Emittance Growth and Image Formation in a Nonuniform Space-Charge-Dominated Electron Beam

An experiment was designed to check theoretical predictions of charge homogenization and emittance growth in nonuniform space-charge-dominated beams due to conversion of field energy into transverse kinetic energy. Five beamlets were masked out of a solid 5-keV electron beam and injected into a periodic solenoidal focusing channel. Phosphor screen images showed that the beamlets merged into an almost uniform density single beam. Images of the five-beamlet configuration were observed at a distance of 7-8 lens periods. Experimental results on merging distance and emittance growth were compared with theory and simulation and good agreement was found.