Research on Magnetic Properties of Nd(Pr)FeB Magnet for Cryogenic Permanent-Magnet Undulator of SSRF

In recent years, the Shanghai Synchrotron Radiation Facility (SSRF) has been studying magnetic properties of Nd(Pr)FeB at low temperature. The results show that with decreasing temperature, the moment of N50M and N48H shows a strong spin reorientation transition near 120 K, and their orientation degree deteriorates gradually. At 120 K, the moment and the coercive force of N48H are 1.50 and 5 T, respectively, which increase by 13.6% and 150% relative to those at normal temperature. With decreasing temperature, the moment of P42H and P46H linearly increases, and their orientation degree increases gradually. At 77 K, the moment and the coercive force of P46H are 1.53 and 7.5 T, respectively, which increase by 16% and 275% relative to those at room temperature. If the cryogenic permanent magnet undulator (CPMU) is not baked above 50 °C, N48H and P46H can be applied for the CPMU with a shorter period. In 2014, the SSRF developed the first CPMU20 prototype with N48H in China. Its period length is 20 mm, and its period number is 80. With the gap of 6 mm and at the temperature of 138 K, the effective peak magnetic field and the phase error of the CPMU20 are 1.03 T and 4.5°, respectively.