Shear flow in a three-dimensional (3D) complex plasma was experimentally studied in microgravity conditions using the Plasmakristall-4 laboratory on board the International Space Station. 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 $0.2–6.7{\mathrm{mm}}^2/\mathrm{s}$. This estimate is much lower than previously reported in ground-based experiments with 3D complex plasmas. Possible reasons for this difference are discussed.

• Received 3 June 2020
• Accepted 20 August 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.033404

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Published by the American Physical Society