Simulation of decays and secondary ion losses in a Betabeam decay ring

Radioactive ions injected into the decay ring of a Betabeam neutrino facility will constitute a continuous source of decay products distributed around the ring. Secondary ions from beta decays will differ in charge state from the primary ions and will follow widely off- momentum orbits. In the racetrack configuration of the ring, they will be mismatched in the long straights and may acquire large amplitudes, but the great majority of losses will be in the arcs. We describe here a comprehensive model of ion decay, secondary ion tracking, and loss detection, which has been implemented in the tracking and simulation code Accsim. Methods have been developed to accurately follow ion trajectories at large momentum deviations as well as to detect their impact coordinates on vacuum chamber walls and possibly inside magnetic elements. Using secondary-ion data from Accsim and postprocessing with Mathematica, we have implemented a follow-on simulation in FLUKA with a 3D geometry of decay ring components and physics models for ion interactions in matter, allowing radiological studies and in particular the visualization and analysis of heat deposition in the dipole magnets which is a critical design factor for the ring. In our simulations we have also implemented absorber elements which are intended to localize the majority of losses outside of the dipoles. These studies provide estimates of ring performance (in terms of loss concentration and management), the effectiveness of absorbers, and the implications for successful superconducting dipole operation.