Channel-cut monochromator withstanding incident powers above 400 W on undulator beamlines

A liquid-nitrogen-cooled silicon channel-cut monochromator was developed and experimentally evaluated under high-thermal-load conditions. Under the maximum load of 417 W, the first reflecting surface exhibited a concave deformation, resulting in only an 11% reduction in vertical beam size at 16 m downstream. The deformation radius was estimated at 510 m. Despite the deformation, no significant changes were observed in the angular profile or intensity of the monochromatic beam. Interference fringes caused by edge diffraction at an upstream slit confirmed excellent preservation of spatial coherence. For the stability test of the monochromator, intensity fluctuation of the monochromatic beam was monitored and linearly fitted with upstream beam-position monitor signals, which were synchronously acquired. A high correlation (R² = 0.95) confirmed that the inherent stability of the channel-cut design remained under cryogenic cooling. Additionally, a double channel-cut monochromator configuration for fixed-exit beam operation was tested and produced the expected output beam intensity. These results confirm the feasibility of using channel-cut monochromators as high-stability high-heat-load-tolerant optical elements for next-generation synchrotron beamlines.