Optic hutch I: The monochromator

The instrumentation common with the diffraction beamline consists of:

  • C-Filter and Beryllium window assembly to reduce the power load on the first optical elements by a factor of 2 and to separate the beamline vacuum from the storage ring.
  • Beam defining slit chamber which allows to define the SAXS beam on three sides before the monochromator in order to reduce the straylight in the downstream beamline sections.

The SAXS beamline optics consists of:

  • A double-crystal monochromator consisting of four individual chambers, in which three interchangeable asymmetric Si(111) crystal pairs are used to select one of three discrete fixed energies:  5.4, 8 and 16 keV. Each of the crystal pairs is optimised for the corresponding energy to accomplish a grazing angle of 2°. The energy resolution deltaE/E of the monochromator is in the range of 0.7 - 2.5 10-3.
  • A baffle chamber after the monochromator is used as an adjustable straylight fenditure.
  • A segmented toroidal mirror focuses the light in horizontal and vertical direction with a 1/2.5 magnification onto the SAXS-detector.
  • An aperture slit reduces the straylight after the monochromator and the toroidal mirror.
  • A guard slit defines the illuminated region around the focal spot. The spot size on the detector is 1.6 mm horizontally and 0.6 mm vertically. The calculated flux at the sample is in the order of 1013 ph/s at 400 mA. For a maximum sample size of 5.4 x 1.8 mm2 correspondingly a flux density of 1012 ph/s/mm2 has been calculated.
Last Updated on Wednesday, 28 September 2011 12:30