Observation of high-power millimeter wave emission from a virtual cathode

Intense bursts of mm wave power have been observed in microwave generation experiments with a relativistic electron beam (REB) virtual cathode oscillator. In this device an electron beam is injected into a drift space at a current above the space-charge-limit, and a potential develops downstream which is large enough to reflect electrons back to the source region. Two mechanisms can give rise to microwave oscillations in a virtual cathode device: electrons reflexing between the real and virtual cathodes, and oscillations in the amplitude and position of the virtual cathode. Typically both mechanisms are present, but in the present experiments reflexing has been shown to be dominant.