Possibility of weakly charged nonlinear solitary dust clouds near the continuum threshold of dust population in a quasi-neutral dusty plasma

Considering the Boltzmann response of the plasma ions and electrons and inertial dynamics of the charged dust grains, the possibility of very weak compressive soliton near the continuum limit of the dust population has been inferred. It is concluded that the behaviour of such coherent structures could be well described by the numerical analysis of the derived nonlinear classical energy integral equation for bounded solutions. These seem to be higher order dispersive structures within acoustic limit of the nonlinear turbulence. It is observed that the dust density enhancement beyond the continuum threshold causes regular increment in width and amplitude of the soliton structures. It is found that the soliton amplitude sensitively depends on the massive impurity’s population. These coherent structures could be visualized as weakly charged solitary dust clouds of finite extension (∼ plasma Debye length) within Boltzmann environment of plasma particles in their local surroundings. The seeding mechanism of such clouds may be attributed to some plasma instabilities driven by either internal or external free energy sources. Numerical analysis of the problem concludes that the experimental observations of such clouds could be possible in low density plasma regime. It is deduced that for plasma density ∼ 10⁶ cm^-3 at temperatures of a few electron volts and for micron to l0nm sized dust grains, the observation of such structures could be possible within wide range variability of the dust population density.     

Effect of polarization force on the Jeans instability of self-gravitating dusty plasma

The effect of polarization force acting on massive charged dust grains is investigated analytically on the Jeans instability of self-gravitating dusty plasma. The gravitational force acting on the massive negatively charged interstellar dust grains are considered in presence of both electrical and polarization forces. The basic equations of the problem are formulated and a general dispersion relation is obtained using plane wave approximation in low frequency wave mode. The effect of polarization force in the dispersion relation of the problem, condition of the Jeans instability and expression of the critical Jeans wave number is examined. The unstable growing modes due to self-gravitational force are studied in the situation when polarization force on the dust grain exceeds over the electrical force in magnitude. It is observed that the polarization force increases the growth rate of the system.     

Effects of dust size distribution on nonlinear waves in a dusty plasma

For two-dimensional unmagnetized dusty plasmas with many different dust grain species, a Kadomtsev--Petviashvili (KP) equation, a modified KP (mKP) equation and a coupled KP(cKP) equation for small, but finite amplitude dust-acoustic solitary waves are obtained for different physical conditions respectively. The influence of an arbitrary dust size distribution described by a polynomial expressed function on the properties of dust-acoustic solitary waves is investigated numerically. How dust size distribution affects the sign and the magnitude of nonlinear coefficient A(D) of KP (mKP) equation is also discussed in detail. It is noted that whether a compressive or a rarefactive solitary wave exists depends on the dust size distribution in some dusty plasmas.     

Large-amplitude dust acoustic solitons in an opposite polarity dusty plasma with generalized polarization force

Linear and nonlinear dust acoustic(DA)waves have been investigated in an opposite polarity dusty plasma comprising negatively and positively charged dust grains,Maxwellian electrons and ions,including the generalized polarization force effect.The properties of linear DA waves have been significantly altered by the dual dust polarity and polarization force.Large amplitude DA solitons have been discussed in the framework of the Sagdeev potential technique.Our results show that both rarefactive and compressive solitons can exist in such a dusty plasma.The basic features of the Sagdeev potential have been examined under the effect of the polarization force parameter R,the ratio of the charge number of the positive dust to that of the negative dust Z,and the Mach number M.The results show that these parameters play a significant role in determining the region of existence of large amplitude DA solitons.     

On the numerical solution of nonplanar dust-acoustic super rogue waves in a strongly coupled dusty plasma

The occurrence of cylindrical and spherical low-frequency dust-acoustic freak waves (DAFWs) in a strongly coupled dusty plasma is numerically investigated in the framework of the phenomenological generalized hydrodynamic model. The basic equations are reduced to a modified/nonplanar nonlinear Schrödinger equation (mNLSE) using a reductive perturbation method. The existing regions of instability structures have been carefully identified. For studying the propagation of rogue waves in case of nonplanar (cylindrical and spherical coordinates), the mNLSE has been solved numerically. The effects of nonplanar geometries on the basic features of the DAFWs for the first- and second-orders rogue waves are discussed. Finally, our results are of relevance in ultradense situations where nonplaner geometrical effects are significant. In particular, we expect for our findings to be important to understand the DA breathers experimentally in a strongly coupled dusty plasma.     

Impacts of neutral shadowing force on dust particle dynamics in cryogenic plasma

Recently, it was shown that the neutral shadowing force can have a strong impact on the structural properties of the charged dust particles in cryogenic dusty plasmas. Therefore, in this work, we have investigated the impact of the neutral shadowing force on the dynamical properties by means of molecular dynamics simulations. By computing the velocity auto‐correlation function of particles and their spectrum, we found that the neutral shadowing force has a strong impact on the dust particle dynamics if the mean free path of neutrals exceeds the mean inter‐dust particle distance.     

Effects of polarization force and nonthermal ions on dust-acoustic (DA) shock waves in a strongly coupled dusty plasma with positively charged dust

The nonlinear propagation of the dust-acoustic (DA) waves in a strongly coupled dusty plasma containing Maxwellian electrons, nonthermal ions, and positively charged dust is theoritically investigated by a Burgers equation. The effects of the polarization force (which arises due to the interaction between electrons and highly positively charged dust grains) and nonthermal ions are studied. DA shock waves are found to exist with positive potential only. It represents that the strong correlation among the charged dust grains is a source of dissipation, and is responsible for the formation of DA shock waves. The effects of polarization force and nonthermal ions significantly modified the basic features of DA shock waves in strongly coupled dusty plasma.     

The effect of negative ions on the dust acoustic wave in dusty electronegative plasma with positively charged dust grains

The effect of negative ions on the modulational instability properties of nonlinear dust acoustic (DA) waves in the electronegative dusty plasmas was investigated by considering Boltzmann-distributed electrons, negative ions, positive ions as well as positively charged dust grain under the ultraviolet irradiation. It is shown that the modulational instability properties of the DA waves were strongly affected by the temperature and proportion of negative ions. The modulational instability can occur only if the proportion of negative ions was smaller than critical value. The instability growth rate has a maximum value when the proportion of negative ions was a critical one in the unstable region. The effect of photoelectron generated by ultraviolet irradiation on the modulational instability of dust acoustic waves was also discussed by numerical method.     

Effects of dust-charge gradient and polarization forces on the waves and Jeans instability in strongly coupled dusty plasma

The effects of dust charge gradient (DCG) force and polarization force have been investigated on the properties of dust acoustic wave (DAW) and linear Jeans instability in strongly coupled dusty plasma. In the kinetic regime, DCG and polarization forces modify the DAW mode and couple with compressional viscoelastic wave mode. The Jeans instability criterion and critical wavenumber have been modified due to DCG force, polarization force and strong coupling effects. The results have been discussed in the warm photodisassociation region and in the laboratory complex plasmas. The strong correlation effect and the charge variation parameter stabilize the growth rate of Jeans instability. But, the polarization parameter stabilize the growth rate for positively charged dust grains and destabilize for negatively charged dust grains. The implications of charge gradient and polarization parameters are discussed for lower and higher charges in the laboratory complex plasma which decreases the growth of the propagating DAW.     

Effects of double spectral electron distribution and polarization force on dust acoustic waves in a negative dusty plasma

The nonlinear features of dust acoustic waves (DAWs) propagating in a multicomponent dusty plasma with negative dust grains, Maxwellian ions, and double spectral electron distribution (DSED) are investigated. A Korteweg de Vries Burgers equation (KdVB) is derived in the presence of the polarization force using the reductive perturbation technique (RPT). In the absence of the dissipation effect, the bifurcation analysis is introduced and various types of solutions are obtained. One of these solutions is the rarefactive solitary wave solution. Additionally, in the presence of the dissipation effects, the tanh method is employed to find out the solution of KdVB equation. Both of the monotonic and the oscillatory shock structures are numerically investigated. It is found that the correlation between dissipation and dispersion terms participates strongly in creating the dust acoustic shock wave. The limit of the DSED to the Maxwell distribution is examined. The distortional effects in the profile of the shock wave that result by increasing the values of the flatness parameter, r, and the tail parameter, q, are investigated. In addition, it has been shown that the proportional increase in the value of the polarization parameter R enhances in both of the strength of the monotonic shock wave and the amplitude of the oscillatory shock wave. The effectiveness of non-Maxwellian distributions, like DSED, in several of plasma situations is discussed as well.     

Formation of dust-acoustic shock waves in a strongly coupled cryogenic dusty plasma

The nonlinear propagation of ultra-low-frequency dust-acoustic (DA) waves in a strongly coupled cryogenic dusty plasma has been investigated, by using the Boltzmann distributed electrons and ions, as well as modified hydrodynamic equations for strongly coupled charged dust grains. The reductive perturbation technique is used to derive the Burger equation. It is shown that strong correlations among negatively charged dust particles acts like a dissipation, which is responsible for the formation of the DA shock waves. The latter are associated with the negative potential, i.e. with the compression of negatively charged cryogenic dust particle density. It is also found that the effective dust-temperature, which arises from electrostatic interactions among negatively charged dust particles, significantly affects the height of the DA shock structures. New laboratory experiments at cryogenic temperature should be conducted to verify our theoretical prediction.     

Modulational instability of dust acoustic waves in a dusty plasma with nonthermal electrons and ions

Effects of nonadiabaticity of variable dust charge, dust fluid temperature, trapped electrons as well as nonisothermality of ions on the amplitude modulation of dust acoustic waves in an unmagnetized dusty plasma are investigated. A modified nonlinear Schr?dinger equation (NLSE) is obtained by the standard reductive perturbation technique and is solved numerically by the split-step Fourier method. The modulational instability and the envelope solitary wave structure are found to be modified somewhat by the effects of nonthermally distributed ions and trapped electrons.     

Simulating the stopping dynamics of highly charged ions in an ultra-cold, strongly coupled plasma

We introduce a method for stopping highly charged ions (HCIs) in a laser-cooled one-component plasma (OCP) of ²⁴Mg⁺ ions and present results on stopping times derived from realistic molecular dynamics simulations of the complete stopping process. This stopping scheme can provide ultra-cold highly charged ions for future in-trap precision mass measurements. The choice of an ultra-cold ion plasma as a stopping medium is governed by the almost negligible charge exchange of the HCI with the laser-cooled ions and the very low temperatures which can be reached. In our analysis we focus on the stability and fast recooling of the plasma – two features essential for the experimental realization of this stopping scheme.      

Streaming instability of a dusty plasma in the presence of mass and charge variation

We study the effect of the mass and charge dynamics on the collective behaviour of a dusty plasma. It is shown that the finite non-zero streaming velocity of the dust grains leads to a novel coupling of the dust mass fluctuation with other dynamic variables of the plasma and the grains. The mass fluctuations causes a collisionless dissipation and provides an alternate channel for the beam mode instability to occur. Physically the negative energy wave associated with the beam mode couples to the mass fluctuation induced dissipative medium to produce the instability. We conclude that the higher value of the ion mass density to the dust mass density ratio reduces the threshold value for the onset of the instability. Its application in the astrophysical context is discussed.     

Viscoelastic effects on asymmetric two‐dimensional vortex patterns in a strongly coupled dusty plasma

Strongly coupled dusty plasma medium is often described as a viscoelastic fluid that retains its memory. In a flowing dusty plasma medium, vortices of different sizes appear when the flow does not remain laminar. The vortices also merge to transfer energy between different scales. In the present work, we study the effect of viscoelasticity and compressibility over a localized vortex structure and multiple rotational vortices in a strongly coupled viscoelastic dusty plasma medium. In case of single rotating vortex flow, a transverse wave is generated from the localized vortex source and the evolution time of generated waves is found to be reduced due to finite viscoelasticity and compressibility of the medium. It is found that the viscoelasticity suppresses the dispersion of vorticity. In the presence of multiple vortices, we find, the vortex mergers get highly affected in the presence of memory effect of the fluid, and thus the dynamics of the medium gets completely altered compared to a non‐viscoelastic fluid. For a compressible fluid, viscoelasticity dampens the energy in the sonic waves generated in the medium. Thus a highly viscoelastic and compressible fluid, in some cases, behaves similarly to an incompressible viscoelastic fluid. The wave‐front like rings propagate in elliptical orbits keeping the footprint of the earlier position of the point‐vortex. The rings collide with each other even within the patch vortex region forming regions of high vorticity at the point of intersection and pass through each other.     

Effect of electron inertia on large amplitude solitary waves in presence of kinematic viscosity in dusty plasma

Nonlinear dust acoustic solitary waves in a dusty plasma are studied for nonzero kinematic viscosity. Sagdeev’s potential can be obtain upto any order in ϕ. The existence of soliton solution is determined by pseudopotential approach. It is seen that the electron inertia has a significant effect on the existence of solitary waves in presence of kinematic viscosity.     

碰撞对尘埃等离子体鞘层中尘埃颗粒影响

在一维平板鞘层中应用流体模型研究了尘埃等离子体鞘层中碰撞对尘埃颗粒密度和带电量的影响。 研究所涉及的碰撞主要有电离碰撞,电子、离子分别与中性粒子的碰撞,以及电子、离子分别与尘埃颗粒的碰撞。通过采用四阶龙格库塔法,得到了数值解。结果表明,随着电离碰撞或者电子、离子分别与中性粒子碰撞的频率 增加,都将导致鞘层中尘埃颗粒的数密度增大,数密度的极值位置向鞘边位置靠近,尘埃颗粒带电量增多。电子、离子与尘埃颗粒的碰撞,使得尘埃带电量减小。此外,从研究的结果来看,由离子产生的碰撞要比电子产生的碰 撞对尘埃颗粒的影响明显得多。     

Effect of relativistic elliptical beam modulation on excitation of surface plasma waves in a magnetized dusty plasma column with elliptical cross section

Abstract

The excitation of surface plasma waves due to the interaction of an elliptical relativistic density modulated electron beam with the magnetized dusty plasma column with elliptical cross-section has been studied. The dispersion relation of surface plasma waves has been retrieved from the derived dispersion relation by considering that the beam is absent and there is no dust in the plasma elliptical cylinder. It is shown that the Cherenkov and fast cyclotron interactions appear between the beam and eigen-modes of plasma column. The growth rate of the instability increases with the beam density and modulation index as one-third power of the beam density in Cherenkov interaction and is proportional to the square root of beam density in fast cyclotron interaction. The numerical results and graphs are presented, too.     

Effect of dust size distribution and dust charge fluctuation on dust ion-acoustic shock waves in a multi-ion dusty plasma

The effects of dust size distribution and dust charge fluctuation of dust grains on the small but finite amplitude nonlinear dust ion-acoustic shock waves, in an unmagnetized multi-ion dusty plasma which contains negative ions, positive ions and electrons, are studied in this paper. A Burgers equation and its stationary solutions are obtained by using the reductive perturbation method. The analytical and numerical results show that the height with polynomial dust size distribution is larger than that of the monosized dusty plasmas with the same dust grains, but the thickness in the case of different dust grains is smaller than that of the monosized dusty plasmas. Furthermore, the moving speed of the shock waves also depend on different dust size distributions.     

The action of an electron beam on dust structures in a plasma

The action of an electron beam on ordered dust structures in glow and low-pressure RF discharges was studied experimentally. The electron beam produces destruction and dynamic displacement of the dust structure. In the center of a dust structure, an electron beam with a low electron energy (tens of eV) at currents up to 1 mA caused structural disordering and “melting” in the region of its action but did not excite external crystal regions. Local action of an electron beam with a high electron energy (25 keV) and a beam current above 10 mA caused deformation of the whole dust structure and shifted it in the horizontal direction so that it was carried away from the RF discharge zone. The effect of dust structure displacements can be used to locally remove particles from a plasma.