Resonant Emittance Transfer Driven by Space Charge

Space charge can lead to emittance and/or energy exchange known as ``equipartitioning issue'' in linacs, or space-charge coupling in high-current synchrotrons. It is described here as an internal resonance driven by the self-consistent space-charge potential of coherent eigenmodes. By a detailed comparison of analytical theory with 2D particle-in-cell simulation for Kapchinskij-Vladimirskij (KV) and waterbag distributions, we discuss characteristic features of this resonance mechanism in the vicinity of the symmetric focusing resonance band-for practical purposes, the most important case-and discuss the applicability of the linearized KV theory.