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.PACS numbers: 52.40. Mj, 52.25.Wz
In the University of Maryland electron beam transport experiment, a 5 kV, 0.2 A electron beam from a thermionic electron source (cathode radius r c = 1.27 cm and cathode temperature kT = 0.12 eV) is injected inio a periodic focusing channel consisting of 38 solenoid lenses with period length S = 13.6 cm. The magnetic focusing fields of the channel, and hence the phase advance without space charge, can be varied over a wide range. We report emittance measurements and results of the effects of beam mismatch, misalignments, and nonlinear lens forces on beam transport and emittance growth.
The evolution of measured beam characteristics such as emittance and radius, as well as details of the beam cross section, have been compared with both theory and simulation, and substantial agreement has been obtained.Simulations have also been employed to identify those deviations from an idealized transport system, such as mismatch and misalignment, which are likely to be the cause of emittance growth in excess of what was expected for the ideal system.
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