Improvement of the performance of a cryo-cooled monochromator at SSRF. Part II: Angular stability of the exit beam

The angular stability of the crystals used in the monochromator is crucial for the beam position, the flux and the resolution for the synchrotron based hard X-ray beamline. In this paper, we report a performance optimization to a double-crystal monochromator (DCM) which has served for nearly 10 years at Shanghai Synchrotron Radiation Facility (SSRF). By upgrading the design of the clamping and the cooling to the 2nd crystal, the layout of the LN2 circuit, the structure of the 2nd crystal assembly and the thermal insulation as well as the temperature stabilization system, the resulted angular stability of the crystals in working condition (LN2 circulation) tested by the angular stability of the exit beam has been greatly improved from approximately 500 nrad RMS/2 h up to better than 200 nrad RMS/2 h in vertical direction (pitch rotation of the crystals) and better than 300 nrad RMS/2 h in horizontal direction (roll rotation of the crystals) respectively, which meets the requirement by 300 nrad RMS/2 h in user experiments of the BSL-2 macromolecular crystallography beamline (P2, BL10U2).

Automated summary

This paper reports the performance optimization of a double-crystal monochromator that has been in use for nearly 10 years at Shanghai Synchrotron Radiation Facility. By upgrading the design and structure, the angular stability of the crystals in working condition has been greatly improved, meeting the requirements of user experiments.