The influence of dust particle geometry on its charge and plasma potential

In this paper, a self‐consistent numerical model describing the behaviour of plasma around isolated highly charged dust particles with different shapes of rotation figures is presented. Dust particles in the form of a sphere, oblate ellipsoids (disk‐like particles), and elongated ellipsoids (rod‐like particles) are considered in the presence of an external electric field. Using the developed model, self‐consistent distributions of a space charge and plasma potential are obtained around non‐spherical dust particles. These distributions are carefully analysed by decomposing them in a series of Legendre polynomials. Decompositions of these distributions are compared with particles of different geometry. In addition, for different geometries of dust particles, the dependencies of the charge of a dust particle on geometry in the absence of an external field are investigated.     

Large amplitude ion-acoustic double layers in a plasma havingvariable-charge dust grain particles

The dust grain charging effect on large amplitude ion-acoustic double layers in a dusty plasma are investigated by the numerical calculation. The nonlinear structures of ion-acoustic double layers are examined, showing that the characteristics of the double layer sensitively depend on the dust charging effect, the influence of the ion temperature, the electrostatic potential, and the Mach number. The flow of the plasma current to the surface of dust particles increases the dust charge numbers. The effect of the ion temperature decreases the propagation speed of the ion-acoustic double layers and decreases the dust charge numbers. It is found that rarefactive double layers can propagate in this system. New findings of large amplitude ion-acoustic double layers with the dust charging effect and finite ion temperature in a dusty plasma are predicted     

Theory of self-organized dust sheaths in edge plasmas

A concept of self-organisation is used to derive the structure of dust sheath close to the wall taking into account self-consistently dust charges and dust distribution together with electron, ion distributions and ion drift. It is shown that instead of Bohm criterion the dust sheath is determined by other criteria allowing Mach number to be in restricted value ranges. The total structure of the dust sheath in dimensionless variables is determined by the Mach number only. Dust sheaths can contain definite number of dust particles per unit area which are determined by the value of the Mach number. The dust sheaths change drastically the electrostatic potential distributions and are usually much thicker than the usual plasma sheaths. A theoretical model together with numerical computations gives all dust sheath parameter distributions and the global characteristics such as the total drop of the potential, the thickness of the sheath, the number of dust particles in the sheath and the criterion of dust levitation. The recent observations on “Textor 94” indicating the long time dust survival in edge region of the present tokamaks, the dust levitation and agglomeration in the volume of edge tokamak plasma are discussed.     

Effect of Anisotropic Ion Pressure on Solitary Waves in Magnetized Dusty Plasmas

The propagation of linear and nonlinear dust ion acoustic waves (DIAWs) are studied in a collisionless magnetized plasma which consists of warm ions having anisotropic thermal pressure, nonthermal (energetic) electrons and static dust particles of positive and negative charge polarity. The anisotropic ion pressure is defined using double adiabatic Chew‐Golberger‐Low (CGL) theory. In the linear regime, the propagation properties of the two possible modes are investigated via ion pressure anisotropy, dust particle polarity and nonthermality of electrons. Using reductive method Zakharov‐Kuznetsov (ZK) equation is derived for the propagation of two dimensional electrostatic dust ion acoustic solitary waves in dusty plasmas. It is found that both compressive and rarefactive solitons are formed in presence of nonthermal electrons using Cairn's distribution [R.A. Cairns, A.A. Mamun, R. Bingham, R.O. Dendy, R. Bostrom, C.M.C. Nairn and P.K. Shukla, Geophys.Res. Lett. 22 , 2709 (1995)] in the system. The ion pressure anisotropy, nonthermality of electrons and charge polarity of the dust particles have significant effects on the amplitude and width of the dust ion acoustic solitary waves in such anisotropic nonthermal magnetized dusty plasmas. The numerical results are also presented for illustration. Our finding is applicable to space dusty plasma regimes having anisotropic ion pressure and nonthermal electrons. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamic Dust Particle Confinement in Corona Discharge Plasma

Usually electrostatic fields created by electrodes of the trap are used for dust particle confinement in plasma devices. In this work the possibility of the dust particle confinement by electrodynamic fields is investigated for improved quadrupole traps. The behavior of dust particles is simulated by Brownian dynamics. Dust particle parameters and parameters of the traps needed for dust particle confinement have been obtained (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Melting of strongly coupled,negatively charged,two-dimensional dust cluster: The role of charge fluctuation amplitude

Structural and melting characteristics are investigated for negatively charged dust particles in the presence of a two-dimensional electrostatic parabolic confinement potential. For a restricted number of dust particles that are subject to the permanent flow of electrons and ions, numerical simulation is conducted taking into account the random charge fluctuation. The amplitude of the charge fluctuation affects the ground-state configuration and melting characteristics of a finite number of particles interacting through Coulomb potential. The melting temperature decreases when the amplitude of the charge fluctuation increases as a result of particles' strong repulsive interaction.     

Simulation of Dust Particle Trajectories in an Electrostatic Probe with the Purpose of Increasing Its Efficiency

Formation of dust particles and clusters is observed in almost all modern fusion devices. Accumulation of dust in next-generation thermonuclear installations can significantly affect plasma parameters and lead to accumulation of unacceptably large amounts of tritium. The use of a specially developed electrostatic probe is planned in the international thermonuclear experimental reactor ITER to collect dust for further analysis. The article describes a numerical model of movement of dust particles in an electrostatic probe. Dust particle trajectories inside the probe are analyzed. Several electrostatic probe design modifications are proposed on the basis of the analysis in order to increase the efficiency of dust collection.     

Kinetic temperature and charge of a dust grain in weakly ionized gas-discharge plasmas

Analytical relations are given for estimating the energy of the stochastic motion of an individual dust grain heated by electrostatic ion oscillations in a weakly ionized gas-discharge plasma. Dust grain charging processes are analyzed, and an empirical approximation is obtained for the ion current to the grain surface. The processes are simulated under conditions similar to those of laboratory experiments on dusty plasmas. It is found that the kinetic temperature of a dust grain heated by electrostatic ion oscillations in a gas-discharge plasma can exceed the background gas temperature.     

Wake potential with mobile positive/negative ions in multicomponent dusty plasmas

We employ the test charge approach to calculate the electrostatic potential for a test charge in a multicomponent dusty plasma, whose constituents are the Boltzmann distributed electrons, mobile positive and negative ions, and immobile positive/negative charged dust particles. By using the modified dielectric constant of the dust-ion-acoustic (DIA) waves, the Debye screening and wake potentials are obtained. It is found that the presence of mobile negative ions significantly modify the DIA speed and the wake potential. The present results are relevant to polar mesosphere and microelectronic in the context of charged particle attraction and repulsion.     

Cylindrical and spherical dust ion-acoustic solitary waves in quantum plasmas

Dust ion-acoustic solitary waves in unmagnetized quantum plasmas are studied in spherical and cylindrical geometries. Using quantum hydrodynamic model, the electrostatic waves are investigated in the weakly nonlinear limit. A deformed Korteweg-de Vries (dKdV) equation is derived by using the reductive perturbation method and its numerical solutions are also presented. The quantum diffraction and quantum statistical effects incorporated in the system modifies the characteristics of dust ion-acoustic waves in cylindrical and spherical geometries. The role of stationary dust particles in quantum plasmas are also discussed. It is shown that the cylindrical and spherical dust ion-acoustic solitary waves behave quite differently from one-dimensional planar solitary waves in quantum plasmas.     

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.     

Analysis of dusty plasma in the positive column of glow discharges

The radial distributions of ions,electrons and dust particles in the positive colum of glow discharges are investigated in a tripled-pole diffusion model.The dust particles are mainly trapped in the region around the column axis where the electrostatic potential is the highest.The presence of the dust particles results in the ion density increasing and the electron density decreasiung in the dust-trapped region.The dust-trapped region is wider for a higher dust temperature or a smaller particulate redius.The ions and electrons in the dust-free region away from the column axis are in ambipolar diffusion.     

On the mechanism of own rotation of dust particles

We analyze the physical reason for own rotation of dust particles. We propose from analysis of literature data and our previous studies that own rotation of dust particles is due to azimuth-symmetric flow of ions to the particle surface, which is associated with a nonuniform distribution of the surface charge. This assumption is in conformity with the results of experiments in which the plasma flow is changed by introducing particles in the horizontal plane (horizontal cluster) and particles aligned along the discharge current (vertical cluster) and with the observation of the rotation threshold for the discharge current and the magnetic field. The experiments are performed with spherical particles using the coordinate tracing method. Our results make it possible to construct a model of spinning of charged dust tops for describing magnetic properties of a complex plasma.     

Dust diagnostics on an inertial electrostatic confinement discharge

Micron size dust particles were used to diagnose the direction of ion flow in an inertial electrostatic confinement discharge. Particles were dropped onto a one-dimensional device and were shown to deflect away from the center. The deflection of the dust particles was then accounted for by ion drag. It is concluded that ions are created at the cathode center and flow outwards. This supports recent work that has reached the same conclusion using Doppler spectroscopy. Moreover, estimates of the ion density from the deflection of dust particles was in agreement with Langmuir probe measurements.     

Nonlinear electrostatic waves in inhomogeneous dense dusty magnetoplasmas

The nonlinear electrostatic drift waves are studied using quantum hydrodynamic model in dusty quantum magnetoplasmas. The dissipative effects due to collisions between ions and dust particles have also been taken into account. The Korteweg-de Vries Burgers (KdVB) like equation is derived and analytical solution is obtained using tanh method. The limiting cases of KdV type solitary waves, Burger type monotonic shock waves and oscillatory shock solutions are also presented. It is found that both hump and dip type solitary structures are possible in quantum dusty plasmas. However, amplitude and width of the nonlinear structure depend on the dust charge polarity and its concentration in electron-ion quantum plasmas. The monotonic shock like structure is independent of the quantum parameter. It is found that shock strength is increased in the presence of positively charged particles in comparison with negatively charged dust particles. The oscillatory shock structures are also obtained and it is found that change in dust charge polarity only shifts the phase of the oscillatory shock in plasmas. The numerical results are also presented for illustration.     

The Kadomtsev-Petviashvili equation for dust ion-acoustic solitons in pair-ion plasmas

Using the reductive perturbation method,we have derived the Kadomtsev-Petviashvili(KP) equation to study the nonlinear properties of electrostatic collisionless dust ion-acoustic solitons in pair-ion(p-i) plasmas.We have chosen the fluid model for the positive ions,the negative ions,and a fraction of static charged(both positively and negatively) dust particles.Numerical solutions of these dust ion-acoustic solitons are plotted and their characteristics are discussed.It is found that only the amplitudes of the electrostatic dust ion-acoustic solitons vary when the dust is introduced in the pair-ion plasma.It is also noticed that the amplitude and the width of these solitons both vary when the thermal energy of the positive or negative ions is varied.It is shown that potential hump structures are formed when the temperature of the negative ions is higher than that of the positive ions,and potential dip structures are observed when the temperature of the positive ions supersedes that of the negative ions.As the pair-ion plasma mimics the electron-positron plasma,thus our results might be helpful in understanding the nonlinear dust ion acoustic solitary waves in super dense astronomical bodies.     

Kadomtsev–Petviashvili equation for dust ion-acoustic solitons in pair-ion plasmas

Using the reductive perturbation method, we have derived the Kadomtsev-Petviashvili (KP) equation to study the nonlinear properties of electrostatic collisionless dust ion-acoustic solitons in the pair-ion (p-i) plasmas. We have chosen the fluid model for the positive ions, the negative ions, and a fraction of static charged (both positively and negatively) dust particles. Numerical solutions of these dust ion-acoustic solitons are plotted and their characteristics are discussed. It is found that only the amplitudes of the electrostatic dust ion-acoustic solitons vary when the dust is introduced in the pair-ion plasma. It is also noticed that the amplitude and the width of these solitons both vary when the thermal energy of the positive or negative ions is varied. It is shown that potential hump structures are formed when the temperature of the negative ions is higher than that of the positive ions, and potential dip structures are observed when the temperature of the positive ions supersedes that of the negative ions. As the pair-ion plasma mimics the electron-positron plasma, thus our results might be helpful in understanding the nonlinear dust ion acoustic solitary waves in super dense astronomical bodies.     

Dusty photoresonant plasma with coulomb collisions

We have studied the charging of dust particles in a dense photoresonant sodium plasma with electron and ion densities as high as 10¹⁶ cm^?3 produced by laser pumping of the resonance level of Na, which was a small admixture (up to 1%) in an argon buffer gas. We show that the charge of dust particles with a radius of 10 mm at maximum reaches 3 × 10⁵ electron charges and that the potential of the dust particles at a low electron bulk loss rate agrees well with the orbital motion limited (OML) model data. The behavior of the electric field near a dust particle was found to be nonmonotonic. We established that the distribution of the potential near a solitary charged dust particle agrees well with the Debye one, but the screening length proves to be much larger than even the electron Debye length; the discrepancies are largest at the afterglow stage of the photoresonant plasma, when the sodium ion with a low recombination coefficient is the main plasma ion. We determined the domain of parameters for a dense plasma where an ensemble of dust particles can crystallize.     

A particle-in-cell simulation of dust charging and shielding in lowpressure glow discharges

The transport of particles (“dust”) in low pressure electrical glow discharges is being studied in regard to its role in contaminating silicon wafers during plasma etching and deposition. Particles (10 s nm-μm) negatively charge in glow discharges and, to first order, appear to be massively large negative ions around which sheaths develop. The forces on particles in plasmas include electrostatic (drift of charged particles in electric fields) and viscous ion drag. The latter force is momentum transfer from ions to particles by either collisions or orbital motion. This force critically depends on the charge on the particle and the shape of the sheath surrounding the particle. In this work, we report on a pseudoparticle-in-cell (PIC) simulation of the transport of electrons and ions in the vicinity of dust particles in low pressure glow discharges. The simulation produces the electrical charge on the dust particle, the sheath structure around the dust particle and the orbital dynamics of the ions. A companion molecular dynamics simulation uses these parameters to produce ion-dust and electron-dust particle cross sections for momentum transfer and collection. Results will be discussed for charge, sheath thickness, cross sections and viscous ion drag forces on dust particles as a function of radius and plasma parameters