Cooled mirror for a double undulator beamline

The design of a contact-cooled horizontally reflecting high-heat-load mirror for use as the first optical element on an Advanced Photon Source (APS) beamline is described. The radiation source consists of a set of two collinear undulators producing an x-ray beam with up to 340 W/mm2 peak normal heat flux at the mirror located 30 m from the source. The beam incident angle is 2.6 mrad (0.15 deg). The mirror is 500 mm long and 75 mm wide. Specifications for this mirror are an rms tangential slope error = 2 μrad and an rms roughness = 2 angstrom. The mirror substrate is single crystal silicon. To selectively reflect photons with cut-off energies in the 7 to 33 keV range, the central part of the mirror may be coated with strips of Rh, Pt, and Be. Thermal and structural analyses of the mirror (steady state and transient) are reported. Two contact-cooling options considered are back and side cooling. The slope error of side cooling is smaller than that for back cooling. The influence of the mirror thickness and the cooling zone are analyzed. Other options to reduce the slope error are discussed