Shear flow in a three-dimensional complex plasma in microgravity conditions

TL;DR

This study experimentally investigates shear flow in a 3D complex plasma under microgravity on the ISS, estimating its viscosity and revealing significantly lower values than ground-based experiments, with implications for plasma physics.

Contribution

First experimental measurement of shear flow and viscosity in 3D complex plasma under microgravity conditions using space-based instrumentation.

Findings

Viscosity estimated between 0.2 and 6.7 mm^2/s

Viscosity lower than ground-based measurements

Discussion of potential reasons for differences

Abstract

Shear flow in a three-dimensional complex plasma was experimentally studied in microgravity conditions using Plasmakristall-4 (PK-4) instrument on board the International Space Station (ISS). The shear flow was created in an extended suspension of microparticles by applying the radiation pressure force of the manipulation-laser beam. Individual particle trajectories in the flow were analyzed and from these, using the Navier-Stokes equation, an upper estimate of the complex plasma's kinematic viscosity was calculated in the range of $0.2$--$6.7~{\rm mm^2/s}$. This estimate is much lower than previously reported in ground-based experiments with 3D complex plasmas. Possible reasons of this difference are discussed.