Gigawatt-level microwave bursts from a new type of virtual cathode oscillator

We describe experiments that demonstrate a new method for producing high-power microwave emission. The unstable oscillations of a virtual cathode which forms when a magnetized relativistic electron beam is injected into a circular waveguide generate the microwave radiation. In contrast to previous virtual cathode microwave generation techniques, electrons in the waveguide cannot be reflected back into the diode. Using this technique, we have produced 1.4 GW at 3.9 GHz with several hundred megawatts radiated in harmonic radiation.