High-power microwave generation from an axially extracted virtual cathode oscillator

An axially extracted virtual cathode oscillator has been fabricated. This u ltra-high-power microwave generator is powered hv the "Chundoong" intense r elativistic electron beam pulser (Max 600 kV, 88 kA, and 60 ns duration). I n this experiment, a solid electron beam with a peak diode current of 21 kA is obtained from the pulser operated at a peak diode voltage of 300 KV. It is found in this experiment that the peak of microwave emission occurred a t the moment of the second peak in electron beam current, where the diode v oltage V-d and diode current I-d are V-d = 290 kV and I-d = 21 kA, respecti vely. This observation might be strongly correlated to the inherent oscilla tions of the electron cloud in time and space originated from both the dyna mics of the reflected electron beam due to virtual cathode and oscillations of the virtual cathode itself, from which the peak of high-power microwave can be generated in this experiment. The major operating output frequencie s have been measured to be 6.68 GHz less than or equal to f less than or eq ual to 7.19 GHz based on the waveguide dispersive delayed line method, whic h is in good agreement with that from "MAGIC" computational results for an electron beam voltage of 290 kV and a diode current of 21 kA. The maximum m icrowave output power from the virtual cathode. oscillator has been measure d to be 200 MW in this experiment, while its power conversion efficiency is approximately 3.3%. The dominant emission mode from the virtual cathode os cillator is shown to he the TM01 mode based on the emission pattern of micr owave induced air breakdown in this experiment,