A UHV-compatible Fixed-Exit Two/four Crystal Monochromator

Simplicity, symmetric design, variable energy range, and support for both sides of the crystals are features of a new fixed-exit crystal monochromator that has been designed, built, and tested. It is less complex; therefore it is less expensive to build, easier to understand, and easier to maintain. The design is a variation of the Cowan boomerang design. Most of the high-precision surfaces are bars ground in parallel. Crystals are supported on both ends by carriages with high-precision ball-bearing wheels. These bearings roll along the bars to carry the crystals and to actuate the rotation of the crystals. By supporting crystals on both sides, water-cooling and dynamic crystal bender systems can be incorporated without adversely affecting the crystal stability. The system is highly symmetric, with no preferred orientation for entrance and exit beams. Angular ranges, and therefore energy ranges, for the system are easily varied by changing the length of the boomerang arms. The system is compact, with an angular range of 80°–3.5° for theta fitting within a length of 840 mm. This angular range corresponds to an energy range of 2.0–30 keV for Si(111).