Halo formation in RMS-matched intense ion beams

Halo formation is studied for ion beam propagation through an alternating-gradient focusing channel with root-mean-squared (RMS) matched envelopes in the space-charge-dominated regime. In particular, an earlier theoretical model [1] is generalized to describe halo formation observed recently in a potassium (K⁺) beam in the 2-MV Heavy Ion Beam Injector Experiment at the LBNL [2], where the measured density profile shows a density depression on the beam axis. This generalization allows qualitative comparisons between the halo theory and the experimental measurements, which are found in good agreement.