Monochromators for high-energy synchrotron radiation

Several monochromators, which are based on the use of cylindrically bent pe rfect Si crystals, have been constructed at the High Energy X-ray Scatterin g beamlines of the ESRF. The monochromators provide different focusing cond itions, and the energy bandpasses are optimized for the needs of different experiments. Formulas are given for calculation of the focal distances, ref lectivity curves, and energy distributions. The lay-out of the beamlines fo llows the Troika concept, where the radiation fan is either split in 3 beam s, or the central beam is utilized successively by semi-transparent monochr omators to serve three experimental stations simultaneously. The radiation sources are a 7-period permanent magnet asymmetric wiggler and a supercondu cting wavelength shifter. The critical energies are 45 keV and 96 keV, resp ectively. The lowest operation energy is 30 keV, and transmission type mono chromators have been used up to 1 MeV photon energies. Typical X-ray flux a t the sample is 10(12) ph/s at energies below 150 keV. The monochromator cr ystals are partly immersed in In-Ga eutectic, which provides thermal contac t between the crystal and the water-cooled support structure. Bending mecha nisms include flexible springs, so that the actuator motions are several or ders of magnitude larger than the crystal motions. This eliminates the effe cts of the thermal drifts of the support structures.