Development of Ultra-High Vacuum System for Cryogenic Permanent Magnet Undulator

At the stage of the High Energy Photon Source-Test Facility(HEPS-TF), a prototype of a cryogenic permanent magnet undulator(CPMU) with a period length of 13.5 mm was developed. The magnetic structures of the CPMU are placed in a vacuum chamber, and have a large amount of material outgassing and entrainment. In order to provide the ultra-high vacuum environment required for the normal operation of the beam, the ultra-high vacuum system of the undulator has been developed. First, the outgassing rate and outgassing load of the undulator were estimated, and then the effective pumping speed required by the vacuum system was calculated. Next, rationally chosen the type and the quality of the pumps; after the machining of the vacuum chamber, the ultimate vacuum test was carried out; and after installation of the CPMU, the base pressure reaches 5×10^-7Pa at room temperature and 4.8×10^-8Pa at 80 K, both of which are better than the requirements.