By Stefano Basso

BEaTriX (Beam Expander Testing X-ray) is a unique facility now operative at the INAF-Osservatorio Astronomico Brera (Merate, Italy). In a small lab, we have created an X-ray beam that approximates the one created by an astronomical source, to perform the X-ray acceptance tests of the Athena Silicon Pore Optics Mirror Modules (MM). The divergent beam produced by a microfocus X-ray source is collimated, monochromatized, and expanded by means of a parabolic mirror and a set of silicon crystals. The beam, at the energy of 4.51 keV, was demonstrated to be collimated to about 2-3 arcsec, with a flux of 60 photons/s/cm2, and sufficiently large (170 mm × 60 mm) to cover the entrance pupil of the MMs. The performance of the beamline was tested with an early prototype of inner radius SPO MM: the results confirmed that both the angular resolution and the Effective Area can be reliably measured at the MM production rate.

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