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences (CAS) in Beijing, China. The Injector-I linac with two accelerating cryomodules (named CM1 and CM2) successfully accelerated the proton beam to 10.67 MeV with the beam current of 10.11 mA in pulse mode and 10.0 MeV with a beam current of 1.6 mA in CW (continuous wave) mode. The cryomodules have been designed, fabricated, assembled and commissioned at IHEP since the beginning of 2012. The thermal performances of the cryomodules were analyzed with numerical simulations and the empirical calculations take into account all the main contributors (support posts, multilayer insulation, current leads, power couplers and cavities) to the static and dynamic heat loads at various temperature levels. Two designs of current leads are developed and analyzed, and the case 2 current leads are tested and used in the CM2. The estimated static heat loads by analysis have been compared with the available experimental measurements. The operation experiences including the cool down, operating parameters and heat load measurements are reported, and the results were shown that the cryomodules can keep in a stable operation at 2 K and 30 mbar ±10 Pa. [ABSTRACT FROM AUTHOR]