Temporal evolution of the microwave spectrum in the course of a radiation pulse from a relativistic Cherenkov plasma maser

A new Cherenkov plasma maser driven by a high-current relativistic electron beam (500 kV, 2 kA, 1 μs) was designed. The frequency of microwaves was tuned from 1.5 to 6 GHz with a power output from 50 to 80 MW and pulse duration from 500 to 700 ns. The radiation frequency depends on the plasma density and may be re-established during less than 100 μs. In different operation regimes microwave spectra were obtained with a width from 40 MHz to 1 GHz, and the spectra changed in the course of the pulses. The results of experiments coincide well with that of analytical theory and numerical simulations.