Search

The PlasmaKristall-4 (PK-4) experiment on the International Space Station (ISS) has been widely used to study collective behavior and self-organization of dust grains immersed in a plasma environment under microgravity conditions. Recently it has been shown that the PK-4 BU, a ground-based replica of the PK-4, supports the presence of inhomogeneous features related to ionization waves moving through the positive column on the microsecond timescale 1 . Plasma conditions within the ionization waves, such as plasma density and electric fields, have been shown to vary by up to an order of magnitude from background values. Previous investigations of dust dynamics within the PK-4 environment have focused on time-averaged plasma conditions, assuming a homogeneous environment. Given the importance of plasma density and electric fields for dust self-organization, it is important to understand the impact of their observed variability. Here results will be presented from an N-body simulation which models dust and ion dynamics, employing initial boundary conditions derived from a 2D particle-in-cell with Monte Carlo collisions (PIC/MCC) simulation of the observed ionization waves.

The role of charged, solid particulate matter (i.e., "dust"’ in plasmas has been considered for several decades. However, beginning with observations of structures in the dust tails of comets and the Voyager observations of radial structures ("spokes"’ in Saturn’s rings, the role of charged dust in the solar system led to the emergence of the field of "dusty" (alternatively, "complex"’ plasmas. Since the early 1990’s there has been a complementary effort in the area of laboratory dusty plasmas that has, over almost four decades, led to the observation of numerous types of plasma and dusty plasma behavior – ranging from appearance of strongly-coupled, self-organized dusty plasma crystals to new types of collective, dust-driven modes, such as the dust acoustic and dust density waves.

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., Comment: 15 pages, 14 figures

The excitation of low frequency dust acoustic (or dust density) waves in a dusty plasma can be driven by the flow of ions relative to dust. We consider the nonlinear development of the ion–dust streaming instability in a highly collisional plasma, where the ion and dust collision frequencies are a significant fraction of their corresponding plasma frequencies. This collisional parameter regime may be relevant to dusty plasma experiments under microgravity or ground-based conditions with high gas pressure. One-dimensional particle-in-cell simulations are presented, which take into account collisions of ions and dust with neutrals, and a background electric field that drives the ion flow. Ion flow speeds of the order of a few times thermal are considered. Waveforms of the dust density are found to have broad troughs and sharp crests in the nonlinear phase. The results are compared with the nonlinear development of the ion–dust streaming instability in a plasma with low collisionality.

A many-body system of charged particles interacting via a pairwise Yukawa potential, the so-called Yukawa One Component Plasma (YOCP) is a good approximation for a variety of physical systems. Such systems are completely characterized by two parameters; the screening parameter, $\kappa$, and the nominal coupling strength, $\Gamma$. It is well known that the collective spectrum of the YOCP is governed by a longitudinal acoustic mode, both in the weakly and strongly coupled regimes. In the long-wavelength limit the linear term in the dispersion (\textit{i.e.} $\omega = s k$) defines the sound speed $s$. We study the evolution of this latter quantity from the weak through the strong coupling regimes by analyzing the Dynamic Structure Function $S(k,\omega)$ in the low frequency domain. Depending on the values of $\Gamma$ and $\kappa$ and $w = s/v_{\textrm{th}}$, (\textit{i.e.} the ratio between the phase velocity of the wave and thermal speed of the particles) we identify five domains in the $(\kappa,\Gamma)$ parameter space in which the physical behavior of the YOCP exhibits different features. The competing physical processes are the collective Coulomb like vs. binary collision dominated behavior and the individual particle motion vs. quasi-localization. Our principal tool of investigation is Molecular Dynamics (MD) computer simulation from which we obtain $S(k,\omega)$. Recent improvements in the simulation technique have allowed us to obtain a large body of high quality data in the range $\Gamma = \{0.1 - 10,000\}$ and $\kappa = \{0.5 -5\}$. The theoretical results based on various models are compared in order to see which one provides the most cogent physical description and the best agreement with MD data in the different domains., Comment: 33 pages, 12 figures

The physics of dusty plasmas in high magnetic field is an area of current interest, spurred by the development of experiments in this area. Dust acoustic (or dust density) waves have been observed in many laboratory dusty plasmas where there is either no or weak magnetic field. These waves may be excited by the flow of ions relative to dust. The effects of high magnetic field on the excitation of dust waves have been considered in the theoretical literature, including instabilities driven by ions streaming either along or across the magnetic field. We review and extend prior theory work on such instabilities, exploring their behavior as the magnetization of the ions is varied, while the electrons are strongly magnetized and the dust is unmagnetized. It is shown that when the ions are magnetized, there can be structure in the unstable wavenumber spectrum under certain conditions. Application to possible experimental parameters is discussed.

The nonlinear development of a low frequency beam-cyclotron instability in a collisional plasma composed of magnetized ions and electrons and unmagnetized, negatively charged dust is investigated using one-dimensional particle-in-cell simulations. Collisions of charged particles with neutrals are taken into account via a Langevin operator. The instability, which is driven by an ion $\boldsymbol{E}\times \boldsymbol{B}$ drift, excites a quasi-discrete wavenumber spectrum of waves that propagate perpendicular to the magnetic field with frequency of the order of the dust plasma frequency. In the linear regime, the unstable wavelengths are of the order of the ion gyroradius. As the wave energy density increases, the dominant modes shift to longer wavelengths, suggesting a transition to a Hall-current-type instability. Parameters are considered that reflect the ordering of plasma and dust quantities in laboratory dusty plasmas with high magnetic field. Comparison with the nonlinear development of this beam cyclotron instability in a collisionless dusty plasma is also briefly discussed.

A description is given of the Magnetized Dusty Plasma Experiment (MDPX) at Auburn University that was designed to study the physics of highly magnetized low temperature plasmas and magnetized dusty plasmas. The central components of the MDPX are a superconducting solenoid capable of operation at magnetic fields up to 4 T, and a parallel plate RF discharge plasma. Results from some of the initial experiments will be presented.A description is given of the Magnetized Dusty Plasma Experiment (MDPX) at Auburn University that was designed to study the physics of highly magnetized low temperature plasmas and magnetized dusty plasmas. The central components of the MDPX are a superconducting solenoid capable of operation at magnetic fields up to 4 T, and a parallel plate RF discharge plasma. Results from some of the initial experiments will be presented.

Recently it has been proposed to alter the interaction between dust grains in a plasma by applying ac electric fields to distort the Debye spheres surrounding the grains, which may lead to interaction potentials with a Lennard-Jones form under certain conditions (e.g., Kompaneets et al., Phys. Plasmas 16, 043705 (2009)). Motivated by this, we consider the dispersion relations of longitudinal and transverse waves in a dusty plasma liquid where the grains interact via a Lennard-Jones potential. We use the Quasi-Localized Charge approximation combined with an analytic expression for the pair distribution function for Lennard-Jones fluids (Matteoli and Mansoori, J. Chem. Phys. 103, 4672 (1995)). Possible dusty plasma experimental parameters are considered. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The dust acoustic, or dust density, wave is a very low frequency collective mode in a dusty plasma that is associated with the motion of the charged and massive dust grains. An ion flow due to an electric field can excite these waves via an ion–dust streaming instability. Theories of this instability have often assumed a shifted-Maxwellian ion velocity distribution. Recently, the linear kinetic theory of this instability was considered using a non-Maxwellian ion velocity distribution (Kählert, Phys. Plasmas, vol. 22, 2015, 073703). In this paper, we present one-dimensional PIC simulations of the nonlinear development of the ion–dust streaming instability, comparing the results for these two types of ion velocity distributions, for several values of the ion drift speed and collision rate. Parameters are considered that reflect the ordering of plasma and dust quantities in laboratory dusty plasma experiments. It is found that, in general, the wave energy density is smaller in the simulations with a non-Maxwellian ion distribution.

The Magnetized Dusty Plasma Experiment (MDPX) device is a newly constructed research instrument for the study of dusty (complex) plasmas. The MDPX device is envisioned as an experimental platform in which the dynamical behavior of all three charged plasma components, the electrons, ions, and charged microparticles (i.e., the ‘dust’) will be significantly influenced by the magnetic force. This brief paper will provide a short overview of the design, magnetic performance, and initial plasma measurements in the MDPX device.

The last decade has seen the development of new experimental devices to explore the physics of magnetized dusty plasmas. Because of the small charge-to-mass ratio of the charged microparticles, it is necessary to operate these experiments at high magnetic fields of several Tesla in order to observe the direct effect of the magnetic forces on the transport properties of the charged microparticles. While the study of magnetized dusty plasmas is still the ultimate goal, these experiments have also provided new opportunities to studies regimes of strongly magnetized, low temperature, laboratory plasmas that have not been extensively explored. Experiments show the formation of new types of self- and imposed-ordered structures that form in both the plasma and among the microparticles. This paper summarizes recent experimental observations of plasma filamentation (in the plasma) and will discuss possible connections to 'dust gridding' phenomena that are observed in the magnetized dusty plasma experiment device.

We report experimental observations of a low-frequency (≪ ion gyrofrequency) electrostatic wave mode in a magnetized cylindrical (Q machine) plasma containing positive ions, very few electrons and a relatively large fraction (n−/ne > 103) of heavy negative ions (m−/m+ ≈ 10), and no magnetic field-aligned current. The waves propagate nearly perpendicular to B with a multiharmonic spectrum. The maximum wave amplitude coincided spatially with the region of largest density gradient suggesting that the waves were excited by a drift instability in a nearly electron-free positive ion–negative ion plasma

Drift wave instability in a magnetized plasma composed of positive ions and negative ions is considered using linear kinetic theory in the local approximation. We consider the case where the mass (temperature) of the negative ions is much larger (smaller) than that of the positive ions, and where the gyroradii of the two ion species are comparable. Weak collisional effects are taken into account. Application to possible laboratory parameters is discussed.

In a magnetized plasma containing charged dust whose motion is magnetized, one of the fundamental collective modes that could occur is the electrostatic dust cyclotron (EDC) wave with frequency near the dust cyclotron frequency. The EDC wave propagates nearly perpendicular to the magnetic field with a small parallel wave number, so that it can be driven unstable by ion flow along the magnetic field. Because unstable parallel wavelengths can be relatively large, this places constraints on the plasma device size. In this paper, we use linear kinetic theory to investigate the excitation of higher harmonic EDC waves that have wavelengths smaller than that of the fundamental mode. Collisions of charged particles with neutrals and Coulomb collisions including dust–dust collisions are taken into account. Constraints on possible parameter ranges arising from collisional effects or from requiring stability of other waves are discussed. Numerical results are presented for possible sets of laboratory dusty plasma parameters.

This paper discusses the design of the new Magnetized Dusty Plasma eXperiment (MDPX) device that is currently under construction at Auburn University. This device, which is envisioned to be operated as a multiuser facility, has incorporated many of the features of current dusty plasma experiments that make use of strong magnetic fields while adding new features-such as an extended plasma volume, programmable linear magnetic field gradients, and variable magnetic field geometries-that will greatly extend the operating space of the new device. This paper discusses the physics criteria used to define the operating parameters of the MDPX device and presents a discussion of the initial configuration of the experiment.

Dust acoustic (or dust density) waves have been observed in many laboratory dusty plasmas. These low-frequency waves involve the dynamics of highly charged and massive dust grains, and can be excited by the flow of ions relative to dust. In this paper, we consider the nonlinear development of the dust acoustic instability, excited by thermal ion flow, in a collisional plasma containing dust with high kinetic temperature (warm dust). It is shown that under certain conditions there may be a long-wavelength secondary instability in the nonlinear stage as dust gets heated by the waves. The characteristics of the nonlinear development are considered as a function of the relative charge density of the dust. Application to possible experimental parameters is discussed.

In a two-dimensional (2D) dusty plasma composed of superparamagnetic, charged dust grains and immersed in an external magnetic field B, the grains interact via both Yukawa and magnetic dipole-dipole potentials. Because the grains' magnetic dipole moments are induced by B, the dipole moments all lie along B. When B is tilted with respect to the normal to the dust layer, the interaction between the grains becomes anisotropic. In our previous paper [Hartmann et al., Phys. Rev. E 89, 043102 (2014)PLEEE81539-375510.1103/PhysRevE.89.043102], we studied the character of waves in such a system, confined strictly to two dimensions, without any spatial extension in the direction perpendicular to the layer. We analyzed how the dispersion of waves depends on the direction of propagation and the relative strengths of the magnetic dipole and Yukawa potentials. In this paper, we consider a more realistic quasi-2D system where the grains are confined by an external potential and can undergo small oscillations perpendicular to the layer. We analyze the effect of the strength of the confining potential on the in-plane correlations and on the wave propagation. In addition to the in-plane compressional and transverse waves, there now appears an out-of-plane transverse wave generated by the oscillation of the grains in the confining potential. The theoretical approach uses the quasi-localized charge approximation paralleled by molecular dynamics simulations.

We consider theoretically the possible wavelength selective absorption of mid or far infrared radiation in a plasma containing micrometer-sized dust grains having surface phonon resonances in these wavelength regimes. Issues related to grain heating and charging are also discussed.

One dimensional Particle in Cell simulations of a dust- dust counter-streaming instability in a plasma containing dust grains of opposite charge polarity are presented. This dust-dust instability has potentially the lowest threshold drift for a dust wave instability in an unmagnetized dusty plasma. The linear and nonlinear development of the dusty plasma instability is investigated, including the effects of collisions with background neutrals, and a background electric field which acts as a driver to impart the drift velocities of the counter streaming charged dust particles. The saturation of the linear instability appears to be dust heating related to dust trapping. Potential double layer formation from dust-dust turbulence is observed in cases with a high neutral collision rate. A comparative study is done with varying collision rates and background electric fields to explore the nonlinear development as a function of collision rate and background electric field. These simulation results could help guide future laboratory and micro-gravity dusty plasma experiments on this instability. The results could also relate to similar counter-streaming instabilities in pair plasmas and negative ion plasmas

It is generally assumed that negatively charged icy dust particles in the mesosphere are charged by the collection of thermal plasma particles. However, there are some indications that there may be a population of hyperthermal electrons in the D-region under auroral activity under certain conditions (e.g. Margot-Chaker and McNamara, Planetary and Space Science 32, 391, 1984). In this brief communication, we speculate on the effect of a hyperthermal distribution of electrons on dust charging, and how this might affect prevailing turbulence scattering theory for polar summer mesophere echoes.

A strongly coupled Yukawa liquid is a system of charged particles which interact via a screened Coulomb interaction and in which the electrostatic energy between neighboring particles is larger than their thermal energy but not large enough for crystallization. Various plasma systems including ultracold neutral plasmas and complex (dusty) plasmas can exist in this strongly coupled liquid phase.Here we investigate instabilities driven by the relative streaming of plasma components in three-dimensional Yukawa liquids with a focus on complex plasmas. This includes a dust acoustic instability driven by weakly coupled ions streaming through the dust liquid, and a dust-dust instability driven by the counter-streaming of strongly coupled dust grains. Compared to the Vlasov behavior we find there can be a substantial modification of the unstable wavenumber spectrum due to strong coupling effects (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of radial boundaries on the ion-dust streaming instability is investigated. Possible applications of our work to certain low-temperature dusty plasma experiments are discussed.

Ion waves excited by charged dust beams streaming across or along the geomagnetic field in the ionosphere may be generated by plasma instabilities during aerosol release experiments. The injection speed of the dust and gas is comparable to or larger than the ion thermal speed in the background plasma. The dust grains can get charged by plasma collection from the ambient ionosphere, and can thus act as a charged beam that excites instabilities in the background plasma. The theory is applied to relatively early time scales of the order of ∼0.1–1s in the dust–gas cloud expansion, with wave frequencies that are larger than the ion gyrofrequency, and collisions with neutrals are included.

Dusty plasmas have been studied in argon, radio frequency (rf) glow discharge plasmas with magnetic fields up to 1.5 T. Plasmas were formed between a powered bottom electrode and a grounded top electrode in which an aluminum wire mesh is fixed in the center. This work will examine the experimental conditions at which imposed, ordered structures form within the dusty plasma. These imposed, ordered structures, as reported in earlier works, are characterized by the alignment of dust particles to the spatial structure of the wire mesh in the top electrode and occur at high magnetic fields (B ≥ 1 T) and low neutral pressure (P ≤ 100 mTorr). A pair of parameters will be established to characterize the degree to which the dust particles are affected by these imposed ordered structures on both long and short time scales. Using these parameters, it will be shown that a correlation exists between the onset of imposed, ordered structures and the magnetization of ions within the plasma.Dusty plasmas have been studied in argon, radio frequency (rf) glow discharge plasmas with magnetic fields up to 1.5 T. Plasmas were formed between a powered bottom electrode and a grounded top electrode in which an aluminum wire mesh is fixed in the center. This work will examine the experimental conditions at which imposed, ordered structures form within the dusty plasma. These imposed, ordered structures, as reported in earlier works, are characterized by the alignment of dust particles to the spatial structure of the wire mesh in the top electrode and occur at high magnetic fields (B ≥ 1 T) and low neutral pressure (P ≤ 100 mTorr). A pair of parameters will be established to characterize the degree to which the dust particles are affected by these imposed ordered structures on both long and short time scales. Using these parameters, it will be shown that a correlation exists between the onset of imposed...

We theoretically investigate conditions for the refraction of long-wavelength dust acoustic waves by arrays of periodic cylinders in a dusty plasma. This is based on a recent analysis of the refraction of shallow water waves by periodic cylinder arrays (Hu and Chan, Phys. Rev. Lett.95 (2005), 154501). In the dusty plasma case, however, the boundary conditions involve the formation of voids around the cylinders. Possible experimental conditions are discussed.

We present a kinetic theory analysis of the electrostatic ion cyclotron (EIC) instability in a plasma containing positive ions, electrons, and negative ions that are much more massive than the positive ions. Conditions are investigated for exciting the fundamental and the higher harmonic EIC waves associated with each ion species. We find that as the concentration of heavy negative ions increases, the wave frequencies increase, the unstable spectrum in general shifts to longer perpendicular wavelengths, and the growth of higher harmonic EIC waves tends to increase within certain parameter ranges. Applications to possible laboratory plasmas are discussed.

Velocity distribution functions of dust particles of various sizes are simulated in different regions of a tokamak using the DUSTT code. It is shown that dust particles accelerated by plasma flows can reach very high speed >1 km/s at the terminal stages of vaporization. Collisions of beryllium and tungsten dust particles with beryllium wall are modeled with the LS-DYNA material structural analysis code. It is demonstrated that the collisions at high speed ∼1 km/s can cause significant damage to the wall or complete dust destruction depending on dust and wall material parameters.

In this paper, we use Mie theory to investigate the temperature-dependent emissivity of small particles composed of a fusion device relevant metal, lithium. We also use classical electromagnetic theory to estimate the high temperature emissivity of flat surfaces of liquid lithium and several metals, such as beryllium, being considered as plasma facing components in fusion devices. We use a Drude theory model for the temperature dependence of the optical constants of the metals. The results may have application to modeling or diagnosing the temperature of various metallic components in fusion environments.

Recently, the sputtering of fast meteoroids by impinging atmospheric particles, and the subsequent interaction of the sputtered material with the atmosphere, has been proposed to explain the meteor luminosity observed at high altitudes. In this brief communication, we consider the possibility of a lower hybrid instability driven by the ionized component of the material sputtered from a fast large meteoroid at high altitudes.

In this work we analyze the size (radius) distribution function of dust particles in tokamak plasmas during a steady state discharge. A relation between the radius distribution function of dust in the plasma and the radius distribution of dust injected from tokamak walls is obtained using a Green's function formalism. Numerical simulations of the dust radius distribution function in a tokamak plasma with the Dust Transport (DUSTT) code are used to obtain the analytical form of the Green's function semi-empirically. It is demonstrated that the Green's function obtained can be used to predict qualitatively the dust size distributions in the tokamak plasmas. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Recently, there has been interest in the properties of strongly coupled dusty plasmas in the liquid phase. Here, we consider theoretically a possible way to generate and detect a dense dusty plasma liquid. The idea is to use noble metal submicron dust particles and detect the dust by scattering at the surface plasmon resonance frequency of the dust. Parameters that may be relevant to possible laboratory dusty plasma experiments are discussed.

The ion-acoustic instability in a dusty negative ion plasma is investigated, focusing on the parameter regime in which the negative ion density is much larger than the electron density. The dynamics of the massive dust grains are neglected, but collisions of electrons and ions with dust grains in addition to other collisional processes are taken into account. The presence of a population of charged dust can change the frequency of the fast wave, lead to additional damping due to ion–dust collisions, and change the conditions for wave growth. Applications to dusty negative ion plasmas in the laboratory and in space are discussed.

We report comparative studies on collective excitations in 2-D complex plasmas, in which particles interact through the Yukawa potential, encompassing both the solid and the strongly coupled liquid states. Dispersion and polarization of the collective modes in the solid state are calculated through the lattice summations, while in the liquid state, through molecular dynamics (MD) simulations in conjunction with the theoretical quasi-localized charge approximation analysis. The latter closely emulates the dispersion, resulting from an angular averaging in the lattice. In general, however, the lattice dispersion is substantially different from that of the liquid. The MD simulations show the dramatic transformation of the anisotropic phonon dispersion of the crystal lattice near the solid-liquid transition into the isotropic liquid dispersion

The beam-plasma instability displays new properties when either the beam or the plasma, or both, are strongly interacting. We have considered theoretically the case when the plasma is in the crystalline phase and forms a lattice, and the beam is moving in the lattice plane. We consider a 2-D plasma crystal in which both the grains and the beam particles interact through a realistic Yukawa potential. The beam particles are assumed to be weakly coupled to each other and to the lattice. Using the full phonon spectrum for a 2-D hexagonal Yukawa lattice, we determine and compare the transverse and longitudinal growth rates. The relationship between the beam speed and the longitudinal and transverse sound speeds, and the direction of the beam with respect to the principle axes of the lattice determine the qualitative behavior of the growth rates. For beam speeds between the longitudinal and transverse sound speeds, the transverse instability could be more important, because it appears at lower wavenumbers

The magnetized dusty plasma experiment (MDPX) is a newly commissioned plasma device that started operations in late spring, 2014. The research activities of this device are focused on the study of the physics, highly magnetized plasmas, and magnetized dusty plasmas. The design of the MDPX device is centered on two main components: an open bore, superconducting magnet that is designed to produce, in a steady state, both uniform magnetic fields up to 4 Tesla and non-uniform magnetic fields with gradients of 1–2 T m−1and a flexible, removable, octagonal vacuum chamber that provides substantial probe and optical access to the plasma. This paper will provide a review of the design criteria for the MDPX device, a description of the research objectives, and brief discussion of the research opportunities offered by this multi-institution, multi-user project.

The understanding of the theoretical structure of phonon dispersion in Yukawa lattices and the relationship between these perfect lattice phonons on the one hand, and the excitations in the disordered and liquid states on the other, is an important issue in analysing experimental and simulation results on plasma crystals. As the first step in this programme, we have numerically calculated the full phonon spectrum for 2D triangular Yukawa lattices, for a wide range of κ (screening parameter) values and along different propagation angles. Earlier calculations of the excitation spectra of the 2D and 3D Yukawa liquids were based on the quasilocalized charge approximation (QLCA), whose implicit premise is that the spectrum of an average distribution (governed by the isotropic liquid pair correlation function) is a good representation of the actual spectrum. To see the implications of this model more clearly, we compare the high r (near crystallization) QLCA phonon spectra with the angle-averaged phonon spectra of the lattice phonons.

Various interactions can play a role between the mesoscopic dust grains of a complex plasma. We study a system composed of dust grains that have both an electric charge and a permanent magnetic dipole moment. It is assumed that the grains occupy lattice sites, as dictated by their Coulomb interaction. In addition, they possess a spin degree of freedom (orientation of magnetic dipole moment) that is not constrained by the Coulomb interaction, thus allowing for the possibility of equilibrium orientational ordering and 'wobbling' about the equilibrium orientations. As a result, collective modes develop. We identify in-plane and out-of-plane wobbling modes and discuss their dispersion characteristics both in the ferromagnetic and in the anti-ferromagnetic ground state.

The well-known problem of beam–plasma instability acquires new aspects when one or both of the two components (the beam and the plasma) are strongly interacting. We have now theoretically considered the case when the plasma is in the solid phase and forms a lattice. In this situation, the inherent anisotropy of the lattice leads to a coupling between the longitudinal and transverse polarizations. One of the novel features of the beam–plasma instability in this scenario is the possible excitation of transverse modes, which should be an experimentally observable signature of the instability. We have initially concentrated on a 2D toy model with the beam lying in the lattice plane. At the same time, we have initiated a molecular dynamics simulation program for studying various aspects of the penetration of a beam into a plasma lattice. The beam parameters can be adjusted in order to see the effects of increasing coupling strength within the beam and to distinguish between collective phenomena and scattering on individual particles. When both components are strongly interacting, a number of remarkable phenomena—trapping of beam particles, creation of dislocations, local melting of the lattice—may be observed.

The conventional Vlasov treatment of beam-plasma instabilities is inappropriate when the plasma is strongly coupled. In the strongly coupled liquid state, the strong correlations between the dust grains fundamentally affect the conditions for instability. In the crystalline state, the inherent anisotropy couples the longitudinal and transverse polarizations, and results in unstable excitations in both polarizations. We summarize analyses of resonant and non-resonant, as well as resistive instabilities. We consider both ion-dust streaming and dust beam-plasma instabilities. Strong coupling, in general, leads to an enhancement of the growth rates. In the crystalline phase, a resonant transverse instability can be excited.

Properties of the coupled dust ion-acoustic drift wave instability in a radially bounded dusty magnetoplasma with an equilibrium sheared parallel ion (SPI) flow are investigated. By using the two-fluid model for the electrons and ions, a wave equation for the low-frequency coupled dust ion-acoustic drift waves in a bounded plasma with stationary charged dust grains is derived. The wave equation admits a linear dispersion relation, which exhibits that the radial boundary affects the growth rate of the coupled ion-acoustic drift wave instability which is excited by the SPI flow. The results should be relevant to dusty magnetoplasma experiments with an SPI flow.

The use of dust plasma crystals as filters of electromagnetic waves in the far-infrared or submillimeter wavelength regime is investigated theoretically. The analysis is based on previous analyses of crystalline colloid array filters that make use of dynamical diffraction theory coupled with theory for electromagnetic wave scattering from small spheres. Theoretical bandwidths, attenuation factors, and limits on wave intensity are considered.

This note investigates an ion-dust streaming instability with frequency ω less than the dust collision frequency νd, in an unmagnetized collisional dusty plasma. Under certain conditions, a resistive instability can be excited by an ion drift on the order of the ion thermal speed, even when the dust acoustic wave is heavily damped. The effect of weak collisions on the usual dust acoustic instability in the regime ω > νd is also considered. Applications to experimental observations of low-frequency fluctuations in laboratory d.c. glow discharge dusty plasmas are discussed.

Wave dispersion relations in the strongly coupled liquid phase of a two-dimensional system of dust grains interacting via both Yukawa and dipole interactions are investigated. The model system comprises a layer of charged superparamagnetic grains in a plasma in an external, uniform magnetic field B whose magnitude and direction can be varied. Because the induced magnetic dipole moments of the grains lie along B, the interaction between the grains becomes anisotropic as B is tilted with respect to the layer. The theoretical approach uses a reformulated quasilocalized charge approximation that can treat dipole interactions, combined with molecular dynamics simulations. The mode dispersion relations are found to depend on the relative strengths of the Yukawa and dipole interactions and the direction of wave propagation in the plane.

We solve the simultaneous equations for continuity of charge, mass, momentum and energy of a meteoroid entering the Earth's atmosphere to study its charging, deceleration, mass loss and heating along its path. In this analysis we also include the effects of thermionic emission from the frictionally heated meteoroid, which hitherto have not been considered. We have limited our analysis to the free-molecular regime which corresponds to meteoroids of radius ⩽1 cm in our altitude range of interest (H⩾80 km ) . We have also limited our treatment to the night side of the Earth so as to avoid the complicating role of photoemission while emphasizing the role of thermionic emission. Our results show that, while the same meteoroid can change its charge polarity during flight, meteoroids with widely different material work functions could have opposite polarity at the same altitude. We find out that, while the escaping thermionic electrons do not constitute a significant source of energy loss from the surface, they could be a larger source of meteoric electrons at high altitude compared to electrons produced by the ablation process, particularly if the work function of the meteoroid is sufficiently small (i.e W⩽2 eV ). Furthermore we find that the altitude range of meteoric ionization is larger than in the case when ionization is due only to collisions between sublimating molecules and background molecules. In addition the ionization has an earlier onset and a later shut-off.

Theoretical studies of dusty plasmas have been performed by focusing attention principally on collective phenomena and on grain motion. This thesis consists of a collection of seven published papers that explore both the collective behavior of a complex plasma system as well as the dynamics of grains in plasmas. In paper 1, a mechanism that explains the energy gain which leads to the self excited grain oscillations is theoretically formulated. The newly developed mechanism explains the observed self excited oscillations through the coupling of plasma sheath fluctuations with the electrostatic force, which holds the dust grain. In paper 2, theoretical and simulation studies have been conducted to study the vertical oscillations of dust grains that are levitated in plasma sheaths, under low pressure conditions. The oscillations were driven either by an external force or by a plasma number density modulation. The proposed model gives a full picture of the dust grains dynamics and is capable of successfully explaining the experimental observations. Paper 3 explores both theoretically and numerically the origin of the nonlinearities that lead to the observed oscillation resonances. The feature of the confining potential well which traps the grain, the influence of an electrode voltage modulation on the trapping well, and hence on the grain dynamics, and the resulting nonlinear resonances are analyzed in detail. The numerical simulations presented successfully reproduce a broad range of dynamical phenomena, including the self excited oscillations, for a range of different parameters. Paper 4 is dedicated to the analysis of the propagation of Dust Acoustic Waves (DAW) in a medium with an equilibrium dust density distribution. It has been theoretically shown that only some harmonics of the dust density distribution will influence the propagation of the DAW, thus modifying its frequency. Paper 5 presents a theoretical and numerical analysis of the excitation of higher harmonics of electrostatic dust cyclotron waves. The instability is driven by the ion and electron currents flowing along the magnetic field. The dispersion relation and the wave instability conditions have been derived, and a detailed numerical analysis has been performed. In Paper 6, we explore theoretically some cross field instabilities of low frequency, long wavelength electrostatic modes in fully and weakly ionized plasmas. It is shown that in a magnetoplasma with a transverse equilibrium dc electric field, the energy associated with the cross field motion of the plasma particles can be coupled to low frequency electrostatic waves. Paper 7 explores the properties and instabilities of low frequency electrostatic waves propagating in a current carrying magnetoplasma with equilibrium density and field aligned ion flow with a transverse gradient. The paper contains previous results as limiting cases, together with additional instabilities related to the equilibrium plasma density distribution.