The Athena x-ray optics development and accommodation

The Athena mission, under study and preparation by ESA as its second Large-class science mission, requires the largest X-ray optics ever flown, building on a novel optics technology based on mono crystalline silicon. Referred to as Silicon Pore Optics technology (SPO), the optics is highly modular and benefits from technology spin-in from the semiconductor industry. The telescope aperture of about 2.5 meters is populated by around 700 mirror modules, accurately co-aligned to produce a common focus. The development of the SPO technology is a joint effort by European industrial and research entities, working together to address the challenges to demonstrate the imaging performance, robustness and efficient series production of the Athena optics. A technology development plan was established and is being regularly updated to reflect the latest developments, and is fully funded by the ESA technology development programmes. An industrial consortium was formed to ensure coherence of the individual technology development activities. The SPO technology uses precision machined mirror plates produced using the latest generation top quality 12 inch silicon wafers, which are assembled into rugged stacks. The surfaces of the mirror plates and the integral support structure is such, that no glue is required to join the individual mirror plates. Once accurately aligned with respect to each other, the surfaces of the mirror plates merge in a physical bonding process. The resultant SPO mirror modules are therefore very accurate and stable and can sustain the harsh conditions encountered during launch and are able to tolerate the space environment expected during operations. The accommodation of the Athena telescope is also innovative, relying on a hexapod mechanism to align the optics to the selected detector instruments located in the focal plane. System studies are complemented by dedicated technology development activities to demonstrate the capabilities before the adoption of the Athena mission

Silicon pore optics mirror modules for inner and outer radii

Athena (Advanced Telescope for High Energy Astrophysics) is an x-ray observatory using a Silicon Pore Optics telescope and was selected as ESA's second L-class science mission for a launch in 2028. The x-ray telescope consists of several hundreds of mirror modules distributed over about 15-20 radial rings. The radius of curvature and the module sizes vary among the different radial positions of the rings resulting in different technical challenges for mirror modules for inner and outer radii. We present first results of demonstrating Silicon Pore Optics for the extreme radial positions of the Athena telescope. For the inner most radii (0.25 m) a new mirror plate design is shown which overcomes the challenges of larger curvatures, higher stress values and bigger plates. Preliminary designs for the mounting system and its mechanical properties are discussed for mirror modules covering all other radial positions up to the most outer radius of the Athena telescope

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

The ATHENA (Advanced Telescope for High Energy Astrophysics) X-ray observatory is an ESA-selected L2 class mission. In the proposed configuration, the optical assembly has a diameter of 2.2 m with an effective area of 1.4 m2 at 1 keV, 0.25 m2 at 6 keV, and requires an angular resolution of 5 arcsec. To meet the requirements of effective area and angular resolution, the technology of Silicon Pore Optics (SPO) was selected for the optics implementation. The ATHENA's optic assembly requires hundreds of SPOs mirror modules (MMs), obtained by stacking wedged and ribbed silicon wafer plates onto silicon mandrels to form the Wolter-I configuration. Different factors can contribute to limit the imaging performances of SPOs, such as i) diffraction through the pore apertures, ii) plate deformations due to fabrication errors and surface roughness, iii) alignment errors among plates in an MM, and iv) co-focality errors within the MMs assembly. In order to determine the fabrication and assembling tolerances, the impact of these contributions needs to be assessed prior to manufacturing. A set of simulation tools responding to this need was developed in the framework of the ESA-financed projects SIMPOSIuM and ASPHEA. In this paper, we present the performance simulation obtained for the recentlyproposed ATHENA configuration in terms of effective area, and we provide a simulation of the diffractive effects in a pair of SPO MMs. Finally, we present an updated sizing of magnetic diverter (a Halbach array) and the magnetic fields levels that can be reached in order to deviate the most energetic protons out of the detector field

VERT-X: VERTical X-ray raster-scan facility for ATHENA calibration. The concept design

Calibration of the ATHENA telescope is a critical aspect of the project and raises significant difficulties due to the unprecedented size, mass and focal length of the mirror assembly. The VERT-X project, financed by ESA and started in January 2019 by a Consortium led by INAF and which includes EIE, Media Lario Technologies, GPAP, and BCV Progetti, aims to design an innovative calibration facility. In the VERT-X design the parallel beam, needed for calibration, is produced placing a source in the focus of an X-ray collimator. This system is mounted on a raster-scan mechanism which covers the entire ATHENA optics. The compactness of the VERT-X design allows a vertical geometry for the ATHENA calibration facility, with several potential benefits with respect to the long horizontal tube calibration facilities

Optimization of array design for TIBr imaging detectors.

Thallium bromide (TlBr) has attracted attention as an exceptional radiation detector material. Due to its high atomic number (81 for Tl, 35 for Br) it has excellent stopping power for hard X-ray and gamma rays and due to its high bandgap (2.7 eV) its operation requires no or only modest cooling. Promising energy resolutions have been demonstrated with detectors fabricated from high-purity samples (3.3 keV for 60 keV photons). These properties make TlBr the material of choice for hard X-ray imaging spectrometers in applications where small weight and/or size is important (e.g. space astrophysics and nuclear medicine). The charge response and spectroscopic performance of a semiconductor imaging array depend not only on material properties but on the pixel properties as well. It has been demonstrated, for instance, that the ratio between pixel size and thickness of the detector is an important factor for the charge response. This is known as the small-pixel or near-field effect. In this paper we investigate the optimization of TlBr pixel properties in a broader context, taking into account material properties (electron and hole mobility, diffusion and trapping), fabrication details and the specific energy range of application, with a view to optimizing both the response and energy resolution

A novel local shielding approach for the laser welding based additive manufacturing of large structural space components from titanium: Paper presented at ICALEO 2019, International Congress on Applications of Lasers and Electro-Optics, October 7-10, 2019, Orlando, Florida

The Advanced Telescope for High-ENergy Astrophysics (ATHENA) will observe ‘the hot and energetic universe’, which was determined one of the most urgent scientific topics for a major future space mission by The European Space Agency (ESA). One of its three main components is the optical bench, a monolithic titanium structure that accommodates 678 mirror modules and has to keep them accurately aligned. The immense but slender structure in the range of a 2.5 to 3 m diameter at a height of 300 mm proves a challenge to manufacturing. A hybrid robot cell is developed using additive build up via laser welding, combined with high-performance machining and state of the art process and metrology monitoring and control. The present work focuses on the shielding of the laser induced melt-pool, a key concern when processing titanium. The sensitive metal with unusual low heat conductivity requires a large area of high purity atmosphere to prevent embrittlement. However, the large hybrid system prohibits the use of a sealed enclosure and therefore a local shielding system is developed for the challenging case of the ATHENA optical bench’s hollow-chamber design. As the thin wall design poses a worst-case scenario in terms of heat dissipation and shielding flow, the effectiveness of the system can be applied to the flexibility of lot size one as well. The key features of the novel approach are the prevention of turbulence while keeping operation economical despite the large shielding area. The first is achieved by means of an integrated honeycomb screen, the latter by employing a layered flow with a higher velocity outer curtain and an air deflecting co-flow. This system was numerically optimized, tested and the effectiveness proven by means of visual inspection, microstructural analysis and measurement of material properties