Building the BEaTriX facility for the ATHENA mirror modules X-ray testing

BEaTriX (Beam Expander Testing X-ray) is the X-ray facility under construction at the INAF-Osservatorio Astronomico Brera (Merate, Italy) to prove that it is possible to perform the X-ray acceptance tests (PSF and Aeff) of the ATHENA mirror modules at the required rate and with the required accuracy. The unique optical setup makes use of a micro-focus X-ray source with anode in Titanium, a paraboloidal mirror with small radius of curvature, and a set of crystals to monochromate and expand the beam to fully illuminate the entrance pupil of the ATHENA MMs. The quality of the optical components, and their precise alignment, guarantees the production of a parallel beam at 4.51 keV, to be extended in a second phase to 1.49 keV able to perform the acceptance requirements for the ATHENA MMs. The facility is completed and the alignment of the various components is now ongoing and expected to be completed in fall this year, with the X-ray beam fully qualified. Then the commissioning will start with the tests on the ATHENA MMs. In this paper, we present the current status.