Synchrotron radiation research: Retrospective view and prospective considerations

Development of past and future light sources for synchrotron radiation research is discussed. Starting with the development of 3rd generation sources, the development of X-ray free electron lasers (XFELs) and new generation storage rings with a multi-bend-achromat lattice configuration is discussed. One future ideal form could be the combination of a pulsed X-ray free electron laser (XFEL) featuring both high peak brilliance and a reasonably high (∼10 kHz) repetition rate, with a CW XFEL offering both time-space coherence and moderate average brilliance.