Design and performance of the flexural hinge-based mirror bender at the SLS protein crystallography beamline X06SA

摘要

The mirror bender installed at the SLS protein crystallography beamline is designed to be capable of adjusting the vertical phase space of the undulator to the acceptance of protein crystals, i.e. to produce micro-beams as well as essentially parallel beams. The two-moment bender is based on the flexural hinge design pioneered at the ESRF but adapted to high-vacuum by making use of in-vacuum motors and high resolution worm-gears. Special care was taken in the design and fabrication of the clamps and the application of the clamping torque. The Rh-coated fused silica substrate (Zeiss) has a free length of 400 mm and a thickness of 30 mm. Metrology tests at ESRF indicate the high quality of the mirror and the bender. Over the useful length of 350 mm the meridional slope error was found to be 0.17-0.3 μrad (rms) prior to, and less than 0.5 μrad after clamping to the bender. In practice this allows the full central cone of an in-vacuum undulator to be focussed to 7μm at an image distance of 7.1 m and to 2.1 μm at 1.75 m, corresponding to effective slope errors of less than 0.25 μrad. The bending is very reproducible and is well described by an interaction matrix. Finally, the long range tails were measured in the context of the generation of fs-pulses by means of bunch slicing. Their level cannot be attributed to the surface roughness of 2.9 A (rms) but rather to scattering from other beamline components such as Be-windows.