Collective resonance model of energy exchange in 3D nonequipartitioned beams

Energy exchange between the longitudinal and transverse degrees of freedom of nonequipartitioned bunched beams (non-neutral plasmas) is investigated by means of 3D simulation. It is found that collective instability may lead to energy transfer in the direction of equipartition, without full progression to it, in certain bounded regions of parameter space where internal resonance conditions are satisfied, in good agreement with stability charts from an earlier derived 2D Vlasov analysis. Nonequipartitioned stable equilibria, however, exist in relatively wide regimes of parameter space. This provides evidence that such regimes may be safely used in the design of future high-intensity linacs.