A particle-core-MD model for intrabeam scattering and halo formation in high current beams in a FODO channel

An essential problem for the successful operation of high current linear ion accelerators is the control of beam losses due to halo particles. As a possible mechanism for the formation of such a halo we concentrate on the interplay between intrabeam scattering (IBS) and the incidence of particles which are driven to high amplitudes by resonances with the nonlinear space charge fields of a mismatched beam. Since a fully microscopic numerical treatment including all the mutual Coulomb interactions between the beam ions requires much too high computational effort, we developed an approximative method. These particle-core-molecular-dynamics (PCMD) simulations suitably join the mean-field description of the time evolution of the beam in framework of the envelope equations and a microscopic calculation of the Coulomb interactions between pseudo-particles with a renormalized charge. With this method we studied matched and mismatched continuous KV-beams in a FODO channel. In first simulation runs we observed a significant difference in the formation of a cloud of particles around the beam core between matched and mismatched beams when IBS is present. While for a matched beam with IBS no particles with increasing amplitudes have been found, such particles appear at the same IBS rate for a mismatched beam. These results suggest that in a mismatched beam even rather small IBS rates seem to act as a non-negligible source for a halo formation. To conclude from these observations on intense real beams in a high current linac needs, however, further verification of the proposed PCMD method.