Beam-Plasma Emission near the Plasma Frequency

This paper presents detailed spectra for electromagnetic emission from a strong relativistic beam-plasma instability. Some emission appears early in the beam voltage pulse, apparently from reflexing. This subsides as beam propagation improves, and emission moves to high frequencies. This is compatible with a collective emission pro-cess from electrostatic waves built up in the chamber by reflection from the walls. Noise levels suggest about 100 emitting sites switching on and off randomly. The emitters comprise about 1 percent of the plasma volume and survive a time comparable to the lifetime of solitons subject to ion damping.