Self-organization of dust grains into stable filamentary dust structures (or “chains”) largely depends on dynamic interactions between individual charged dust grains and complex electric potential arising from the distribution of charges within a local plasma environment. Recent studies have shown that the positive column of the gas discharge plasma in the Plasmakristall-4 (PK-4) experiment at the International Space Station supports the presence of fast-moving ionization waves, which lead to variations of plasma parameters by up to an order of magnitude from the average background values. The highly variable environment resulting from ionization waves may have interesting implications for the dynamics and self-organization of dust particles, particularly concerning the formation and stability of dust chains. Here, we investigate the electric potential surrounding dust chains in the PK-4 experiment by employing a molecular dynamics model of the dust and ions with boundary conditions supplied by a particle-in-cell with Monte Carlo collision simulation of the ionization waves. The model is used to examine the effects of the plasma conditions within different regions of the ionization wave and compare the resulting dust structure to that obtained by employing the time-averaged plasma conditions. The comparison between simulated dust chains and experimental data from the PK-4 experiment shows that the time-averaged plasma conditions do not accurately reproduce observed results for dust behavior, indicating that more careful treatment of plasma conditions in the presence of ionization waves is required. It is further shown that commonly used analytic forms of the electric potential do not accurately describe the electric potential near charged dust grains under these plasma conditions.
Liquid Plasma Crystals on the ISS
This study examines the structure and stability of filamentary dusty plasmas using data
from the Plasmakristall-4 (PK-4) facility on board the International Space Station. Under the
action of a polarity-switched DC electric field, the dust particles in the PK-4 discharge have
been found to organize into field-aligned extended filaments, which has been compared to the
filamentary state in electrorheological (ER) fluids. Here we discuss how, in addition to an
ER-type structural transition, the PK-4 dusty plasmas exhibit structural states reminiscent of
those observed in liquid crystals (LCs) with rod-shaped molecules. We find that dust particles
within the filaments are strongly coupled in a crystalline-like structure, while the coupling of
particles across filaments is liquid-like. In addition to a common orientation along a director
axis (nematic behavior), the dust filaments also appear to align in large-scale nested structures,
or shells (smectic behavior). Finally, these filaments are found to further arrange in hexagonal
patterns within the plane orthogonal to the director axis, suggesting the possibility for smectic-B
and smectic-C structural states. As the observed ER and LC features of the filamentary
dusty plasma states are sensitive to variations in the PK-4 discharge conditions, we argue that
these dusty plasmas can provide a controlled analogous system for the study of fundamental
phenomena in soft matter, such as the origins of pattern formation and universality of phase
transitions.
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- Award ID(s):
- 1903450
- NSF-PAR ID:
- 10469446
- Publisher / Repository:
- American Institute of Aeronautics and Astronautics
- Date Published:
- Subject(s) / Keyword(s):
- ["dusty plasma","complex plasma","self-organization","liquid crystals"]
- Format(s):
- Medium: X
- Location:
- National Harbor, MD & Online
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.2514/6.2023-2615
