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.

中文翻译：

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微重力条件下三维复合等离子体中的剪切流

使用国际空间站上的Plasmakristall-4实验室在微重力条件下对三维（3D）复杂等离子体中的剪切流进行了实验研究。通过施加操纵激光束的辐射压力，在延长的微粒悬浮液中产生剪切流。分析了流动中的单个粒子轨迹，并根据这些轨迹，使用Navier-Stokes方程，计算出了在范围内的复杂等离子体运动粘度的上限。$0.2–6.7{\mathrm{毫米}}^2/\mathrm{s}$。该估计值比以前在3D复杂等离子体的地面实验中报告的要低得多。讨论了造成这种差异的可能原因。