Recent Advancements of Undulator Technologies

Insertion devices—or more specifically, undulators—play a crucial role in actually producing intense light from a high-energy electron beam in synchrotron radiation (SR) and X-ray free electron laser (XFEL) facilities. Their function is quite simple; i.e., to let the electrons move periodically. Even so, there are many different concepts of undulators, and thus, technologies to realize these concepts are quite diverse. There are a variety of requirements dictated by the experimental users of SR and XFEL, mainly in terms of the polarization and wavelength of radiation. In addition, the specifications of undulators should meet these requirements under the given boundary conditions, such as the minimum operational gap, electron energy, and available area for installation. However, necessity is the mother of invention; undulator technologies and concepts have continuously advanced year by year to meet users' demands.