Production of halo particles by excitation of collective modes in high-intensity charged particle beams

This paper examines analytically and numerically the effects of self-consis tent collective oscillations excited in a high-intensity charged particle b eam on the motion of a test particle in the beam core. Even under ideal con ditions, assuming a constant transverse focusing force (smooth focusing app roximation), and perturbations about a uniform-density, constant radius bea m, it is found that collective mode excitations, in combination with the ap plied focusing force and the equilibrium test fields, can eject particles f rom the beam core to large radii. Test particle orbits are calculated for c ollective oscillations with n = 1 and 2 radial mode structure, and an estim ate is obtained for the range of initial conditions for which particles wil l be expelled from the beam interior. Resonances for meridional particles a re found to be unimportant, while a class of particles with nonzero angular momentum are found to participate in resonant behavior. Once expelled from the beam, numerical solutions of the orbit equations indicate that Kolmogo rov-Arnold-Moser curves, phase space spanning integrals of motion, confine particles within 1.5 times the beam radius for moderately low mode amplitud es, but are successively destabilized for higher amplitudes.