Li, H.H.LiFeng, H.H.FengMULERI, FABIOFABIOMULERIBellazzini, R.R.BellazziniMinuti, M.M.MinutiSOFFITTA, PAOLOPAOLOSOFFITTABrez, A.A.BrezSpandre, G.G.SpandrePinchera, M.M.PincheraSgró, C.C.SgróBaldini, L.L.BaldiniShe, R.R.SheCosta, E.E.Costa2020-04-142020-04-1420150168-9002http://hdl.handle.net/20.500.12386/24021Acknowledgements H.F. acknowledges funding support from the National Natural Science Foundation of China under Grant no. 11222327 , and the Tsinghua University Initiative Scientific Research Program.The gas pixel detector (GPD) dedicated for photoelectric X-ray polarimetry is selected as the focal plane detector for the ESA medium-class mission concept X-ray Imaging and Polarimetry Explorer (XIPE). Here we show the design, assembly, and preliminary test results of a small GPD for the purpose of gas mixture optimization needed for the phase A study of XIPE. The detector is assembled in house at Tsinghua University following a design by the INFN-Pisa group. The improved detector design results in a good uniformity for the electric field. Filled with pure dimethyl ether (DME) at 0.8 atm, the measured energy resolution is 18% at 6 keV and inversely scales with the square root of the X-ray energy. The measured modulation factor is well consistent with that from simulation, up to ~0.6 above 6 keV. The residual modulation is found to be 0.30 ± 0.15 % at 6 keV for the whole sensitive area, which can be translated into a systematic error of less than 1% for polarization measurement at a confidence level of 99%. The position resolution of the detector is about 80 μm in FWHM, consistent with previous studies and sufficient for XIPE requirements.STAMPAenArticle10.1016/j.nima.2015.09.0602-s2.0-84944080359000364133700022https://www.sciencedirect.com/science/article/pii/S0168900215011158?via%3Dihub2015NIMPA.804..155LFIS/05 - ASTRONOMIA E ASTROFISICAScienze Fisiche Settori ERC (ERC) di riferimento::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation