Halo formation in intense bunched beams

The latest designs for high current ion linacs (Accelerator for the Transmutation of Waste, Accelerator for the Production of Tritium, Heavy Ion Drivers, Spallation Neutron Source injector) require minimal radioactivation by the beam striking the beam pipe. As a result, efforts are being made to understand and control the growth of beam halo. There is general agreement that halos develop as a result of the parametric resonance between the ion oscillations in the beam bunch and collective oscillations of the bunch itself induced by mismatch in the linac. Analytic studies for a 2-D KV beam were found to give excellent agreement with corresponding computer simulations, which were then extended to other 2-D beams. Recently, analytic and numerical studies were performed for 3-D beam bunches (6-D phase space distributions), focusing attention on the formation of longitudinal halos and the possibility of bunch growth or loss of longitudinal bunch stability, as well as coupling between the longitudinal and transverse halos