EXPERIMENTAL OBSERVATIONS OF LARGE-AMPLITUDE SOLITARY WAVES IN ELECTRON BEAMS

The longitudinal dynamics of space charge dominated beams plays an important role in particle accelerators and other applications such as heavy ion fusion, spallation neutron sources and free electron lasers (FELs). All beams are space-charge dominated near the source [1]. By means of experiments on the University of Maryland Electron Ring (UMER), we studied how a perturbation to the line charge density could affect the beam propagation. By varying the initial amplitude of the perturbation, we access nonlinear space charge physics. When starting with large-amplitude perturbations, we have observed, for the first time in charged particle beams, solitary waves for which the nonlinear steepening exactly balances the wave dispersion, leading to persistent waves that preserves their shape over a long distance. This paper presents the results of the soliton experiments, including systematic studies of the dependence of the soliton propagation on beam current, perturbation strength and width.