Effects of space charge on decoherence in ion beams

This paper studies dipolar and quadrupolar decoherence of a bunch in presence of space charge. The centroid of a bunch displaced transversely or longitudinally decoheres due to nonlinearities that cause phase space filamentation and mixing. Here we show that space charge can inhibit decoherence and keep the beam centroid oscillations undamped over long times. This feature complicates the detection of echoes for diagnostics purposes. An echo requires in fact a fully decohered beam to show up as a coherent signal at later times than the excitations. Results are qualitatively compared with experiments in the GSI synchrotron SIS.