A general-purpose high-resolution double-channel-cut monochromator for use on the ChemMatCARS insertion-device beamline at the Advanced Photon Source.

The high-brilliance radiation provided by third-generation synchrotron x-ray facilities such as the Advanced Photon Source has greatly enhanced the power of such chemical and materials research techniques as x-ray-absorption spectroscopy, surface scattering, small-angle x-ray scattering, and chemical crystallography. In order to take full advantage of these source properties, we propose the development of a general-purpose high-energy-resolution double-channel-cut monochromator based on a similar device developed for nuclear-resonant-scattering techniques by the Experimental Facilities Division at the APS. The instrumentation will be installed at the APS on the ChemMatCARS insertion-device beamline at sector 15. It will be used primarily for valence-specific static and time-resolved chemical-crystallography experiments as well as anomalous-scattering experiments planned for surface diffraction and small-angle/wide-angle x-ray scattering. Two channel-cut crystals placed in a dispersive (-n, +n, +n, -n) geometry provide a fixed-offset beam with an energy resolution Delta E/E similar to 10(-5). Several sets of channel-cut-crystal pairs, designed to cover an energy range from 6 to 35 keV with a matching angular acceptance to the source, are used in conjunction with the beamline high-heat-load double-crystal monochromator.