Insertion Devices, Future Developments, Limitations

The first generation of insertion devices having reached maturity (or almost), it is appropriate to survey directions along which new developments are expected. These include: Beam cooling with undulators, elementary particle physics with wigglers and undulators, microwigglers, dynamic (i.e. electromagnetic) insertion devices, bunched electron beam wigglers, time compression of photon pulses, the confinement and compression of radiation, optimized insertion devices, damage resistant optics, photon bunch contouring, and the rebunching of electron beams by phase switching. A theorem will be mentioned which limits the number of photons emitted by a relativistic electron (e.g. one passing through an insertion device).