Fourth Generation Light Sources

Concepts and designs are now being developed at laboratories around the world for light sources with performance levels that exceed present sources, including the very powerful and successful third generation synchrotron radiation sources that have come on line in the past few years. Workshops[1,2], have been held to review directions for future sources. A main thrust is to increase the brightness and coherence of the radiation using storage rings with lower electron-beam emittance or free-electron lasers (FELs). In the infra-red part of the spectrum very high brightness and coherence is already provided by FEL user facilities driven by linacs and storage rings. It now appears possible to extend FEL operation to the VUV, soft X-ray and even hard X-ray spectral range, to wavelengths down to the angstrom range, using high energy linacs equipped with high-brightness rf photoinjectors and bunch-length compressors. R&D to develop such sources is in progress at BNL, DESY, KEK, SLAC and other laboratories. In the absence of mirrors to form optical cavities, short wavelengths are reached in FEL systems in which a high peak current, low-emittance electron beam becomes bunch-density modulated at the optical wavelength in a single pass through a long undulator by self-amplified spontaneous emission (SASE); i.e.; startup from noise. A proposal to use the last kilometer of the 3 kilometer SLAC linac (the first 2 kilometers will be used for injection to the PEP II B-Factory) to provide 15 GeV electron beams to reach 1.5 Å by SASE in a 100 m long undulator is in preparation. [1] M. Cornacchia and H. Winick (eds), Workshop on Fourth Generation Light Sources, Feb. 24-27, 1992, SSRL Report 92/02 [2] J.-L. Laclare (ed), ICFA Workshop on Fourth Generation Light Sources, ESRF report, Jan. 22-25, 1996 Presented at the17th IEEE Particle Accelerator Conference (PAC 97); Accelerator Science, Technology and Applications, Vancouver, British Columbia, Canada, May 12-16, 1997 * Work supported by the US Dept. of Energy, Office of Basic Energy Sciences, Contract DE-AC03-76SF00515 Fourth Generation Light Sources Herman Winick, Stanford Linear Accelerator Center Stanford, CA 94309, USA