arXiv subjects

T. W. Hyde

Publications and source records attributed to T. W. Hyde.

At least 19 recordsLinked to original sources

arXiv2024

Ion density waves driving the formation of filamentary dust structures

The PlasmaKristall-4 experiment on the International Space Station allows for the study of the 3-dimensional interaction between plasma and dust particles. Previous simulations of the PK-4 environment have discovered fast moving ionization waves in the dc discharge[1]. These ionization waves vary the plasma parameters by up to an order of magnitude, which may affect the mechanisms responsible for the self-organization of chains seen in the PK-4 experiment. Here, we adapt a molecular dynamics simulation to employ temporally varying plasma conditions in order to investigate the effect on the dust charging and electrostatic potential. In order to describe the differences between the average of the plasma conditions and the time-varying plasma condition, we present a model to reproduce the potential that takes into account the negative potential from the dust grain and the positive potential from the ion wake.

physics.plasm-ph↗

arXiv2021

Effect of ionization waves on dust chain formation in a DC discharge

An interesting aspect of complex plasma is its ability to self-organize into a variety of structural configurations and undergo transitions between these states. A striking phenomenon is the isotropic-to-string transition observed in electrorheological complex plasma under the influence of a symmetric ion wakefield. Such transitions have been investigated using the Plasma Kristall-4 (PK-4) microgravity laboratory on the International Space Station (ISS). Recent experiments and numerical simulations have shown that, under PK-4 relevant discharge conditions, the seemingly homogeneous DC discharge column is highly inhomogeneous, with large axial electric field oscillations associated with ionization waves occurring on microsecond time scales. A multi-scale numerical model of the dust-plasma interactions is employed to investigate the role of the electric field on the charge of individual dust grains, the ion wakefield, and the order of string-like structures. Results are compared to dust strings formed in similar conditions in the PK-4 experiment.

physics.plasm-ph↗

arXiv2020

Anomalous Diffusion in One-Dimensional Disordered Systems: A Discrete Fractional Laplacian Method

This work extends the applications of Anderson-type Hamiltonians to include transport characterized by anomalous diffusion. Herein, we investigate the transport properties of a one-dimensional disordered system that employs the discrete fractional Laplacian, $(-Δ)^s,\ s\in(0,2),$ in combination with results from spectral and measure theory. It is a classical mathematical result that the standard Anderson model exhibits localization of energy states for all nonzero disorder in one-dimensional systems. Numerical simulations utilizing our proposed model demonstrate that this localization effect is enhanced for sub-diffusive realizations of the operator, $s\in (1,2),$ and that the super-diffusive realizations of the operator, $s\in (0,1),$ can exhibit energy states with less localized features. These results suggest that the proposed method can be used to examine anomalous diffusion in physical systems where strong interactions, structural defects, and correlated effects are present.

math-ph↗

arXiv2019

Detailed Model of the Growth of Fluffy Dust Aggregates in a Protoplanetary Disk: Effects of Nebular Conditions

Coagulation of dust aggregates plays an important role in the formation of planets and is of key importance to the evolution of protoplanetary disks (PPDs). Characteristics of dust, such as the diversity of particle size, porosity, charge, and the manner in which dust couples to turbulent gas, affect the collision outcome and the rate of dust growth. Here we present a numerical model of the evolution of the dust population within a PPD which incorporates all of these effects. The probability that any two particles collide depends on the particle charge, cross-sectional area and their relative velocity. The actual collision outcome is determined by a detailed collision model which takes into account the aggregate morphology, trajectory, orientation, and electrostatic forces acting between charged grains. The data obtained in this research reveal the characteristics of dust populations in different environments at the end of the hit-and-stick growth, which establishes the foundation for the onset of the next growth stage where bouncing, mass transfer and fragmentation become important. For a given level of turbulence, neutral and weakly charged particles collide more frequently and grow faster than highly charged particles. However, highly charged particles grow to a larger size before reaching the bouncing barrier, and exhibit a "Runaway" growth, in which a few large particles grow quickly by accreting smaller particles while the rest of the population grows very slowly. In general, highly charged aggregates have a more compact structure and are comprised of larger monomers than neutral/weakly charged aggregates. The differences in the particle structure/composition not only affect the threshold velocities for bouncing and fragmentation, but also change the scattering and absorption opacity of dust, influencing the appearance of PPDs.

astro-ph.EP↗

arXiv2019

The initial structure of chondrule dust rims II: charged grains

In order to characterize the early growth of fine-grained dust rims (FGRs) that commonly surround chondrules, we simulate the growth of FGRs through direct accretion of monomers of various sizes onto the chondrule surfaces. Dust becomes charged to varying degrees in the radiative plasma environment of the solar nebula (SN), and the resulting electrostatic force alters the trajectories of colliding dust grains, influencing the structure of the dust rim as well as the time scale of rim formation. We compare the growth of FGRs in protoplanetary disks (PPD) with different turbulence strengths and plasma conditions to previous models which assumed neutral dust grains. We use a combination of a Monte Carlo method and an N-body code to simulate the collision of dust monomers with chondrules: a Monte Carlo algorithm is used to randomly select dust particles that will collide with the chondrule as well as determine the elapsed time interval between collisions; at close approach, the detailed collision process is modeled using an N-body algorithm, Aggregate Builder (AB), to determine the collision outcome, as well as any restructuring of the chondrule rim. The collisions are driven by Brownian motion and coupling to turbulent gas motion in the protoplanetary disk. The charge distribution of the dust rim is modeled, used to calculate the trajectories of dust grains, and then analyze the resulting morphology of the dust rim. In a weakly turbulent region, the decreased relative velocity between charged particles causes small grains to be repelled from the chondrule, causing dust rims to grow more slowly and be composed of larger monomers, which results in a more porous structure. In a highly turbulent region, the presence of charge mainly affects the porosity of the rim by causing dust particles to deviate from the extremities of the rim and reducing the amount of restructuring.

astro-ph.EP↗

arXiv2018

The initial structure of chondrule dust rims I: electrically neutral grains

In order to characterize the early growth of fine-grained dust rims (FGRs) that commonly surround chondrules, we perform numerical simulations of dust accretion onto chondrule surfaces. We employ a Monte Carlo algorithm to simulate the collision of dust monomers having radii between 0.5 and 10 $μ$m with chondrules whose radii are between 500 and 1000 $μ$m, in 100-$μ$m increments. The collisions are driven by Brownian motion and solar nebula turbulence. After each collision, the colliding particles either stick at the point of contact, roll or bounce. We limit accretion of dust monomers (and in some cases, dust aggregates) to a small patch of the chondrule surface, for computational expediency. We model the morphology of the dust rim and the trajectory of the dust particle, which are not considered in most of the previous works. Radial profiles of FGR porosity show that rims formed in weak turbulence are more porous (with a porosity of 60-74\%) than rims formed in stronger turbulence (with a porosity of 52-60\%). The lower end of each range corresponds to large chondrules and the upper end to small chondrules, meaning that the chondrule size also has an impact on FGR porosity. The thickness of FGRs depends linearly on chondrule radius, and the slope of this linear dependency increases with time, and decreases with the turbulence strength. The porosity of FGRs formed by dust aggregates is $\sim 20\%$ on average greater than that of FGRs formed by single monomers. In general, the relatively high porosities that we obtain are consistent with those calculated by previous authors from numerical simulations, as well as with initial FGR porosities inferred from laboratory measurements of rimmed chondrule samples and rimmed chondrule analogs.

astro-ph.EP↗

arXiv2014

Dusty plasma cavities: probe-induced and natural

A comprehensive exploration of regional dust evacuation in complex plasma crystals is presented. Voids created in 3D crystals on the International Space Station have provided a rich foundation for experiments, but cavities in dust crystals formed in ground-based experiments have not received as much attention. Inside a modified GEC RF cell, a powered vertical probe was used to clear the central area of a dust crystal, producing a cavity with high cylindrical symmetry. Cavities generated by three mechanisms are examined. First, repulsion of micrometer-sized particles by a negatively charged probe is investigated. A model of this effect developed for a DC plasma is modified and applied to explain new experimental data in RF plasma. Second, the formation of natural cavities is surveyed; a radial ion drag proposed to occur due to a curved sheath is considered in conjunction with thermophoresis and a flattened confinement potential above the center of the electrode. Finally, cavity formation unexpectedly occurs upon increasing the probe potential above the plasma floating potential. The cavities produced by these methods appear similar, but each are shown to be facilitated by fundamentally different processes.

physics.plasm-ph↗

arXiv2011

Charging and coagulation of dust in protoplanetary plasma environments

Combining a particle-particle, particle-cluster and cluster-cluster agglomeration model with an aggregate charging model, the coagulation and charging of dust particles in various plasma environments relevant for proto-planetary disks have been investigated. The results show that charged aggregates tend to grow by adding small particles and clusters to larger particles and clusters, leading to greater sizes and masses as compared to neutral aggregates, for the same number of monomers in the aggregate. In addition, aggregates coagulating in a Lorentzian plasma (containing a larger fraction of high-energy plasma particles) are more massive and larger than aggregates coagulating in a Maxwellian plasma, for the same plasma densities and characteristic temperature. Comparisons of the grain structure, utilizing the compactness factor, ϕσ, demonstrate that a Lorentzian plasma environment results in fluffier aggregates, with small ϕσ, which exhibit a narrow compactness factor distribution. Neutral aggregates are more compact, with larger ϕσ, and exhibit a larger variation in fluffiness. Measurement of the compactness factor of large populations of aggregates is shown to provide information on the disk parameters that were present during aggregation.

physics.plasm-ph↗

arXiv2010

The Development of a Probalistic Model for Tholin Aggregation in Titan's Atmosphere

Titan is one of the more distinctive bodies in our solar system. In addition to being the largest of Saturn's moons, its thick atmosphere gene-rates interest because of its similarities and differences with Earth [1, 2]. Like Earth, Titan's lower atmosphere contains clouds which precipitate as rain [2]. This rain forms lakes and rivers of liquid methane and ethane which erode and shape the surface, much like water does on Earth, before evaporating into the atmosphere [2]. In Titan's atmospheric system, a single dominating factor controls the weather, the concentration of the organic molecule tholin.

astro-ph.EP↗

arXiv2009

Effect of dipole-dipole charge interactions on dust coagulation

This study examines the effect that dipole-dipole charge interactions between fractal aggregates have on the growth of dust grains. Aggregates in a plasma or radiative environment will have charge distributed over their extended surface, which leads to a net dipole moment for the charged grains. A self-consistent N-body code is used to model the dynamics of interacting charged aggregates. The aggregates are free to rotate due to collisions and dipole-dipole electrostatic interactions. These rotations are important in determining the growth rate and subsequent geometry (fractal dimension) of the grains. In contrast to previous studies which have only taken charge-dipole interactions into account, like-charged grains are found to coagulate more efficiently than neutral grains due to preferential incorporation of small aggregates into mid-sized aggregate structures. The charged aggregates tend to be more compact than neutral aggregates, characterized by slightly higher fractal dimensions.

physics.plasm-ph↗

arXiv2007

Charging of Fractal Dust Agglomerates in a Plasma Environment

The charge on micron-sized dust grains plays a crucial role in the structure and evolution of forming aggregates within the dust population during the coagulation process. The manner in which the charge is arranged on developing irregular structures can affect the fractal dimension of aggregates formed during collisions, which in turn influences the coagulation rate and size evolution of the dust cloud. Preliminary models for the charge evolution on fractal aggregates immersed in a plasma environment calculated using a modification to the orbital-motion-limited (OML) theory are presented in this paper. The model calculates currents to each point on the aggregate surface using a line-of-sight (LOS) approximation: only those electron or ion trajectories which are not blocked by another grain within the aggregate contribute to the charging current. Both the total charge and the dipole moment are calculated for the dust aggregate. While most coagulation theories assume that it is difficult for like-charged grains to coagulate, the OML_LOS approximation indicates that the electric potentials of aggregate structures are often reduced enough to allow significant coagulation.

astro-ph↗

arXiv2007

Structure and Vertical Modes in Finite 2D Plasma Crystals

In this research, formation of finite two-dimensional (2D) plasma crystals was numerically simulated. The structure was investigated for systems with various Debye length and it was found there is a transition from a complete hexagonal structure to a structure with concentric rings on the outer edge and hexagonal lattice in the interior as the Debye length increases. The vertical as well as horizontal oscillation modes thermally excited in the 2D dust coulomb clusters were investigated. The horizontal mode spectra is shown to agree with published results while the vertical mode spectra obtained from numerical simulation and analytical method agree with one another. The frequency of the vertical modes is shown to have a maximum corresponding to the whole system acting as a solid plane. For low frequency modes, the largest amplitude particle motion is concentrated in a few inner rings with the outer rings remaining almost motionless in contrast to the horizontal modes for which the strongest motion of the particles is concentrated in the inner rings at high frequencies.

physics.plasm-ph↗

arXiv2006

Structural Phases of Bounded Three-Dimensional Screened Coulomb Clusters (Finite Yukawa System)

The formation of three-dimensional (3D) dust clusters within a complex plasma modeled as a spatially confined Yukawa system is simulated using the box_tree code. Similar to unscreened Coulomb clusters, the occurrence of concentric shells with characteristic occupation numbers was observed. Both the occupation numbers and radii were found to depend on the Debye length. Ground and low energy meta-stable states of the shielded 3D Coulomb clusters were determined for 4<N<20. The structure and energy of the clusters in different states was analyzed for various Debye lengths. Structural phase transitions, including inter-shell structural phase transitions and intra-shell structural phase transitions, were observed for varying Debye length and the critical value for transitions calculated.

astro-ph↗

arXiv2006

Low-Velocity Impacts on Targets Containing Embedded Carbon Nanotubes

A one stage Light Gas Gun (LGG) at CASPER [1] was employed to test the shielding capabilities of tiles composed of four different laminated nanotube combinations. These target tiles were named CSNEAT1, CSCNT1, HYCNTUT1 and HYCNTT1. For calibration purposes, a 3003- aluminum plate was also impacted and the craters formed on the various composition tiles compared.

physics.acc-ph↗

arXiv2005

Numerical Study of Structural Phase Transitions in a Vertically Confined Plasma Crystal

Dusty plasmas consists of an ionized gas containing small (usually negatively charged) particles. Dusty plasmas are of interest in both astrophysics and space physics as well as in research in plasma processing and nanofabrication. In this work, the formation of plasma crystals confined in an external one-dimensional parabolic potential well is simulated for a normal experimental environment employing a computer code called BOX_TREE. Such crystals are layered systems, with each layer a two dimensional lattice composed of grain particles. The number of layers is dependent upon the external potential parameter. For constant layer number, the intralayer structure transits from a square lattice to a hexagonal (triangular) lattice as the confining potential decreases. For hexagonal lattices, both hcp and fcc characteristics were found but hcp structures dominate. The relative thickness of the system was also examined. The results were compared with previous experimental and theoretical results and found to agree.

physics.atm-clus↗

arXiv2005

Vertical modes of two-dimensional dust coulomb clusters in complex plasmas

The vertical as well as horizontal oscillation modes in a thermally excited two-dimensional (2D) dust coulomb cluster were investigated for particle numbers between and using both a box_tree simulation and an analytical method. The horizontal mode spectra is shown to agree with published results while the vertical mode spectra obtained from the box_tree simulation and the analytical method are shown to agree with one another. The maximum frequency of the vertical modes is shown to be the vertical oscillation frequency of the whole system acting as a solid plane and the frequency is shown to decrease as the mode number l decreases. The oscillation patterns of the vertical modes are also investigated. For clusters with large numbers of particles, the high frequency modes are shown to have oscillation patterns similar in shape to Bessel-Fourier functions with various index m and n. For specified values of n, modes with higher m (except for) have lower frequencies and for specified m, modes with higher n have lower frequencies. For low frequency modes, the largest amplitude particle motion is concentrated in a few inner rings with the outer rings remaining almost motionless. This is in contrast to the horizontal modes where the strongest motion of the particles is concentrated in the inner rings at high frequency. For clusters with small numbers of particles (), these modes where the strongest vertical motion is concentrated in the inner rings does not exist resulting in oscillation magnitudes for all the modes appearing in the shape of Bessel-Fourier functions.

astro-ph↗

arXiv2005

Kuiper Binary Object Formation

It has been observed that binary Kuiper Belt Objects (KBOs) exist contrary to theoretical expectations. Their creation presents problems to most current models. However, the inclusion of a third body (for example, one of the outer planets) may provide the conditions necessary for the formation of these objects. The presence of a third massive body not only helps to clear the primordial Kuiper Belt but can also result in long lived binary Kuiper belt objects. The gravitational interaction between the KBOs and the third body causes one of four effects; scattering into the Oort cloud, collisions with the growing protoplanets, formation of binary pairs, or creation of a single Kuiper belt object. Additionally, the initial location of the progenitors of the Kuiper belt objects also has a significant effect on binary formation.

astro-ph↗

arXiv2005

Dynamics of a Dust Crystal with Two Different Size Dust Species

A self-consistent three-dimensional model for a complex (dusty) plasma is used to study the effects of multiple-sized dust grains in a dust crystal. In addition to the interparticle forces, which interact through a Yukawa potential, the model includes the effects of gravity, the variation of the sheath potential above the powered electrode, and a radial confining potential. Simulations studied various ratios of a mix of 6.5- and 8.9-micron monodisperse particles and compared their correlation functions, electric potential energy of the crystal formations, and the dispersion relations for in-plane and out-of-plane dust lattice wave (DLW) modes for two different sheath thicknesses. In the 7 mm sheath, the particles formed two layers in the vertical direction by size, and acted as a two-layer crystal with weak correlation between the layers. In the 3 mm sheath, the particles formed an essentially monolayer crystal; however the crystal dynamics showed some characteristics of a bilayer crystal.

astro-ph↗