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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.

We use molecular dynamics (MD) and particle-in-cell (PIC) simulation methods, in which dust grains are treated as discrete particles and the background plasma is included in the potential shielding (MD) or as a Boltzmann fluid (PIC), to investigate dust-acoustic waves in a one-dimensional, strongly coupled (with the Coulomb coupling parameter {Gamma} equal to the ratio of the Coulomb energy to the thermal energy, which is greater than 1) dusty plasma. We study cases both where the dust is represented by a small number of simulation particles that form into a regular array structure at large {Gamma} (crystal limit) and where the dust is represented by a much larger number of particles (fluid limit). We show that the measured frequency for dust acoustic waves satisfies either a fluidlike dispersion relation or a lattice wavelike dispersion relation, depending on {Gamma} and the number of simulation particles. Other PIC simulations, either with plasma ions represented as particles rather than as a Boltzmann fluid or with collisions between the dust and the background gas, have also been carried out and shown to agree with theoretical predictions. Numerical issues associated with smoothing of the accumulated charge density in PIC simulations have also been addressed; smoothingmore » is shown to affect wave dispersion at high wave numbers in the fluid limit and low wave numbers in the crystal limit. {copyright} {ital 1999} {ital The American Physical Society}« less

In this paper, we consider theoretically conditions for forming crystals of positively charged dust, when the dust is heated by a laser or by a strong infrared source and emits electrons thermionically. We discuss parameters for grains dispersed in an inert gas at pressure of a few mbar. We briefly discuss levitation by forces associated with gas flow or photon flux. A possible experimental scheme for achieving such a crystal is briefly outlined.

The effect of charged dust on the Farley-Buneman instability is investigated. Linear kinetic theory is used to estimate the critical electron drift in the presence of either negatively or positively charged dust. The charge-to-mass ratio of the dust is much smaller than that of the ions, and the dust influences the instability through its effect on equilibrium charge neutrality. It is shown that in certain regimes, the critical drift can decrease as the charge density carried by negatively charged dust increases. Possible application to dusty plasmas in the upper D/lower E region boundary region of the Earth's ionosphere is discussed.

We study the nonlinear behavior of the low-frequency dust acoustic instability in a collisional dusty plasma by means of particle simulations. The instability arises due to the streaming of plasma ions and neutrals relative to charged dust grains. According to linear theory, the presence of collisions between the plasma ions and a neutral gas background reduces the growth rate of the instability. Nonlinearly, however, the presence of drifting neutrals maintains the initial relative drift between plasma and dust ions until the unstable waves grow to large amplitude and collisions due to wave-particle interactions exceed the neutral collisions. As a result, stronger nonlinear effects, as manifested by enhanced fluctuations, larger amounts of plasma and dust heating, and a temporary reduction of the relative drift velocity, can occur in the presence of collisions.

A dusty (or complex) plasma is a four-component plasma system consisting of electrons, ions, neutral atoms, and charged, nanometer to micrometer-sized particles (i.e., the “dust”). Because these dust grains are charged, they fully participate in the plasma dynamics and can be used to reveal details about transport, instabilities, and charging properties of plasmas. However, one important area that has not been studied extensively is the area of magnetized dusty plasmas. Even though the charged dust grains in a typical laboratory experiment can acquire several thousand elementary charges, the large mass of the grains ensures that the charge-to-mass ratio is quite low. As a result, it is technically challenging to design an experiment that can achieve full magnetization of ions, electrons, and the charged dust grains.

In a plasma containing charged dust grains, the dust acoustic instability (DAI) can be driven by ions streaming through the dust with speed less than the ion thermal speed. When the dust is strongly coupled in the liquid phase, the dispersion relation of the dust acoustic modes changes in a way that leads to an enhancement of the growth rate of the DAI. In this paper, we show how strong coupling enhances the DAI growth rate and consider application to microgravity experiments where subthermal ion flows are in general possible.

The use of ultraviolet (UV) radiation to reduce the negative charge on dust particles and modify force balance in particle traps in processing plasmas is investigated theoretically. Possible photophoresis associated with the UV flux is also discussed. The use of UV to facilitate moving contaminant particles from traps is considered.

A scheme for forming a Coulomb lattice of positively charged dust grains in a high-pressure (P>torr) gas is discussed theoretically. The grains are charged positively by photoemission in the presence of a flux of ultraviolet (UV) photons with energy larger than the work function of the grains, but lower than the ionization potential of the background gas. Methods for levitating and containing the dust using photophoretic forces (both UV and non-UV), gas drag, and electrostatic forces are considered.

Modified two-stream instabilities are investigated in dusty plasmas in which electrons and/or ions drift across an external magnetic field. The usual high requency instability ( ω ce ⪢ ω ⪢ ω ci ) driven by treaming electrons is modified due to n i ≠ n e . Low frequency instabilities in the regime ω ci ⪢ ω ⪢ ω cd ( ω cd is the dust gyrofrequency) are considered for both long wavelengths, kϱ i ⪡ 1, and short wavelengths, kϱ i ⪢ 1 ( ϱ i is the ion gyroradius). It is found that low frequency instability can occur even when T i ⪢ T e . Applications of the results to dusty plasmas in protostellar clouds and planetary rings are discussed.

The effect of charged dust on the collisionless electrostatic ion cyclotron instability is investigated. Standard linear Vlasov theory is used to estimate the critical electron drift in the presence of either positively or negatively charged dust. The dust is assumed to be uniform in both mass and charge with the dust mass much greater than the ion mass. It is shown that the critical drift decreases as the charge density carried by negatively charged dust increases. Possible applications to the current system connecting Jupiter and its satellite Io, as well as that of the Saturnian rings are discussed.

The Magnetized Dusty Plasma Experiment at Auburn University has been operational for over one year. In that time, a number of experiments have been performed at magnetic fields up to B = 2.5 T to explore the interaction between magnetized plasmas and charged, micron-sized dust particles. This paper reports on the initial results from studies of: (a) the formation of imposed, ordered structures, (b) the properties of dust wave waves in a rotating frame, and (c) the generation of plasma filaments.

High frequency drift instabilities with ωce ⪢ ω ⪢ ωci are investigated in a dusty magnetized plasma in which locally there is an electron density gradient which is opposite in sign to a dust density gradient. Two different equilibria are considered, characterized by ρ d ≶ L nd , where ρd is the dust gyroradius and Lnd is the dust density scale length. Possible application to Saturn's F-ring is discussed.

A previous model for secondary electron emission from small grains is modified to calculate yields for micron sized grains, both spherical and cylindrical, when the primary electrons constitute a high energy parallel beam. It is found that, in general, the secondary electron yield is significantly higher than for the case of normal incidence. Moreover, the equilibrium potentials of the grain are always positive due to this enhanced secondary emission. These results are compared with experimental data recently available for micron sized glass particles, and equilibrium potentials, calculated based on the model presented here, and are found to be in reasonably good agreement with their measured potentials. >

Ground-state structures of finite, cylindrically confined two-dimensional Yukawa systems composed of charged superparamagnetic dust grains in an external magnetic field are investigated numerically, using molecular dynamic simulations and lattice summation methods. The ground-state configuration of the system is identified using, as an approximation, the experimentally obtained shape of the horizontal confinement potential in a classical single-layer dusty plasma experiment with nonmagnetic grains. Results are presented for the dependence of the number density and lattice parameters of the dust layer on (1) the ratio of the magnetic dipole-dipole force to electrostatic force between the grains and (2) the orientation of the grain magnetic moment with respect to the layer.

Summary form only given. To study the effects of rocket engine burns in the ionosphere, Naval Research Laboratory (NRL) plans to conduct the second Charged Aerosol Release Experiment (CARE II) using a solid rocket motor burning in the ionosphere. The measurements of the rocket includes plume optical emissions with ground cameras, and radio wave scatter with HF, VHF, UHF and higher frequency radars. The exhaust vapors initiate plasma turbulence in the ionosphere that can scatter the radar waves launched from ground transmitters. Hypersonic exhaust flow impacting the ionospheric plasma may yield an electromagnetic pulse that is detectable using electric field booms on an instrumented section of the rocket. If the exhaust cloud itself passes over in situ detectors, increased ion-acoustic wave turbulence, enhanced neutral and plasma densities, enhanced ion temperatures, and magnetic field perturbations are expected to be detected. Plasma theory has been used to predict the nature of the ion waves excited by charged dust beams streaming across or along the geomagnetic field in ionospheric. These waves could be generated by plasma instabilities during the aerosol release experiment. The injection speed of the dust and gas is generally larger than the ion thermal speed in the background ionosphere. Because the dust grains can be charged negatively by plasma collection from the ionosphere, the dust could act like a charged beam that excites instabilities in the background plasma. The theory is applied to relatively early time scales (on the order of 0.1 to 1 seconds) in the dust-gas cloud expansion. Wave frequencies larger than the ion gyro frequency are considered, and collisions with neutrals are included.

We review dust and meteoroid fluxes and their dusty plasma effects in the interplanetary medium near Earth orbit and in the Earth’s ionosphere. Aside from in-situ measurements from sounding rockets and spacecraft, experimental data cover radar and optical observations of meteors. Dust plasma interactions in the interplanetary medium are observed by the detection of charged dust particles, by the detection of dust that is accelerated in the solar wind and by the detection of ions and neutrals that are released from the dust. These interactions are not well understood and lack quantitative description. There is still a huge discrepancy in the estimates of meteoroid mass deposition into the atmosphere. The radar meteor observations are of particular interest for determining this number. Dust measurements from spacecraft require a better understanding of the dust impact ionization process,as well as of the dust charging processes. The latter are also important for further studying nanodust trajectories in the solar wind. Moreover understanding of the complex dependencies that cause the variation of nanodust fluxes is still a challenge. 540010117 Gästprofessur Mann 540010110 Driftsmedel Pellinen-Wannberg

It is shown that, for a moderately long time scale, two‐body collisions can actually help in maintaining a non‐Maxwellian ion velocity distribution in a plasma. This effect occurs when the ions have orbits large enough to transit spatial regions with different physical parameters in a single collision time. The effect is applied to ions confined in a spherically convergent ion focus (SCIF), where collisions at the edge of a spherical potential well help maintain convergent non‐Maxwellian flow in the rest of the device.

A brief, critical review of dust-plasma interactions in the cosmic environment is presented, with emphasis on certain results. Both single-particle (e.g., gravitoelectrodynamics) and collective (e.g., appearance of new wave models) effects are discussed and some areas in which further research is needed are pointed out. The pressing need for laboratory studies, both to provide the necessary data for the theoretical studies and to test the predictions of these theories, is emphasized. >

A classical dusty plasma experiment was performed using two different dust grain sizes to form a strongly coupled asymmetric bilayer (two closely spaced interacting monolayers) of two species of charged dust particles. The observation and analysis of the thermally excited particle oscillations revealed the collective mode structure and wave dispersion in this system; in particular the existence of the theoretically predicted $k=0$ energy (frequency) gap was verified. Equilibrium molecular dynamics simulations were performed to emulate the experiment, assuming Yukawa type inter-particle interaction. The simulations and analytic calculations based both on lattice summation and on the QLCA approach are in good agreement with the experimental findings and help identifying and characterizing the observed phenomena., Submitted to PRL

We consider a 2D Yukawa lattice of grains, with a beam of other charged grains moving in the lattice plane. In contrast to Vlasov plasmas, where the electrostatic instability excited by the beam is only longitudinal, here both longitudinal and transverse instabilities of the lattice phonons can develop. We determine and compare the transverse and longitudinal growth rates. The growth rate spectrum in wave number space exhibits remarkable gaps where no instability can develop. Depending on the system parameters, the transverse instability can be selectively excited.

Recently there has been interest in the properties of dusty negative ion plasmas, including dust charging and collective behavior. Electronegative dusty plasmas are of interest from the perspective of both basic physics and applications. Because the addition of negative ions to a dusty plasma can change the dust charge state, and add new sources of free energy such as ion currents, such plasmas could provide useful tools with which to study the physics of dust wave instabilities. Moreover, electronegative dusty plasmas can occur in industrial processing plasma devices, where the control of dust is an issue.

Dust is commonly found in current magnetic fusion devices. In reactors like ITER dust can pose safety hazards and impact plasma performance. However, the properties, generation rate, dynamics, and role of dust in fusion plasmas are still not well understood. In this work we simulate dynamics of dust particles in tokamaks with the Dust Transport, DUSTT, code and analyze the visibility of dust particles of different sizes in fusion plasmas by modern fast framing cameras. Using the DUSTT code, the dust density, radius and velocity distributions at different locations in the edge plasma are simulated and evaluated against the available experimental data. We compare the simulated dust trajectories with ones experimentally measured on NSTX with the fast camera imaging technique. The imaging is possible because dust heating and ablation by plasma creates two sources of radiation: thermal radiation from the heated dust particle and radiation from the ablation cloud interacting with the surrounding plasma. The analysis of spectral characteristics of the radiation can provide information as on dust (size, temperature, composition), as well as on dust-plasma interaction processes (ablation dynamics, local plasma parameters). We calculated the intensity of both the thermal radiation from a carbon dust particle and the radiation from the ablation cloud surrounding it for various plasma parameters. This allows to estimate minimal size of the visible dust and the ablation cloud characteristics in different tokamak plasma regions. We have also analyzed dust radius distribution resulting from laser scattering measurements on DIII-D taking into account non-Rayleigh regimes of light scattering as well as dust evaporation due to heating by laser radiation.

Naturally occurring and injected dust particles are observed in the DIII-D tokamak in the outer midplane scrape-off-layer (SOL) using a fast-framing visible camera. Sources of naturally occurring dust include material eroded from plasma facing components by transient events such as edge-localized-modes (ELMs) or disruptions. Dust particles ablate when they enter a hot region of plasma near the separatrix, or when an ELM filament intercepts a dust particle already present in the SOL. Modeling shows that line radiation from the ablation cloud dominates thermal radiation from the dust particle when the plasma temperature is greater than ∼10–50 eV for typical edge plasma densities in DIII-D. The size of dust particles is estimated using the observed particle lifetime and theoretical ablation rate of a carbon sphere. Using this method, the lower limit of detected dust diameter is ∼6 mm and particles with inferred diameter ≫1 mm are observed. Dust particle 2D velocities range from approximately 10 to 300 m/s, with larger velocities measured for smaller particles. The observed scaling of the dust velocity as a function of size R d is in rough agreement with the v ∝ R d −1/2 scaling predicted by a simple 1D analytic model of spherical carbon dust particles accelerated due to ion drag in a uniform plasma, for a fixed distance between the dust origin and the observation region. Pre-characterized 2–4 mm diameter diamond dust particles are introduced at the lower divertor in an ELMing H-mode discharge using the divertor materials evaluation system (DiMES), and these particles are found to be at the lower size limit of camera detection using resolution of ∼0.2 cm2 per pixel and exposure time of 330 ms. Injection of pre-characterized 6 mm median diameter dust indicates that the inferred size of naturally occurring dust may be overestimated by up to a factor of 10.

A kinetic approach is presented for obtaining slowly time-dependent, self-consistent plasma, and magnetic field configurations for this region, using anisotropic particle distributions. At present, a 2D configuration is used. The time variation of the plasma/field configuration is assumed to be driven by a slowly varying, externally imposed electric field (representing, for example, a change in solar wind conditions). The numerical approach involves solving a 2D nonlinear Poisson equation for the magnetic vector potential at each time step. The local current density is calculated from particle velocity distributions under the assumption of adiabatic particle motion. The obtained equations of state are compared with those of double-adiabatic theory. Numerical examples of self-consistent responses of the near-earth plasma and field to an externally imposed electric field pulse are presented.

Dust production and accumulation present potential safety and operational issues for the ITER. Dust diagnostics can be divided into two groups: diagnostics of dust on surfaces and diagnostics of dust in plasma. Diagnostics from both groups are employed in contemporary tokamaks; new diagnostics suitable for ITER are also being developed and tested. Dust accumulation in ITER is likely to occur in hidden areas, e.g., between tiles and under divertor baffles. A novel electrostatic dust detector for monitoring dust in these regions has been developed and tested at PPPL. In the DIII-D tokamak dust diagnostics include Mie scattering from Nd:YAG lasers, visible imaging, and spectroscopy. Laser scattering is able to resolve particles between 0.16 and 1.6 microm in diameter; using these data the total dust content in the edge plasmas and trends in the dust production rates within this size range have been established. Individual dust particles are observed by visible imaging using fast framing cameras, detecting dust particles of a few microns in diameter and larger. Dust velocities and trajectories can be determined in two-dimension with a single camera or three-dimension using multiple cameras, but determination of particle size is challenging. In order to calibrate diagnostics and benchmark dust dynamics modeling, precharacterized carbon dust has been injected into the lower divertor of DIII-D. Injected dust is seen by cameras, and spectroscopic diagnostics observe an increase in carbon line (CI, CII, C(2) dimer) and thermal continuum emissions from the injected dust. The latter observation can be used in the design of novel dust survey diagnostics.

金沢大学理工研究域電子情報学系, Influence of thermal radiation emissivity on the lifetime of a dust particle in plasmas is investigated for different fusion relevant metals (Li, Be, Mo, and W). The thermal radiation is one of main cooling mechanisms of the dust in plasmas especially for dust with evaporation temperature higher than 2500 K. In this paper, the temperature- and radius-dependent emissivity of dust particles is calculated using Mie theory and temperature-dependent optical constants for the above metallic materials. The lifetime of a dust particle in uniform plasmas is estimated with the calculated emissivity using the dust transport code DUSTT [A. Pigarov, Physics of Plasmas 12, 122508 (2005)], considering other dust cooling and destruction processes such as physical and chemical sputtering, melting and evaporation, electron emission etc. The use of temperature-dependent emissivity calculated with Mie theory provides a longer lifetime of the refractory metal dust particle compared with that obtained using conventional emissivity constants in the literature. The dynamics of heavy metal dust particles are also presented using the calculated emissivity in a tokamak plasma. © 2008 American Institute of Physics.

Summary form only given. We explore the charging of a dust particle immersed in a plasma in the presence of a magnetic field. The dust particle charges due to the flowing electrons and ions within the plasma. A simple case with no magnetic field is compared with basic OML theory as a basis for comparison. The simulations are then run with varying magnitudes of magnetic field to study the effects of the dust particle charging in the presence of a magnetic field. These results are then compared against existing theories.

Summary form only given. Dusty or complex plasmas are plasmas containing micron-sized charged solid particulates (dust grains). Highly charged dust confined in low temperature laboratory plasmas can form two-dimensional (2D) or quasi-2D crystalline or liquid-like structures because of their mutual Coulomb repulsion. Because the structures can be easily visualized by light scattering, such strongly coupled complex plasmas are used to investigate many physics issues intrinsic to strongly coupled Coulomb systems. We propose and discuss theoretically a novel type of 2D complex plasma formed by positioning charged dust grains on the surface of liquid helium (He). Liquid He provides a nearly ideal flat substrate, has very low polarizability and conductivity, and has been used previously to study 2D systems of electrons, ions, and charged clusters. The 2D cryogenic complex plasma has possible advantages compared with traditional 2D complex plasmas. These include: (1) a more controlled environment, (2) an unscreened Coulomb interaction between the grains, (3) the possibility' that new-types of strongly coupled systems could be studied, including (a) systems composed of nanoparticles in addition to those composed of micron-size particles, (b) systems of grains placed in a strong external magnetic field, (c) systems of grains with intrinsic magnetic dipole moments, and (d) binary mixtures of grains with different charges and masses. These features could lead to new basic physics studies of new phenomena that could be explored with the 2D cryogenic complex plasma. At the same time, there are issues that require further investigation: (i) the type of grain to use, (ii) the possible use of other cryogenic liquids, (iii) methods for charging and discharging, (iv) means of confinement, (v) possible diagnostic methods, (vi) possible He transmitted damping mechanisms.

We study analytically and by molecular dynamics simulations the ground state configuration of a system of magnetic dipoles fixed on a two-dimensional lattice. We find different phases, in close agreement with previous results. Building on this result and on the minimum energy requirement we determine the equilibrium lattice configuration, the magnetic order (ferromagnetic versus antiferromagnetic), and the magnetic polarization direction of a system of charged mesoscopic particles with magnetic dipole moments, in the domain where the strong electrostatic coupling leads to a crystalline ground state. Orders of magnitudes of the parameters of the system relevant to possible future dusty plasma experiments are discussed.

Dusty plasmas have been studied in argon, radio frequency (rf) glow discharge plasmas at magnetic fields up to 2.5 T where the electrons and ions are strongly magnetized. Plasmas are generated between two parallel plate electrodes where the lower, powered electrode is solid and the upper electrode supports a dual mesh consisting of #24 brass and #30 aluminum wire cloth. In this experiment, we study the formation of imposed ordered structures and particle dynamics as a function of magnetic field. Through observations of trapped particles and the quasi-discrete (i.e., “hopping”) motion of particles between the trapping locations, it is possible to make a preliminary estimate of the potential structure that confines the particles to a grid structure in the plasma. This information is used to gain insight into the formation of the imposed grid pattern of the dust particles in the plasma.

Dusty plasmas have been studied in argon, rf glow discharge plasmas at magnetic fields up to 2 T, where the electrons and ions are strongly magnetized. In this experiment, plasmas are generated between two parallel plate electrodes where the lower, powered electrode is solid and the upper, electrically floating electrode supports a semi-transparent, titanium mesh. We report on the formation of an ordered dusty plasma, where the dust particles form a spatial structure that is aligned to the mesh. We discuss possible mechanisms that may lead to the formation of the “dust grid” and point out potential implications and applications of these observations.

In a recent attempt to understand the enhanced backscatter from Space Shuttle exhaust in the ionosphere, Bernhardt et al. (1995) conjectured on the possible excitation of dust acoustic waves. The condensation of the water vapor of the expanding shuttle exhaust plume into ice grains, and their subsequent charging, may create a dusty plasma in which such modes may exist. In this brief report, we point out that for the parameters as reported by Bernhardt et al. (1975) instabilities on the dust time scale may occur.

An analytical and numerical kinetic analysis of the collisionless electrostatic ion cyclotron instability in dusty plasmas (Chow and Rosenberg, Planet. Space Sci. , 43 , 613–618, 1995) is compared with recent experimental results (Barkan et al., Planet. Space Sci. , 43, 905–908, 1995). The analysis uses standard linear Vlasov theory to predict the critical drift required to drive the instability. It is shown that the results are consistent with the observations of the laboratory experiment.

Conditions are investigated for forming a Coulomb lattice of dust grains which are charged positively by the ultraviolet induced photoemission of electrons. >

A combined theoretical and molecular dynamics (MD) simulation study of the collective modes and their dispersion in a two-dimensional Yukawa system in the strongly coupled liquid state is presented. The theoretical analysis relies upon the quasilocalized charge approximation; the MD simulation generates static pair correlation functions and dynamical current-current correlation spectra.

Summary form only given. Dusty plasmas (plasmas containing charged dust grains of micron to sub-micron size) occur in a wide variety of space and laboratory environments. The presence of dust, with a much smaller charge-to-mass ratio than the ions, can both modify the properties of standard ion waves and instabilities and give rise to new low frequency dust waves and instabilities. Dusty plasmas in the laboratory may exhibit strong coupling (i.e., the electrostatic interaction energy between neighboring grains exceeds their kinetic energy) which also affects wave properties. Here, recent theoretical work on several instabilities in collisional dusty plasmas is summarized, with applications to dusty plasmas in the Earth's lower ionosphere and in laboratory experiments where neutral densities are relatively high. Instabilities driven by electron cross-field drifts are considered with application to dusty plasmas in the upper mesosphere or low E-region (e.g., dusty meteor trails or polar mesosphere summer echo regions). This includes studies of the effects of charged dust on electrojet instabilities and conditions for exciting low frequency dust acoustic instabilities, along with implications for radar scattering. Dust wave instabilities driven by ion drifts are discussed with application to various laboratory dusty plasma wave experiments. This includes studies of a very low frequency resistive instability, and the effects of strong coupling on ion-dust streaming instabilities. Aspects of the interaction of electromagnetic waves with strongly coupled dusty plasmas are also considered.

Summary form only given. Dust grains, or solid particles of micron to sub-micron size, are observed in various space plasma environments (e.g. planetary rings, comets, noctilucent clouds) and also various low temperature laboratory plasmas (e.g. process plasmas, plasma crystals). Dust grains in a plasma are generally highly charged, and the presence of massive charged dust particles has been shown to lead to new low frequency modes such as dust-acoustic waves within the context of standard plasma theory. In certain laboratory environments, however, the dust may be strongly coupled, as characterized by the parameter /spl Gamma//sub d/=Q/sub c//sup 2/ exp (-d//spl lambda//sub D/)/dT/sub d/, where Q/sub d/ is the dust charge, d is the intergrain spacing, T/sub d/ is the dust thermal energy, and /spl lambda//sub D/ is the plasma screening length. In this paper we investigate the dispersion relation for dust-acoustic waves in a three-component plasma with strongly coupled negatively charged dust grains, and classical electrons and positive ions. In doing this, we examine the use of the quasi-localized charge approximation scheme, generalized to take into account electron and/or ion screening. This scheme relates the small-k dispersion to the total correlation energy of the system which can be determined either through analytic or numerical simulation methods. Some effects of charged particle-neutral collisions are also taken into account. Applications to laboratory dusty plasmas are discussed.

Summary form only given, as follows. Dust grains (solid particles of micron to sub-micron sizes) can be charged positively by electron emission processes such as photoemission, thermionic emission, or secondary electron emission. Recently a theoretical scheme for forming a Coulomb lattice of positively charged dust grains in a high-pressure gas has been discussed. In that scheme, the grains are charged positively by the emission of photo-electrons in the presence of a flux of ultraviolet (UV) photons with energy larger than the work function of the grain, but lower than the ionization potential of the gas. We extend that theoretical analysis to explore grain charging processes such as photoemission or thermionic emission as a source of ionization (electrons) in a gas. In the simplest case of an inert gas, the electron density generated may be determined by balancing the electron emission from the grains with the electron loss processes involving recombination onto the grains. Some example regimes of dust, gas, and photon flux parameters are investigated. Aspects of basic physics issues relevant to these dust ionization processes are also explored, including the effect of grain size and background gas parameters on the electron emission process, and the heating and cooling of small grains via radiation or conduction.

Heavy negatively charged ions have recently been detected at relatively high altitudes in the ionosphere of Titan, and it has been suggested that perhaps they are supported by electric fields. In this short communication, we discuss the possibility of ion-acoustic instability in this environment.

Ionized gases laden with fine charged dust grains are loosely referred to as dusty plasmas. Recently, lattice structures of negatively charged strongly coupled dust grains, called Coulomb crystals, have been formed in several laboratory plasma experiments. This three year project conducted fundamental theoretical research on issues important for understanding the basic physics of Coulomb crystallization in dusty plasmas. Models of the intergrain forces were developed, including attractive induced dipole forces in addition to repulsive screened Coulomb forces, and applied to modeling experimental data. The properties of low frequency dust acoustic waves and instabilities in strongly coupled dusty plasmas were investigated. Novel schemes for forming Coulomb lattices of positively charged grains were developed, involving grains that are charged positively either by ultraviolet (UV)-induced photoemission in a high-pressure gas, or by thermionic emission under laser heating. The use of UV to reduce dust trapping in process plasmas was also explored, and studies began on the use of dust as an electron source resulting from photoemission or thermionic emission. In addition, various waves and instabilities in collisional dusty plasmas were investigated.

Secondary dust density waves were observed in conjunction with high amplitude (nd/nd0>2) dust acoustic waves (DAW) that were spontaneously excited in a dc glow discharge dusty plasma in the moderately coupled, Γ∼1, state. The high amplitude dust acoustic waves produced large dust particle oscillations, displacements, and trapping. Secondary dust density waves were excited in the wave troughs of the high amplitude DAWs. The waveforms, amplitudes, wavelengths, and wave speeds of the primary DAWs and the secondary waves were measured. A dust-dust streaming instability is discussed as a possible mechanism for the production of the secondary waves.

The Polywell is a magnetic version of a Spherically Convergent Ion Focus (SCIF) device which was proposed as a significant variation of earlier studies on electrostatic confinement. The idea of this device is to inject high energy electrons into a quasi-spherical magnetic field; the electrons create a potential well of sufficient depth to accelerate ions from low energy at the periphery to fusion energies within a focus at the center of the sphere. Injection of electrons keeps the system electrically nonneutral, so that the potential well which accelerates the ions is maintained at a constant value sufficient to confine the ions within the device, returning them again and again at high velocity to the central focus. Essential to the success of the scheme is that the ions maintain their nonthermal velocity distribution, with primarily radial flow, long enough to produce fusion in the dense focus at the center of the sphere.

The visibility of carbon dust particles in fusion plasmas with fast framing cameras is evaluated using computer and theoretical modelling. Dust heating and ablation in the plasmas, ionization dynamics of the ablation cloud around the dust particle, thermal radiation of the dust and line radiation of the cloud are considered. The minimal size of carbon dust particles visible with the cameras is calculated as a function of the plasma parameters and the distance from the dust to the camera objective. The relative contributions of thermal radiation from the grain and line radiation from the cloud to the total dust radiation are analysed.

In this note, we extend the calculation of ion loss due to collisional upscattering in the core of the Polywell/SCIF device to include effects of ion-ion scattering in the rest of the device. As the ions transit through the device, collisional processes, such as upscatter or deflection, can alter their velocity distributions, leading to Maxwellization of initially monoenergetic distributions, or isotropization of initially anisotropic distributions. These effects can contribute to ion loss mechanisms. We consider the effects of ion-ion collisions outside the core and estimate the loss rates due to associated loss mechanisms. We consider the scattering in azimuthal velocity of ions in the bulk of the device, where the radial ion energies are much larger than the azimuthal energies. Perpendicular deflection and conversion of radial to azimuthal velocity by collisions could lead to a degradation of the ion focus. We also consider the effects of thermalization in the edge region of the device, where the ion energy is low and of the order of the ion birth energy.

It has been known for a long time that microscopic dust appears in plasmas in fusion devices. Recently it was shown that dust can be responsible for the termination of long- discharges. Also, in ITER-scale experiments dust can pose safety problems related to its chemical activity, tritium retention and radioactive content. In particular, the presence of dust in the vacuum chamber of ITER is one of the main concerns of the ITER licensing process. Here we review recent progress in the understanding of different experimental and theoretical aspects of the physics of dust dynamics and transport in fusion plasmas and discuss the remaining issues.

Ion-dust streaming instability in a plasma containing dust grains with large thermal speeds is considered using kinetic theory. The results are compared with experimental measurements of the dispersion relation of dust acoustic waves performed at the University of Iowa and Auburn University.

We investigate the thermal radiation from small metallic dust grains heated to high temperatures, using a Drude model for the temperature dependence of the optical constants of the grain material. We use both Mie theory and approximate expressions for the absorption efficiency of the grains and compare the corresponding results. The thermal radiation from dust particles composed of fusion relevant metals is computed, and comparisons are made with available data on the emissivity of metal flat surfaces at high temperatures. For fixed temperature T, we find that the maximum of the thermal radiation intensity (normalized by the black body radiation intensity) occurs when the grain radius is roughly of the order of 1/2π times the wavelength where maximum thermal radiation occurs as given by Wien's law. Because of this, in certain parameter ranges smaller grains can have higher emissivity than larger ones. The analysis may have application to several areas including dust in fusion devices.

The determination of dust radius distributions from the measurement of laser scattering intensity in tokamaks is presented. The analysis takes into account non-Rayleigh regimes of light scattering for different complex refractive indices of dust materials, as well as dust evaporation due to heating by laser radiation. The model is applied to calculate the dust particle radius distribution in tokamaks during normal plasma operation. It is shown that a relatively small amount of large dust particles in the distribution may play a significant role for estimation of the dust mass inventory in tokamaks.