Experiment and model for a Stokes layer in a strongly coupled dusty plasma

TL;DR

This study experimentally observed a Stokes layer in a strongly coupled dusty plasma and developed a generalized Maxwell-fluid model that accurately describes the flow dynamics, including penetration depth and wavelength.

Contribution

The paper presents the first experimental observation of a Stokes layer in a strongly coupled dusty plasma and introduces a generalized model for two-phase viscoelastic fluids.

Findings

Experimental visualization of a Stokes layer in dusty plasma

Model agrees with experimental measurements of flow features

Characterization of flow penetration speed and wavelength

Abstract

A Stokes layer, which is a flow pattern that arises in a viscous fluid adjacent to an oscillatory boundary, was observed in an experiment using a two-dimensional strongly coupled dusty plasma. Liquid conditions were maintained using laser heating, while a separate laser manipulation applied an oscillatory shear that was localized and sinusoidal. The evolution of the resulting flow was analyzed using space-time diagrams. These figures provide an intuitive visualization of a Stokes layer, including features such as the depth of penetration and wavelength. Another feature, the characteristic speed for the penetration of the oscillatory flow, also appears prominently in space-time diagrams. To model the experiment, the Maxwell-fluid model of a Stokes layer was generalized to describe a two-phase liquid. In our experiment, the phases were gas and dust, where the dust cloud was viscoelastic due to strong Coulomb coupling. The model is found to agree with the experiment, in the appearance of the space-time diagrams, and in the values of the characteristic speed, depth of penetration, and wavelength.