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X-ray pencil beam facility for IXO optics characterization at BESSY II


The International X-ray Observatory (IXO) , a joint ESA/NASA/JAXA mission candidate, will be the largest X-ray telescope ever flown with an effective area of more than 2.5 m² at 1.25 keV, a focal length of 20 m and an angular resolution better than 5”. Due to the required grazing incidence angle, the mirror area is about 1300 m². A possible approach to realize this large area in a stiff and lightweight configuration is to use commercially available highly-polished silicon wafers with ribs on the back side and to stack them to stiff blocks to form pores with a cross section of about 1 mm² in which the radiation is reflected at the surface of the underlying wafer. The quality of these ‘buried’ surfaces in terms of tangent error and roughness can not be investigated as usual from the top, but has to be determined in the geometry of the intended application using X-ray reflection at grazing incidence angles around 1°. To study the reflecting surface in individual pores, an X-ray pencil beam is required.

Within a research cooperation with ESA, the X-ray pencil beam facility (XPBF) in the synchrotron radiation laboratory of the PTB at BESSY II was recently upgraded. Now, a monochromatic pencil beam with a typical diameter of 50 µm and a divergence below 1” is available for the characterization of X-ray optics for IXO at three different photon energies: 1 keV, 2.8 keV and 7.6 keV. The optics to be investigated can be translated and rotated by an in-vacuum hexapod with a reproducibility of 2 µm and below 1“, respectively. The direct and the reflected beam can be registered with a spatially resolving CCD-based detector at 5 m or at 20 m distance from the optics. For the latter distance, corresponding to the current IXO focal length, a vertical motion of the CCD detector by more than 2 m has been implemented.



M. Krumrey, 7.11, E-mail: Michael.Krumrey(at)ptb.de