Development and application of x-ray topography for the Diamond-II upgrade

Abstract

Diamond Light Source has established an extensive x-ray topography measurement program on its test beamline B16 to inspect crystals for Diamond’s own beamlines as well as for other facilities as an industrial service. This beamline is now being used extensively to test crystal optics for the low-emittance, high-brightness upgraded source Diamond-II. In addition, the current bending-magnet source at B16 will be replaced with an undulator, and future x-ray topography measurements will have to adapt to the resulting smaller beam size. Case studies of crystal optics developed as part of the Diamond-II upgrade will be shown. Of particular interest are crystal optics for Diamond-II wiggler beamlines, where wide beams and an expected large increase in emitted power make the design of the optics’ cooling system especially challenging. Surface defects and long-range lattice strains are measured with high resolution both at room temperature and under cryocooling. Because limited detector field of view generally prevents large test crystals from being imaged in one shot, a stitching algorithm has been developed. It has so far been applied to arrays of up to 35 images and will be further refined for use with the undulator beam in Diamond-II. Tilt stages of microdegree angular resolution have also been tested and applied to the increasingly common case of high-order Bragg reflections diffracting x-rays of energy > 20keV, for which the Darwin width is on the order of 1μrad. In this way, lattice strains of a few tenths of a μrad have been measured.