Numerical simulation on cool-down and warm-up processes of superconducting quadrupole magnet for BEPC Ⅱ

A pair of superconducting quadrupole(SCQ) magnets are applied for Beijing Electron-Positron Collider Upgrade (BEPC Ⅱ). The magnet can be destroyed by the excess mechanical stress caused by thermal gradients during the cool-down and warm-up processes. This paper presents the cool-down and warm-up processes in terms of magnet safe operation. A mathematical model and an analytical method are developed and the time of cool-down and warm-up is calculated, which is respectively 120 minutes and 150 minutes. The transient changes of the operation parameters are obtained, including the inlet and outlet temperature and pressure of helium to cooling loop of the magnet, the highest and lowest temperature of the magnet, and the maximum temperature difference along the magnet. The peak maximum temperat