Expérimental Developments for the Lamb-Shift Investigation in Heavy Ions

International audience; Results of the latest commissioning experiment of a two arm transmission crystal x-ray spectrometer in combination with a high-performance position-sensitive mircostrip germanium detector are presented. Due to the low photon efficiency of only 10(-8), both the position-sensitivity and the energy-resolution of the 2D-germanium detector are absolutely essential to perform experiments using crystal x-ray spectrometers. In this experiment we were aiming for a precise determination of the Ly-alpha transitions in H-like Ph81+ produced in collisions with a krypton gas jet at the ESR storage ring. Up to now, the most accurate determination of QED corrections to the ground state binding energy in a high-Z, H-like system was performed for H-like uranium with an accuracy on the 1% level.