A virtual cathode oscillator (vircator) is a special type of oscillator capable of generating high-power microwaves. We studied an axially extracted vircator by installing a cone-shaped reflector in our pulsed power device, “Chundoong” and numerically studied by using a three-dimensional particle-in-cell simulation, MAGIC. In the simulation, we varied the inner diameter of the reflector between 9?cm and 17?cm; a diameter of 13?cm showed the maximum power enhancement measured at the end of the drift tube position. The dominant oscillating frequencies without and with reflector were determined to be 3.42?GHz and 3.37?GHz, respectively, in the simulation and 3.40?GHz and 3.31?GHz, respectively, in the experiment. The numerically predicted frequencies showed good agreement with those observed during the experiment. The microwave power generated from the conventional axial vircator was 571?MW with the efficiency approximately 20%; which is increased by the interference up to 835?MW with the efficiency of 29.4% with reflector. The microwave power increased to 46% with the reflector. The microwave emission mode from the axial vircator wasTM01with and without reflector, based on the vector electric and magnetic fields observed during the simulation. The presented reflector increases the microwave power significantly. This reflector may possibly be used to increase the microwave power by the interference to increase efficiency of vircator sources.
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