A beamline has been constructed at Stanford Synchrotron Radiation Laboratory (SSRL) whose radiation source is a multipole permanent magnet '\.\iggler installed in a straight section of the SPEAR 3-3.5 GeV electron storage ring. The wiggler is a hybrid design that utilizes Nd-Fe alloy magnet material combined with Vanadium Permendur poles. It is approximately 2 m long and has 15 full wiggler periods. Its field is regulated by varying its gap height. It has a peak operating field, limited by the electron beam vacuum chamber vertical aperture, of 1.4 T. The beamline consists ofvacuum, safety, and optical components capable oftransporting photons to one hard xray (3-30 keV) end station, with provisions for implementing up to two additional branch lines. The existing hard x~ray branch can be focused by a Pt-coated toroidal mirror with a cutoff energy of approximately 22 keV. The experimental end station is serviced by a Hower-Brown type double crystal monochromator. The wiggler and beamline construction was completed in the fall of 1987 and was operated for a brief period for characterization and experimental use. We present design details and results of the initial characterization studies.
An Enraf-Nonius CAD-4 diffractometer has been specially adapted and mounted on a computerautomated alignment carriage for use with the synchrotron radiation X-ray source at SSRL. A separatedfunction focusing monochromator system is used [Hastings, Kincaid & Eisenberger (1978). Nucl. Instrum. Methods, 152,[167][168][169][170][171] to provide radiation which is rapidly tuneable from 3-9 keV. Software for automatic alignment of the goniometer for wavelength calibration and for monitoring the decay of the stored beam have been developed. Integrated reflection intensities were 40 times higher than for the same reflections recorded using a fine-focus X-ray tube (Nifiltered Cu Ke, 40 keV, 30 mA), for SPEAR conditions of 3.7 GeV and 20 mA with colliding beams. For crystals of low mosaic spread, the reflection widths were around 0.015 °. For such narrow reflections, intcgratcd intensities can be measured to 2.7Y/o accuracy. For wider reflections, 2.1~ accuracy has been obtained. A comparison of data collected with synchrotron radiation and a sealed-tube source gave an R factor based on F of 1.8Yo. Thus, accurate structure factors are easily obtained from the synchrotron radiation data. The use of a highly mosaic monochromator crystal resulted in intensity gains at the expense of wider scan widths. The apparatus makes possible anomalous scattering experiments close to absorption edges, rapid data collection from weakly diffracting samples and possible increases in signal-to-noise ratios from samples of low mosaicity.
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