The design and performance of a soft X-ray double crystal monochromator beamline at Aladdin

Abstract

We report the design, construction, and performance of a soft X-ray beamline with accessible photon energy 0.8–4.0 keV at the Synchrotron Radiation Center, University of Wisconsin-Madison. The beamline features an ultrahigh vacuum (UHV) compatible high precision double crystal monochromator (DCM) which was designed and built by the Physical Science Laboratory (PSL), University of Wisconsin-Madison. It employs a Boomerang mechanism both to keep the crystals parallel and to maintain a fixed exit beam height during spectral scans (Bragg angle 12°–72°). The monochromator X-rays are focused by a bent cylindrical mirror (Ni-coated fused silica, located 7.5 m from the source) into the experimental chamber (located 5.5 m from the mirror) down to a spot less than 1 mm (h)×3 mm (v). During the initial runs, the DCM used a pair of InSb(111) crystals and covered photon energy 1.75–3.7 keV. At the silicon K-edge (1840 eV), the beamline delivered about 4×10 10 photons/s (while stored electron beam was at 100 mA at 1 GeV), among the most intense and stable sources (over 6 months continuous operation) currently available at this energy. The energy resolution is about or better than 0.9 eV at the Si K-edge. High beam stability makes it possible to obtain routinely, for the first time, good EXAFS spectra as far as 1000 eV above the silicon K-edge. A detailed analysis of the effects due to misalignment of all DCM components is given in the appendix.