Emittance Coupling in High Intensity Beams Applied to the Sns Linac

Space charge can lead to emittance and/or energy exchange in non-equipartitioned high intensity linacs, which is interpreted here in terms of ”coherent resonance”. In this paper we first compare 2D and 3D simulations in constant focusing, and relate them to self-consistent resonant charts based on analytical theory. We then use these charts to interpret PARMILA simulation results for the SNS linac and find that the SNS design shows little sensitivity to such resonances for the nominal (longitudinal to transverse) emittance ratio; with doubled input longitidinal emittance we have identified modest emittance transfer by crossing of the fourth order 2:2 resonance stopband in the DTL and SRF.