Preliminary Design of the BEPCII-Upgrade Cryogenic System

The Beijing Electron-Positron Collider II (BEPCII) cryogenic system was officially put into operation in January, 2006, including cooled for two superconducting radio frequency (SRF) cavities, two superconducting (SC) quadrupole magnets, and one detector solenoid magnet. To achieve a higher luminosity at higher energy, the BEPCII upgrade (BEPCII-U) was proposed and approved in June 2021, and the core purpose is to improve the efficiency of collision data acquisition in the high energy range and to increase the colliding beam energy from 2.1 GeV to 2.8 GeV. According to the operation requirements of SRF cavities and SC magnets for BEPCII-U, cooling capacity of BEPCII-U cryogenic plant for SRF cavities is upgraded from the original 500 W to 1 kW at 4.5 K due to the increased number of SRF cavities (4 cavities), and two cryostats with current leads for SC magnets are optimally designed. In this paper, the overview of the preliminary design of the BEPCII upgrade cryogenic system is described.