Observations and simulations of particle-density oscillations in an apertured, space-charge dominated electron beam

Experiments and particle-in-cell (PIC) simulations in connection with the University of Maryland Electron Ring demonstrate the appearance and evolution of transverse space-charge waves in a space-charge dominated electron beam. The waves are observed regardless of the focusing system, although the strength of the focusing affects their onset and evolution. An aperture induces the perturbation in the particle distribution in an initially freely-expanding beam. Simulations show that the effect of the aperture can be modeled approximately by a beam with an initially semi-Gaussian particle distribution with a temperature profile. Furthermore, simple tracking of test particles initially near the aperture´s edge reproduce well the onset of the perturbation. For the parameters investigated, simulations further indicate that the perturbation damps out over a few plasma periods without causing any emittance growth