High-frequency electron beam modulation in a diode with an active plasma cathode

We have carried out experiments with an active plasma cathode showing the possibility to generate a modulated electron beam with a repetition rate of 2 Hz without the use of a high-frequency power supply. The modulation of the beam current amplitude reaches values ⩾30%. This modulation is found to have a frequency of 325±5 MHz for a discharge capacitor of 1 nF and a duration ⩾1 μs. In addition, the modulated electron beam is accompanied by electromagnetic radiation with the same frequency. We suggest that this high-frequency modulation is caused by electron oscillations within the potential well which is created inside the cathode structure by the positive potential of the plasma.