A study of the pressure profiles near the first pumping aperture in a high pressure photoelectron spectrometer - Kahk, JM; Villar-Garcia, IJ; Grechy, L; Bruce, PJK; Vincent, PE; Eriksson, SK; Rensmo, H; Hahlin, M; Ahlund, J; Edwards, MOM; Payne, DJ (Journal of Electron Spectroscopy and Related Phenomena, 2015)