Effect of the Distance of Plasma-Beam Interaction on the Oscillation Regimes in a Plasma Relativistic Microwave Oscillator

We study the effect of the distance of plasma-beam interaction on the parameters of the output radiation of a plasma relativistic microwave generator (PRMO). In the experimental PRMO based on the Sinus 550-80 accelerator, the characteristics of the output microwave radiation (spectral width, spectral density of the amplitude of the radiation) vary during a single pulse of the relativistic electron beam (REB). We analyze and numerically simulate the experimental data; the geometric and physical parameters of the device used in the simulation are close to those in the experiments. We show that increase in the distance of the plasma-beam interaction (the length of the system) causes the duration of the effective microwave pulse generation to approach that of the REB despite the presence of ion background and the plasma density profile modification, i.e., no disruption or change in the generation regime occurs during the REB pulse, while the microwave radiation spectrum broadens.