The dynamics of an intense relativistic electron beam injected into the atmosphere

We have injected an intense relativistic electron beam into the atmosphere and observed the beam in visible light caused by direct beam excitation of air molecules. This light, primarily emission in the Ni 2nd positive system, was delayed with respect to the beam current by ∼6 ns. Streak photographs show that the beam consisted of a single current filament which oscillated about its initial direction as it propagated through the atmosphere, and that the beam had the characteristic trumpet-like shape. Beam and net current monitors were used to determine the beam current and the plasma return current. The net current was also predicted using a simple circuit model to represent the beam propagating in the atmosphere and agreed well with the measured net current.