A diode design study of the virtual cathode oscillator with a ring-type reflector

A numerical simulation study of the high-power microwave generation from the vircator (virtual cathode oscillator) is carried out for coaxial diode structure by using a three-dimensional particle-in-cell (PIC) code called MAGIC. The coaxial vircator has a centered annular cathode body, cathode ring and cylindrical meshed-anode in order to enlarge the active interaction region in the virtual cathode space. In order to enhance a conversion efficiency of the output microwave power, ring-type reflector was installed to coaxial-type diode structure. The simulation results show that the output microwave frequency has a narrow bandwidth and its output microwave power sensitively depends upon the position and width of ring-type reflector. The maximum output microwave power is obtained by adopting a ring-type reflector 10 mm in width and 40 mm in the distance from the intense relativistic electron beam to the ring-type reflector. The output microwave mode without a ring-type reflector is a mixture of TM and TE mode. However, the TM₀₁ mode with its resonance frequency of 2.2 GHz is dominant for the ring-type reflector.