Influence of anode-cathode gap distance on output characteristics of high power microwave from coaxial virtual cathode oscillator

We have investigated an influence of anode-cathode (A-K) gap distance on output characteristics of high power microwave from coaxial virtual cathode oscillator (vircator). This high power microwave generator is powered by the 'Chundoong' (Max 600 kV, 88 kA, 60 ns), which is an intense relativistic electron beam-pulse generator. In this experiment, we observed that the microwave power has been dependent upon the A-K gap distance, where A-K gap has been varied from 4 mm to 10 mm. The maximum microwave power is observed to be 240 MW, whose efficiency is about 3.45%, at the AK gap distance of 4 mm. Also the microwave frequencies are measured to be 5.7 GHz from combination of coupled line band pass filter with 1 GHz band-gap and dispersive delay line. It is noted that and this measured frequency is in good agreement with that of simulation. It is also found that the dominant mode of output microwave is a TM01 mode from both results of experiment and simulation.