Axially extracted virtual cathode oscillator with an annular cathode for enhancement of the microwave conversion efficiency

A numerical simulation study of a virtual cathode oscillator with an annular cathode has been performed by using a 3-dimensional particle-in-cell (PIC) code called MAGIC. Also, experimental studies are performed for comparison with the numerical results. The annular diode consists of a circular anode mesh and an annular cathode. The object of this investigation is to find the optimized width and radius of an annular cathode in our high power microwave pulser, "Chundoong". Both the simulation and the experimental results show that the output microwave power and frequency depend on the annular cathode width and radius and that the dominant mode of output microwaves is TM01 under an optimized width of 4 mm and radius of 20 mm.