Propagation of an Intense Relativistic Electron Beam Through a Plasma Background

Experiments have been performed to study the propagation of an intense relativistic electron beam [input (ν/γ)≃2.5] in a drift tube filled with either neutral gas or preexisting plasma. Beam front velocity, magnetic neutralization, and energy transport are measured. Results for propagation into neutral gas confirm previous work. Propagation into a preionized background is characterized by nearly complete magnetic neutralization. However, the beam front velocity never exceeds 60% of its potential value, and a two-stream instability is suggested as a possible explanation. The efficiency of beam energy propagation through the plasma is found to depend on the neutral background density, and a possible cause of this effect is suggested. Hollow beam profiles are observed under suitable conditions.