Temporal Growth of a Plasma Oscillation

A plasma oscillation excited due to beam plasma interaction forms sometimes a standing wave between electrodes. The oscillation is suppressed by modulating the beam with high frequency signal as previously reported. When the modulation is removed, the oscillation begins to grow. From displays of this phenomenon on an oscilloscope the growth rate is directly observed. Indirect method based on a van der Pol equation is also tried for the same oscillation. The results are compared with the theory.