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The formation and dynamics of vertical dust chains in the radio frequency discharge plasma sheath have been investigated. The spatiotemporal evolution diagram allows the visualization of the dust chain formation process as well as the oscillation phenomenon. A clear stratification was observed, and spatially nonuniform self‐organizing behavior of the dust chains, such as fractures and reconnections, was also observed, showing that the lower layers of the large‐grained chains are less restricted, softer, and more prone to rearrangement. The spatial distribution characteristics of the charged particles in the sheath and the modified two‐particle model, which takes into account the interparticle attraction, partially explain the mechanisms of the fracture and reorganization behavior of the dust chains. [ABSTRACT FROM AUTHOR]

The parameters of the plasma of a low-pressure glow discharge in neon with microparticles, at which regions with equal values of the ion confinement efficiency in the cloud of microparticles are realized, are determined numerically. It is noted that such features are characteristic of dissipative synergetic systems controlled by the feedback. The simulation of a complex plasma of glow discharge in neon with microparticles shows that feedback in the plasma is realized through the source of the main losses of its energy—a cloud of microparticles. Controlling the discharge parameters by changing the concentration of microparticles in the cloud makes it possible to control the concentration of the ions in the plasma. [ABSTRACT FROM AUTHOR]

Changes in the surface of micron-sized melamine-formaldehyde microparticles in dust structures in a glow-discharge plasma in Ne and Kr are experimentally studied. The microparticles are placed in plasma-dust structures with subsequent extraction. Two effects depending on the exposure time in plasma are established in the experiment: a comprehensive decrease in the particle size and a change in the morphology of their surface. A model is considered, which makes it possible to estimate the contribution of various mechanisms of the interaction of charged plasma particles with the surface of melamine formaldehyde. The estimates obtained are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

A molecular dynamics simulation of a system of massive charged particles on a compensating homogeneous background confined by a spherical surface has been carried out. A crystallized cluster is a set of nested spherical shells of almost the same structure and a core. It is shown that cluster melting is a combination of shell and core melting. It is found that the values of the Coulomb coupling parameter Γ corresponding to these two types of melting do not depend on the cluster size. Methods for determining Γ based on the Wigner–Seitz cell model are discussed. It is shown that the estimate based on the root-mean-square deviation of a particle from the center of its cell is unreliable due to the self-diffusion of particles. A relation is proposed that defines Γ in terms of the root-mean-square velocity and acceleration of the particle and does not include the root-mean-square deviation of the particle from its average position. It is shown that this relation is satisfied with high accuracy not only for the crystallized, but also for the liquid state. Thus, it has been demonstrated that the Wigner–Seitz cell model is applicable to the strongly inhomogeneous system under consideration. [ABSTRACT FROM AUTHOR]

A model for calculating the surface tension coefficient of a spherical cloud of charged microparticles in a plasma is proposed. The coefficients of the surface tension of Coulomb spheres obtained in a low-pressure glow discharge in neon at a temperature of 77 K for particles with a diameter of 4 μm and a temperature of 295 K for particles with a diameter of 2 μm are calculated. The potential energy of microparticles on the surface of a sphere is determined. In the calculations, a hydrodynamic model of a positive column with charged microparticles is used. The obtained values of the surface tension coefficient are compared with the data obtained by other authors for ball lightnings. A hypothesis is proposed for the formation of Coulomb spheres in the Earth's atmosphere. [ABSTRACT FROM AUTHOR]

The effect of random forces, which are caused by fluctuations in a complex plasma, on the dynamics of charged dust grains is studied. Analytical dependences are obtained for the kinetic energy, the autocorrelation functions of velocities, the mass transfer functions, and the mean-square average displacements of the grains in the case of a grain moving under the effect of two random forces. A method is proposed for accounting for more than two random forces of different nature. The possibility is discussed of simulating the motion of dust grains in complex plasma by the Langevin equations with a temperature that is not equal to the temperature of the surrounding gas. [ABSTRACT FROM AUTHOR]

Cylindrical three dimensional dust–ion–acoustic (DIA) solitary waves (SWs) in a complex plasma medium consisting of nonthermal electrons, adiabatically warm ions, and immobile positively charged dust (PCD) species are studied. The reductive perturbation method, which is valid for small but finite amplitude waves, is used to derive the (3 + 1)-dimensional cylindrical Kadomstev–Petviashvili (cKP) equation (also known as cylindrical Korteweg–de Vries equation). The parametric regimes for the existence of solitary structures are shown. The plasma model under consideration supports both the positive and negative DIA SWs. Moreover, the effects of the physical plasma parameters (the ratio of the dust to ion number density, the nonthermal parameter, etc.) on the basic features (amplitude, width, and speed, etc.) of DIA SWs are discussed. Depending on the plasma parameters (the PCD and ion number density ratio, nonthermality of electron, and temperature ratio of ion and electron) the solitary pulses change their polarity. The present investigation may be helpful to the understanding of the properties of the DIA SWs in different astrophysical plasma environments as well as in laboratory devices. [ABSTRACT FROM AUTHOR]

We study the collision frequencies of charged particles in the complex plasmas with the two-parameter and three-parameter non-Maxwellian velocity distributions. The average collision frequencies of electron–ion, electron–electron and ion–ion for the distributions are derived, respectively. We show that the average collision frequencies in the complex plasmas depend strongly on the parameters in the non-Maxwellian distributions and thus are significantly different from those cases in the plasmas with a Maxwell velocity distribution. The significant effects of the non-Maxwell parameters on the average collision frequencies are numerically analyzed. The results have important impacts on the transport coefficients and transport properties of charged particles in the highly or fully ionized complex plasmas. [ABSTRACT FROM AUTHOR]

In complex plasmas, microparticles can form ordered crystalline structures under specific conditions. Accurately identifying these structures, such as face-centered cubic, hexagonal close-packed, and body-centered cubic, is a common task in physics. Previous methods rely on detecting symmetries in the spatial arrangement of particles, often requiring extensive calculations. This study presents a novel approach by utilizing a PointNet-based deep learning algorithm, called WignerNet, to classify these structures directly from three-dimensional reconstructions of their Voronoi cells. The model was trained exclusively on artificial and labeled data, incorporating various noise levels, and subsequently tested on real experimental data. The results demonstrate that our method effectively classifies structures, reducing computational complexity and improving accuracy compared to conventional techniques. This advancement opens up new possibilities for real-time analysis of complex plasma systems in various research.

Under different plasma conditions and electric fields in a complex plasma the plasma particles organize themselves in a string-like or chain-like manner. A phase transition from string-like to an isotropic particle distribution is observed at different electrical conditions. The streaming of charged ions around plasma particles with the surrounding electric field gives the plasma its electrorheological properties. The visibility of individual particles in a complex plasma opens up the opportunity to examine properties and phase transitions of such electrorheological fluids in detail. Because of the limited one-dimensional symmetry, determining the configuration of a particle and recognizing strings in particle distributions is not always straightforward. Several approaches have already been used to analyse particle clouds while either considering each particle locally or considering the particle cloud as a whole without providing information about single particle configurations. This paper presents a new machine learning approach that takes advantage of particle distributions over the entire particle cloud and detects all string-like particles at once, using a convolutional neural network in form of an encoder-decoder network with asymmetric kernel convolutions. This not only enhances the result quality but also accelerates the evaluation process, possibly enabling real-time analyses on electrorheological phase transitions, while achieving an accuracy of over 95% on manually labelled data.

Plasma dust formations with liquid particles (microdroplets) are studied. Methods used for the formation of liquid microdroplets in a vacuum are analyzed in the study, and a laboratory bench for studying liquid plasma dust formations is constructed. The phenomenon is examined and photographed. [ABSTRACT FROM AUTHOR]

Spectral analysis is a commonly used effective method for plasma diagnostics. However, due to the large amount of plasma spectral data and the complex and unclear quantitative relationship with discharge parameters, the plasma diagnosis is sometimes not so straightforward and obvious to perform. In this paper, in order to realize the spectral recognition in an ethylene discharge plasma under different gas pressures, the plasma spectral recognition model based on LGBM (light gradient boosting machine) was constructed and compared with four typical recognition models. The results show that the LGBM model has the best efficiency for plasma spectra recognition and the accuracy can be as high as 99.16%. The spectral analysis on the ethylene plasma under different gas pressures shows that some specific wavelengths play the key roles in the feature recognition. In addition, this paper further analyzes the correlation between the characteristic wavelengths and the discharge gas pressures. [ABSTRACT FROM AUTHOR]

We propose a low-density discharge plasma model that takes into account the impact of oxygen admixture in typical conditions of complex (dusty) plasmas. Numerical simulations based on this model show that the concentration of negative ions turns out to be very high, and they play an important role in the overall kinetics in this particular range of plasma conditions. The ambipolar diffusion electric field drags these negative ions into the center of the plasma. The density of negative ions is high enough to push the negatively charged dust component out of the center, both by weakening the radial electric field and by increasing the thermophoretic force. This phenomenon was observed in the published experiment and qualitatively supports the proposed model. Additionally, the proposed model allows an alternative explanation of the experiment. [ABSTRACT FROM AUTHOR]

We consider the efficiency of an ion confinement inside a cloud of charged microparticles in a low-pressure DC discharge. To describe the ion confinement efficiency in such complex plasma, we propose the indicators calculated taking into account the processes responsible for the generation, the losses, and the accumulation of ions in a cloud of charged microparticles in a plasma using a fluid model. The efficiency of ion accumulation by a microparticle cloud shows the ratio of the average ion densities in discharge with microparticles and without them. The efficiency of ion accumulation by a microparticle shows the difference of average ion densities in a discharge with microparticles and without them, related to microparticle number density. The specific power costs of the existence of one ion in a microparticle cloud determines the linear power costs of the discharge in a cloud related to the linear number of ions in it. The power efficiency of ion accumulation by a microparticle cloud is defined as a ratio of specific power costs in a discharge without microparticles, to specific power costs of ion existence in a cloud. A strong dependence of indicators on the microparticle number density has been revealed. Inefficient conditions of ion confinement inside a cloud are found. Experimental data on dynamic instabilities of a discharge with microparticles was analyzed. It is found that efficiency of ion confinement is connected with dynamic processes in complex plasma. The limiting microparticle number density is shown to serve as the criterion of the occurrence of plasma instability. Exceeding the limiting microparticle number density results, generally, in the development of dynamic instability of complex plasma, and, in inefficient states, in quenching of the discharge. [ABSTRACT FROM AUTHOR]

Charged fine particles are confined in a high-frequency argon plasma and their motions are observed. They show perturbed motions and several particles undergo circular motions. When charged short rods are confined, they stand vertically and shorter rods spin around their vertical axis. For mono-dispersed silica particles, they also form a cloud. Moreover, it is commonly observed that a portion of the particles move in pairs. They fluctuate all the time; however, particles in a pair do not separate nor collide with each other. The mechanism of the motions of paired particles is discussed in relation to local potential structures. [ABSTRACT FROM AUTHOR]

The results are presented from numerical studies of the dynamics of limited-size ensembles of charged dust grains in the potential field of electrostatic trap. The simulations were performed for the cluster systems with a number of grains of up to one thousand with the Coulomb interaction in a wide range of parameters close to the conditions of laboratory experiments in gas-discharge plasma. The processes of particle diffusion in the extended and limited-size systems are compared. [ABSTRACT FROM AUTHOR]

In an experiment, the power that sustains a plasma was extinguished, so that microspheres, which had been levitated, fell downward toward a lower electrode. At the beginning of their fall, the microspheres were self-organized with a crystalline structure. This structure was found to be preserved as the microspheres accelerated all the way to the lower electrode. Although microspheres had, in this afterglow plasma, large positive charges of 12,500 e, their interparticle repulsion was unable to significantly alter the crystalline arrangement of the microspheres, as they fell. After their impact on the lower electrode, the microspheres bounced upward, and only then was the crystalline structure lost.

Microparticles immersed in a low‐temperature plasma acquire strong negative charges and thus repel each other. Nevertheless, effective attraction between the microparticles in such a complex plasma can occur due to the interplay between the fluxes of plasma ions and the microparticles. Here, we report the observation of droplets formed in a complex plasma during a parabolic flight, and explain their formation in terms of the ion drag force that sustains the droplet. We have found a good agreement between the experimentally determined droplet size and its theoretical estimate using the ion drag force mechanism. Lower values of the electron temperature result in better agreement, as is consistent with the pulsed mechanism of discharge used experimentally. [ABSTRACT FROM AUTHOR]

We propose a low-density discharge plasma model that takes into account the impact of oxygen admixture in typical conditions of complex (dusty) plasmas. Numerical simulations based on this model show that the concentration of negative ions turns out to be very high, and they play an important role in the overall kinetics in this particular range of plasma conditions. The ambipolar diffusion electric field drags these negative ions into the center of the plasma. The density of negative ions is high enough to push the negatively charged dust component out of the center, both by weakening the radial electric field and by increasing the thermophoretic force. This phenomenon was observed in the published experiment and qualitatively supports the proposed model. Additionally, the proposed model allows an alternative explanation of the experiment.

The creation of a spatially extended stable DC complex plasma crystal is a big experimental challenge and a topical area of research in the field of dusty plasmas. In this paper we describe a newly built and commissioned dusty plasma experimental (DPEx-II) device at the Institute for Plasma Research. The device can support the formation of large sized Coulomb crystals in a DC glow discharge plasma. The plasma in this L-shaped table-top glass chamber is produced between a circular anode and a long tray shaped cathode. It is characterized with the help of various electrostatic probes over a range of discharge conditions. The dust particles are introduced by a dust dispenser to form a strongly coupled Coulomb crystal in the cathode sheath region. The unique asymmetric electrode configuration minimizes the heating of dust particles and facilitates the formation of crystalline structures with a maximum achievable dimension of 40 cm × 15 cm using this device. A larger crystal has numerous advantages over smaller ones, such as higher structural homogeneity, fewer defects, lower statistical errors due to finite size effects etc. A host of diagnostics tools are provided to characterize the Coulomb crystal. Results of a few initial experiments aimed at demonstrating the technical capabilities of the device and its potential for future dusty plasma research, are reported. [ABSTRACT FROM AUTHOR]

Dusty plasmas are plasmas containing solid particles in the size range of about 10 nm—10 μm. The particles acquire an electrical charge by collecting electrons and ions from the plasma, or by photo-electron emission if they are exposed to UV radiation. The charged dust particles interact with the electrons and ions, forming a multi-component plasma. Dusty plasmas occur in a number of natural environments, including planetary rings, comet tails, and solar nebulae; as well as in technological devices used to manufacture semiconductor chips, and in magnetic fusion devices. This article focuses on the physics underlying dusty plasmas, which are studied by plasma physicists, aeronomists, space physicists, and astrophysicists. The article begins with an introduction explaining what we mean by a dusty plasma, where they are found, and a summary of their basic properties. The article then presents the fundamental physics of dust charging, forces on dust particles, a description of devices used to produce dusty plasmas, strongly coupled dusty plasmas, collective phenomenon (waves) in dusty plasmas, magnetized dusty plasmas, and the emerging technologies based on dusty plasmas. It concludes with a few perspective comments on how the field has developed historically and the prospects for future advances.

In this theoretical work nonlinear behavior of dust ion acoustic solitary waves (SWs) has been investigated, and then the effect of the adiabatic change on them has been observed. The complex plasma system consists of inertial positive and negative ions, Maxwell's electrons, and positively and negatively charged stationary dust particles. The effects of dust polarity on the dust ion acoustic SWs have also been observed. Using the reductive perturbation method, we first derive K-dV equation which lets to analyze both the positive (bright) and negative (dark) solitons in a very limited region. After that mK-dV equation has been derived, and this let to analyze positive soliton for a large region, but cannot show the negative soliton. Finally, the Gardner equation has been derived employing the same method, through which we were able to analyze both the positive and negative solitons for a large region. It has been found that both the positive and negative solitons significantly depend on the mass number density, ion number density, and dust polarity in the adiabatic and isothermal system.

The rotational motion of a strongly coupled unmagnetized 1-D-dusty plasma ring was studied. The particles rotated within the ring-shaped potential that was formed using a circular grooved electrode with a center post. Particle position data from the rotating dust ring were analyzed and the angular velocity of the particles was calculated. The rotation rate of the ring depended on the number of particles, the interparticle spacing, and the shape of the potential well. The driving force for rotation was also examined. [ABSTRACT FROM AUTHOR]

The energy exchange processes are studied in the systems of non-identical interacting particles (with different sizes, masses, and charges) with the spatially inhomogeneous distribution of the stochastic kinetic energy sources. To analyze the energy balance in such systems, a theoretical model is considered. The analytical relations are presented that describe the redistribution of the stochastic kinetic energy between two charged particles. The relations proposed are verified by means of simulating numerically the problem for particles with the Coulomb interaction between them. The numerical analysis is performed of the process of the stochastic kinetic energy redistribution in the two-dimensional ensembles with the separated fractions of particles with different sizes and temperatures. The results of this work can be applied to the systems with any type of pair interaction. They can be also used for analyzing the energy exchange processes in inhomogeneous systems that are of interest in plasma physics and in physics of polymers and colloid systems. [ABSTRACT FROM AUTHOR]

Two-dimensional complex plasma crystal is a suspended single-layer of micron-size grains in a plasma. The narrow and long two-row crystals are likely to be used as electrostatic wigglers. Therefore, electric properties of such system is studied in the present work. The frequency of longitudinal electric field is twice the frequency of transverse electric field. In two-row crystals, far from the crystal center, both longitudinal and transverse electric fields decrease continuously. Frequency of longitudinal field decreases also, but the frequency of transverse field is fix. By increasing distance between the crystal rows, the frequency of transverse field does not change but the frequency of longitudinal field decreases. Value of both fields decrease while their ratio increases. By increasing longitudinal distance between the grains, the frequency of transverse field does not change but the frequency of longitudinal field increases until become twice the frequency of transverse field, and both electric fields increase while their ratio decreases. These results may be useful in various fields of physics. [ABSTRACT FROM AUTHOR]

We study the dynamics of dust particles in a stratified glow discharge in inhomogeneous magnetic fields. Dust structures are formed in standing striations, in which traps for dust particles arise. When a magnetic field is applied, these structures begin to rotate. The observations were carried out in striations near the end of the solenoid, where the region of an inhomogeneous magnetic field begins. With an increase in the magnetic field, the dusty structure can be deformed. The rotation of a dusty structure in an inhomogeneous magnetic field has been studied in detail; it has its own peculiarities in comparison with rotation in a uniform field. We have considered the mechanisms of such rotation and estimated its velocity.

The formation of a 1D chain-like structure of dust particles in a low-temperature argon plasma was studied. A new numerical model for calculation of the self-consistent spatial distribution of plasma parameters around a chain of dust particles was presented. The model described the motion of positively charged ions in the electric potential of several negatively charged dust particles, taking into account the action of an external electric field. The main advantage of the model was that the charges of the dust particles and the interparticle distances were determined self-consistently. As a result of numerical simulations, the dependencies of the spatial distributions of the plasma parameters (the densities of electrons and ions and the self-consistent electric potential) near the dust particles chain on the strength of the external electric field, an external force acted on the last particle, and the mean free path of the ions was determined. The obtained results made it possible to describe the process of the formation of chain-like structures of dust particles in discharge plasma.

Structures of Coulomb crystals were analyzed in cylindrical discharge plasmas under gravity and microgravity by using an apparatus similar to the PK-4 on the International Space Station (ISS). Under gravity, layers of cylindrical dust clouds were found to locally form the lattices of the face-centered orthorhombic (FCO) structure, which is a deformation from the face-centered-cubic structure. We also observed that the average density increases with the size of dust clouds. Under microgravity, the structure could be regarded as an assembly of linear chains along the cylinder axes. At the same time, the interparticle distance and the plasma parameters measured by a double-probe method indicated that the structure was formed not only from the wake potential but also from mutual interactions between dust particles in neighboring chains. [ABSTRACT FROM AUTHOR]

The properties of one single melamine formaldehyde microparticle, levitated in the sheath of a low‐pressure radio frequency‐driven plasma, are determined with a novel procedure using in situ Mie scattering. By placing the measurement equipment inside the vacuum vessel, optical access is not limited to available viewports, and the complete scatter profile can be measured. The developed fitting routine uses peaks and valleys in the angular scatter profile to accurately determine the particle's refractive index, size, and plasma‐induced etch rate. In plasma at a pressure of 13 Pa operated at 10 W, obtained refractive indices of 1.657 ± 0.01 are close to those specified by the supplier, while the initial size (2.168 ± 0.007 μm) is relatively 8% off from the supplier‐specified value. With an estimated contamination of ambient air of 4 ± 1% in pristine Ar, etch rates of 1.9 ± 0.2 nm/min are measured. [ABSTRACT FROM AUTHOR]

The PK-4 laboratory consists of a direct current plasma tube into which microparticles are injected, forming a complex plasma. The microparticles acquire many electrons from the ambient plasma and are thus highly charged and interact with each other. If ion streams are present, wakes form downstream of the microparticles, which lead to an attractive term in the potential between the microparticles, triggering the appearance of microparticle strings and modifying the complex plasma into an electrorheological form. Here we report on a set of experiments on compressional waves in such a string fluid in the PK-4 laboratory during a parabolic flight and on board the International Space Station. We find a slowing of acoustic waves and hypothesize that the additional attractive interaction term leads to slower wave speeds than in complex plasmas with purely repulsive potentials. We test this hypothesis with simulations, and compare with theory.