Power efficiency enhancement of a coaxial virtual cathode oscillator with ring-type reflector

We have investigated simulation and experimental studies on the high power microwave generation from virtual cathode oscillator (vircator) in a coaxial geometry. It consists of a coaxial annular cathode and cylindrical mesh anode. This high power microwave generator is powered by the "Chondong" intense relativistic electron beam pulser (Max: 600 kV, 88 kA and 60 ns duration). It is noted that the microwave power can be further enhanced by adding a reflector to the coaxial vircator. The microwave output power depends sensitively on the position and geometry of the reflector. It is observed that the output microwave power is measured to be about 400 MW and its conversion efficiency is about 6%. The frequency of the observed output microwave has been measured to be about 5.6 GHz, which is in good agreement with that of simulation. The dominant mode of output microwave is also shown to be a TM01 mode from a simulation with a 3 dimensional particle-in-cell (PIC) code called MAGIC.