Toward controllable high-power nanosecond microwave pulses: Research on the antenna-amplifier dielectric Cherenkov maser

Results of recent investigations of the device that seems a promising candidate for a high-power microwave amplifier are reviewed. This is a dielectric Cherenkov maser with a rod slow-wave structure, antenna-amplifier, in which an annular moderately relativistic electron beam amplifies the fundamental, non-axisymmetric HE₁₁ mode of the dielectric rod antenna. The RF drive signal is formed in a resonant microwave pulse compressor, so that the amplifier input power is of the order of megawatt, and the RF drive pulse duration is of a few nanosecond. The first experiments with this amplifier are described, in which a maximum gain of ~12.5 dB and a maximum output power of ~16 MW for the pulse duration of ~4 ns at a frequency of 9.388 GHz were obtained. The electron beam was generated in a compact module of linear induction accelerator (250-350 kV, 1-2 kA). Also reviewed are model experiments on plasma observation at a surface of a quartz rod inside an annular electron beam produced from a knife-edge cathode in a guiding magnetic field. In these experiments, time- and space-resolved light emission imaging was implemented, and important finding was the existence of a threshold voltage, below which the plasma formation can be avoided. Finally, possibilities of the drive frequency tuning are considered and experiments with a prototype of a frequency-agile X-band compressor are described.