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Cryogenically cooled bent double-Laue monochromator for high-energy undulator X-rays (50–200 keV)

2002; Wiley; Volume: 9; Issue: 5 Linguagem: Inglês

10.1107/s0909049502009986

1600-5775

S. D. Shastri, Kamel Fezzaa, A. Mashayekhi, W.-K. Lee, P. B. Fernandez, P.L. Lee,

Crystallography and Radiation Phenomena

A liquid-nitrogen-cooled monochromator for high-energy X-rays consisting of two bent Si(111) Laue crystals adjusted to sequential Rowland conditions has been in operation for over two years at the SRI-CAT sector 1 undulator beamline of the Advanced Photon Source (APS). It delivers over ten times more flux than a flat-crystal monochromator does at high energies, without any increase in energy width (DeltaE/E approximately 10(-3)). Cryogenic cooling permits optimal flux, avoiding a sacrifice from the often employed alternative technique of filtration - a technique less effective at sources like the 7 GeV APS, where considerable heat loads can be deposited by high-energy photons, especially at closed undulator gaps. The fixed-offset geometry provides a fully tunable in-line monochromatic beam. In addition to presenting the optics performance, unique crystal design and stable bending mechanism for a cryogenically cooled crystal under high heat load, the bending radii adjustment procedures are described.