arXiv subjects

Lorin S. Matthews

Publications and source records attributed to Lorin S. Matthews.

At least 19 recordsLinked to original sources

arXiv2025

Anisotropic anomalous diffusion and nonequilibrium in microgravity dusty plasma. Part Two: Spectral Analysis

Anisotropic anomalous dust diffusion in microgravity dusty plasma is investigated using experimental data from the Plasmakristall-4 (PK-4) facility on board the International Space Station. The PK-4 experiment uses video cameras to track individual dust particles, which allows for the collection of large amounts of statistical information on the dust particle positions and velocities. In Part One of this paper, these statistics were used to quantify anomalous dust diffusion caused by anisotropies in the plasma-mediated dust-dust interactions in PK-4. Here we use scaling relations to convert statistical parameters extracted from data into input parameters for a Hamiltonian spectral model. The kinetic energy term of the Hamiltonian (modeling anomalous diffusion) is informed from the dust displacement distribution functions, while the potential energy term (modeling stochasticity) is informed from fluctuations in the dust positions. The spectrum of energy states for each Hamiltonian is studied to assess probability for extended states (i.e., a continuous portion of the spectrum). The spectral model shows that the combination of nonlocality and stochasticity leads to high probability for transport at certain scales in Hilbert space, which coincide with the characteristic spatial scales of dust particle jumps observed in the experiments. Lastly, we discuss how this spectral approach is generalizable to many complex systems, such as electron transport in 2D materials where statistical models are not feasible.

physics.plasm-ph↗

arXiv2025

Chondrule dust rim growth: Influence of restructuring using molecular dynamics simulations

We investigate the influence of disruptive collisions on chondrule rim growth, emphasizing the role of kinetic energy in determining the outcomes of these interactions. We establish a threshold of approximately 10 cm/s for the "hit-and-stick" collision regime, beyond which significant changes occur in the structure of rimmed chondrules. Our findings highlight that at low collision energies (KE $< 10^{-12}$ J), minimal structural alteration takes place, while higher energies (KE up to $10^{-10}$ J) lead to compaction of the rim, reducing both its thickness and porosity. Collisions with energies exceeding $10^{-8}$ J result in the complete disruption of the rim, with particles being expelled from it. These results are correlated with the turbulence levels within the disk, as kinetic energy scales with the relative velocities of colliding particles. Leveraging machine learning models trained on our collision data, we predict changes in rim characteristics and employ these predictions in a Monte Carlo simulation to explore rim growth dynamics. Our simulations reveal that rim development is sustained in low-turbulence environments ($α\leq 10^{-5}$), while intermediate turbulence levels ($α$ = $10^{-3}$ to $10^{-4}$) lead to erosion, preventing further rim accumulation in high-turbulence contexts.

astro-ph.EP↗

arXiv2023

Outcomes of Planetary Collisions: Importance of Gravity and Material Properties

The final sizes, composition, and angular momenta of solid planetary bodies depend on the outcomes of collisions between planetary embryos. The most common numerical method for simulating embryo collisions is to combine a gravity solver with a hydrodynamic solver, allowing pressure gradients, shock waves, and gravitational torques to loft material into orbit. Here, we perform the first direct comparison between hydrodynamic methods and a simplified method employing only gravity and a quadratic repulsive force. The formation of Earth's Moon, perhaps the most heavily simulated planetary collision, is used as a test case. Many of the main features of a collision between two planetary embryos, including collisions in which an orbiting disc of material and/or intact moons are formed, are controlled solely by gravitational forces. Comparison of the methods shows that the mass and orbit of the satellite, as well as the extent of physical mixing between the protoearth and impactor, are similar regardless of the inclusion of the inclusion of hydrodynamic effects or the equation of state employed. The study of thermal and chemical effects of the impact, and determining the time scale for lunar accretion, still require a full hydrodynamic calculation. The simplified gravity plus quadratic repulsive force approach allows rapid testing of various initial conditions to identify cases for further detailed study.

astro-ph.EP↗

arXiv2022

Experimental Measurement of Overlapped Sheaths

Due to the complicated environment of the plasma sheath, it is difficult to experimentally measure plasma characteristics in the narrow geometry where sheaths from opposite boundaries overlap. Since such geometries are often found in industrial plasma applications, accurate measurements of this type are of significant interests. In this paper, we employ micron-sized dust grains as non-perturbative probes of the plasma environment. A particle-freefall technique is then used to measure the sheath profiles produced by a rf plasma within a glass box. The results show that this technique can identify the plasma operating conditions for which the sheaths on opposite walls begin to overlap as well as the magnitude of the effect.

physics.plasm-ph↗

arXiv2022

Influence of Temporal Variations in Plasma Conditions on the Electric Potential Near Self-Organized Dust Chains

The self-organization of dust grains into stable filamentary dust structures (or "chains") largely depends on dynamic interactions between the individual charged dust grains and the complex electric potential arising from the distribution of charges within the local plasma environment. Recent studies have shown that the positive column of the gas discharge plasma in the Plasmakristall-4 (PK-4) experiment onboard the International Space Station (ISS) 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 by employing a molecular dynamics model of the dust and ions with boundary conditions supplied by a Particle-in-Cell with Monte Carlo collisions (PIC-MCC) 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. Comparison between simulated dust chains and experimental data from the PK-4 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.

physics.plasm-ph↗

arXiv2020

Dust as probes: determining confinement and interaction forces

Complex plasmas are interesting systems as the charged dust can self-assemble into different types of ordered structures. To understand the mechanisms which govern the transitions from one type of structure to another, it is necessary to know both the dust charge and the confining electric fields within the environment, parameters which 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. The differences in local ion density caused by the wake field change the equilibrium dust charge and shielding distance of the dust grains, and thus affect the interaction between grains. Here we use a molecular dynamics simulation of ion flow past dust grains to investigate the interaction between the dust particles and ions. We consider a long vertical chain of particles confined within a glass box placed on the lower electrode of a GEC rf reference cell. Ions stream from the bulk plasma at the top of the box to the negative lower electrode. We apply the model iteratively to self-consistently determine the dust charge, electric field, and ion density along the length of the chain as well as the ion flow speed. Simulation results indicate that the ion flow speed within the box is subsonic.

physics.plasm-ph↗

arXiv2020

A machine learning based Bayesian optimization solution to nonlinear responses in dusty plasmas

Nonlinear frequency response analysis is a widely used method for determining system dynamics in the presence of nonlinearities. In dusty plasmas, the plasma-grain interaction (e.g., grain charging fluctuations) can be characterized by a single particle nonlinear response analysis, while grain-grain nonlinear interactions can be determined by a multi-particle nonlinear response analysis. Here, a machine learning-based method to determine the equation of motion in the nonlinear response analysis for dust particles in plasmas is presented. Searching the parameter space in a Bayesian manner allows an efficient optimization of the parameters needed to match simulated nonlinear response curves to experimentally measured nonlinear response curves.

physics.plasm-ph↗

arXiv2020

Ion wake induced mode coupling in a horizontal chain in complex plasmas

Ion wake induced mode coupling is investigated experimentally for a horizontal dust chain formed in a complex plasma, verifying results from previous simulation. A double branch of faint spectral lines is detected in the mode spectra which verifies the predicted rule of mode coupling between the vertical z(j=i$\pm$1) modes and the longitudinal mode x(i). Discreet instabilities are observed as the branches of x- and z-modes intersect each other. The mode spectra in the vicinity of the instabilities exhibit enhanced energy density at specific coupled x and z modes, serving as direct evidence that these instabilities are caused by resonance between the coupled modes. The instability-induced melting threshold was found to obey the Lindemann criterion through analysis of the instantaneous relative interparticle distance fluctuation (IDF). The relation between mode spectra and dispersion relations was further studied by multiplying the mode spectra with a transition matrix connecting the bases of normal mode eigenvectors and Fourier series in k space. Typical dispersion relations corresponding to the longitudinal and out-of-plane transverse Dust Lattice Waves (DLWs) are obtained, which also exhibit characteristics unique to finite systems, including discrete bands and strong fluctuations in the energy density.

physics.plasm-ph↗

arXiv2018

Self-diffusion in two-dimensional quasi-magnetized rotating dusty plasmas

The self-diffusion phenomenon in a two-dimensional dusty plasma at extremely strong (effective) magnetic fields is studied experimentally and by means of molecular dynamics simulations. In the experiment the high magnetic field is introduced by rotating the particle cloud and observing the particle trajectories in a co-rotating frame, which allows reaching effective magnetic fields up to 3000 Tesla. The experimental results confirm the predictions of the simulations: (i) super-diffusive behavior is found at intermediate time-scales and (ii) the dependence of the self-diffusion coefficient on the magnetic field is well reproduced.

physics.plasm-ph↗

arXiv2018

Non-perturbative experiments on plasma-mediated particle interaction and the ion wake potential

A non-perturbative method is introduced to measure the particle-particle interaction strengths and in-situ confinement for a vertically aligned dust particle pair in a complex plasma. The intrinsic thermal motion of each particle is tracked, allowing the interaction strengths and confinement in both the vertical and horizontal directions to be determined simultaneously. The method is validated through quantitative agreement with previous measurements of the non-reciprocal interaction strength in the vertical direction, the horizontal ion wake attraction, and the charge reduction and heating of the lower particle when located in the wake of the upper particle. The experiment also verifies both theoretical and numerical predictions for the ion wake potential by investigating the ratios among the interaction strengths in the vertical and horizontal directions, as well as in the up- and down-stream directions at varying powers. The upstream potential is shown to be asymmetric with unequal screening lengths in the vertical and horizontal directions, implying a subsonic ion flow at low rf powers. Additionally, it is shown that the ratio between the down and up-stream strengths in the vertical direction remains constant at high power, then increases at low power, in agreement with the theoretically predicted increase in the magnitude of the wake potential as the Mach number decreases. Finally, the measured ratio of approximately 5 between the downstream and upstream strengths in the horizontal direction is shown to agree with simulations conducted employing similar plasma parameters.

physics.plasm-ph↗

arXiv2017

Discrete stochastic charging of aggregate grains

Dust particles immersed in a plasma environment become charged through the collection of electrons and ions at random times, causing the dust charge to fluctuate about an equilibrium value. Small grains (with radii less than 1 \mum) or grains in a tenuous plasma environment are sensitive to single additions of electrons or ions. Here we present a numerical model that allows examination of discrete stochastic charge fluctuations on the surface of aggregate grains and determines the effect of these fluctuations on the dynamics of grain aggregation. We show that the mean and standard deviation of charge on aggregate grains follows the same trends as those predicted for spheres having an equivalent radius, though aggregates exhibit larger variations from the predicted values. In some plasma environments, these charge fluctuations occur on timescales which are relevant for dynamics of aggregate growth. Coupled dynamics and charging models show that charge fluctuations tend to produce aggregates which are much more linear or filamentary than aggregates formed in an environment where the charge is stationary.

physics.plasm-ph↗

arXiv2017

Dust cluster spin in complex (dusty) plasmas

The spontaneous rotation of small dust clusters confined inside a cubical glass box in the sheath of a complex plasma was observed in experiment. Due to strong coupling between the dust particles, these clusters behave like a rigid-body where cluster rotation is contingent upon their configuration and symmetry. By evaluating the effects of distinct contributing forces, it is postulated that the rotation observed is driven by the net torque exerted on the cluster by the ion wake force. The configuration and symmetry of a cluster determines whether the net torque induced by the ion wake force is nonzero, in turn leading to cluster rotation. A COPTIC (Cartesian mesh, oblique boundary, particles and thermals in cell) simulation is employed to obtain the ion wake potential providing a theoretical model of cluster rotation which includes both the ion wake force and neutral drag and predicts rotation rates and direction in agreement with experimental results. These results are then used to diagnose the ion flow within the box.

physics.plasm-ph↗

arXiv2017

Determination of interaction between a dust particle pair in complex plasmas

A non-intrusive method to measure particle interaction using only the thermal motion of the particles is applied to a vertically aligned dust particle pair in a complex plasma. The scanning mode spectra (SMS) are obtained by tracking the thermal motion of the grains, with the interaction strength then determined from the frequencies and the eigenvector configuration of the normal modes. The interaction of the bottom particle acting on the top particle is shown to be Yukawa-like with the screening length suppressed against the ion flow. The interaction of the top particle acting on the bottom particle is repulsive in the vertical direction and attractive in the horizontal direction. The vertical interaction from the top to bottom particle is stronger than that from the bottom to top particle, agreeing with an extended ion wake tail as predicted by the inhomogeneous ion wake theory. Determination of the horizontal attraction strength serves as a direct verification and quantification of the ion wake effect. Heating of the lower particle in both the vertical and horizontal directions is observed and quantitatively related to the nonreciprocity of the interaction. The in situ confinement strength at the position of the bottom particle is found to be consistently lower than at the position of the top particle, caused by decharging of the lower particle by 10-30% while inside the ion wake of the top particle.

physics.plasm-ph↗

arXiv2016

Temperature measurement of a dust particle in a RF plasma GEC reference cell

The thermal motion of a dust particle levitated in a plasma chamber is similar to that described by Brownian motion in many ways. The primary differences between a dust particle in a plasma system and a free Brownian particle is that in addition to the random collisions between the dust particle and the neutral gas atoms, there are electric field fluctuations, dust charge fluctuations, and correlated motions from the unwanted continuous signals originating within the plasma system itself. This last contribution does not include random motion and is therefore separable from the random motion in a normal temperature measurement. In this paper, we discuss how to separate random and coherent motion of a dust particle confined in a glass box in a Gaseous Electronic Conference radio frequency reference cell employing experimentally determined dust particle fluctuation data analyzed using the mean square displacement technique.

physics.plasm-ph↗

arXiv2016

Ion-wake Field inside a Glass Box

The confinement provided by a glass box is proving ideal for the formation of vertically aligned structures and a convenient method for controlling the number of dust particles comprising these dust structures, as well as their size and shape. In this paper, the electronic confinement of the glass box is mapped and the particle interactions between the particle pairs inside the glass box are measured. The ion-wake field is shown to exist within the glass box and its vertical and horizontal extent is measured.

physics.plasm-ph↗

arXiv2015

Dust Coagulation in the Vicinity of a Gap-Opening Jupiter-Mass Planet

We analyze the coagulation of dust in and around a gap opened by a Jupiter-mass planet. To this end, we carry out a high-resolution magnetohydrodynamic (MHD) simulation of the gap environment, which is turbulent due to the magnetorotational instability. From the MHD simulation, we obtain values of the gas velocities, densities and turbulent stresses a) close to the gap edge, b) in one of the two gas streams that accrete onto the planet, c) inside the low-density gap, and d) outside the gap. The MHD values are then supplied to a Monte Carlo dust coagulation algorithm, which models grain sticking and compaction. We consider two dust populations for each region: one whose initial size distribution is monodisperse, with monomer radius equal to 1 $μ$m, and another one whose initial size distribution follows the Mathis-Rumpl-Nordsieck distribution for interstellar dust grains, with an initial range of monomer radii between 0.5 and 10 $μ$m. Our Monte Carlo calculations show initial growth of dust aggregates followed by compaction in all cases but one, that of aggregates belonging to the initially monodisperse population subject to gas conditions outside the gap. In this latter case, the mass-weighted (MW) average porosity of the population reaches extremely high final values of 98\%. The final MW porosities in all other cases range between 30\% and 82\%. The efficiency of compaction is due to high turbulent relative speeds between dust particles. Future studies will need to explore the effect of different planet masses and electric charge on grains.

astro-ph.EP↗

arXiv2015

Multipole Expansions of Aggregate Charge: How Far to Go?

Aggregates immersed in a plasma or radiative environment will have charge distributed over their extended surface. Previous studies have modeled the aggregate charge using the monopole and dipole terms of a multipole expansion, with results indicating that the dipole-dipole interactions play an important role in increasing the aggregation rate and altering the morphology of the resultant aggregates. This study examines the effect that including the quadrupole terms has on the dynamics of aggregates interacting with each other and the confining electric fields in laboratory experiments. Results are compared to modeling aggregates as a collection of point charges located at the center of each spherical monomer comprising the aggregate.

physics.comp-ph↗

arXiv2014

Mode couplings and resonance instabilities in dust clusters

The normal modes for three to seven particle two-dimensional (2D) dust clusters in a complex plasma are investigated using an N-body simulation. The ion wakefield downstream of each particle is shown to induce coupling between horizontal and vertical modes. The rules of mode coupling are investigated by classifying the mode eigenvectors employing the Bessel and trigonometric functions indexed by order integers (m, n). It is shown that coupling only occurs between two modes with the same m and that horizontal modes having a higher shear contribution exhibit weaker coupling. Three types of resonances are shown to occur when two coupled modes have the same frequency. Discrete instabilities caused by both the first and third type of resonances are verified and instabilities caused by the third type of resonance are found to induce melting. The melting procedure is observed to go through a two-step process with the solid-liquid transition closely obeying the Lindemann criterion.

physics.plasm-ph↗