The mechanical design and implementation of the WFM cameras for eXTP

Abstract

The WFM (Wide Field Monitor) instrument of eXTP (Enhanced X-ray Timing and Polarimetry Mission) covers a large fraction of the sky in the (2 - 50) keV energy range, with good angular (5 arcmin - FWHM) and energy (better than 500 eV - FWHM at 6 keV) resolutions. The WFM instrument is part of the scientific payload of the eXTP X-ray satellite, together with the Spectroscopic Focusing Array (SFA), the Large Area Detector (LAD) and the Polarimetry Focusing Array (PFA) instruments. The WFM is distributed in three camera pairs with a broad field of view (180° × 90° FWZR). Each camera is composed by a coded mask assembly, a collimator, a DSP (detector support plate) which hosts four DAs (Detector Assemblies) - each DA including an SDD (Silicon Drift Detector) and its corresponding FEE (Front-End Electronics) - and one BEE (Back-End Electronics). The coded mask area is 260 × 260 mm. It is manufactured from 150 μm thick Tungsten foil. The mask shall keep a flatness of ±50 μm over its surface for the whole operating temperature range of the WFM instrument. A pretension mechanism is carried out with a set of mask frames to fulfil this requirement. A collimator structure supports the coded mask assembly and the detector box. The collimator will provide the stiffness required to avoid deformations due to accelerations and thermal stresses. In this paper, we present the mechanical design drivers of the camera structure (i.e. coded mask assembly, collimator and DSP), the alignment procedure of the detector plane (i.e. the four Silicon tiles) and the detector plane with the coded mask and the camera thermal control system.