Optics - Hard branch

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experiments hutch    safety shutter  focusing mirror  monochromator  splitter vessel
Lay-out of the hard-line optics



Schematics of the hard-edge branch


The two techniques on the hard-edge branch (SAXS/WAXS and ID) use focused, monochromatic radiation with a moderate energy resolution.
The first optical element is a double-crystal monochromator with sagittal focusing on the second crystal it is followed by a meridionally focusing mirror with an angle of incidence of 2.8 mrad. Both focusing units are adjustable, so that the X-ray beam can be focused from the SAXS/WAXS sample position (48.6 m from the source) to the center of the ID diffractometer (57.6 m from the source). The minimum spot size at focusing position is 300 x 300 µm.

Two different mirror coatings are used to provide the discrimination against higher harmonics without changing the mirror angles. Using the Pt mirror coating, the beamline operates from 12-30 keV, while with the Si coating the operational energy is 5-12 keV. Together with the possibility of detuning the monochromator, this should yield a harmonic content of less than 10 -4 using Si(111) or Si(311), except for very low energies. The appropriate mirror coating is positioned in the beam by a sideways translation.

The characteristics of the optics of the H station are summarized bellow.

Station H
Optical elements Si (111) double-crystal
Si mirror
Distance from source 32.7 m 35.2 m
Type sagittal focusing meridional focusing
Pt/Si coating
Energy range 5-30 keV  
Beamsize at sample ‹0.4 mm (H) x 0.35 mm (V)
Flux 2 x 1011 photons/sec  
Energy resolution dE/E 5 x 10-4  
Horizontal acceptance ‹ 2 mrad