Change in the Generation Mode of the Plasma Relativistic Microwave Oscillator

Abstract

Time evolution of the parameters of output radiation of a plasma relativistic microwave oscillator (PRMO) based on the Sinus 550-80 accelerator during a single relativistic electron beam (REB) pulse was studied experimentally. Analysis of the experimental data was accompanied by numerical simulations under conditions close to the experimental ones. It is shown that qualitative changes in the parameters of the PRMO output radiation are associated with a change in the generation mode. The first half of the REB pulse is characterized by the maximum output radiation power and a broadband spectrum consisting of a great number of harmonics. The nonlinear beam–plasma interaction limits the growth of the field amplitude, decreases the number of plasma electrons, and leads to the emergence of longitudinal plasma inhomogeneity. The appearance of an ion background in the drift tube volume and the formation of a radially nonuniform plasma waveguide alter the conditions of beam–plasma interaction in the second half of the pulse. The second half of the REB pulse is characterized by a decrease in the output microwave power and the narrowing of the generation frequency band. Spectral analysis demonstrates preservation of a stable narrow spectral component throughout the microwave pulse.