Coulomb Balls Research Articles

Surface tension of Coulomb balls

Herein, we have calculated plasma parameters corresponding to those of a dc discharge in neon at 77 K temperature at self-organization of dense Coulomb balls with a dust particle number density of more than 4×1011m−3. To calculate the plasma parameters, we employed the fluid model of the positive column of the glow discharge with dust particles. The potential energy of the dust particle and the analogue of the surface tension coefficient of the Coulomb ball at neon pressures from 20 to 160 Pa have been obtained. For the obtained values of the surface tension coefficient analogue, a comparison with data obtained by other authors has been carried out.

Self-organization of Coulomb balls in glow DC discharge in neon at cryogenic temperature

Dense dust structures have been observed in a glow DC discharge in neon at a temperature of 77 K. Dependencies of shape, axial and radial sizes of dust structures on discharge current, gas pressure and longitudinal electric field have been studied. At the intersection points of dependencies of radial and axial sizes of dust structures on discharge current, the Coulomb balls have been observed at pressures between 0.15 and 1.2 Torr. The correlation between the discharge parameters, at which Coulomb balls form, and their size, composition, phase and dynamic state of components has been revealed.

Structural properties of anisotropically confined binary Coulomb balls.

We investigate the structural properties of a small binary system of dusty plasma subjected to an anisotropic external confinement. We have found that the ground state can form various symmetrical configurations, which generally correspond to variations of a multiple-ring structure. The presence of such structures is given through a detailed phase diagram constructed for the systems with N=18 and 24 particles. Furthermore, we show that the configurations of multiple rings can present a persistent behavior for the case in which the number of less-charged particles is equal to a multiple of the number of particles per ring. Finally, we discuss the main characteristics of the transitions of first and second orders since these are related to the main configurational changes of the ground states.

Theoretical description of Coulomb balls: Fluid phase

A theoretical description for the radial density profile of a finite number of identical charged particles confined in a harmonic trap is developed for application over a wide range of Coulomb coupling (or, equivalently, temperatures) and particle numbers. A simple mean-field approximation neglecting correlations yields a density profile which is monotonically decreasing with radius for all temperatures, in contrast to molecular dynamics simulations and experiments showing shell structure at lower temperatures. A more complete theoretical description including charge correlations is developed here by an extension of the hypernetted chain approximation, developed for bulk fluids, to the confined charges. The results reproduce all of the qualitative features observed in molecular dynamics simulations and experiments. These predictions are then tested quantitatively by comparison with benchmark Monte Carlo simulations. Quantitative accuracy of the theory is obtained by correcting the hypernetted chain approximation with a representation for the associated bridge functions.

Studying the response of a Coulomb ball of charged dust particles to external pulsed loads

The behavior of Coulomb balls of charged spherical dust particles under conditions of pulsed uniform loading of their outermost shells at various intensities has been studied by molecular dynamics modeling. If the intensity of the external load is below a certain threshold, the shell structure of the Coulomb ball is retained and the oscillations of outer shells are characterized by gradually decaying beats. As the intensity of the uniform loading increases, the shell structure exhibits smearing and, under the action of a threshold load, the system passes to a fluid-like state. The oscillation frequency of the outermost shell is independent of the intensity of uniform loading. Calculations show that, as the number of dust particles in a Coulomb ball increases, this frequency tends to a certain limiting value.

Plasma Crystals - Structure and Dynamics

This overview describes the confinement and structure of two-dimensional plasma crystals. Phonons and Mach cones in monolayer systems can be used for diagnostic purposes. Three-dimensional plasma crystals are found as multilayer systems or as Yukawa balls. The differences between Coulomb and Yukawa balls are described by means of a simple model. Optical diagnostic methods for studying dynamical phenomena in three-dimensional plasma crystals are discussed.

Structural features of bicomponent dust Coulomb balls formed by the superposition of fields of different origin in plasma

A binary mixture of dust particles in plasma which are in an external electrostatic harmonic confining field as well as in the field consisting of gravitational, thermophoretic, and electrostatic force is simulated. The interparticle interaction is described by the Yukawa isotropic pair potential. The structural properties of the binary mixture of particles depending on composition are investigated. The segregation features of a system of particles of two species under the conditions of recent experiments on Coulomb ball formation are studied. It is shown that particles form a shell structure in which every shell contains only its own species of particles; in so doing, smaller-sized particles make up outer shells with respect to larger-sized particles. When the size difference between the particles becomes more and more pronounced, they are spatially separated up to the formation of two independent Coulomb balls.

Structure of binary dust Coulomb balls in confining fields of different origin

We study for the first time a binary mixture of dust particles in plasma which are in the external electrostatic harmonic confining field as well as in the field of gravitational, thermophoretic and electrostatic forces. The interparticle interaction is described by the Yukawa potential. The spatial distribution of the binary mixture of particles depending on their content is investigated. It is shown that particles form an onion-shell structure in which every shell contains only its own species of particles; in so doing, smaller-sized particles make up outer shells with respect to larger-sized particles. With increasing size difference between particles, they are spatially segregated up to the formation of two independent Coulomb balls.

Structural features of two-component dusty plasma Coulomb balls

A binary mixture of dust particles in plasma occurring in an external electrostatic spherical confinement field has been numerically simulated. Calculations have been performed within the framework of the molecular dynamics method, with the interparticle forces described in terms of an isotropic Yukawa pair potential. It is shown that the particles form a shell structure, each particular shell consisting of particles of the same kind. The structural properties of such a binary mixture of particles and the specific features of their segregation under the conditions of recent experiments on the formation of Coulomb balls have been studied.

Three-dimensional stereoscopy of Yukawa (Coulomb) balls in dusty plasmas

A stereoscopic approach with standard video cameras for positioning and tracking of micrometer sized polymer particles in a radio-frequency gas discharge is presented. The stereoscopy is applied to simultaneously determine the positions of all particles in a three-dimensional strongly coupled spherical dusty plasma (Yukawa ball). The accuracy of the stereoscopic method is discussed. The shell structure and the occupation number of various Yukawa balls are determined and compared to recent simulations and models.

Confinement of Coulomb balls

A model for the confinement of the recently discovered Coulomb balls is proposed. These spherical three-dimensional plasma crystals are trapped inside a rf discharge under gravity conditions and show an unusual structural order in complex plasmas. Measurements of the thermophoretic force acting on the trapped dust particles and simulations of the plasma properties of the discharge are presented. The proposed model of confinement considers thermophoretic, ion-drag, and electric field forces, and shows excellent agreement with the observations. The findings suggest that self-confinement does not significantly contribute to the structural properties of Coulomb balls.

3D Coulomb balls: experiment and simulation

Spherically symmetric three-dimensional charged particle clusters are analyzed experimentally and theoretically. Based on accurate molecular dynamics simulations ground state configurations and energies with clusters for N ⩽ 160 are presented which correct previous results of Hasse and Avilov [Phys. Rev. A 44, 4506 (1991)]. A complete table is given in the appendix. Further, the lowest metastable states are analyzed.

Dust Coulomb Balls: Three-Dimensional Plasma Crystals

First experimental investigations of spherical three-dimensional plasma crystals consisting of hundreds or thousands of micrometer-sized polymer particles suspended in a radio-frequency gas discharge are described. These "Coulomb balls" are not subject to the formation of dust-free regions (voids) and have an unusual structure of nested crystalline shells. While small systems are in a solid phase, large systems show melting effects.