Effect of longitudinal magnetic field on microwave efficiency of virtual cathode oscillator

The effect of a longitudinal magnetic field on the microwave efficiency of a virtual cathode oscillator is investigated by particle-in-cell simulations. The mechanism of the oscillation associated with microwave emission is physically understood. It is found that the reflection of the electron beam back to the diode region is important to the oscillation. When a longitudinal magnetic field is applied, the residence time of the electrons in the potential well is lengthened, resulting in a large energy spread of the electron beam, which reduces the output power of the microwave.