In the end, the FWHM is not dominated by these factors but by the manufacturing errors which lead to imperfect geometry and limit the FWHM. 25 of this objects forms a multifiber (25 x 25 pores). 4), with uniform manufacturing errors at this scale, was a good compromise between computation time and representativeness of the geometry. We found that using a 5 x 5 pores subset (see Fig. Performing this process with a subset of 1 pore is much too fine and takes a too long time to simulate. Various manufacturing errors can be introduced at the subset level, like an orientation error or a pore shape error. The spherical geometry of the “lobster eye” is quite easy to implement. The programming of this loop can be done using the ZPL language and dedicated macros. As it is impossible to represent simultaneously the ~12 million pores involved in MXT optics, the way to proceed is to represent a small subset of pores, launch rays for this subset, measure the energy on a detector, move the subset onto the aperture and cumulate the energy deposited on the CCD.
By defining a section and stretching it along one direction, Zemax can represent this way pores or group of pores. The basic element we use is an “extruded object”. In non-sequential mode (NSC), Zemax assumes that all the objects are defined before launching the rays. This allows to consider only reflected rays and to use traditional ray tracing in a quite simple manner. Hence, in the soft X-rays range, even a small thickness of glass is enough to stop rays. The glass used for the MPO has a high density. The size of the pores and of the wedges between them (few µm to tens of µm) is much larger than the criteria of 10 λ (here typically 10 nm). For this last point, we used the database of the Center for X-Rays Optics (CXRO). It can be used to model small wavelengths provided the objects are not too small (>10 λ) and the index data are available.
Zemax is a general optical software widely used in the world and which benefits from a high level of validation. Then we focus on the straylight analysis and present the design impacts of our simulations. We compare the results with the simulations made by UoL. After recalling the general description of the instrument and the basic principles of its optics, we present first the simulations of the X-rays and UV PSF in the field of view (FOV).
The computations combine a geometric raytracing with the effects of diffraction and scattering in the pores.
In the frame of the French payload phase B, under CNES responsibility, we developed a simplified model of the optics using the Zemax code with customized procedures in non-sequential mode.
The main requirements are a full width half maximum (FWHM) of 4.5 arcmin and an effective area of 30 cm 2 at 1.0 keV.
These plates are integrated on a mounting frame by the University of Leicester (UoL) to operate like a soft X-ray lens using a “lobster eye” design. MXT is based on a cooled silicium based detector, provided by the Max-Planck-Institut für Extraterrestrische Physik (MPE) and encapsulated in a camera developed by CEA, and a set of microchannel plates manufactured by Photonis. The other main on board instruments are ECLAIR (gamma, french), GRM (gamma, Chinese) and VT (visible, chinese). The main SVOM general objective is the survey of Gamma Ray Bursts, in coordination with ground telescopes. The launch is planned in 2021 by a LM-2C rocket. The Microchannel X-ray Telescope (MXT) is a soft X-rays instrument on board SVOM, a Sino French mission.