Study on the influence of gap dependent error on the cryogenic permanent magnet undulator performance

Abstract

The mass production of the first stage of HEPS (High Energy Photon Source) is approaching its final stage. 6 CPMUs (cryogenic permanent magnet undulators) have been manufactured, with four successfully finalizing the tuning of the magnetic field. To ensure radiation performance, HEPS's CPMUs enforce stringent phase error protocols. Moreover, the contraction properties at cryogenic temperature lead to a decrease in phase error after cooling. In the process of CPMU commissioning, a technique for forecasting the change of magnetic errors from room to cryogenic temperature was discovered and studied, as will be demonstrated in this paper.