Berlin-Adlershof, Germany--The International X-Ray Observatory satellite's grazing-incidence mirror will be tested by a monochromatic X-ray pencil beam with a 50 micron diameter and a divergence of less than one arc second. The new measuring device has been installed at Physikalisch-Technische Bundesanstalt (PTB) synchrotron radiation laboratory at BESSY II.
To launch in 2021, but testing already begun
The International X-Ray Observatory (IXO), a cooperative effort between NASA, ESA, and Japan's Aerospace Exploration Agency (JAXA), will be launched into space in 2021 to study black holes. The surface of the X-ray mirror will be 1300 m2 in size and will consist of commercially available silicon wafers with pores of a few millimeters in size underneath. The quality of these "hidden" surfaces will be tested at the PTB with the pencil beam.
IXO can capture the X-ray radiation of very distant black holes, because this kind of radiation penetrates cosmic dust in an unhindered way. The mirror in the telescope must be very large, but at the same time light enough. The IXO optics will have a collection surface of approx. 3 m2, a focal length of 20 m, and an angular resolution of less than 5 arc seconds. Due to the required grazing-incident angle to adequately reflect X-rays, the whole surface of the mirror must be 1300 m2 in area. For simultaneous lightness and stability, the underneath of the highly polished silicon wafers will have ribs to allow the wafers to be stacked in rigid blocks.
Through this, pores with a cross-section of approximately 1 mm2 will be formed in which the radiation is reflected at the surface of the respective lower wafer. With respect to tangent errors and roughness, the quality of these "hidden" surfaces cannot be investigated as usual from above, but must be determined in the intended application geometry with X-ray reflection at grazing incident angles of about 1 degree.
Hexapod control in vacuum
The X-ray pencil-beam facility (XPBF) will characterize the X-ray lens systems for IXO at three different photon energies: 1, 2.8, and 7.6 keV. The lens systems can be adjusted or turned with a hexapod in vacuum with reproducibilities of 2 µm or below one arc second, respectively. The direct beam and the reflected beam are registered with a spatial-resolving detector based on a CCD at a distance of 5 m or 20 m from the lens system. For the last-mentioned distance, which corresponds to the intended focal length of IXO, a vertical movement of the CCD detector by more than 2 m has been implemented. First test measurements at this distance were performed in May 2010; complete commissioning of the extended XPBF is planned for the beginning of November 2010.
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