Single Particle and Collective Effects Observed in the Electron Beam of the Maryland ERA Experiment

The formation of rotating, relativistic electron beams with properties suitable for collective ion acceleration has been studied under a variety of experimental conditions. A straight, cylindrical, relativistic electron beam (typical energy 2-3 MeV, typical current 2-10 kA) is passed through a narrow magnetic cusp, and the resulting rotating downstream beam has been studied using a number of diagnostic techniques. Two current regimes have been investigated: one in which the self-fields of the downstream electron beam are small compared to the applied fields, and one in which the self-fields are comparable to the applied fields. The beam characteristics in both regimes have been compared to single particle expectations. Experiments have also been conducted in which the effect of an inner and outer conducting boundary on the time-resolved beam cross section has been measured. Results will be discussed in the context of collective ion acceleration experiments now in preparation.