Parametric Suppression of a Large-Amplitude Plasma Instability

The intensity of a large-amplitude, unstable plasma mode has been reduced by applying a pump signal to parametrically couple it to another damped, natural mode of the plasma column. A suppression of the mode is observed when the frequency of the pump ${\omega }_0$ is equal to the difference between the damped-mode frequency ${\omega }_a$ and the unstable-mode frequency ${\omega }_b$ (${\omega }_0={\omega }_a-{\omega }_b$). The observed behavior of the mode energies is compared with a weak parametric-mode-coupling theory for lumped circuits, which includes nonlinear saturation terms for the unstable mode.