Cleaning the beam halo using nonlinear ac magnets

Recently, nonlinear effects have been used to cool a special beam represented by an annular distribution in a 2D phase space. This outcome was accomplished using an ac dipole combined with amplitude detuning generated by static nonlinear magnets. In this paper, we investigate a more realistic scenario, in which a beam distribution in a 4D phase space includes the presence of a beam halo and demonstrate how the latter can be removed using nonlinear effects. The proposed approach employs high-order nonlinear ac magnets to trap into nonlinear resonances and to perform an adiabatic transport of the beam halo in phase space. Theoretical models are formulated and examined using numerical simulations to evaluate their efficacy.