Slumping technique for the manufacturing of a representative x-ray grazing incidence mirror module for future space missions

Abstract

The Astronomical Observatory of Brera (INAF-OAB, Italy), with the financing support of the European Space Agency (ESA), has concluded a study regarding a glass shaping technology for the production of grazing incidence segmented x-ray optics. This technique uses a hot slumping phase, in which pressure is actively applied on thin glass foils being shaped, to form a cylindrical approximation of Wolter I x-ray segments, and a subsequent cold slumping phase, in which the final Wolter I profile is then freeze into the glass segments during their integration in elemental X-ray Optical Units. The final goal of this study was the manufacturing of a prototype containing a number of slumped pair plates (meaning parabola and hyperbola couples) having representative dimensions to be tested both in UV light and in x-rays at the Panter facility (Germany). In this paper, the INAF-OAB slumping technique, comprising a shaping step and an integration step is described, together with the results obtained on the manufactured prototype modules: the first prototype was aimed to test the ad-hoc designed and built semi-automatic Integration MAchine (IMA) and debug its control software. The most complete module comprises 40 slumped segments of Schott D263 glass type of dimension 200 mm x 200 mm and thickness of 0.4 mm, slumped on Zerodur K20 mould and stacked together through glued BK7 glass structural ribs to form the first entire x-ray optical module ever built totally composed by glass. A last prototype was aimed at demonstrate the use of Schott glass AF32 type instead of D263. In particular, a new hot slumping experimental set-up is described whose advantage is to permit a better contact between mould and glass during the shaping process. The integration procedure of the slumped segments into the elemental module is also reviewed.

Manufacturing and testing a thin glass mirror shell with piezoelectric active control

“…However, Slu mped Glass Optics (SGO) represents a viable alternative to manufacture high-resolution, lightweight and densely nested optical modules [2] . In this approach, already experienced for the NuSTA R telescope [3] , thin foils of glass are formed at high temperature onto a precisely figured mould and, kept at the correct distance by ribs , stacked into an XOU.…”

Evaluation of the surface strength of glass plates shaped by hot slumping process

“…In particular, a new method for pressure application has been developed: while the original approach developed at OAB makes use of a thin metal membrane for applying pressure on the glass plate being shaped to force it into full contact with the mold, the new approach allows for the application of pressure directly on the glass plate without intermediate materials. 22 In this way, it is possible to avoid random local deformations and surface damage introduced by the metal pressing membrane that have detrimental effects both on the mirror segments' shape, meaning optical performances, and on strength. In both cases, the entire process of slumping is realized inside a stainless steel muffle for thermal and cleaning reasons: in the first case, the muffle is divided in two separate volumes by a 25-μm-thick metal membrane, whereas in the second case the glass foil itself acts as a membrane to separate the muffle in two different chambers.…”

Evaluation of the surface strength of glass plates shaped by hot slumping process

“…During the course of the activities, lots of improvements have been obtained in the hot slumping technology with pressure assistance. In particular, a new method for pressure application has been developed: while the original approach developed at OAB makes use of a thin metal membrane for applying pressure on the glass plate being shaped so to force it in full contact with the mould, the new approach allows for the application of pressure directly on the glass plate, without intermediate materials [22]: in such a way, it is possible to avoid random local deformations and surface damages introduced by the metal pressing membrane that have detrimental effects both on mirror segments shape, meaning optical performances, and strength. In both cases, the entire process of slumping is realized inside a stainless steel muffle for thermal and cleaning reason: in the first case, the muffle is divided in two separate volumes by a 25µm-thick metal membrane, while in the second case the glass foil itself acts as a membrane to separate the muffle in two different chambers where a differential pressure can be established.…”