Variable exit beam height double-crystal monochromator for high-power insertion devices

A variable exit beam height double-crystal monochromator for high-power insertion devices was built and tested at the Photon Factory. The second crystal is mounted on a high-precision XY translational stage and its position in the parallel and perpendicular direction to the reflecting plane (x,y) is computer controlled. In this design, the exit beam height (y) and geometrically required positioning of the second crystal (x) are separately controlled. Either a fixed or variable exit beam height is obtained over the Bragg angle (θ) range from 6 degree to 25 degree. A systematic noise caused by degraded parallelity between the two crystals is observed in extended x-ray absorption fine structure spectra when x and y are simultaneously controlled. This noise is significantly reduced by a versatile control of (x,y): for a typical scan (∼1 keV) only y is allowed to vary while both coordinates are controlled when a monochromator is tuned over a wider energy range. copyright 1996 American Institute of Physics