arXiv subjects

Lorin Swint Matthews

Publications and source records attributed to Lorin Swint Matthews.

6 recordsLinked to original sources

arXiv2026

Modeling Torque Induced Alignment in a Dusty Plasma System

Irregular dust aggregates immersed in plasma sheaths experience several orientation-dependent torques that can modify their rotational dynamics and stability. Here, we investigate the rotational dynamics of charged irregular aggregates under conditions representative of a GEC rf plasma cell using self-consistent numerical simulations. The aggregates rotate freely in a unidirectional sheath electric field that drives an ion flow, allowing the torque contributions acting on the aggregate to be evaluated throughout the motion. The results show that the sheath electric field is the main driver of rotation and aligns the aggregate electric dipole moment with the sheath field direction. The ion wake modifies this alignment: its axial field component produces an opposing torque, while its transverse components introduce a destabilizing contribution that leads to small oscillations about the equilibrium orientation. The rotational equilibrium is described by an interaction energy well whose spring constant and depth increase with the sheath electric field magnitude, indicating stronger alignment and greater resilience to angular perturbations at higher fields. A second order multipole expansion of the aggregate ion interaction shows that the dipolar term governs the ion contribution to the aligning torque, supporting a dipole ion approximation across the examined conditions. These results identify the sheath electric field as the principal stabilizing mechanism for irregular aggregate rotation and clarify how ion wake fields perturb the equilibrium orientation.

physics.plasm-ph↗

arXiv2026

Ion wake-mediated dust interactions under PK-4 conditions: a generalized and compact potential formulation

Dusty plasmas, composed of electrons, ions, neutral particles, and charged dust grains, exhibit self-organization phenomena such as string-like structures observed in microgravity experiments. The formation of these structures is influenced by ion wakes generated by streaming ions under external electric fields, as well as by time-evolving plasma inhomogeneities such as ionization waves. Existing ion wake models, such as point charge and Gaussian-based representations, often rely on configuration-specific parameters, limiting their general applicability. In this work, we present a robust and general potential model for dust and ion wake systems under PK-4-like conditions. Using a small set of coefficients determined from molecular dynamics simulations, the model captures the potential distributions for multiple interparticle distances. Its application to test cases and implementation in a small scale dust dynamics simulation demonstrates its applicability to a wide range of dust arrangements beyond string-like configurations.

physics.plasm-ph↗

arXiv2026

Sparse identification of effective microparticle interaction potential in dusty plasma from simulation data

Identification of the particle interaction potential is a challenging and important task in dusty plasma, colloids, and smart materials as it allows the characterization of structure formation and helps predict phase transitions. With the advent of machine learning methods, this interaction can be extracted from particle position data, leading to a generalizable expression which is applicable in different systems. Methods such as sparse regression aim to provide a physically interpretable model that can generalize well, while avoiding unnecessary complexity due to overfitting. In this work, we present the use of the Sparse Identification of Nonlinear Dynamics (SINDy) with the weak formulation to learn equations of motion for noisy data from simple simulations of two dust particles interacting with a Yukawa (shielded Coulomb) potential. The application of these methods to experimental dusty plasma data is discussed, particularly in the case of simulation data and glass box experiments in RF discharge gravity environments and DC discharge microgravity environments, such as the Plasmakristall-4 (PK-4) experiment.

physics.plasm-ph↗

arXiv2019

Dust charging in dynamic ion wakes

Micron-sized dust grains have been successfully employed as non-perturbative probes to measure variations in plasma conditions on small spatial scales, such as those found in plasma sheaths. The dynamics of the grains can be used to map the forces due to electric fields present in the sheath, but the particle charge and electric field are difficult to measure independently. The problem is further complicated by the ion wake field which develops downstream of the dust grains in a flowing plasma. Within a sheath, ions are accelerated towards the charged boundary, and this ion flow creates a positively-charged spatial region downstream of the dust grain, called the ion wake. The ion wake in turn modifies the interaction potential between the charged grains. Here we use a molecular dynamics simulation of ion flow past dust grains to investigate the interaction between the charged dust particles and ions. The charging and dynamics of the grains are coupled self-consistently and derived from the ion-dust interactions, allowing for detailed analysis of the wakefield-mediated interaction as the structural configuration of the dust grains changes. The decharging of a dust grain as it moves through the wake of an upstream particle and the attractive ion wakefield force are mapped for a range of ion flow speeds.

physics.plasm-ph↗

arXiv2016

Charge of dust particles in a particle chain

Charged dust particles form structures which are extended in the vertical direction in the electrode sheath of a rf discharge when confined within a glass box. The charge on each particle as a function of height varies due to the changing plasma conditions and the wakefield of upstream particles. Here an analysis of the equilibrium state of chains of varying number of particles is analyzed to determine the charge on each particle within a vertically extended chain as well as the magnitude of the positive wakefield charge.

physics.plasm-ph↗

arXiv2004

Effects of the Charge-Dipole Interaction on the Coagulation of Fractal Aggregates

A numerical model with broad applications to complex (dusty) plasmas is presented. The self-consistent N-body code allows simulation of the coagulation of fractal aggregates, including the charge-dipole interaction of the clusters due to the spatial arrangement of charge on the aggregate. It is shown that not only does a population of oppositely charged particles increase the coagulation rate, the inclusion of the charge-dipole interaction of the aggregates as well as the electric dipole potential of the dust ensemble decreases the gelation time by a factor of up to twenty. It is further shown that these interactions can also stimulate the onset of gelation, or "runaway growth," even in a population of particles charged to a monopotential where previously it was believed that like-charged grains would inhibit coagulation. Gelation is observed to occur due to the formation of high-mass aggregates with fractal dimensions greater than two which act as seeds for runaway growth.

physics.plasm-ph↗