DEVELOPMENT OF A FOCUSING IN-LINE MONOCHROMATOR WITH FOUR LAUE CRYSTALS AT THE X17B3 BEAMLINE OF NSLS, BNL

The ability of asymmetric Laue crystal to focus high-energy X-ray sagittally has recently demonstrated and characterized [1]. In addition to their focusing properties, sagittally bent Laue crystals typically have integrated reflectivity an order of magnitude larger than traditional flat crystals. This class of monochromator offers unique opportunity for geosciences since lot of geoscientists require focused monochromatic high-energy x-ray beam for their high-pressure research. We already developed the angle dispersive X-ray diffraction technique with asymmetric two Laue crystals at X17C beam line previously [2], which has used routinely for high pressure experiments with diamond anvils cell for years. A prototype sagittal focusing monochromator using four asymmetric Laue crystals, providing 30 keV X-rays, has been designed, constructed and tested at the X17B3 beam line at the NSLS. Compared with our 2-crystal monochromator, the new monochromator with 4 Laue crystals was designed to deliver the monochromatic beam in the same path as the incident white beam, thus allowing in switch experiments between angle dispersive X-ray diffraction and energy dispersive X-ray diffraction easily without relocating the samples. The test results of the new 4-Laue monochromator show that a 5 mm x-ray beam can focused to about 0.5 mm in the horizontal dimension's The recently testing show that the sagittally focused beam provided by this monochromator can be further refocused to about 50um by using a 200mm Si-KB mirror with 1.6mrad incident angle. Now we are working on optimizing the flux of the defocusing x-ray and designing an energy-tunable version. We hope that this powerful tool will serve the earth science, geophysics and related field scientists soon.

[1] Z. Zhong, et. al. Acta. Cryst. A 59, 1-6, 2003 [2] J. Hu et al., EOS, Tran. Am. Geophys. Union, 2003