New Technologies: Permanent Magnet Undulators

Following a discussion of the circumstances under which permanent magnets have a performance that is superior to magnets that are excited by coils (room temperature or superconducting), the properties of two specific types of linear permanent magnet undulators are described. The discussion of the performance limitations of these undulators is complemented by a description of design details to the extent necessary to appreciate the importance of some seemingly unimportant features. Effects of tolerances are clearly important and will be even more important for the very long undulators that one might build in the future. It is shown what has been done in the past, and what one may want to do in the future, to reduce the detrimental effects of tolerances. In addition to these discussions of linear undulators, a conceptual design of a helical permanent magnet undulator (with adjustable length, if desired) is shown, and the performance limitation of this device is discussed.