Collaborative Research: Study of Anisotropic Dust Interactions in the PK-4 Experiment

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This award supports a collaborative effort between Auburn University and Baylor University to study behavior of a complex plasma under microgravity in the PlasmaKristall-4 (PK-4) experiment on the International Space Station. Complex plasmas, also known as dusty plasmas, are collections of micron-sized dust particles immersed in a plasma, or ionized gas. The dust grains typically become charged by collecting electrons and ions on their surface. When dusty plasmas are placed in external electric fields, anisotropic interactions between dust grains and ion flows can lead to the formation of filamentary dust structures. Anisotropic interactions, which depend on the relative orientation of interacting particles, are known to arise in some of the most interesting complex systems, including proteins and smart materials. A fundamental open question in the study of these systems is how anisotropic interactions lead to structure formation. This project addresses this question using a combined analytical, numerical, and experimental approach to investigate how anisotropic interactions lead to structure formation in dusty plasma experiments on the International Space Station (ISS).This project will use data from several PK-4 campaigns to investigate the form and origins of the anisotropic dust-dust interaction potential that leads to the formation of filamentary dusty plasma structures. Data collected from PK-4 experiments will be used to quantify structural anisotropy as a function of plasma conditions using statistical analysis and data-driven methods. Molecular dynamics (MD) simulations of dust and ions will be used to calculate the dust–ion wakefield potential. A machine learning (ML) model will be applied to experimental data to identify the most likely form of the interaction forces as a function of plasma parameters. Interaction forces and potentials learned with the ion-dust MD simulation and the ML model will be applied in MD simulations of larger dust clouds to validate against the experimental data. Experiments in the PK-4 BU device, a ground-based replica of the PK-4 ISS with additional diagnostic capabilities, will be used to determine the relationship between plasma conditions and the onset of plasma ionizations waves. Finally, an analytic model will be employed to determine the spectrum of energy states of the Hamiltonian representing the anisotropic interaction potential. This method will be used to determine the relationship between PK-4 filamentary dusty plasma and other filamentary structures, such as electrorheological materials and liquid crystals.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.