Optical simulations for design, alignment, and performance prediction of silicon pore optics for the ATHENA x-ray telescope

Abstract

The ATHENA X-ray observatory is a large-class ESA approved mission, with launch scheduled in 2028. The technology of silicon pore optics (SPO) was selected as baseline to assemble ATHENA's optic with hundreds of mirror modules, obtained by stacking wedged and ribbed silicon wafer plates onto silicon mandrels to form the Wolter-I configuration. In the current configuration, the optical assembly has a 3 m diameter and a 2 m 2 effective area at 1 keV, with a required angular resolution of 5 arcsec. The angular resolution that can be achieved is chiefly the combination of i) the focal spot size determined by the pore diffraction, ii) the focus degradation caused by surface and profile errors, iii) the aberrations introduced by the misalignments between primary and secondary segments, iv) imperfections in the co-focality of the mirror modules in the optical assembly. A detailed simulation of these aspects is required in order to assess the fabrication and alignment tolerances; moreover, the achievable effective area and the angular resolution depend on the mirror module design. Therefore, guaranteeing these optical performances requires: a fast design tool to find the most performing solution in terms of mirror module geometry and population, and an accurate point spread function simulation from local metrology and positioning information. In this paper, we present the results of simulations in the framework of ESA-financed projects (SIMPOSiuM, ASPHEA, SPIRIT) to prepare the ATHENA X-ray telescope: we deal with a detailed description of diffractive effects in an SPO mirror module, show ray-tracing results including mirror module misalignments, study in detail diffractive effects in different configurations, and assess the focal spot correspondence in X-rays and in the UV light, an important aspect to perform the mirror module alignment and integration. We also include a proton tracing simulation through a magnetic diverter in Halbach array configuration.

X-ray testing at PANTER of optics for the ATHENA and Arcus Missions

“…These are adapted to conform with the needs and the status of the development of the different optics. Before the tests take place input from simulations [14] and if available measurements taken at other beamlines (i.e. BESSY) are used to prepare and optimize the measurement plan.…”

Simulating the optical performances of the ATHENA x-ray telescope optics

“…Finally, also the invariance of the PSF centroids positions of X-ray and UV images, even in presence of profiles longitudinal errors, was already presented one year ago. 8 That confirmed that an integration process based on UV illumination is well suitable for SPOs to achieve the requested alignment accuracy.…”

“…The effective area of ATHENA can be calculated by means of the IDL code presented in previous papers. 7,8 The code is based on the analytical computation of the illuminated area of each pore, extended to the full optical system. The code takes the following input information:…”

“…Results from the collaboration were already presented in previous papers. 7,8 Here we report the latest results on the simulations of ATHENA configuration 3. ASPHEA (Alignment of Silicon Pore Optics for Height Energy Astrophysics) is a project led by Media Lario, involving INAF-OAB in the cofocality and diffraction simulation of MMs aligned on an UV bench.…”

“…Results of this project were reported in previous works. [7][8][9] Here we report the work obtained for the case of two MMs with alignment simulated at an X-ray test facility with source at finite distance, the PANTER facility of MPE. .…”