High power microwave generation by a coaxial vircator

The coaxial virtual cathode oscillator (vircator) at Texas Tech University (USA) was studied with typical electron beam parameters of 500 kV, 40 kA, and 30 ns. The peak microwave power obtained was 400 MW giving a peak-to-peak microwave power efficiency of 2.2 %, although the peak of microwave power was /spl sim/10 ns delayed relative to that of the electron beam. The frequency spectrum of the microwaves was obtained by using a high-speed digital oscilloscope where a sharp peak was observed at /spl sim/2 GHz. To enhance the interaction between the microwave and the electron beam, the microwave extraction ratio was decreased by inserting a microwave reflector in the waveguide. The experimental results have shown that both the power and the field polarization of the microwaves are very sensitive to the position and the size of the microwave reflector. The highest microwave power efficiency obtained so far was 5% at a microwave power of /spl sim/900 MW, which is expected to be improved by further optimization.