Theory of longitudinal beam halo in RF linacs: II. Envelope-particle resonances

Using the core/test-particle model described in a companion paper in these proceedings(1) ("Theory of Longitudinal Halo in rf Linacs: I. Core/Test-Particle Formulation," by J. J. Barnard and S. M. Lund), we analyze longitudinal beam halo produced by resonant self-held interactions in intense, ion-beam rf linacs. It is shown that particles moving in the presence of the space-charge forces of an oscillating, mismatched ellipsoidal beam bunch can be resonantly driven to large longitudinal amplitude. This resonantly produced halo is first analyzed in a limit where it is most simply understood, with particles moving purely longitudinally and with linear rf focusing. Then modifications of the resonance induced by nonlinear rf and transverse-longitudinal coupling are explored.