Soft x-ray beamline and a double-crystal monochromator of UVSOR (abstract)

Abstract

The UVSOR is a 750-MeV dedicated electron storage ring in the Institute for Molecular Science at Okazaki, Japan. The ring was constructed mainly for the use of VUV photons. However, the intensity of the soft x-ray region around 10 Å region is not negligible. The ring is also equipped with a 4 T superconducting three-pole horizontal wiggler. We have constructed a beamline equipped with a monochromator in order to utilize the soft and normal x-ray photons from the ring. In order to separate the vacuum of the ring from that of the monochromator, a light tight Be foil of 10 μm in thickness is placed in the upstream of the monochromator in the beamline. The monochromator constructed is a high vacuum compatible with double crystal which provides constant offset of the output beam. The constant offset during the rotation of crystal plane was realized by a simple linkage of linear motions of the two crystals with two linear guides placed on both input and output beam levels. The mechanical movement was found to be very smooth through a full rotation of 60° (between 15° and 75° of Bragg angle). Monochromator crystals such as beryl (101̄0), quartz (101̄0), InSb(111), Ge(111), and Ge(220) whose 2d value is 15.965, 8.512, 7.481, 6.532, and 4.00 Å, respectively, are being used with a reasonable intensity and signal-to-noise ratio of output signal. The range of photon energy which can be used with this line is from 850 eV to 4 keV in the bending magnet section, and from 850 eV to 6 keV with a wiggler. Because of the comparatively low energy of 750 MeV of the electron, the heat load is not a severe problem, and no radiation damage was observed for the first beryl crystal during an exposure to the beam for several months. We have measured the Na K-edge XANES spectrum of a thin film of NaCl which was evaporated in situ on a collodion film in the sample chamber at room temperature by using beryl as monochromator crystal. From the doublet separation of the spectrum, we can estimate the resolution better than 1 eV, which is sufficient for this energy range. With Ge(220) as monochromator crystal, K edge of potassium has been measured with a reasonable signal-to-noise ratio. Therefore, the practical limit of the energy attainable in this beamline of bending magnet section is about 4 keV.