PERFORMANCE OF VERY THIN SILICON SINGLE-CRYSTAL FOILS UNDER HIGH X-RAY POWER-DENSITY

In this paper x-ray diffraction tests of very thin silicon single crystals exposed to a wiggler beam that can generate a power density up to 200 W/mm2 are reported on. This beam was provided by the beamline X25 at NSLS, where 75 W total power are focused into a spot of 0.8 mm (h) x 0.45 mm(v). An 11-mu-m "thin" Si foil glued at its periphery onto an aluminium ring at 30-degrees-C was applied to a box that could be pressurized with He. The whole assembly was then mounted on an optically polished and watercooled Be support. By increasing the temperature of the water and thus of the Al ring above 30-degrees-C it was possible to apply a stretching force to the Si membrane in order to keep it flat. Rocking curves 3.3 arcsec wide were obtained with a strongly attenuated beam. The rocking curve width increased to 3.9 arcsec when the power density was increased to 15 W/mm2. The crystal was destroyed at 125 W/mm2 because of the limited thermal conductivity across the small He gap.