Quality Factor Enhancement of 650 MHz Superconducting Radio-Frequency Cavity for CEPC

Peng Sha,Chao Dong,Song Jin,Jiyuan Zhai,Zhenghui Mi,Feisi He,Weimin Pan,Xiangcong He,Baiqi Liu,Lingxi Ye,Shiao Zheng

doi:10.3390/app12020546

Abstract

Medium-temperature (mid-T) furnace baking was conducted at 650 MHz superconducting radio-frequency (SRF) cavity for circular electron positron collider (CEPC), which enhanced the cavity unloaded quality factor (Q0) significantly. In the vertical test (2.0 K), Q0 of 650 MHz cavity reached 6.4 × 1010 at 30 MV/m, which is remarkably high at this unexplored frequency. Additionally, the cavity quenched at 31.2 MV/m finally. There was no anti-Q-slope behavior after mid-T furnace baking, which is characteristic of 1.3 GHz cavities. The microwave surface resistance (RS) was also studied, which indicated both very low Bardeen–Cooper–Schrieffer (BCS) and residual resistance. The recipe of cavity process in this paper is simplified and easy to duplicate, which may benefit the SRF community.

Highlights

superconducting radio-frequency (SRF) cavities made of niobium are broadly adopted for the modern accelerators, which have demonstrated much higher Q0 and lower RS than cavity made of copper
The mid-T furnace baking of 1.3 GHz single-cell cavities succeed at High Energy Accelerator Research Organization (KEK), which was conducted in a vacuum furnace
Mid-T furnace baking was attempted at 650 MHz single-cell cavity, which achieved a state-of-the-art high Q0 at the accelerating gradient of 30 MV/m

Summary

Introduction

SRF cavities made of niobium are broadly adopted for the modern accelerators, which have demonstrated much higher Q0 and lower RS than cavity made of copper. The technology of medium-temperature (mid-T, 250–400 ◦ C) baking is used to increase Q0 of 1.3 GHz cavities successfully, which dissolves the oxides in the surfaces of niobium [1,2,3]. It is more convenient and easier than nitrogen doping/infusion [4,5,6]. The mid-T furnace baking of 1.3 GHz single-cell cavities succeed at High Energy Accelerator Research Organization (KEK), which was conducted in a vacuum furnace. The mid-T furnace baking of 650 MHz cavity for CEPC was carried out at IHEP, which obtained high Q0 and low RS successfully

The Process of Mid-T Furnace Baking

Vertical Test after Mid-T Furnace Baking

Conclusions