Deformation analysis of ATHENA test filters made of plastic thin films supported by a mesh under differential static pressure

Within ESA Cosmic Vision 2015-2025 Science Program, ATHENA was selected to be a Large-class high energy astrophysics space mission. The observatory will be equipped with two interchangeable focal plane detectors named X-Ray Integral Field Unit (X-IFU) and Wide Field Imager (WFI). In order to optimally exploit the detector sensitivity, X-ray transparent filters are required. Such filters need to be extremely thin to maximize the X-ray transparency, that is, no more than a few tens of nm, still they must be able to sustain the severe stresses experienced during launch. Partially representative test filters were made with a thin polypropylene film, coated with Ti, and supported by a thin highly transparent mesh either in stainless steel or niobium. Differential static pressure experiments were carried out on two filter samples. In addition, the roles of the mesh on the mechanical deformation is studied, adopting a finite element model (FEM). The numerical analysis is compared with experimental results and found in good agreement. The FEM is a promising tool that allows to characterize materials and thicknesses in order to optimize the design.