The Magnetic Field Measurement Systems for a Cryogenic Undulator and a Superconducting Undulator at SSRF

Two cryogenic permanent magnet undulators (CPMU) have been developed and assembled into storage ring at Shanghai Synchrotron Radiation Facility (SSRF) in order to produce higher brilliance in the hard X rays domain. At low temperatures, permanent magnet materials can provide both higher magnetic field and higher resistance to radiation-induced demagnetization of the magnet compared to room temperature operation. Test results indicate that lowering the temperature of permanent magnets (Nd2Fe14B) increases the magnetic field strength about by 11%. The magnetic field distribution of the CPMU must be measured after the magnetic arrays are installed into the vacuum chamber and cooled to cryogenic temperature. We have finished a magnetic measurement bench based on a Hall probe to perform cryogenic temperature measurement. In this papers, the details of the magnetic field measurement system and some test results of a CPMU20 with 20mm period and Nd2Fe14B type are described. In addition, two superconducting planar undulator (SCU) prototypes with period 16mm are also under development at SSRF to research some key technologies. (paper)