Anisotropic electric potential distribution of dust filaments in the PK-4 experiment

Dust particles within the Plasmakristall-4 (PK-4) facility on board the International Space Station (ISS) have been observed to form extended filaments when exposed to a DC polarity-switched electric field. These filaments align in the direction of the applied electric field. Along this direction, the particles are strongly coupled, forming structures that resemble crystalline filaments. In contrast, the system shows liquid-like behavior in the transverse direction due to the weaker coupling between particles across the filaments. The electric field in PK-4 switches polarity with a frequency so high that the dust grains are unable to respond to the changing field direction. Since the ions are less massive than the dust, they can respond to the polarity change of the electric field. Hence, they flow past the negatively charged dust grains and focuses into a region of higher ion density downstream of a grain, known as the ion wake. The presence of dust particles and ion wakes alters the spatial potential distribution within the plasma leading to anisotropies in the potential distribution near the dust filaments. These variations depend on factors such as interparticle distance, gas pressure, and ion number density, among others. We analyze the anisotropic potential distribution in these dusty plasmas using N-body numerical simulations of the dust and ions for several plasma conditions representative of the PK-4 experiment. Results are used to develop a potential model which reproduces the effect of the dust and ion wake potential in the region near dust chains as a function of the dust interparticle distance. The resulting effective potential will be implemented in a one-component dust dynamics model.