Novel insertion devices

Permanent magnet planar undulators are used at synchrotrons worldwide and serve as versatile radiation sources. For some experiments however, photon characteristics other than what is achievable with planar devices are desired. Undulators can be tailored to adjust photon characteristics, such as brightness, tuning curves, polarization harmonic content, and heat load to suit them to a particular experiment. One specialized device is the electromagnetic circularly polarizing undulator at the Advanced Photon Source (APS). At a few facilities, plans are underway to build superconducting undulators with short period lengths to provide higher energy radiation. At APS, the possibility of building an undulator with a variable period is also being investigated. Some users, driven by a desire for lower on-axis heat load or for circular polarization, prefer other types of devices, such as Apple-style undulators or figure-eight devices. Characteristics of the radiation output and advantages of these various types of devices are presented.