An expanded X-ray beam facility (BEaTriX) to test the modular elements of the ATHENA optics

摘要

Future large X-ray observatories like ATHENA will be equipped with very largeoptics, obtained by assembling modular optical elements, named X-ray OpticalUnits (XOU) based on the technology of either Silicon Pore Optics or SlumpedGlass Optics. In both cases, the final quality of the modular optic (a 5 arcsecHEW requirement for ATHENA) is determined by the accuracy alignment of the XOUswithin the assembly, but also by the angular resolution of the individual XOU.This is affected by the mirror shape accuracy, its surface roughness, and themutual alignment of the mirrors within the XOU itself. Because of the largenumber of XOUs to be produced, quality tests need to be routinely done toselect the most performing stacked blocks, to be integrated into the finaloptic. In addition to the usual metrology based on profile and roughnessmeasurements, a direct measurement with a broad, parallel, collimated anduniform X- ray beam would be the most reliable test, without the need of afocal spot reconstruction as usually done in synchrotron light. To this end, wedesigned the BEaTriX (Beam Expander Testing X-ray facility) to be realized atINAF-OAB, devoted to the functional tests of the XOUs. A grazing incidenceparabolic mirror and an asymmetrically cut crystal will produce a parallelX-ray beam broad enough to illuminate the entire aperture of the focusingelements. An X-ray camera at the focal distance from the mirrors will directlyrecord the image. The selection of different crystals will enable to test theXOUs in the 1 - 5 keV range, included in the X-ray energy band of ATHENA(0.2-12 keV). In this paper we discuss a possible BEaTriX facilityimplementation. We also show a preliminary performance simulation of theoptical system.