Control system for cryogenic permanent magnet undulator (CPMU) of high energy photon source (HEPS)

Background High energy photon source (HEPS) is the fourth-generation light source, which uses a large number of high-performance insertion devices to generate synchrotron radiation. The control system is an important part of the insertion device (ID). Purpose Cryogenic permanent magnet undulator (CPMU) is one kind of IDs that works in liquid nitrogen temperature and ultra-high vacuum environment, and its control system is more difficult and complex than in-air ID. The design of the control system for CPMU will be introduced in detail. Method The sub-systems include high-precision magnetic gap control, safety protection, measurement and compensation of magnetic gap at cryogenic temperature and cryogenic temperature monitoring. Mature, reliable, stable technical schemes are designed to meet the technical specifications of sub-systems. Results The experiment results show that the magnetic gap motion accuracy can be controlled within 0.2–0.3 μm under the step size of 1 μm. The safety protection system has been tested in turn, and the predetermined protection can be achieved. The average value of magnetic gap cold contraction is 1.512 mm measured by optical micrometer, and the compensation is realized by software. The average temperature of the main magnet structure measured by the temperature sensors is 81.0 K, and the temperature gradient is 0.7 K/m. The temperature monitoring is reliable and stable. Conclusion The CPMU control system which is based on EPICS has been successfully applied to the CPMU prototype, and the test results have met the design specifications.