Possibilities for a Diffraction-Limited Upgrade of a Soft X-ray Light Source

Abstract

Over the last few decades, synchrotron radiation generated by storage rings has been the dominant source of high-brightness photons in a spectrum spanning from infrared to hard X-rays for a multitude of scientific applications. During those years, accelerator and source development have seen several step changes denoted by three generations of ring-based synchrotron light sources. Since the advent of third-generation sources about 20 years ago, development has continued but, until recently, had been mostly evolutionary. In the meantime, free electron lasers (FELs) have emerged as alternative sources of soft and hard X-rays, offering peak brightness many orders of magnitude higher than storage ring sources, with ultra-short photon pulses having nearly complete transverse coherence and an energy bandwidth that approaches the transform limit with seeding. Yet, in spite of these spectacular beam properties, a consensus has emerged that ring-based sources will continue to play a vital role in X-ray science into the future because they offer beam properties that are complementary to FEL sources. Storage rings provide photon beams with lower peak brightness but high average brightness and higher pulse repetition rates on a large number of parallel beamlines with excellent stability and quick tunability [1, 2]. Recent advances in accelerator physics and engineering have made it feasible to provide another step change in brightness over third-generation storage rings. The first rings applying some of those technologies are under construction now.