Time-dependent imaging of space-charge dominated electron beams

Abstract

When considered as non-neutral plasmas, space-charge dominated charged particle beams have significantly smaller Debye lengths than their beam sizes. Therefore, collective effects due to space-charge forces are very important to the beam dynamics. As an example, density perturbations generated in a space-charge dominated charge particle beam will stimulate longitudinally space-charge waves. To study the modification of transverse beam distributions by longitudinal beam dynamics, experimental studies of low-energy electron beams, with and without longitudinal density perturbations, have been undertaken at the University of Maryland’s electron ring and the Long Solenoid Experiment (LSE). We have taken time-resolved beam images on these machines using two different diagnostics: Optical transition radiation, produced from an intercepting aluminized silicon screen, and a fast (<3ns decay time) phosphor screen. Results from both techniques show that both the transverse size and transverse particle distribution of a space-charge dominated beam are affected by the longitudinal dynamics of the beam. In addition to the fast imaging measurements, longitudinal mean energy profiles of different beams have also been measured at different locations in the LSE system.