Trapped-Particle Instability

A simple model for a new instability resulting from particles trapped in a large-amplitude electrostatic wave is invoked to explain the generation of satellite frequencies in a recently reported experiment by Wharton, Malmberg, and O'Neil. The model predicts satellites on the large-amplitude wave at a frequency separation proportional to $\sqrt{E}$, where $E$ is the amplitude of the large wave. The predicted growth rates reasonably account for the observed growth of these satellites.