Experience with small-gap undulators

Over the past year, we have gained some experience with small-gap undulators through operation of the NSLS Prototype Small-Gap Undulator (PSGU). PSGU is a small R&D insertion device intended for investigation of the fundamental limitations of small-gap devices. At the same time, PSGU aptly demonstrates the enhanced performance offered by such devices, through generation of radiation with a 16 mm period pure-permanent-magnet undulator. In what follows, we present a brief description of PSGU and a summary of operating experience to date. This includes a spectrum of the undulator radiation produced at a 5.6 mm magnet gap, and the appearance of operational limitations, namely lifetime degradation, beam instabilities, and increased bremsstrahlung radiation