Radiation of SPring-8 very long undulators

A key feature of the SPring-8 storage ring is the presence of four 30 m long straight sections for the installation of very long insertion devices. Two characteristics of very long undulators are presented here: first, the problems brought by the necessity to phase the individual segments, which in turn, imposed the use of the in-vacuum technology; next, the near-field effects which appear on-axis as these undulators length is comparable to the distance between the observation point and the source.