A long-pulse, frequency-stabilized virtual cathode oscillator using a resonant cavity

Previous work at Los Alamos has demonstrated that by surrounding the oscillating virtual cathode with a resonant cavity, one can achieve stable, single-mode operation with the microwave output at a constant frequency. This result is a significant departure from the behavior of a free-running virtual cathode oscillator where the frequency depends on the (current density) ^1/2. Also, a virtual cathode amplifier has been produced by driving the cavity surrounding the virtual cathode with a signal from a low-power source. In both of these cases the output pulse length has been limited to approximately 100 ns by the available pulsed power. Recent experiments have demonstrated that significantly longer, narrow-band microwave pulses are obtainable from the virtual cathode oscillator when driven by an appropriate electron beam. These recent experimental results are presented.