Time-Dependent Shear Motion in a Strongly Coupled Dusty Plasma in PK-4 on the International Space Station (ISS)

Time-dependent shear motion of dust particles in a three-dimensional (3-D) strongly coupled dusty plasma under microgravity conditions was investigated using the European Space Agency–Roscosmos facility Plasma-Kristall 4 (PK-4) on the International Space Station (ISS). The dust particles, which were negatively charged, were trapped in a glow discharge plasma powered by a dc voltage that switched its polarity periodically. They self-organized themselves into a structure resembling a cold liquid. A manipulation laser beam of a circular cross section pushed a stream of particles, moving them through the surrounding sample region; its power was modulated using a rectangular pulse, causing an impulsive unsteady flow. At the onset of the impulsive motion, the flow was observed as it grew in space and time. Later, during the steady manipulation, we find the thickness of the flow region fluctuated significantly over time.