Cryogenic permanent magnet and superconducting undulators

Abstract Cryogenically-cooled permanent-magnet-based undulators (CPMUs) have been developed and built at several places around the world in the last decade. They currently operate successfully at many synchrotron radiation facilities, and they are planned as radiators in compact light sources based on laser plasma accelerated electrons. CPMUs have become the undulators of choice at medium energy storage rings. In the past few years, the performance of CPMUs has been brought closer to the physical limit; future incremental improvements will allow the limit to be reached. Superconducting undulators (SCUs), however, despite having a longer history than CPMUs, had not attracted the same level of investment. SCU programs have only relatively recently been given significant funding priority at the Advanced Photon Source (APS). The investment at APS has resulted in the construction of the specialized SCU facility, and in the design and fabrication of several SCUs which are currently operating on the APS ring. KIT invested in the development of a cold vacuum chamber (COLDDIAG) for beam heat load studies, in a precise horizontal conduction cooled magnetic characterization facility as well as in a strong collaboration with the industrial partner Bilfinger Noell. This led to the production of two undulators successfully tested in the KIT synchrotron light source. The combination of mature CPMU technology and developing SCU technology will provide significant flexibility in the choice of advanced undulators for new and upgraded light source facilities. This review paper covers the status of operations and development of CPMUs and SCUs.