Advanced manufacturing techniques for X-ray and VHE gamma-ray astronomical mirrors.

The main theme of this thesis is on the development of the technologies for the future X-ray astronomy telescopes and specifically for the New Hard X-ray Mission and eROSITA (Spectrum-RG) missions. Other important next future X-ray missions, currently under advanced study and/or manufacturing are NuSTAR (USA), ASTRO-H (Japan) and GEMS (USA). The New Hard X-ray Mission (NHXM) is being developed in Italy as an evolution of the original HEXIT-SAT project and is now the hard x-ray project of reference for the Italian high energy community. NHXM is meant to provide a real breakthrough on a number of hot astrophysical issues, by exploiting the most advanced technology in broad-band (0.2 \u2013 80 keV) high angular resolution (<20 arc seconds HEW) grazing incidence mirrors and spectroscopic detectors, together with the use of a high efficiency imaging polarimeter. Such issues can be summarized in two main headings: \u25cf making the census of the population of black holes in the Universe and probing the physics of accretion in the most diverse conditions; \u25cf investigating the particle acceleration mechanisms at work in different contexts, and the effects of radiative transfer in highly magnetized plasmas and strong gravitational fields. These topics were identified as top priority in the study commissioned by the Italian Space Agency (ASI) in 2004 to the Italian scientific community with contracts involving Thales-Alenia Space Italy (TAS-I, Turin), the Media Lario Technologies (MLT, Lecco) company and the INAF institution. NHXM benefits from the phase A study of the canceled French-Italian-German SIMBOL-X mission (2007-2008) and has been recently subjected to a scientific phase B study financed by ASI. Media Lario Technologies company received a contract from ASI in 2009 for a Technology Development Program (ASI-TDP) aiming at improving the technology readiness level with also in-house adoption of hardware for the metrology/manufacturing of the multilayer x-ray optics. Spectrum-RG is a Russian - German x-ray astrophysical observatory scheduled for lunch in 2013. German Space Agency (DLR) is responsible for the development of the key mission instrument - the x-ray grazing incident mirror telescope eROSITA. The second experiment is ART-XC - an x-ray mirror telescope with a harder response than eROSITA, which is being developed by Russia (IKI, Moscow and VNIIEF, Sarov). The name eROSITA stands for extended Roentgen Survey with an Imaging Telescope Array. The general design of the eROSITA x-ray telescope is derived from that of ABRIXAS: a bundle of 7 mirror modules with short focal lengths make up a compact telescope which is ideal for survey observations. Similar designs had been proposed for the missions DUO and ROSITA but were not realized. Compared to those, however, the effective area in the soft x-ray band has now much increased by adding 27 additional outer mirror shells to the original 27 ones of each mirror module. The requirement on the on-axis resolution has also been confined, namely to 15 arc seconds HEW. For these reasons the prefix \u201cextended\u201d to the original name \u201cROSITA\u201d had been added. The scientific motivation for this extension is founded in the ambitious goal to detect about 100000 clusters of galaxies which trace the large scale structure of the Universe in space and time. The main scientific goals are: \u25cf to detect the hot intergalactic medium of 50-100 thousand galaxy clusters and groups and hot gas in filaments between clusters to map out the large scale structure in the Universe for the study of cosmic structure evolution; \u25cf to detect systematically all obscured accreting Black Holes in nearby galaxies and many (up to 3 Million) new, distant active galactic nuclei; \u25cf to study in detail the physics of galactic x-ray source populations, like pre-main sequence stars, supernova remnants and x-ray binaries. Max-Planck-Institute f\ufcr extraterrestrische Physik (MPE) is the scientific institute responsible for the eROSITA Payload. Media Lario Technologies (MLT) is the industrial enabler for the manufacturing of the Optical Payload for eROSITA - including the flight quality mandrels, and it is currently in the C/D Phase of the project. The research activity described in this thesis has been carried out at Media Lario Technologies company and at the Brera Astronomical Observatory under the supervision of INAF-OAB researchers Dott. Giovanni Pareschi and Dott. Gianpiero Tagliaferri. The research activity of the author of this thesis is focused on the development of an advance polishing technique for the mandrels to be used as masters in the mirrors replication by electroforming. The goal is to implement a process where the mandrels can be manufactured with a high accuracy (< 6 arc seconds HEW) and low roughness (< 0.2 nm rms) within a consistent short time. In the contest of the eROSITA and NHXM (projects currently running in MLT) the author participated as technical/scientific responsible, investigating innovative mandrels manufacturing technologies (e.g. Single Point Diamond Turning, shape corrective polishing) representing an evolution of the standard approach used so far. In this frame the author has also contributed to the adoption of a customized deterministic polishing machine and a customized 3D metrology device for the mandrel geometrical characterization. An additional research activity, performed by the author at Media Lario Technologies company and at the Brera Astronomical Observatory, is focused on the development of lightweight glass mirrors manufactured via cold-slumping technique for Imaging Atmospheric Cherenkov Telescopes (IACT). Very High Energy (VHE) gamma rays, with photon energies in the TeV range, can be detected by ground based experiments. In fact, such high energy photons interact high in the upper atmosphere and generate an air shower of secondary particles. These particles emit the so-called Cherenkov light, a faint blue light. The mirror elements here developed have a sandwich-like structure where the reflecting and backing facets are composed by glass sheets with an interposed honeycomb aluminum core. This effort found application at the world\u2019s largest IACT, the 17m MAGIC II telescope (currently operating in Roque de los Muchachos - La Palma, Canary Islands), where 112 mirrors (~ 1 squared meter each), manufactured with the newly developed cold-slumping technique here described, are installed

Characterization of multilayer stack parameters from X-ray reflectivity data using the PPM program: measurements and comparison with TEM results

Future hard (10 -100 keV) X-ray telescopes (SIMBOL-X, Con-X, HEXIT-SAT, XEUS) will implement focusing optics with multilayer coatings: in view of the production of these optics we are exploring several deposition techniques for the reflective coatings. In order to evaluate the achievable optical performance X-Ray Reflectivity (XRR) measurements are performed, which are powerful tools for the in-depth characterization of multilayer properties (roughness, thickness and density distribution). An exact extraction of the stack parameters is however difficult because the XRR scans depend on them in a complex way. The PPM code, developed at ERSF in the past years, is able to derive the layer-by-layer properties of multilayer structures from semi-automatic XRR scan fittings by means of a global minimization procedure in the parameters space. In this work we will present the PPM modeling of some multilayer stacks (Pt/C and Ni/C) deposited by simple e-beam evaporation. Moreover, in order to verify the predictions of PPM, the obtained results are compared with TEM profiles taken on the same set of samples. As we will show, PPM results are in good agreement with the TEM findings. In addition, we show that the accurate fitting returns a physically correct evaluation of the variation of layers thickness through the stack, whereas the thickness trend derived from TEM profiles can be altered by the superposition of roughness profiles in the sample image

Simbol-X Hard X-ray Focusing Mirrors: Results Obtained During the Phase A Study

Simbol-X will push grazing incidence imaging up to 80 keV, providing a strong improvement both in sensitivity and angular resolution compared to all instruments that have operated so far above 10 keV. The superb hard X-ray imaging capability will be guaranteed by a mirror module of 100 electroformed Nickel shells with a multilayer reflecting coating. Here we will describe the technogical development and solutions adopted for the fabrication of the mirror module, that must guarantee an Half Energy Width (HEW) better than 20 arcsec from 0.5 up to 30 keV and a goal of 40 arcsec at 60 keV. During the phase A, terminated at the end of 2008, we have developed three engineering models with two, two and three shells, respectively. The most critical aspects in the development of the Simbol-X mirrors are i) the production of the 100 mandrels with very good surface quality within the timeline of the mission; ii) the replication of shells that must be very thin (a factor of 2 thinner than those of XMM-Newton) and still have very good image quality up to 80 keV; iii) the development of an integration process that allows us to integrate these very thin mirrors maintaining their intrinsic good image quality. The Phase A study has shown that we can fabricate the mandrels with the needed quality and that we have developed a valid integration process. The shells that we have produced so far have a quite good image quality, e.g. HEW <~30 arcsec at 30 keV, and effective area. However, we still need to make some improvements to reach the requirements. We will briefly present these results and discuss the possible improvements that we will investigate during phase B.Comment: 6 pages, 3 figures, invited talk at the conference "2nd International Simbol-X Symposium", Paris, 2-5 december, 200

Thin-shell plastic lenses for space and laboratory applications

We have identified an inexpensive, readily available, mechanically stable, extremely smooth, elastic, and mechanically uniform plastic suitable for thin film X-ray optics. Polyethylene terephthalate (PET) is easily deformed without losing its elastic properties or surface smoothness. Most important, PET can be coated with mono- or multilayers that reflect X-rays at grazing incidence. We have used these properties to produce X-ray optics made either as a concentric nest of cylinders or as a spiral. We have produced accurately formed shells in precisely machined vacuum mandresl or used a pin and wheel structure to form a continuously wound spiral. The wide range of medical, industrial and scientific applications for our technology includes: a monochromatic X-ray collimater for medical diagnostics, a relay optic to transport an X-ray beam from the target in a scanning electron microscop0e to a lithium-drifted silicon and microcalorimeter detectors and a satellite mounted telescope to collect celestial X-rays. A wide variety of mono- and multilayer coatings allow X-rays up to ~100 keV to be reflected. Our paper presents data from a variety of diagnostic measurements on the properties of the PET foil and imaging results form single- and multi-shell lenses

Assembly integration and testing facility for the x-ray telescope of ATHENA

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Thin-shell plastic lenses for space and laboratory applications

We have identified an inexpensive, readily available, mechanically stable, extremely smooth, elastic, and mechanically uniform plastic suitable for thin film X-ray optics. Polyethylene terephthalate (PET) is easily deformed without losing its elastic properties or surface smoothness. Most important, PET can be coated with mono- or multilayers that reflect X-rays at grazing incidence. We have used these properties to produce X-ray optics made either as a concentric nest of cylinders or as a spiral. We have produced accurately formed shells in precisely machined vacuum mandresl or used a pin and wheel structure to form a continuously wound spiral. The wide range of medical, industrial and scientific applications for our technology includes: a monochromatic X-ray collimater for medical diagnostics, a relay optic to transport an X-ray beam from the target in a scanning electron microscop0e to a lithium-drifted silicon and microcalorimeter detectors and a satellite mounted telescope to collect celestial X-rays. A wide variety of mono- and multilayer coatings allow X-rays up to ~100 keV to be reflected. Our paper presents data from a variety of diagnostic measurements on the properties of the PET foil and imaging results form single- and multi-shell lenses

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