In this paper, we report on the design and x-ray diffraction properties of cryocooled silicon single crystals exposed to the following wiggler beams: power density: 150 W/mm2, total power: 75 W and power density: 0.5 W/mm2, total power: 100 W. First, thermomechanical and engineering aspects of low-temperature crystal cooling are discussed, leading to two basic cooling geometries: internal cooling and side cooling. Experimental tests of both these cooling schemes at NSLS on beam lines X25 and X17 are then described and discussed. Finally, engineering problems related to the integration of cryogenic cooling on ESRF beam lines are presented.

The lateral coherence length is of the order of 100 micron at the 'long' (145 m) ID19 beamline of the ESRF, which is mainly devoted to imaging. Most of the optical elements located along the X-ray path can thus act as ;phase objects', and lead to spurious contrast and/or to coherence degradation, which shows up as an enhanced effective angular size of the source. Both the spurious contrast and the coherence degradation are detrimental for the images (diffraction topographs, tomographs, phase-contrast images) produced at this beamline. The problems identified and the way they were solved during the commissioning of ID19 are reported. More particularly, the role of the protection foils located in the front end, the beryllium windows, the filters and the monochromator defects (scratches, dust, small vibrations) is discussed.

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Interest in solid scintillators down to liquid helium temperature and below has grown recently, fuelled by searches for exotic processes in particle physics. We describe a closed-cycle optical cryostat with a 2.8 K base temperature and a compact optical geometry for multiple photon counting. The large numerical aperture achieved, of the order of 0.79 from the optical center to each of the two windows and amounting to 40% of the total solid angle, allows a significant gain in the efficiency of photon collection. This and the relatively big sample size that can be used facilitate the study of scintillators under gamma irradiation. These features should be an asset for multiple photon counting techniques at low temperatures.

An original design for a cooled exchangeable polychromator for energy-dispersive XAFS (X-ray absorption ®ne structure) working either in the transmission con®guration (Laue case) or in the re¯ection con®guration (Bragg case) is presented. It enables the acquisition of X-ray absorption spectra between 5 and 25 keV with a spot size on the sample that can reach to less than 20 mm FWHM for some energies. Only 1 h is needed to exchange both benders in operative mode. Parallel transmission spectra with a bandpass between 5 and 10% can be obtained in the full energy range. The dispersive optics and mechanics of ID24 (ESRF, Grenoble, France) have been designed to obtain XAFS spectra in less than 1 s and, in some cases, in the millisecond range.