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![[Figure 5]](kv5005fig5mag.jpg)
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Figure 5
Schematic drawing (not to scale) of a windowless beamline designed specifically for soft X-ray diffraction. The design is close to that which existed at beamline A1 of HASYLAB (DESY, Hamburg, Germany) until 1996. There are no windows between the source and the detector. The toroidal mirror M1 at about 20 m distance from the source is the first focusing element in the beam (the second is a focusing capillary between the monochromator crystal and the sample, not shown). Using a grazing angle of 6° the gold-coated surface reflects X-rays with λ > 1.0 Å. The second plane quartz mirror M2 contains both a gold and a quartz band. The quartz surface will reflect X-rays with λ > 2.4 Å onto the monochromator Mo. This pre-monochromatization is chosen in such a way that the monochromator crystal will reflect the fundamental wavelength only. The chamber R may contain XY slits etc. Its function is also that of a buffer, if the vacuum is lost accidentally in the monochromator box or the camera. The pressure limit in R is 10−5 mbar. In the monochromator box Mo, where the pressure should not exceed 10−4 mbar, various monochromator crystals (Si111, Ge111, InSb111 and Si311) are held resident. The latter crystal is used when reference measurements at shorter wavelengths are required. As there is only one monochromator crystal, the diffractometer has to follow the direction of the beam, which changes with the wavelength. In order to cover the range 55° < 2θ < 125° the cylindrical monochromator box has to have a movable exit slit. With such a system, wavelengths between 1.25 Å and 6.9 Å, free of higher harmonics, are possible. The camera C has to be kept at a pressure below 10−2 mbar. It contains three area detectors of 300 mm × 300 mm surface at a distance of 190 mm to the sample S covering scattering angles from −109° to +145°, with two gaps of about 15°. The out-of-plane angular range is ±38°. Thus, such a detector system can cover 38% of the unit sphere. The large composite detector windows are described by Scholl et al. (1995  ). An improvement over this could be a detector system comprised of cylindrically bent imaging plates which can cover up to about two-thirds of the unit sphere. |
![[Figure 5]](kv5005fig5.jpg)
 | JOURNAL OF SYNCHROTRON RADIATION |
ISSN: 1600-5775
