Refurbishment of a cryogenic permanent magnet undulator for the Shanghai Synchrotron Radiation Facility

Abstract Shortening the period length is one direction of development in undulator technology, and it is also an effective approach for obtaining short-wavelength radiation and miniaturizing free electron laser facility. In 2017, the Shanghai Synchrotron Radiation Facility (SSRF) project team successfully developed a cryogenic permanent magnet undulator (CPMU) based on PrFeB magnets. This CPMU features a period length of 18mm and consists of 144 periods. With a magnetic gap of 6 mm, it achieves an effective peak magnetic field of 0.91 T. In September of the same year, successful radiation emission was achieved in the 13W straight section of the SSRF storage ring. However, due to operational issues, some components suffered damage, rendering it difficult to operate normally. In 2023, it was decided to refurbish the undulator by reprocessing the damaged components. Currently, it is undergoing integration and debugging, with plans for reinstallation in the storage ring during the summer of 2024. This paper reports the refurbishment project for CPMU, including magnetic field measurement and debugging results.