Improvement of the Performance of a Cryo-Cooled Monochromator at SSRF. Part I: Double-crystal Parallelism

To meet the requirements on the stability of the exit beam during the energy scanning in the multi-wavelength anomalous scattering experiments at Shanghai Synchrotron Radiation Facility (SSRF), strict specifications are placed on the double-crystal parallelism (@ pitch direction) of the double crystal monochromator (DCM) , which should be better than 0.25′′∕∘. In this case, the specifications of the existing cryo-cooled monochromator does not meet the requirements well in the energy range 5∼6.7 keV, which affects the stability of the flux of exit beam. To solve the problem, the 2nd crystal is optimized by designing an indirect cooling method, improving the structure of flexure hinge of the fine-tuning angular mechanism and meanwhile reducing weight for related structural parts. All these methods together have effectively improved the double-crystal parallelism of the DCM. The parallelism in pitch direction is 6.3”/30°, which is about 65% better than that before the improvement (18.1”/30°). All these works have significantly consolidated the foundation of the stability improvement of the DCM exit beam.