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

Abstract

Future large X-ray observatories like ATHENA will be equipped with very large optics, obtained by assembling modular optical elements, named X-ray Optical Units (XOU) based on the technology of either Silicon Pore Optics or Slumped Glass Optics. In both cases, the final quality of the modular optic (a 5 arcsec HEW requirement for ATHENA) is determined by the accuracy alignment of the XOUs within the assembly, but also by the angular resolution of the individual XOU. This is affected by the mirror shape accuracy, its surface roughness, and the mutual alignment of the mirrors within the XOU itself. Because of the large number of XOUs to be produced, quality tests need to be routinely done to select the most performing stacked blocks, to be integrated into the final optic. In addition to the usual metrology based on profile and roughness measurements, a direct measurement with a broad, parallel, collimated and uniform Xray beam would be the most reliable test, without the need of a focal spot reconstruction as usually done in synchrotron light. To this end, we designed the BEaTriX (Beam Expander Testing X-ray facility) to be realized at INAF-OAB, devoted to the functional tests of the XOUs. A grazing incidence parabolic mirror and an asymmetrically cut crystal will produce a parallel X-ray beam broad enough to illuminate the entire aperture of the focusing elements. An X-ray camera at the focal distance from the mirrors will directly record the image. The selection of different crystals will enable to test the XOUs 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 facility implementation. We also show a preliminary performance simulation of the optical system.

Design and advancement status of the Beam Expander Testing X-ray facility (BEaTriX)

“…A negligible fraction of X-rays undergoes total reflection on the beam expander, but 5% of the traced rays is absorbed in asymmetric diffraction. The remaining 5% finally form the expanded and collimated beam: the performance is higher than in the previous design [9] owing to the higher peak reflectivity of the crystals. Fig.…”

“…Finally, all the system needs to be evacuated to avoid X-ray absorption in air. The total range of X-rays from source to detector at the end of the 12 m long tube is 17 m. Fortunately, the reduced dimensions of the facility require only a moderate vacuum level: a previous simulation [9] showed that even a 0.1 mbar residual pressure would suffice to preserve 75% of the beam intensity at 1.49 keV and more than 98% at 4.51 keV. In this design, four dry pumps can be used to reach a vacuum level of 10 -2 mbar and independently evacuate four sections of the facility: of these, only the XOU vacuum tank will periodically be vented/evacuated at the operation time, with a considerable time saving when the XOU under test is to be changed.…”

Open-source simulator for ATHENA X-ray telescope optics

“…• Calibration: The calibration of the ATHENA's MA will be obtained in steps. The calibration of single MMs at 2 energies (1.5 and 4.5 keV) with a collimated beam (with a divergence smaller than the MMs one) are planned to be performed at a facility like the BEATRIX [12] in construction at INAF-OAB. The calibration of the full MA is planned at the VERT-X calibration facility [13] and at the upgraded PANTER facility [14].…”

BEaTriX, expanded x-ray beam facility for testing modular elements of telescope optics: an update

“…The feasibility of BEaTriX has been already demonstrated. 7 The performance of the collimated beam in terms of collimation, intensity, and uniformity, crucially depends on the optical quality of the components. For example, the X-ray source has to be very small (less than 30 µm required, with a 10 µm goal) in order to produce a accurately spherical wavefront and, after the collimation, maintain the residual divergence below 1 arcsec in the vertical plane.…”