arXiv subjects

Lorin Matthews

Publications and source records attributed to Lorin Matthews.

At least 19 recordsLinked to original sources

arXiv2026

Spacecraft heat shield study in the DIII-D tokamak

We report a new experimental platform developed at the DIII-D National Fusion Facility to investigate carbon ablation and spallation under extreme heat fluxes relevant to fusion plasma-facing components and high-enthalpy atmospheric entry. Carbon samples were exposed to parallel heat fluxes of $30$--$40~\mathrm{MW\,m^{-2}}$ in the scrape-off layer using two complementary approaches: stationary carbon rods inserted near the divertor strike point and slow-launch carbon pellets injected vertically into the edge and core plasma. Pellets penetrating the core experienced heat fluxes approximately an order of magnitude higher. The conditions reproduce key aspects of the shock-layer environment encountered by the Galileo probe during entry into Jupiter's atmosphere. Fast visible imaging, divertor spectroscopy, infrared thermography, CO$_2$ interferometry, and post-exposure profilometry provided measurements of ablation rates, surface recession, and temperature evolution. Measured mass-loss rates of $(1$--$3)\times10^{-2}~\mathrm{g\,cm^{-2}\,s^{-1}}$ agree with semi-empirical aerospace ablation models, while wedge-shaped rods exhibited greater ablation than cylindrical and concave samples. UEDGE-DUSTT simulations incorporating parallel plasma flows, ${\bf j}\times{\bf B}$ forces, and ablation-cloud shielding reproduce the measured pellet trajectories and ablation timescales. These results establish tokamak plasma as a high-heat-flux environment for validating carbon ablation models and studying material response and impurity dynamics in reactor-relevant divertor plasmas.

physics.plasm-ph↗

arXiv2026

DustNET: enabling machine learning and AI models of dusty plasmas

Dusty plasmas are ubiquitous throughout the universe, spanning laboratory and industrial plasmas, fusion devices, planetary environments, cometary comae, and interstellar media. Despite decades of research, many aspects of their behavior remain poorly understood within a unified framework. While numerous theoretical and numerical models describe specific phenomena, such as dust charging, transport, waves, and self-organization, fully predictive models across the wide range of spatial and temporal scales in both laboratory and natural systems remain elusive. Conventional plasma descriptions rely on coupled differential equations for particle densities, momenta, and energies, but their solutions are often limited by computational cost, numerical uncertainties, and incomplete knowledge of boundary conditions and transport processes. Recent advances in machine learning (ML), particularly deep neural networks, offer new opportunities to complement traditional physics-based modeling. Here we review ML and artificial intelligence (AI) approaches, termed bottom-up data-driven methods, for dusty plasma research. Central to this effort is Dust Neural nEtworks Technology (DustNET), a community-driven dataset initiative inspired by ImageNet, integrating experimental, simulation, and synthetic data to enable predictive modeling, uncertainty quantification, and multi-scale analysis. DustNET-trained models may also be deployed in real-time experimental settings under edge computing constraints. Combined with emerging multi-modal AI foundation models and autonomous agents, this framework provides a pathway toward a unified, physics-informed understanding of dusty plasmas across laboratory, industrial, space, and astrophysical environments.

physics.plasm-ph↗

arXiv2025

Structural States of Filamentary Microgravity Dusty Plasma

This study investigates the filamentary structural states of microgravity dusty plasma using data from the Plasmakristall-4 (PK-4) facility on board the International Space Station. The dust particles in the PK-4 discharge are observed to form field-aligned filaments and nested (layered) structures in response to changes in the plasma conditions, neutral gas pressure, and externally applied electric field. This work explores the possibility that these filamentary dusty plasmas exhibit properties of liquid crystals. The structural characteristics of the dust clouds are studied for nine sets of pressure-current conditions using pair correlation functions calculated for particles (i) within individual filaments, (ii) within the central plane of the dust cloud, and (iii) within successive planes of the cloud (the 3D cloud). It is observed that, at low pressure ($\approx$30 Pa), the entire cloud is in a weakly crystalline state with similar coupling of particles within filaments and among neighboring filaments. At high pressure ($\approx$70 Pa), the order within filaments improves (enhanced crystalline behavior), while the degree of freedom of filaments to move with respect to each other increases (enhanced liquid behavior). Since neutral gas pressure in dusty plasma acts as inverse temperature, we argue that the structural changes observed with increasing pressure are analogous to a transition to a nematic liquid crystal state. It is further observed that the filaments exhibit alignment in nested surfaces for several pressure-current conditions, suggesting the possibility of a smectic liquid crystal state. These results are confirmed by molecular dynamics simulations of the dust and ions using the DRIAD (Dynamic Response of Ions And Dust) code.

physics.plasm-ph↗

arXiv2025

Anisotropic anomalous diffusion in microgravity dusty plasma. Part One: Nonextensive Statistical 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 the collection of large amounts of statistical information on the dust particle positions and velocities. These statistics are used to quantify anomalous dust diffusion caused by anisotropies in the plasma-mediated dust-dust interactions in PK-4. Anisotropies are caused by an externally applied polarity-switched electric field, which modifies the ion wakefields surrounding the dust grains. Video data for nine sets of pressure-current conditions are used to recover Mean Squared Displacement (MSD) plots after subtracting particle drift. Position and velocity histograms are fitted to Tsallis nonextensive probability distribution functions (PDFs). Both MSDs and PDFs indicate a crossover from suprathermal to Lévy diffusion in the axial direction at higher pressure conditions. In addition, increasing the pressure enhances dust thermal equilibrium, while increasing the current drives the system away from equilibrium.

physics.plasm-ph↗

arXiv2022

Evolution of Ion Wake Characteristics with Experimental Conditions

Two-dimensional microparticle crystals can be formed in the sheath of a gas discharge plasma. Ions from the bulk plasma are accelerated in the sheath electric field, flowing past the grains to create a positive ion wake downstream from the grains. Interaction between the ion wake and neighboring grains creates additional coupling between oscillation modes and can trigger mode-coupling instability (MCI). Recent experiments have shown that at a fixed discharge power there are threshold pressures above and below which the monolayer always crystallizes or melts, respectively. The melting is due to MCI being triggered in the crystal monolayer, while the crystallization is due to the suppression of MCI by neutral damping in the fluid monolayer. The relationship between the discharge parameters and ion wake characteristics is unknown. A molecular dynamics simulation of ion dynamics and dust charging is used to self-consistently determine the dust charge and ion wake characteristics for different experimental conditions. It is found that the ion wake is strongly dependent on discharge pressure but not affected much by the discharge power.

physics.plasm-ph↗

arXiv2016

Using Dust as Probes to Determine Sheath Extent and Structure

Two in-situ experimental methods are presented in which dust particles are used to determine the extent of the sheath and gain information about the time-averaged electric force profile within a RF plasma sheath. These methods are advantageous because they are not only simple and quick to carry out, but they also can be performed using standard dusty plasma experimental equipment. In the first method, dust particles are tracked as they fall through the plasma toward the lower electrode. These trajectories are then used to determine the electric force on the particle as a function of height as well as the extent of the sheath. In the second method, dust particle levitation height is measured across a wide range of RF voltages. Similarities were observed between the two experiments, but in order to understand the underlying physics behind these observations, the same conditions were replicated using a self-consistent fluid model. Through comparison of the fluid model and experimental results, it is shown that the particles exhibiting a levitation height that is independent of RF voltage indicate the sheath edge - the boundary between the quasineutral bulk plasma and the sheath. Therefore, both of these simple and inexpensive, yet effective, methods can be applied across a wide range of experimental parameters in any ground-based RF plasma chamber to gain useful information regarding the sheath, which is needed for interpretation of dusty plasma experiments.

physics.plasm-ph↗

arXiv2013

Charging of Aggregate Grains in Astrophysical Environments

The charging of dust grains in astrophysical environments has been investigated with the assumption these grains are homogeneous spheres. However, there is evidence which suggests many grains in astrophysical environments are irregularly-shaped aggregates. Recent studies have shown that aggregates acquire higher charge-to-mass ratios due to their complex structures, which in turn may alter their subsequent dynamics and evolution. In this paper, the charging of aggregates is examined including secondary electron emission and photoemission in addition to primary plasma currents. The results show that the equilibrium charge on aggregates can differ markedly from spherical grains with the same mass, but that the charge can be estimated for a given environment based on structural characteristics of the grain. The "small particle effect" due to secondary electron emission is also important for determining the charge of micron-sized aggregates consisting of nano-sized particles.

astro-ph.EP↗

arXiv2013

Glow and dust in plasma boundaries

The sheath region is probed in different complex plasma experiments using dust particles in addition to measurement of the optical emission originating from the plasma. The local maximum in optical emission coincides with the breaking of quasi-neutrality at the sheath boundary as indicated by the vertical force profile reconstructed from dust particle trajectories, as well as by the local onset of dust density waves in high density dust clouds suspended in a dielectric box.

physics.plasm-ph↗

arXiv2011

Determination of the levitation limits of dust particles within the sheath in complex plasma experiments

Experiments are performed in which dust particles are levitated at varying heights above the powered electrode in a RF plasma discharge by changing the discharge power. The trajectories of particles dropped from the top of the discharge chamber are used to reconstruct the vertical electric force acting on the particles. The resulting data, together with the results from a selfconsistent fluid model, are used to determine the lower levitation limit for dust particles in the discharge and the approximate height above the lower electrode where quasineutrality is attained, locating the sheath edge. These results are then compared with current sheath models. It is also shown that particles levitated within a few electron Debye lengths of the sheath edge are located outside the linearly increasing portion of the electric field.

physics.plasm-ph↗

arXiv2011

The effect of dust charge variation, due to ion flow and electron depletion, on dust levitation

Using a fluid model, the plasma densities, electron temperature and ion Mach number in front of a powered electrode in different plasma discharges is computed. The dust charge is computed using OML theory for Maxwellian electrons and ions distributed according to a shifted-Maxwellian. By assuming force balance between gravity and the electrostatic force, the dust levitation height is obtained. The importance of the dust charge variation is investigated.

physics.plasm-ph↗

arXiv2011

Charging of Interstellar Dust Grains Near the Heliopause

The deflection of interstellar dust grains in the magnetic field near the heliopause has been investigated based on the assumption that interstellar grains are homogeneous spheres. However, remote observations have shown that interstellar grains are more likely to be composites of a large number of subunits. This has profound significance when interpreting data obtained through in-situ measurements, for the deflection of interstellar grains depends on their charge-to-mass ratio, and aggregates acquire different surface charges from spheres due to their complex structure. In this paper, the charging of aggregates near the heliopause is examined including both plasma charging and secondary electron emission. The results show that aggregates generally have a higher charge-to-mass ratio than spheres, and the small particle effect from secondary electron emission is evident for aggregates consisting of nano-sized particles. A new approach to estimate the aggregate charge with the aid of its structural characteristics is presented. The charge-to-mass ratio is used to derive the mass distribution of interstellar dust near the heliopause, and the result shows an overall agreement with Ulysses data.

physics.plasm-ph↗

arXiv2011

One-dimensional vertical dust strings in a glass box

The oscillation spectrum of a one-dimensional vertical dust string formed inside a glass box on top of the lower electrode in a GEC reference cell was studied. A mechanism for creating a single vertical dust string is described. It is shown that the oscillation amplitudes, resonance frequencies, damping coefficients, and oscillation phases of the dust particles separate into two distinct groups. One group exhibits low damping coefficients, increasing amplitudes and decreasing resonance frequencies for dust particles closer to the lower electrode. The other group shows high damping coefficients but anomalous resonance frequencies and amplitudes. At low oscillation frequencies, the two groups are also separated by a π-phase difference. One possible cause for the difference in behavior between the two groups is discussed.

physics.plasm-ph↗

arXiv2011

Dust particle charge in plasma with ion flow and electron depletion

The charge of micrometer-sized dust particles suspended in plasma above the powered electrode of radio-frequency (RF) discharges is studied. Using a self-consistent fluid model, the plasma profiles above the electrode are calculated and the electron depletion towards the electrode, as well as the increasing flow speed of ions towards the electrode, are considered in the calculation of the dust particle floating potential. The results are compared with those reported in literature and the importance of the spatial dust charge variation is investigated.

physics.plasm-ph↗

arXiv2010

The effect of thermophoresis on the discharge parameters in complex plasma experiments

Thermophoresis is a tool often applied in complex plasma experiments. One of the usual stated benefits over other experimental tools is that changes induced by thermophoresis neither directly depend on, nor directly influence, the plasma parameters. From electronic data, plasma emission profiles in the sheath, and Langmuir probe data in the plasma bulk, we conclude that this assumption does not hold. An important effect on the levitation of dust particles in argon plasma is observed as well. The reason behind the changes in plasma parameters seems to be the change in neutral atom density accompanying the increased gas temperature while running at constant pressure.

physics.plasm-ph↗

arXiv2010

Probing the sheath electric field with a crystal lattice by using thermophoresis in dusty plasma

A two-dimensional dust crystal levitated in the sheath of a modified Gaseous Electronics Conference (GEC) reference cell is manipulated by heating or cooling the lower electrode. The dust charge is obtained by measuring global characteristics of the levitated crystal obtained from top-view pictures. From the force balance, the electric field in the sheath is reconstructed. From the Bohm criterion, we conclude that the dust crystal is levitated mainly above and just below the classical Bohm point.

physics.plasm-ph↗

arXiv2010

Vibrational Modes and Instabilities of a Dust Particle Pair in a Complex Plasma

Vibrational modes and instabilities of a dust particle pair in a terrestrial laboratory complex plasma are investigated employing an analytical method whereby the plasma wakefield induced by an external electric field is modeled using an image charge method. It is found that for both horizontally and vertically aligned dust particle pairs in equilibrium, four normal modes exist. Variations of the confinement parameters cause a single type of instability in the horizontal pair and two types of instabilities in the vertical pair.

physics.plasm-ph↗

arXiv2010

A Simple Method to Measure the Interaction Potential of Dielectric Grains in a Dusty Plasma

A simple minimally perturbative method is introduced which provides the ability to experimentally measure both the radial confining potential and the interaction potential between two individual dust particles, levitated in the sheath of a radio-frequency (RF) argon discharge. In this technique, a single dust particle is dropped into the plasma sheath to interact with a second individual dust particle already situated at the system's equilibrium point, without introducing any external perturbation. The resulting data is analyzed using a method employing a polynomial fit to the particle displacement(s), X(t), to reduce uncertainty in calculation. Employing this technique, the horizontal confinement is shown to be parabolic over a wide range of pressures and displacements from the equilibrium point. The interaction potential is also measured and shown to be well-described by a screened Coulomb potential and to decrease with increasing pressure. Finally, the charge on the particle and the effective dust screening distance are calculated. It is shown for the first time experimentally that the charge on a particle in the sheath of an RF plasma decreases with increasing pressure, in agreement with theoretical predictions. The screening distance also decreases with increasing pressure as expected. This technique can be used for rapid determination of particle parameters in dusty plasma.

physics.plasm-ph↗

arXiv2010

Dipole-Dipole Interactions of Charged Magnetic Grains

The interaction between dust grains is an important process in fields as diverse as planetesimal formation or the plasma processing of silicon wafers into computer chips. This interaction depends in large part on the material properties of the grains, for example whether the grains are conducting, non-conducting, ferrous or non-ferrous. This work considers the effects that electrostatic and magnetic forces, alone or in combination, can have on the coagulation of dust in various environments. A numerical model is used to simulate the coagulation of charged, charged-magnetic and magnetic dust aggregates formed from ferrous material and the results are compared to each other as well as to those from uncharged, non-magnetic material. The interactions between extended dust aggregates are also examined, specifically looking at how the arrangement of charge over the aggregate surface or the inclusion of magnetic material produces dipole-dipole interactions. It will be shown that these dipole-dipole interactions can affect the orientation and structural formation of aggregates as they collide and stick. Analysis of the resulting dust populations will also demonstrate the impact that grain composition and/or charge can have on the structure of the aggregate as characterized by the resulting fractal dimension.

physics.plasm-ph↗