  This work studies the fundamental plasma processes involved in the
neutralization of an ion beam's space-charge by electrons emitted by a filament
using Particle-in-Cell simulations. While filament neutralization is
economical, previous experiments have shown that a variety of waves become
excited in this process that limit the space-charge neutralization. In this
work, the formation and movement of electrostatic solitary waves(ESWs), which
have low dissipation rates, are characterized for 2D planar and 3D cylindrical
beams and are observed to generate waves that survive for a long time and slow
the process of beam neutralization. Further, through a 1D
Bernstein-Greene-Kruskal (BGK) analysis, we find that the non-Maxwellian nature
of the beam electrons gives rise to large-sized ESWs that are not predicted by
theory which assumes that the electrons may be described by a Maxwellian
distribution. Our PIC simulations are sufficiently sensitive to be able to
resolve important three-dimensional effects in a 3D cylindrical geometry that
lead to the excitation of Trivelpiece-Gould surface waves due to high-energy
electrons present at the beginning of neutralization.
