Has the atomic beam source reached a hard intensity limit

The intensity of Atomic Beam Sources for Storage Cell targets is reviewed. The limitations of present sources are analyzed, in particular losses by residual gas scattering and intra-beam scattering. Simple quantitative estimates are given in order to illustrate their relative importance. More general calculations covering the full range of flow regimes are required to extract basic information from the many empirical studies performed up to now. Several new ideas as the Microwave dissociator and the Carrier Jet may substantially improve ABS targets for storage rings.