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The mechanical concept for the XMA uses a straightforward cantilever design. The four paraboloidal mirrors are mounted at one end to a central supporting flange, which carries the four hyperboloidal shells on its opposite side. The central flange, which is 78 mm thick Invar steel, actually consists of 5 solid annuli which are interconnected by 16 radial struts. Flanges of similar shape but much thinner stabilize the mirror shells at the entrance and exit planes. The area obstructed by the struts is about 10% of the total. The outermost annulus of the central flange connects the mirror system to the optical bench via a short conically shaped tube which produces the axial stiffness and stability. The mirror shells are made of Zerodur with a wall thickness ranging from 16 to 25 mm increasing with mirror diameter. The supporting plates and flanges are made of Invar. For the optical bench and the stiffening cone, a carbon fibre compound material was chosen. In order to accommodate the slightly different thermal expansion rate of Zerodur, Invar, and carbon fibre the mirrors are not mounted directly to the Invar support plates but are bonded to thin-walled Invar sleeves, which are bolted to the Invar support flange.
In order to suppress stray-light, which arises primarily from singly reflected rays either off the parabolas or the hyperbolas, a set of stops in the form of circular blades has been incorporated at the front aperture, in the section about midway down the parabolas and hyperbolas and at the exit plane.