Hybrid undulator design considerations

Abstract Permanent magnet undulators have become an important part of short-wavelength free electron lasers. The properties and tolerances of the materials employed in undulators become a major issue as the requirements for maintaining interaction strength become more stringent with shorter wavelength FELs. The engineering approach, the magnet specifications, pairing, sorting, arrangement, and field and mechanical tolerances form critical parts of the construction of an acceptable magnetic field configuration with real magnets. This is particularly true as the length of the undulator increases and the photon and undulator wavelengths decrease. This paper will discuss several of the modeling, design, and engineering aspects employed to obtain the required high quality magnetic properties with a hybrid permanent-magnet undulator. The impact of these design choices on the recently completed tapered hybrid undulator (THUNDER) and its performance are also discussed.