Green-Kubo relation for viscosity tested using experimental data for a 2D dusty plasma

TL;DR

This study experimentally tests the Green-Kubo relation for viscosity in a 2D dusty plasma by measuring particle dynamics and comparing the calculated viscosity with previous experiments and simulations.

Contribution

It provides the first experimental validation of the Green-Kubo relation for viscosity in a dusty plasma using direct particle measurements.

Findings

Measured viscosity agrees with previous hydrodynamic experiments

Validated the Green-Kubo relation for a nonequilibrium dusty plasma

Compared experimental results with theoretical predictions and simulations

Abstract

The theoretical Green-Kubo relation for viscosity is tested using experimentally obtained data. In a dusty plasma experiment, micron-size dust particles are introduced into a partially-ionized argon plasma, where they become negatively charged. They are electrically levitated to form a single-layer Wigner crystal, which is subsequently melted using laser heating. In the liquid phase, these dust particles experience interparticle electric repulsion, laser heating, and friction from the ambient neutral argon gas, and they can be considered to be in a nonequilibrium steady state. Direct measurements of the positions and velocities of individual dust particles are then used to obtain a time series for an off-diagonal element of the stress tensor and its time autocorrelation function. This calculation also requires the interparticle potential, which was not measured experimentally, but was obtained using a Debye-H\"{u}ckel-type model with experimentally determined parameters. Integrating the autocorrelation function over time yields the viscosity for shearing motion amongst dust particles. The viscosity so obtained is found to agree with results from a previous experiment using a hydrodynamical Navier-Stokes equation. This comparison serves as a test of the Green-Kubo relation for viscosity. Our result is also compared to the predictions of several simulations.