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Abstract: A high power input coupler for a 500MHz superconducting cavity (SCC) of the upgrade project of Beijing Electron Positron Collider (BEPCII) has been developed in China. Several prototypes have been fabricated and tested successfully. A maximum of 420kW continuous wave (CW) RF power in traveling wave (TW) mode was achieved in the high power test. The detailed design, fabrication and test of the coupler are described in this paper. [Copyright &y& Elsevier]

In order to accommodate the luminosity improvement strategy, two superconducting 499.8 MHz radio frequency (rf) cavities have been adopted for the Upgrade project of Beijing Electron Positron Collider (BEPCII), a double-ring electron–positron collider as well as a synchrotron radiation (SR) light source. The in-house development of the 499.8 MHz superconducting cavity system was initiated at IHEP since 2008. One prototype niobium cavity with all the parts except for the flanges and the pickup port formed by spinning was fabricated and then vertical-tested successfully in July 2011. Four prototype input couplers were manufactured and high-power tested with one reaching a maximum rf power of continuous wave (cw) 420 kW. One prototype HOM damper with a satisfactory absorbing efficiency at the desired frequency band was also constructed and high power tested up to cw 4.4 kW. In the meanwhile, a frequency tuner consisting of a stepping motor and a piezoelectric oscillator was developed. Finally, the bare cavity was dressed with one input coupler, two HOM dampers and one frequency tuner, mounted in a domestic-developed cryostat and then high-power tested successfully in Oct. 2011. The achieved accelerating voltage is 2.2 MV with corresponding Q 0 measured to be 5.8 × 10 8 , beyond the designed goal. This is the first in-house developed 499.8 MHz HOM-damped superconducting cavity system in China. The design, fabrication, post processing and tests of the niobium bare cavity and its auxiliaries, as well as the horizontal high-power test of the cavity system are presented. [ABSTRACT FROM AUTHOR]

The China Spallation Neutron Source (CSNS), located in Dongguan city, Guangdong Province, is the country's first and only spallation neutron source. It is also the fourth spallation neutron source in the world. Meanwhile, it is one of the core large-scale scientific facilities of the Guangdong-Hong Kong-Macao Greater Bay Area Comprehensive National Science Center. The China Spallation Neutron Source phase II (CSNS-II) upgrade design will increase the total beam power from 100 kW to 500 kW and boost the beam energy from 80 MeV to 300 MeV in the linac by adding a superconducting linear accelerator to the existing accelerator complex. The double spoke resonator is used in the energy range of 80 MeV to 165 MeV. At present, the double spoke resonator (DSR) prototypes have been designed, fabricated and tested. The two prototypes underwent vertical testing five times, resulting in a maximum accelerating gradient of 15 MV/m. Additionally, the value of Q 0 exceeded 4 × 1 0 10 at an E a c c of 7.3 MV/m. [ABSTRACT FROM AUTHOR]

The High Energy Photon Source (HEPS) is a 6 GeV diffraction-limited synchrotron light source under construction in Beijing. It will use five 166.6 MHz superconducting radio frequency (rf) cavities to accelerate the 200 mA electron beam in the storage ring. In the current lattice design, each straight section is 6 meters long to accommodate two 166.6 MHz cavities. The cavity adopts β =1 quarter-wave geometry, and the damping of the higher order modes is realized by using an enlarged cavity beam pipe to 505 mm and a ferrite absorber installed on the beam pipe. The low rf frequency, as well as the large beam aperture, added great challenges to the design of the 166.6 MHz cavity module to fit into a strictly limited longitudinal space. In addition, heat load optimization for the transition from room temperature to the cryogenic temperature, smooth tapering from the 505 mm beam aperture to the small diameter of the gate valves for impedance control, proper collimation of the synchrotron light to prevent thermal damage of delicate components, are also demanding requirements for a compact design. Accessibilities are also preserved for tuners and vacuum components to enable online maintenance. Finally, rf field leakage in the vacuum seal groove of the cavity is carefully examined to prevent overheating on the superconducting flange, which, in the worst scenario, may cause a thermal runaway, thus limiting the achievable accelerating gradient of the cavity. This paper presents the first compact design of the 166.6 MHz srf section for HEPS. [ABSTRACT FROM AUTHOR]

A low-frequency quarter-wave superconducting β = 1 structure has been proposed as a main accelerating cavity for the newly planned storage ring light source with ultra-low emittance. In the development of High Energy Photon Source, a 6 GeV diffraction-limited light source at the Institute of High Energy Physics, a compact 166.6 MHz proof-of-principle cavity was designed. By optimizing its geometry, the cavity's mechanical properties have been significantly improved with a focus on stress, pressure sensitivity, Lorentz-force detuning, microphonics and tuning capabilities. The cavity was later fabricated, post-processed and tested in a vertical manner at cryogenic temperatures. High peak electromagnetic fields have been achieved with an excellent cryogenic performance, largely exceeding the design goal and project specifications. In addition, the measured mechanical parameters are in good accordance with simulation results. Small Lorentz coefficients and low pressure sensitivities were measured during the tests. This constitutes the first demonstration of a solid low-frequency β = 1 superconducting cavity design with compact geometry and favorable mechanical properties. [ABSTRACT FROM AUTHOR]