Analyses on the Cooling Performance of the CPMU Magnetic Structure at SSRF

The cryogenic permanent magnet undulator (CPMU), utilizing the magnetic characteristics of the magnets made of NdFeB or PrFeB that both the remanence and the intrinsic coercivity increase with the decrease of temperature, is a promisingly competitive insertion device type to obtain high magnetic field in short period. The Shanghai Institute of Applied Physics (SINAP) has been studying the related key technology since the early of 2013. An NdFeB based hybrid CPMU prototype with a period of 20 mm and a magnetic length of 1.6 m was developed for the Shanghai Synchrotron Radiation Facility (SSRF). This paper presents the study on the CPMU magnet cooling technique in details. The cooling technique of the CPMU magnet array has been studied by both theoretical analyses and experimental tests. The design of the magnets cooling structure and the experimental tests are provided.