Monochromator development at 4W1B beamline of BSRF

The 4W1B is a X-ray monochromator beamline for XAFS at BSRF. During the upgrading phase, we have redesigned the monochromator to improve the performance of the beamline. It is a goniometer based, fixed exit double crystal monochromator. A mechanical linkage is employed to adjust the distance between the surfaces of the two crystals as the Bragg angle is changed to keep the outgoing beam direction constant. The whole mechanism is driven by only one stepping motor. The testing result shows that over the scanning range of 5–30°, the shift of outgoing beam position is less then 70 μm in the vertical direction. The basic principle, the mechanical realization, and the error analysis are discussed in detail. The performance and the testing results are also presented in this paper.