OBSERVATIONS OF LOW-FREQUENCY OSCILLATIONS DURING RELATIVISTIC-ELECTRON-BEAM PLASMA INTERACTIONS

During propagation of a relativistic electron beam in hydrogen gas at sub-torr pressures using a foil-less diode, low frequency oscillations in the megahertz range are observed in the net current wave forms, and continue even after passage of the beam. The novel feature of the experiment is that both beam generation and propagation take place in the same low-pressure regime, and hence the beam parameters are functions of gas pressures. Analysis of the experimental results shows that the low-frequency oscillations result from the resistive-hose instability.