Fine Particle Plasmas Research Articles

Phase diagram of strongly coupled fine particle (dusty) plasmas with limited Spacial extents: Theory and simulation

AbstractPhase separations in strongly coupled fine particle (dusty, complex) plasmas are discussed and phase diagrams are expressed in the ‐‐plane or in terms of strengths of the Coulomb coupling between fine particles and the screening by the ambient electron‐ion plasma. Two possibilities, separations into phases with different electrons, ion, and fine particle densities and ones into phases with a common electron density, are analyzed and it is shown that, when the spacial extent is limited as in usual experiments, only the latter is realized. Based on a model of fine particle plasma as a Yukawa system with non‐uniformity taken into account, molecular dynamics simulations are performed with constant electron density. Fine particles are moved as particles while position‐dependent local averages of ion and fine particle distributions are treated as continuum. Though the critical point is located at a smaller coupling by about a factor of two compared with the theoretical prediction, the results of simulations confirm the existence of such phase separations with a common electron density.

Fine Particles as Solute in Fine Particle (Dusty) Plasmas

Analysis has been made on a possibility of phase separation and critical point as a solution of fine particles in plasmas, extending the previous work which pointed out this as one of two such possibilities. Fine particles are treated as a solute in the solvent of weakly coupled plasmas of electrons and ions. Examples of phase diagram have been obtained and coexisting phases are shown to have fine particles which differ in densities by almost one order of magnitude.

Static behavior of fine particle clouds in fine particle (dusty) plasmas under gravity

Static behavior of fine particle cloud in fine particle (dusty) plasmas under gravity is analyzed numerically on the basis of the drift-diffusion equations. The system is assumed to have one-dimensional structure and the effect of the ion drag force is taken into account. The results confirm the analytically obtained prediction that we have an enhanced charge neutrality in fine particle clouds under gravity as well as under microgravity. They are also compared with a simple model based on the enhanced charge neutrality in clouds to show its applicability.

Strongly coupled fine particle clouds in fine particle (dusty) plasmas

Based on drift‐diffusion equations, we show a large enhancement of the charge neutrality in fine particle clouds analytically and confirm it by numerical solutions, in both cases of microgravity and gravity. This observation enables us to construct simple models of fine particle clouds in both cases. Combined with the analysis of the Helmholtz free energy of inhomogeneous systems, our results give a formulation to obtain microscopic structures of fine particles in fine particle clouds.

Charge neutrality of fine particle (dusty) plasmas and fine particle cloud under gravity

The enhancement of the charge neutrality due to the existence of fine particles is shown to occur generally under microgravity and in one-dimensional structures under gravity. As an application of the latter, the size and position of fine particle clouds relative to surrounding plasmas are determined under gravity.

Distribution of electrons, ions, and fine (dust) particles in cylindrical fine particle (dusty) plasmas: drift-diffusion analysis

Based on the drift-diffusion equations, the behaviour of electrons, ions and fine particles in fine particle plasmas is analysed both analytically and numerically. The cylindrical symmetry of the system is assumed and the cases of up to two species (sizes) of fine particles are considered. It is shown that, in the domain where fine particles exist, the charge neutrality is satisfied to a much higher accuracy, so that the electrostatic potential and the electron distribution are almost flat, and the change in the negative charges due to fine particles is compensated by the ion distribution. This occurs when the charge density of particles multiplied by their charge number exceeds the electron and ion charge densities, and is analytically attributed to the participation of fine particles to the screening of the space charge. The condition for the formation of void at the centre is obtained and the behaviour of particle distribution for parameters around the condition is observed. In the case of two species, the possibility is shown that smaller particles are distributed inside of the domain of larger particles and, when the larger ones form a void, it is filled with smaller ones, the enhanced charge neutrality being recovered.

Modeling Fine-Particle (Dusty) Plasmas and Charge-Stabilized Colloidal Suspensions as Inhomogeneous Yukawa Systems

In order to give a basis for the structure and correlation analysis of fine particle (dusty) plasma and colloidal suspensions, thermodynamic treatment of mixtures of macroscopic and microscopic charged particles within the adiabatic response of the latter is extended to include the case where the system is finite and weakly inhomogeneous. It is shown that the effective potential for macroscopic particles is composed of two elements: mutual Yukawa repulsion and a confining (attractive) Yukawa potential from their `shadow' (the average charge density of macroscopic particles multiplied by the minus sign). The result clarifies the relation between two approaches hitherto taken where either a parabolic one-body potential is assumed or the average distribution is assumed to be flat with finite extension. Since the satisfaction of the charge neutrality is largely enhanced by the existence of macroscopic particles, the assumption of the flat electrostatic potential and therefore flat average distribution of macroscopic particles in the domain of their existence is expected to be closer to reality than the assumption of the parabolic potential in that domain.

Increasing Surface Hardness of AISI 1045 Steel by AIH-FPP/Plasma Nitriding Treatment

In order to increase surface hardness of AISI 1045 steel, a new hybrid surface modification; combination of atmospheric-controlled induction-heating fine particle peening (AIH-FPP) and plasma nitriding, was developed. Surface microstructures of plasma nitrided specimens pre-treated with AIH-FPP using Cr shot particles were characterized by an optical microscope, a scanning electron microscope (SEM), an energy dispersive X-ray spectrometer (EDX) and X-ray diffraction analysis (XRD). As results, the nitrided layer was formed at the surface of the specimen with Cr diffused layer induced by AIH-FPP. This nitrided layer showed higher hardness than that of without AIH-FPP specimen. This was because CrN was formed at the surface of the AIH-FPP/Plasma nitriding treated specimen. And, the surface hardness of the nitrided layer tended to increase as the Cr concentration in the surface layer decreased. It was clarified that the pore formation during the AIH-FPP/Plasma nitriding treatment was inhibited by decreasing Cr concentration. These results suggest that the proposed hybrid surface treatment remarkably increases surface hardness of AISI 1045 steel. [doi:10.2320/matertrans.MBW201205]

Structures and dynamics of fine particles in fine particle plasmas under microgravity and friction between two-dimensional layers of charges

Low temperature structures and dynamics of fine (dust) particles in the ambient (background) plasma with the cylindrical symmetry are analyzed by numerical simulations and theory. Fine particles are modeled as Yukawa particles and the one- and two-component cases are considered. In the one-component case, particles form well-defined concentric cylindrical shells and the structures are expressed by simple interpolation formulas to a good accuracy. When we introduce the difference into charges of particles forming a shell, particles are separated into a smaller shell of larger charges and a larger shell of smaller charges. In the two-component Yukawa system, we usually have structures composed of charge-separated shells where larger and smaller charges appear alternately in the order of radius. When we have charge-dependent forces along the symmetry axis, shells of larger and smaller charges can move relative to each other keeping their own structures and the mobility for the relative motion can be defined. We give examples obtained for some combinations of parameters. It is found that, when appropriate conditions are satisfied, concentric shells form a kind of 'fine-particle (dust) screw' and the mobility is increased.

Structures of Yukawa and Coulomb particles in cylinders: Simulations for fine particle plasmas and colloidal suspensions

Low-temperature structures of Yukawa particles in systems with cylindrical symmetry are analyzed by numerical simulations. Particles are organized into well-defined thin concentric shells forming triangular lattices with defects on each shell and structural parameters are expressed by simple interpolation formulas including the limiting case of Coulomb particles. In outer shells, the local structure can be regarded as three-dimensional closest packing as in the case of the background of uniform spheres. These formulas can be directly compared with fine particle experiments in long cylindrical chambers under microgravity or colloidal suspensions in cylinders and may be useful as a basis of structural analyses in cylindrical systems.

Possible Observation of Critical Phenomena in Fine Particle (Dusty, Complex) Plasmas

The possibility to observe critical phenomena in fine particles plasmas is discussed in terms of both characteristic dimensionless parameters of statistical mechanics and real conditions such as densities and temperatures in fine particle (dusty, complex) plasma experiments. In addition to the possibility originating from the divergence of the isothermal compressibility of strongly coupled one-component plasmas and Coulomb-like systems, it is shown that we have another possibility in the domain of intermediate coupling with feasible experimental conditions. In both cases, the Coulomb and Coulomb-like interactions between fine particles drive the system to thermodynamic instability and critical phenomena belong to the same universality class. The mechanisms, however, are completely different.

Development of fine-particle plasma systems for basic and applied research

Two plasma systems for basic and applied research on fine-particle plasmas have been developed. One is a planar-magnetron plasma system, by which fine particles are suspended apart from the region of plasma production and are driven upward, for the basic research of fine-particle plasmas. Fine particles are observed to be horizontally arranged even when they have a size of 6.5 µm. The other one is a hot-filament-assisted plasma chemical vapor deposition system for nano-carbon synthesis. Synthesis processes have been analyzed by mass spectroscopy, light scattering and self-bias voltage. It was shown that negatively charged carbon fine particles were confined for a long time in plasmas during generation and growth. Synthesized carbon fine particles were confirmed to contain single-walled carbon nanotubes by analyzing the results of Raman spectroscopy and transmission electron microscopy.

On Estimation of Three-Dimensional Pair Distribution Function from Two-Dimensional Sliced Data

In order to observe the three-dimensional distribution of micron-sized particles, it is a common practice to shed a sheet laser beam and record the positions and other twodimensional data of particles which scatter the light beam with the intensity beyond some threshold. In fine particle (dusty) plasmas, for example, fundamental properties of charged particle systems have been analyzed based on the two-dimensional particle orbits captured by CCD cameras. By scanning the laser beam perpendicularly to the sheet, one is able to obtain three-dimensional data of particle distribution. The most important of the latter may be the pair distribution function which is closely related to statistical properties of particles. The scanning in the perpendicular direction, however, may not be always possible in experiments and it may sometimes become necessary to estimate the three-dimensional pair distribution function from two-dimensional data. Since the thickness of laser beam is not always sufficiently smaller than mean distance between particles, it is necessary to evaluate the effect of finite thickness of laser beam sheet. To the author’s knowledge, there seems to be no explicit results on such an effect. The purpose of this note is to give a practical expression including the finite thickness effect. We take the xyz-coordinate so that xy-plane is parallel to the sheet of the beam and the intensity of the beam is expressed by a function FðzÞ. We assume that FðzÞ decreases monotonously with jzj both for z > 0 and z < 0 and the particle counting is limited in the domain jzj b=2 by properly setting the threshold in experiments. Let the position of a particle be ð0; 0; z0Þ with jz0j b=2. The definition of the two-dimensional pair distribution function (2dpdf) gðR; 2dÞ reads: When we have a particle at ð0; 0; z0Þ with jz0j b=2, the average number of particles dNð2dÞ in the cylindrical domain jzj b=2, R ðx þ y2Þ ðRþ dRÞ is given by dNð2dÞ 1⁄4 nð2dÞgðR; 2dÞ2 R dR: ð1Þ Here nð2dÞ is the two-dimensional number density (integrated along z) which is related to the three-dimensional one nð3dÞ by nð2dÞ 1⁄4 nð3dÞb: ð2Þ

Thermodynamic instability and the critical point of fine particle (dusty) plasmas: enhancement of density fluctuations and experimental conditions for observation

We analyze thermodynamics of fine particle (dusty) plasmas, regarding them as systems composed of charged particles with hard cores interacting via the repulsive Yukawa potential and the ambient plasma (of ions and electrons), taking the contribution of the latter properly into account. When the Coulomb coupling between fine particles becomes sufficiently strong, the isothermal compressibility of the whole system diverges and we have a phase separation and an associated critical point. The enhancement of long-wavelength density fluctuations near the critical point is shown. Experimental conditions of fine particle plasmas, densities and temperatures of components and the fine particle size are obtained corresponding to characteristic parameters around the critical point and the dependence on ion species and other factors is discussed. These phenomena will be observed in the bulk three-dimensional system which may be realized on the ground by somehow canceling the effect of gravity on fine particles. Experiments under the microgravity environment are naturally expected to provide a chance of observation.

Thermodynamics of strongly coupled repulsive Yukawa particles in ambient neutralizing plasma: Thermodynamic instability and the possibility of observation in fine particle plasmas

The thermodynamics is analyzed for a system composed of particles with hard cores, interacting via the repulsive Yukawa potential (Yukawa particulates), and neutralizing ambient (background) plasma. An approximate equation of state is given with proper account of the contribution of ambient plasma and it is shown that there exists a possibility for the total isothermal compressibility of Yukawa particulates and ambient plasma to diverge when the coupling between Yukawa particulates is sufficiently strong. In this case, the system undergoes a transition into separated phases with different densities and we have a critical point for this phase separation. Examples of approximate phase diagrams related to this transition are given. It is emphasized that the critical point can be in the solid phase and we have the possibility to observe a solid-solid phase separation. The applicability of these results to fine particle plasmas is investigated. It is shown that, though the values of the characteristic parameters are semiquantitative due to the effects not described by this model, these phenomena are expected to be observed in fine particle plasmas, when approximately isotropic bulk systems are realized with a very strong coupling between fine particles.

Experimental Parameters of Fine Particle Plasmas Explicitly Expressed by Dimensionless Characteristic Parameters

Experimental parameters of fine particle plasmas, densities and temperatures of components and the fine particle size, are explicitly expressed in terms of dimensionless characteristic parameters, such as Coulomb coupling and strength of screening, and typical examples are given. Though characteristic parameters are readily obtained from experimental parameters, the reverse is not trivial and it is shown that the charge neutrality condition limits the characteristic parameters realized by fine particle plasmas within the domain (a/λ) 2 /(Γ/A) ≥ 3. Here, a and λ are the mean distance between fine particles and the screening length, respectively, Γ = (Qe) 2 /akBTp is the Coulomb coupling of fine particles, and A = (neTe + niTi)/npTp is the ratio of the ideal gas pressures of ambient plasma (of ions and electrons) and fine particles.

Thermodynamic Instability in Strongly Coupled Fine Particle Plasmas and Critical Phenomena

Thermodynamic Instability in Strongly Coupled Fine Particle Plasmas and Critical Phenomena

Radial Ordering of Fine Particles in Plasma under Microgravity Condition

Microgravity experiments on fine-particle plasma were carried out and the ordering and behavior of fine particles were analyzed under the microgravity condition as well as under a change in gravitational conditions. Fine particles aligned in radial directions were observed under microgravity, although they were aligned in the vertical direction under the gravity condition. It has been suggested by comparison with the result obtained under microgravity that under the gravity the mutual influence between positive ion flow and negative fine particles results in the vertical alignment of fine particles and in the vertical flow of ions toward fine particles along with the deformation of plasma.

Ordering and behavior of fine particles in plasmas under gravity and microgravity conditions

Experiments of fine-particle plasma have been performed using a drop experiment facility in order to analyze the ordering and behavior of fine particles under microgravity and during the change of gravitational conditions. Aligned fine particles in the radial directions were observed under microgravity, although they were aligned in the vertical direction under gravity. It has been suggested that the vertical alignment of fine particles under gravity is caused by the mutual influence between positive ion flow and negative fine particles following the deformation of plasma.

B243 帯電微粒子の回転運動の研究

Fine particle plasma has large charge in comparison with gaseous plasma and indicates various singular behaviors due to strongly coupled character. Research of fine particle plasma is not only useful for investigation of space phenomena (formation and behavior of planetary ring) but also contains various possibilities of application through control of particles. As part of such purpose, we experiment that negatively charged particle irradiated by electron beam is confined and makes rotation in logarithmic potential around coaxial cylindrical electrodes. Particles used in this experiment are volcanic ashes of Mt. Usu and we used particles with radius of 90μm measured diameter by laser scattering and sorted by wind tunnel. In the experiment, we could confirm orbital motion of particle around central electrode by adding positively voltage to central electrode. By analyzing motion of particle in VTR pictures recorded this motion, we can calculate mass-to-charge ratio, and particle charged one estimated to be several thousand electrons.