Upgrade of a laboratory X-ray diffractometer to extend its operating range towards soft energies

The optical properties of X-ray mirror samples are commonly measured using diffractometers based on laboratory sources; like the Bede D1 diffractometer operating at INAF-OAB. This instrument can generate a collimated X-ray beam up to 60 keV, even though the most interesting energy region for x-ray astronomy applications is usually below 10 keV. In the softest part of this range (below 6 keV), high X-ray absorption in air hinders a full and precise characterization of optical components. In this work, we present an upgrade of the Bede D1 diffractometer that extends the operative range of the instrument below 6 keV; this is done by maximizing the flux at lowest energies and by reducing absorption by means of a helium-rich atmosphere. The upgraded instrument will be used for the tests of X-ray mirrors with innovative soft X-ray coatings, with potential application to the next generation X-ray telescopes (such as ATHENA and eXTP).