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High power microwaves in the dominant TE10 mode emitted from the radially extracted vircator were studied experimentally at the diode voltages from 660 kV up to 1.2 MV and at diode currents from 37 up to 88 kA. The dominant microwave source is in the region of the virtual cathode. The return-current rods on the virtual cathode side of the anode narrows the output microwave frequency. There are dominant frequencies observed in the experiments. For example, three dominant narrow-band microwave pulses were observed at 8.63±0.05, 9.75±0.03, and 10.53±0.03 GHz. They are tunable and scaled linearly with the diode current at the inflection point. All the observed dominant frequencies are in good agreement with the scaling law f=(4.77/d)ln[γ0+(γ20−1)1/2] derived either from the two-dimensional virtual-cathode oscillation or from the one-dimensional harmonic reflexing-electron oscillation. This agreement also confirms that these two oscillations in our vircator generate nearly the same frequency. The maximum observed powers are 120 MW at 8.63 GHz, 75 MW at 9.75 GHz, and 60 MW at 10.53 GHz.

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