The impact of the break-up of molecules in the stripper on the AMS performance

The break-up of molecules in the stripper of an AMS facility induces an energy and angular spread in the beam. This can cause beam losses, thereby reducing the performance of an AMS facility. With an appropriate design, these effects can be minimised and the efficiency enhanced. As an example, the break-up of BeO molecules is discussed here. First the basic physics is described and corresponding models and computer codes are explained. Then experimental data are shown and compared with the models. For gas stripping, beam profiles are available for small and large facilities. All show tails which can be attributed to the dissociation of the molecules. The size of the effect depends on various parameters such as beam energy, selected charge state, stripping gas type and ion optics. Foil stripping leads to energy distributions which are much wider, and show typically a double peak.