The Two-crystals monochromator is the second optical element in the Optics Hutch and it is positioned at a distance of 27.2 m from the source. It is a double-crystal fixed-exit Bragg monochromator equipped with two Si(111) crystals and working in the energy range of 6-60 keV.

The diffracted x-ray beam is shifted by +20 mm from the incident beam. Both crystals are mounted on the same disk whose horizontal axis of rotation is situated at +17.1 mm from the incident beam height. When the Bragg angle is changed the beam wanders across the crystals and the fixed-exit is ensured by the translation of the second crystal. Over the whole angular range the fixed-exit position is within Dz =85 x 10^-6 m vertically and Dy= 55 x 10^-6 m horizontally. The first silicon crystal is 250mm x 60mm x 40mm and is water-cooled. The second flat crystal of 150mm x 60mm x 10 mm can be replaced by a sagittally focusing crystal working in the energy range of 6-30 keV.

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