RECOIL-ION MOMENTUM SPECTROSCOPY AT THE EXPERIMENTAL STORAGE RING ESR OF GSI H. Kollmus1, R. Moshammer1, W. Schmitt1, R. Mann2, L. Adoui3, A. Cassimi3, C.L. Cocke4, J. Ullrich1 1University of Freiburg, 2GSI Darmstadt, 3CIRIL Caen, 4KSU Manhatten, Recoil-ion spectroscopy has been applied to explore inner shell ionization of few-electron heavy ions. Measuring the transverse momentum imparted to the recoil-ion allows to determine the impact parameter of the reaction. A thin gas target required for such measurements and the small cross section associated with inner shell processes of high Z-atoms dictate a more intense beam than available with a single pass beam. Storage rings are ideal to meet such requirements.