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

An axially extracted virtual cathode oscillator has been fabricated. This ultra-high-power microwave generator is powered by the “Chundoong” intense relativistic electron beam pulser (Max: 600 kV, 88 kA, and 60 ns duration). In 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 at the moment of the second peak in electron beam current, where the diode voltage V_d and diode current I_d are V_d=290 kV and I_d=21 kA, respectively. This observation might be strongly correlated to the inherent oscillations of the electron cloud in time and space originated from both the dynamics 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 frequencies have been measured to be 6.68 GHz⩽f⩽7.19 GHz based on the waveguide dispersive delayed line method, which 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 microwave output power from the virtual cathode oscillator has been measured to be 200 MW in this experiment. while its power conversion efficiency is approximately 3.3%. The dominant emission mode from the virtual cathode oscillator is shown to be the TM₀₁ mode based on the emission pattern of microwave induced air breakdown in this experiment