Characterization of the eXTP-LAD collimators

The enhanced X-ray Timing and Polarimetry mission (eXTP) is a next-generation flagship X-ray astronomy satellite currently in phase-B study. The large Area Detector (LAD) on board eXTP contains 40 modules, each consisting of a set of 4\(\times \)4 large area SDDs and 4\(\times \)4 collimators, and has a designed effective area of 3.0 m\(^2\) at 8 keV and a Field of View (FoV) of 1\(^\circ \). To achieve such a large effective area, the collimator’s Open Area Ratio (OAR) should be greater than 70%. In this paper, we introduce the measurement methods used to determine the OAR and the rocking curve (angular response) of the LAD collimator at the 100-m X-ray Test Facility (100XF) of the Institute of High Energy Physics (IHEP) in Beijing, and report the results of the collimators manufactured under different conditions. The measured OARs of the collimators are usually smaller than the theoretical values by a few percent, which is due to the non-uniformity and irregularity of the pores. The measured rocking curves are usually broader than the theoretical triangular curves, and the lower the energy of the incident X-ray the broader the rocking curve. This broadening of the rocking curve is the result of reflection on the inner wall of the pores. Our results also show that increasing the etching time in the manufacturing of the collimators can increase the OARs but does not change significantly the shape of the rocking curves.