title: Frequency modulation of the ion-acoustic instability.
abstract: In a double-plasma device with a negatively biased grid separating source and target chamber, the ion-acoustic instability is recorded during the injection of an ion beam whose velocity is chosen between the ion-acoustic velocity and twice this value. The observed broad power spectra of the density fluctuations are found to be related to a strong modulation of the frequency inside the bursts of unstable waves. This modulation is interpreted as being a consequence of the existence of propagating strongly nonlinear coherent structures that arise in the course of the nonlinear spatiotemporal evolution of the ion-acoustic instability.
authors.affiliation: Equipe Turbulence Plasma, PIIM, UMR 6633 CNRS-Université de Provence, Case 321 Centre de St. Jéroinsertion markme, Marseille, France.
authors.forename: H
authors.initials: H
authors.lastname: Klostermann
authors.forename: T
authors.initials: T
authors.lastname: Pierre