Undulators and wiggler insertion magnets for the ESRF

The ESRF (European Synchrotron Radiation Source) 6-GeV storage ring will accommodate 29 insertion devices each 5-m long. A review is given of the technologies available to build the insertion devices. A segmentation into three 1.7-m sections is justified by the resulting easier design of the mechanical supports and the vacuum chamber to specified tolerances, the easier magnetic-field measurement, the high flexibility for adjusting the field to the required X-ray spectrum, and the ability to reduce the power density at the monochromator.