Detection of stochastic waves in plasma monolayer crystals from video images

Abstract

The motion of dust particles confined in plasma monolayer crystals is analyzed from video images, under conditions dominated by dust-neutral collisions. In these crystals, dust-neutral collisions will act as a random driving force, exciting phonons with a stochastic nature. The phonons are investigated using standard statistical tools, including both single- and multiparticle correlation functions. Single-particle correlations as obtained from the velocity autocorrelation function yield oscillations in a very narrow frequency band. Similar behaviors have previously been reported for strongly coupled one-component plasmas, and for trapped Brownian particles. Spatial correlations in the crystal lattice are studied from multiparticle correlation functions, suggesting an average wavelength slightly larger than the dimension of the crystal. Throughout the crystal, the dust velocity amplitude and polarization vary significantly, with the main variation in the radial direction out of the crystal center. This suggests the observed wave feature is a standing wave with a stochastic amplitude, dominated by its lowest eigenfrequency.