The effect of magnetic field on plasma particles in dusty plasma

In this work, we present the investigation of the formation features and internal structure of dust clouds created in plasma of glow discharge in the external magnetic field corresponding to a range of moderate and strong fields, at which the ion component is magnetized. The analysis of the plasma magnetization in the presence of dust components is carried out. We defined the values of magnetic induction at which the changes in dynamics of plasma particles in magnetic field in light inert gases are expected. The experimental setup was built in two versions. For the purpose of generating of magnetic field, the first setup was equipped with ordinary magnetic coils, and the second one included a superconducting solenoid. The discharge tubes, the main chambers where plasma was ignited and maintained in a glow discharge in lowered pressure, also have certain peculiarities, which we describe below. While using helium as a bulk gas, our study focused only on the dust trap in the region of narrowing discharge current. For neon, we used two traps: the striation trap and one just mentioned above placed in the narrowing of the discharge tube. As a result, the steady dust structures in a glow discharge under the magnetization of ions and electrons were obtained for the first time. Dust structures were rotated and tended to form a dust cluster and shell structure. A number of parameters of magnetization achieved in experiments were calculated.     

Pattern phenomena in an rf discharge dusty plasma system

Various dust patterns are observed in an rf discharge dusty plasma system. According to the dust growth process from small to large in size, the formation of different dust patterns can be divided into two stages: the small-particle stage (or dust cloud stage), and the large-particle stage (or dust crystal stage). The evolution relations between different dust patterns with gas pressure changing are investigated. Dust voids, dust acoustic waves and strong turbulence modes are presented at the small-particle stage. The self-organized dust lattices and dust clusters are investigated at the large-particle stage. The static structure of a dust lattice is characterized by means of the pair correlation function. Dust clusters formed by particles with different numbers and the regular evolution of the clusters with gas pressure are also investigated. The packing sequences of dust clusters are verified through two-dimensional confined molecular dynamics simulations.     

Study of the modification of spherical melamine-formaldehyde particles levitating in complex plasma

The surface modification of spherical melamine-formaldehyde particles during their levitation in a dusty plasma as a part of plasma–dust structures in a trap formed in strata in a neon glow discharge has been investigated using scanning electron microscopy. The dependence of the particle size on the time of plasma exposure has been found and measured, and the modification of the surface structure has been studied. The source of the observed modification has been interpreted.     

Measurement of temperature of a dusty plasma from its configuration

A new concept called “configurational temperature” is introduced in the context of dusty plasma, where the temperature of the dust particles submerged in the plasma can be measured directly from the positional information of the individual dust particles and the interaction potential between the dust grains. This method does not require the velocity information of individual particles, which is a key parameter to measure the dust temperature in the conventional method. The technique is initially tested using two-dimensional (2D) OpenMP parallel molecular dynamics and Monte Carlo simulation and then compared with the temperature evaluated from experimental data. The experiment have been carried out in the Dusty Plasma Experimental (DPEx) device, where a 2D stationary plasma crystal of melamine formaldehyde particles is formed in the cathode sheath of a DC glow discharge argon plasma. The kinetic temperature of the dust is calculated using the standard particle image velocimetry technique at different pressures. An extended simulation result for the three-dimensional case is also presented, which can be employed for the temperature measurement of a three-dimensional dust crystal in laboratory devices.     

Theoretical analysis for transmission of Gaussian and sine time irradiance of electromagnetic beam in collisional dusty plasmas

A theoretical model of propagation of Gaussian and Sine time irradiance of an electromagnetic beam in collisional dusty plasma has been done in the present analysis. It contains equilibrium of dust charge, particle density, and energy of plasma ingredients having charge neutrality. Ionization of neutral particles, recombination of free electrons with ions, adsorption and emission of electrons from dust grain surface, and binary collisions between plasma components are also considered in this treatment. Time varying behaviour of modified electron temperature and collision frequency has been illustrated numerically as a function of dust densities. Also, the comparative analyses of variation of beam waist parameter with the dimensionless length of transmission for both the Gaussian and Sine time irradiance are involved in this model as a function of distinguishable time width, collision frequencies, and dust densities under the condition that the size of dust nebulous is greater than the electrons mean free path for the adsorption on the dust grain surface. The observed results are significant for the applications in industry and astrophysics.     

Physical aspects of dust–plasma interactions

Low-pressure gas discharge plasmas are known to be strongly affected by the presence of small dust particles. This issue plays a role in the investigations of dust particle-forming plasmas, where the dust-induced instabilities may affect the properties of synthesized dust particles. Also, gas discharges with large amounts of microparticles are used in microgravity experiments, where strongly coupled subsystems of charged microparticles represent particle-resolved models of liquids and solids. In this field, deep understanding of dust–plasma interactions is required to construct the discharge configurations which would be able to model the desired generic condensed matter physics as well as, in the interpretation of experiments, to distinguish the plasma phenomena from the generic condensed matter physics phenomena. In this review, we address only physical aspects of dust–plasma interactions, that is, we always imply constant chemical composition of the plasma as well as constant size of the dust particles. We also restrict the review to two discharge types: dc discharge and capacitively coupled rf discharge. We describe the experimental methods used in the investigations of dust–plasma interactions and show the approaches to numerical modelling of the gas discharge plasmas with large amounts of dust. Starting from the basic physical principles governing the dust–plasma interactions, we discuss the state-of-the-art understanding of such complicated, discharge-type-specific phenomena as dust-induced stratification and transverse instability in a dc discharge or void formation and heartbeat instability in an rf discharge.     

Influence of gas pressure on the pattern evolutions of dust clusters and fractals in a dusty plasma system

Dusty plasma has been produced through chemical reaction in a capacitively coupled radio frequency (rf) discharge system. Dust clusters with a few particles and dust fractals are observed. As gas pressure is increased, the suspended height of dust particles descends and the average interparticle distance decreases accordingly. The influence of gas pressure on the pattern evolutions is investigated. Dust clusters or fractals not only can evolve regularly on a horizontal plane, but also can evolve from a horizontal plane to a vertical line array. Under appropriate conditions, the evolutions are reversible. When the evolution is from a symmetrical pattern with a centre particle to another pattern, the centre particle will first show its unsteadiness.     

A Method of Separation of Polydisperse Particles in the Plasma of Radio‐Frequency Discharge

A method of separation of polydisperse dust particles in the plasma of radio‐frequency (RF) capacitive discharge is considered. Investigations of plasma equipotential field enabled us to determine conditions for separation of polydisperse dust particles. The simplicity of the technology made it possible to obtain small dispersed particles of different materials. Samples of small dispersed microparticles of silica and alumina were obtained. The size and chemical composition of samples were examined using a Quanta 3D 200i scanning electron microscope (SEM, FEI, USA). The average size of separated silica nanoparticles was 600 nm, that of silica and alumina microparticles was 5 μm. Two separation methods were developed: the first one used a special trap and shape of the bottom electrode of RF discharge (for separation of microparticles) and the second used an electrical trap (for separation of nanoparticles). The graphs of particle size distribution were constructed using graphical and mathematical calculations. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the thermophoresis in dense dust structures in neon plasma

Numerical study of the effect of dust particle concentration on the thermophoretic force acting on a dust particle inside a dust structure in plasma has been carried out. The experimental data on the formation of voids in dust structures formed by 2.55 μm dust particles in a glow dc discharge in neon have been used. The simulation has been performed using the diffusion-drift model with taking into account joule heating of discharge. The dependence of the thermophoretic force acting on a dust particle in a dust structure on the ratio of atom mean free path to the distance between the adjacent particles in the dust structure has been obtained.     

Study of glow discharge positive column with cloud of disperse particles

The study aims to describe plasma parameters changes induced by clouds of disperse micron size particles. Dust clouds were formed in the positive column of glow discharge in air at pressure 0.1-0.6 torr and current 0.1-3 mA. The simultaneous registration of discharge voltage and dust cloud parameters was carried out. Experimental results were simulated using diffusion model. The dust cloud is shown to smooth the radial electron concentration profile, increase electric field strength and electron temperature and stabilize the discharge. The cloud is demonstrated to be a trap for positive ions without increase of discharge current.     

Radar studies of ionospheric dusty plasma phenomena

We discuss the influence of charged dust on radar observations in the Earth ionosphere. This region in the upper Earth atmosphere can be described as a partially ionized, low‐temperature plasma. Plasma parameters vary by orders of magnitude spatially and in time. Dust particles influence the charge balance, in some cases dusty plasma condition is met. The polar mesospheric echoes are an example of dust plasma interactions observed with radar. The mesosphere is a region where atmospheric temperature decreases with altitude and can reach frost point temperature. The formation of the polar mesospheric radar echoes involves neutral atmosphere dynamics, which is latitude dependent and it involves charged dust particles, especially icy dust that forms in the polar summer mesosphere. Charged dust can also influence incoherent scatter that results from electromagnetic waves scattering off electrons, where the electrons are coupled to other charged components. Observers rarely report charged dust signatures in the incoherent scatter spectra; we show that there is a good chance for doing so with improved observations. The incoherent scatter can possibly also be used to estimate the amount of charged dust in the direct vicinity of a meteor, as we show based on the order of magnitude considerations. This prospect of new observational results makes theoretical investigations of radio‐wave scattering in the presence of charged dust with size distributions worthwhile.     

Sizing of particles levitating in a glow discharge dusty plasma

The dust particle size distribution in a volume glow discharge dusty plasma is studied. Polydisperse quartz particles are used as a dust component. It is found that a dusty plasma forms in a glow discharge not only in a dust trap but also near the wall at the bottom of the discharge chamber. Dust objects in the latter region are large: they contain up to 30000 particles. The size of particles levitating in discharge striations is three times larger than that of particles levitating near the wall. The idea of using the glow discharge dusty plasma for particle-size fractionation of polydisperse powder is put forward.     

Experimental observation of dust circulation in unmagnetized cogenerated dusty plasma

The vortex motion of a dust cloud was experimentally observed in unmagnetized cogenerated dusty plasma in different experimental parameters. Particle image velocimetry analysis demonstrated that several vortex zones exist in the dust cloud at relatively low pressures (0.06 mbar (or 6 Pa)–0.08 mbar (or 8 Pa)) and low discharge voltages (peak‐to‐peak voltage 540–560 V), whereas in relatively high pressure (0.4 mbar (or 40 Pa)–0.7 mbar (or 70 Pa)) and high discharge voltage (peak‐to‐peak voltage 690–740 V), dust vortices formed in dense dust cloud with background plasma fluctuation.     

Rotation of a single vortex in dusty plasma

A single vortex is obtained in radio-frequency capacitive discharge in argon gas. The dust subsystem is confined in the horizontal plane with an asymmetrical saw structure placed on the lower electrode. The vortex rotates as a whole along the long side of the saw-teeth. Asymmetry of the saw structure plays an important role in the rotation of the vortex. Nonzero curl of the total force resulting from the local ion flow and the electric field in the plasma sheath could be attributed to the persistent rotation of vortex.     

Collective Phenomena in Strongly Coupled Dissipative Systems of Charged Dust: from Ground to Microgravity Experiments

In present work the formation of dusty plasma structures in cryogenic glow dc discharge was investigated. The ordered structures from large number (～10⁴) of charged diamagnetic dust particles in a cusp magnetic trap have been also studied in microgravity conditions. The super high charging (up to 5·10⁷e) of dust macroparticles under direct stimulation by an electron beam is experimentally performed and investigated. The results of the investigation of Brownian motion for strongly coupled dust particles in plasma are presented. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modification of the texture of a polymer material surface in dust plasma

We have analyzed the modification of the texture of polymer particle surface in a dust plasma. Monodisperse spherical melamine formaldehyde particles were injected into the glow discharge plasma in neon. At a certain discharge current and gas pressure in the discharge tube, the particles were suspended in dust-plasma traps and experienced the action of the plasma of 5–25 min. Then, the particles were extracted and the collected material was studied using the scanning electron microscope. Among the results, a change in the diameter and roughness of the surface depending on the residence time of particles in the dust plasma was established. It was found that the absolute deviation of all points of the surface profile averaged over the evaluation length were in the nanometer range. The time of complete degradation of particles in the experimental conditions has been established.

     

Slowing down of charged particles in dusty plasmas with power‐law kappa‐distributions

We study the slowing down of a particle beam passing through the dusty plasma with power‐law κ‐distributions. Three plasma components, electrons, ions, and dust particles, can have a different κ‐parameter. By using Fokker‐Planck theory, the deceleration factor and slowing down time are derived and expressed by a hyper‐geometric κ‐function. Numerically, we study the slowing down property of an electron beam in the κ‐distributed dusty plasma. We show that the slowing down in the plasma depends strongly on the κ‐parameters of plasma components, and dust particles play a dominant role in the deceleration effects. We also show dependence of the slowing down on mass and charge of a dust particle in the kappa‐distributed plasma.     

Quantitative simulations of ratchet potential in a dusty plasma ratchet

Using a dusty plasma ratchet, one can realize the rectification of charged dust particle in a plasma. To obtain the ratchet potential dominating the rectification, here we perform quantitative simulations based on a two-dimensional fluid model of capacitively coupled plasma. Plasma parameters are firstly calculated in two typical cross sections of the dusty plasma ratchet which cut vertically the saw channel at different azimuthal positions. The balance positions of charged dust particle in the two cross sections then can be found exactly. The electric potentials at the two balance positions have different values. Using interpolation in term of a double-sine function from previous experimental measurement, an asymmetrical ratchet potential along the saw channel is finally obtained. The asymmetrical orientation of the ratchet potential depends on discharge conditions. Quantitative simulations further reproduce our previous experimental phenomena such as the rectification of dust particle in the dusty plasma ratchet.     

弱电离尘埃等离子体层反射与透射的SO-FDTD方法分析

将弱电离尘埃等离子体复介电常数表示以jω 为自变量的分式多项式形式, 利用移位算子时域有限差分(SO-FDTD)方法, 给出了弱电离尘埃等离子体频域本构关系的时域形式. 推导了弱电离尘埃等离子体电磁特性的时域递推关系式. 用SO-FDTD方法计算了弱电离尘埃等离子体层的反射和透射系数, 分析了尘埃粒子浓度和尘埃粒子半径的变化对反射系数和透射系数的影响. 结果表明: 有尘埃粒子时的反射系数比没有尘埃粒子时反射系数小, 而透射系数要比没有尘埃粒子时的透射系数大; 当尘埃粒子浓度或尘埃粒子半径增大时, 其反射系数均减小.