Measurement and Behavior Analysis of Beam Current Modulation in a Virtual Cathode Oscillator

Modulation and amplitude of transmitted electron beam current in a virtual cathode oscillator have been measured by using two beam detectors, large detector and small detector. The objective is to understand the mechanism of microwave oscillation in a virtual cathode oscillator. The large detector has given us information about amplitude of the transmitted beam current from which the condition of virtual cathode formation has been obtained. The small detector has been used to measure the current modulation in the transmitted electron beam. The results have provided direct evidence of the virtual cathode existence and oscillation. The time–frequency behavior of the beam modulation has matched with that of the output microwave.