Test results of the BEaTriX paraboloidal mirror at PANTER

Abstract

Scope of this technical note is to report on the X-ray tests of the BEaTriX collimating mirror that have been carried out at the PANTER X-ray facility, before (May 4th-17th 2021) and after the coating with a Cr+Pt reflective layer at DTU, in the framework of the joint activities on optics for the ATHENA X-ray telescope. The tests planned before the deposition of the coating were aimed at confirming the mirror’s imaging quality expectations from the metrology tests, performed along with the polishing and finishing processes. Post-coating tests are oriented to the final qualification of the mirror and to ascertain that the mirror has maintained the focusing properties. Prior to coating, only tests at 1.49 keV are possible on the mirror. At this energy, PANTER can test the mirror in either diverging beam setup or making the beam parallel by means of a dedicated zone plate, canceling in this way the focus aberrations due to the finite distance of the source. After coating, in addition to the same tests at 1.49 keV, a test in diverging beam will be performed at 4.51 keV. The ZP cannot be used to collimate the 4.51 keV beam, but a comparison of the best focus at 1.49 keV and 4.51 keV will allow us to estimate the X-ray scattering that can be expected in the operation of the BEaTriX parabolic mirror. Simulations carried out from metrology on the uncoated mirror currently demonstrate a very low impact of the roughness on the mirror focusing performance.