Ultrahigh accelerating gradient and quality factor of CEPC 650 MHz uperconducting radio-frequency cavity
Peng Sha1,2,3,4，Wei-Min Pan1,2,3,4, Song Jin1,2,3, Ji-Yuan Zhai1,2,3,4, Zheng-Hui Mi1,2,3,4, Bai-Qi Liu1,2,3, Chao Dong1,2,3, Fei-Si He1,2,3,4,
Rui Ge1,2,3,4, Liang-Rui Sun1,2,3, Shi-Ao Zheng1,2,3,4, Ling-Xi Ye1,2,3,4
Nuclear Science and Techniques Vol.33, Issue 10, Article number:125 (2022)
Plain Language Summary
The Novelty
This study demonstrated that the Circular Electron Positron Collider (CEPC) 650 MHz single-cell superconducting radio-frequency (SRF) cavities could achieve ultrahigh accelerating gradient (Eacc) by applying a combination of buffered chemical polishing (BCP) and electropolishing (EP). The values of Eacc achieved were above 40 MV/m. Besides, after medium-temperature furnace baking, the SRF cavities achieved an ultrahigh Q0 of 8 × 1010 at 22 MV/m and an extremely low BCS resistance (RBCS) of ~1.0 nΩ at 2.0 K. Two 650 MHz SRF cavities were involved throughout the process of validating the effect of the combination of BCP and EP. By showing the pivotal roles of surface treatments on the performance of SRF cavities, the research output paved a clear path for future research on large SRF cavities.
The Background
The superconducting radio-frequency (SRF) cavity is a crucial component of particle accelerators, such as high-energy colliders, proton/neutron sources, free electron lasers and synchrotron light sources. The Circular Electron Positron Collider (CEPC) is a high-energy collider of the Higgs factory. The collider ring of the CEPC is equipped with hundreds of 650 MHz SRF cavities. To meet the high requirements of accelerators, the SRF cavities must exhibit high accelerating gradient (Eacc) and high intrinsic quality factor (Q0). The cavities are commonly treated by either buffered chemical polishing (BCP) or electropolishing (EP). However, SRF cavities processed by BCP face challenge in achieving high Eacc, owing to the high surface roughness brought about by BCP. On the other hand, although EP could render higher Eacc, it is a complicated process which also involves higher cost. As such, it was speculated that the combination of BCP and EP could be a feasible way for large SRF cavities to achieve high Eacc. To validate the feasibility of the combination of BCP and EP, this study applied the combined treatment on two 650 MHz SRF cavities and excellent results were obtained. Since the treatment procedures can be replicated easily, the output facilitates the advancement of future studies related to SRF.
The SDG Impact
Particle accelerators play an important role in the advancement of high-energy and nuclear physics. The performance of SRF cavities is very critical as they greatly affect the scale and cost of particle accelerators. In order to contribute to the advancement of research related to SRF, this study developed a highly-feasible and remarkable technique which significantly enhanced the performance of 650 MHz SRF cavities. Therefore, its output showed good alignment with UNSDG 9: Industry, Innovation & Infrastructure.
Graphical Abstract
