Diamond double-crystal monochromator at SPring-8

Beam quality of diamond double-crystal monochromator was characterized at undulator beamlines of SPring-8. The <001<-growth (111) IIa diamond crystals were used for high-heat-load double-crystal monochromator. Main issue of IIa diamond monochromator was intensity non-uniformity of reflected beam that was enhanced at the experimental station more than 10 m apart from monochromator. The simple Fresnel diffraction models from segments of the crystal are introduced to explain the origin of non-uniformity. Lattice inclination across growth sector boundary with 0.5 μrad or more, or lattice step due to stacking faults may cause phase shift between segments. The non-uniformity increases up to ~50% using the simple models. We also characterized recently-available <111<-growth crystals at 1-km beamline of SPring-8. The quality is similar to that of previous <001<-growth crystals, regarding rocking curve width for whole region irradiation.