Article title: Nitrogen doping/infusion of 650 MHz cavities for CEPC

CEPC 650 MHz超导腔的氮掺杂研究

DOI: 10.1007/s41365-021-00881-3

One sentence summary:

一句话概要：

The buffered chemical polishing (BCP) processing is a feasible alternative to electro-polishing (EP) for nitrogen doping/fusion of 650 MHz cavities for CEPC.

缓冲化学抛光(BCP)可以替代电抛光(EP)，用于CEPC 650 MHz超导腔氮掺杂前的预处理 。

http://www.nst.sinap.ac.cn/newsDetails/112/4688/en/

 The Novelty (What)

This study has found that nitrogen doping/infusion could increase the intrinsic quality factor (Q₀) of the 650 MHz cavities used in a circular electron-positron collider (CEPC). Adopting a buffered chemical polishing (BCP) surface baseline prior to the nitrogen infusion of a 650 MHz 2-cell cavity yielded a Q₀ of 6 × 10¹⁰ at 22 MV/m in the vertical test and a maximum gradient of 25 MV/m. The Q₀ exceeded the specification of CEPC, i.e., 4 × 10¹⁰ at 22 MV/m.  By optimizing nitrogen infusion and BCP, the performance of the 650 MHz cavity can be further enhanced.

创新性（主要内容）

研究发现,氮掺杂可以提高环形正负电子对撞机(CEPC)中650 MHz腔体的固有品质因数(Q₀)。 650 MHz 2-cell超导腔经过缓冲化学抛光(BCP)处理后,再进行氮掺杂处理后，垂直测试结果达到Q₀=6×10¹⁰@22MV/m，超过了CEPC的指标(4×10¹⁰@22MV/m)，最大加速梯度为25 mV/m。未来，通过优化氮掺杂和BCP的工艺，可以进一步提高650 MHz超导腔的性能。

The Background (Why)

研究背景（主要原因）

The CEPC is a high-energy collider of the Higgs factory. Constructed 100 m underground, two hundred and forty 650 MHz 2-cell cavities and ninety-six 1.3 GHz 9-cell cavities exist in the collider and the booster. The 650 MHz 2-cell cavities economically support the cryogenics system by operating in continuous wave mode with high-quality factor (Q). Electro-polishing (EP) is commonly adopted for the nitrogen doping/infusion of the cavities abroad. However, in China, buffered chemical polishing (BCP) is relatively more feasible to be adopted instead. This study conducted a nitrogen infusion and doping study on 650 MHz cavities BCP treated to confirm its feasibility. Results showed that the Q₀ achieved exceeded the specifications of CEPC. Therefore, nitrogen doping/infusion of cavities BCP treated is effective and easy to promote.

CEPC是一台用作“希格斯工厂”的高能对撞机。在地下100米深处，CEPC的对撞环里有240个650 MHz 2-cell超导腔，增强器里有96个1.3 GHz 9-cell超导腔。 650 MHz 2-cell超导腔运行在连续波的模式下，其Q值非常高，以降低低温系统的负荷。 国际上对超导腔进行掺氮时，一般先对其进行电抛光（Electro-polishing, EP）处理。而在我国，采用缓冲化学抛光(BCP)更加方便、可行。 为了证实BCP处理能否用于超导腔的氮掺杂，我们针对BCP处理过的650 MHz超导腔开展了氮掺杂研究，最终获得的Q₀值超过了CEPC的要求。 因此，超导腔经过BCP处理后、再进行氮掺杂的方法是可行的、易于推广。

The SDG impact (Big Why)

SDG影响力（研究意义）

Superconducting cavities with high Q and gradient are advocated by many applications, such as wastewater and sludge treatment, safety, flue gas treatment, nuclear waste destruction, etc. The highly effective BCP surface baseline reported in this study offers an alternative option to researchers seeking a feasible surface baseline for nitrogen doping/infusion besides EP. Hence, this study aligns with the objectives of UNSDG 9: Industry, Innovation & Infrastructure, to enhance scientific research.

高Q&高梯度的超导腔应用非常广泛，如废水和污泥处理、安检、烟气处理、核废料处置等，本研究介绍的对超导腔表面进行BCP处理为人们开展氮掺杂研究提供了一个替代EP的选择。 因此，本研究报告符合联合国可持续发展目标9：工业、创新和基础设施的目标，以加强科学研究。