The objective is to study the dynamics of the counterions in a charged porous medium, which is part of a larger project which couples multiscale experiments and simulations in order to identify the factors which control the dynamics of charged species in porous media (ANR Dypolypo). The model porous system is made of charged silica spheres assembled in dense assemblies. We now control the charge of the walls of the porous and the size of porosity through volume fraction. Hydrogenated tetramethylammonium (TMA) counterions in D2O allow to study the dynamics of the counterions from incoherent scattering. Previous measurements by TOF (MIBEMOL, LLB) show some quasielastic signal for TMA however long times are missing so that the dynamics of TMA counterions cannot be completely determined. It is essential to use a higher resolution technique, such as backscattering, to access the slow dynamics of the counterions.