Dust Neutral Collisions Research Articles

Observation of the Rayleigh-Bénard convection cells in strongly coupled Yukawa liquids

Using “first principles” molecular dynamics simulation, we report for the first time the formation of Rayleigh-Bénard convection cells (RBCC) in two-dimensional strongly coupled Yukawa liquids, characterized by coupling strength Γ (ratio of average potential energy to kinetic energy per particle) and screening parameter κ (ratio of average inter-particle distance to Debye length). For typical values of (Γ, κ), existence of a critical external temperature difference is demonstrated, beyond which RBCC are seen to set in. Beyond this critical external temperature difference, the strength of the maximum convective flow velocity is shown to exhibit a new, hitherto unsuspected linear relationship with external temperature difference and with a slope independent of (Γ, κ). The time taken for the transients to settle down (τs) to a steady state RBCC is found to be maximum close to the above said critical external temperature difference and is seen to reduce with increasing external temperature difference. For the range of values of (Γ, κ) considered here, τs ≈ 10 000–20 000 ωpd−1, where ωpd is dust plasma frequency. As Γ is increased to very high values, due to strong coupling effects, cells are seen to be in a transient state without attaining a steady state for as long as 100 000 ωpd−1, even for a very high external temperature difference. Role of system size, aspect ratio, and dust-neutral collisions has also been addressed.

Influence of the Collisions on the Dusty Plasma Sheath in the Presence of an Oblique Magnetic Field

The dust dynamics in a magnetized collisional plasma-sheath are numerically studied by using the fluid model. Isothermal electrons, cold fluid ions, cold fluid dust grains and immobile neutral particles are taken into account in the sheath. As dust can be created by detaching small pieces of the wall limiting plasma, naturally, these grains can have different sizes. Therefore, the influence of dust size on the sheath characteristics is considered. Assuming the dust–neutral collision cross section has a power law dependency on the dust velocity. The comparison of the effect of the dust radius in both specific collisional models shows that in the constant cross section model, dust size plays a more role with respect to the constant collision frequency. The effect of the dust size on dust velocity is investigated for different values of the power factor. It shows that dust velocity when reaching near the wall in constant cross section model is much less than constant mobility model, and the velocity of the smaller dust is lower on the wall. If dust density is very small, the kind of collisional model has no significant influence on the electric potential. But by increasing dust density, a little fall in the local electric potential and a little rise in the sheath thickness are seen in constant cross section model.

Two-dimensional dissipative structures in spatially nonuniform dusty plasmas in planetary magnetospheres with kappa distributed ions

Linear and nonlinear propagation of coupled dust drift acoustic waves are investigated in the presence of a kappa distributed ion population and Boltzmannian electrons. It is observed that the frequency of the dust drift acoustic wave decreases by increasing the kappa value. Using the drift approximation, a nonlinear equation is derived for the dust drift acoustic shock wave that reduces to a Kadomtsev–Petviashvili–Burgers (KPB)-like equation in the comoving frame of reference. It is found that the nonlinear structure of dust drift acoustic shock waves modifies in the presence of increasing values of kappa, dust number density, ambient magnetic field, and the dust neutral collision frequency. Interestingly, it is found that the non-Maxwellian ion population modifies the scale lengths over which the nonlinear structures are formed. The results obtained are applied in Saturnʼs magnetosphere, where the non-Maxwellian distribution of particles has been reported by several satellite missions.

Quasilongitudinal soliton in a two-dimensional strongly coupled complex dusty plasma in the presence of an external magnetic field.

The propagation of a nonlinear low-frequency mode in two-dimensional (2D) monolayer hexagonal dusty plasma crystal in presence of external magnetic field and dust-neutral collision is investigated. The standard perturbative approach leads to a 2D Korteweg-de Vries (KdV) soliton for the well-known dust-lattice mode. However, the Coriolis force due to crystal rotation and Lorentz force due to magnetic field on dust particles introduce a linear forcing term, whereas dust-neutral drag introduce the usual damping term in the 2D KdV equation. This new nonlinear equation is solved both analytically and numerically to show the competition between the linear forcing and damping in the formation of quasilongitudinal soliton in a 2D strongly coupled complex (dusty) plasma. Numerical simulation on the basis of the typical experimental plasma parameters and the analytical solution reveal that the neutral drag force is responsible for the usual exponential decay of the soliton, whereas Coriolis and/or Lorentz force is responsible for the algebraic decay as well as the oscillating tail formation of the soliton. The results are discussed in the context of the plasma crystal experiment.

Dispersion relations for the dust-acoustic wave under experimental conditions

The dust acoustic wave dispersion relation is tested to quantify its sensitivity to many physical processes that are important in laboratory dusty plasmas. It is found that inverse Landau damping and ion-neutral collisions contribute about equally to the growth rate ωi, pointing to the advantage of using a kinetic model for the instability. The growth rate ωi increases the most with an increase of dust number density, followed by an increase in ion-drift speed. The quantities that cause ωi to decrease the most when they are increased are the dust-neutral collision rate followed by the ion-neutral collision rate, ion collection current onto dust particles, and the ion thermal speed. In general, ωi is affected more than ωr by the choice of processes that are included. Strong Coulomb-coupling effects can be included in a compressibility term. The susceptibilities derived here can be combined in various ways in a dispersion relation to account for different combinations of physical processes.

Collision and recombination driven instabilities in variable charged dusty plasmas

The dust-acoustic instability driven by recombination of electrons and ions on the surface of charged and variably-charged dust grains as well as by collisions in dusty plasmas with significant pressure of background neutrals have been theoretically investigated. The recombination driven instability is shown to be dominant in the long wavelength regime even in the presence of dust-neutral and ion-neutral collisions, while in the shorter wavelength regime, the dust-neutral collision is found to play a major role. In an earlier research work, the dust-neutral collision was neglected in comparison to the effect due to the recombination for estimating the dust-acoustic instability; later the other report shows that the recombination effect is negligible in the presence of dust-neutral collisions. In line of this present situation our investigation revealed that the recombination is more important than dust-neutral collisions in laboratory plasma and fusion plasma, while the dust-neutral collision frequency is dominant in the interstellar plasmas. The effects of ion and dust densities and ion streaming on the recombination and collision driven mode in parameter regimes relevant for many experimental studies on dusty plasmas have also been calculated.

Dust drift shock waves with non-Maxwellian ion population in nonuniform collisional dusty plasmas in planetary environments

Linear and nonlinear propagation of dust drift waves are investigated in the presence of Cairns and Kappa distributed ion population and Boltzmannian electrons. It is found the frequency of the dust drift wave is greatest for the Cairns, intermediate for Kappa and the least for the Maxwellian distributed ions. Using the drift approximation, a nonlinear equation is derived for the dust drift shock waves which reduces to a Korteweg-de Vries-Burgers (KdVB)-like equation in the comoving frame of reference. The solution of the KdVB-like equation is obtained using the tanh method. It is found that the non-Maxwellian ion population, dust neutral collision frequency as well as the inverse dust density scale length inhomogeneity alter the propagation characteristics of the nonlinear dust drift shock waves. Interestingly, it is found that the non-Maxwellian ion population modifies the scale lengths over which the nonlinear structures are formed. The work presented here may be useful to understand the low frequency electrostatic shock waves in inhomogeneous dusty plasmas such as those found in planetary environments.

The dust ion acoustic waves propagation in collisional dusty plasmas with dust charge fluctuations: Effect of ion loss and ionization

AbstractIn the present research paper, the nonlinear propagation of dust ion acoustic solitary waves in a collisional dusty plasma, which consists of negatively charged small dust grains, positively charged ions and isothermal electrons with background neutral particles, is investigated. The low rates compared to the ion oscillation frequency, of the charge-fluctuation dynamics of the dust grains, the ionization, ion-neutral and dust-neutral collisions (i.e. weak dissipations) are considered. Using the reductive perturbation theory, a damped Korteweg-de Vries (DKdV) equation is derived. On the other hand, the dynamics of solitary waves at a critical phase velocity is governed by a damped modified Korteweg-de Vries (DMKdV) equation. The nonlinear properties of dust ion acoustic waves in the presence of weak dissipations in the two cases are discussed.

On dust ion acoustic solitary waves in collisional dusty plasmas with ionization effect

The propagation of solitary waves in an unmagnetized collisional dusty plasma consisting of a negatively charged dust fluid, positively charged ions, isothermal electrons, and background neutral particles is studied. The ionization, ion loss, ion–neutral, ion–dust, and dust–neutral collisions are considered. Applying a reductive perturbation theory, a damped Korteweg–de Vries (DKdV) equation is derived. On the other hand, at a critical phase velocity, the dynamics of solitary waves is governed by a damped modified Korteweg–de Vries (DMKdV) equation. The nonlinear properties of solitary waves in the two cases are discussed.

Effects of Adiabatic Dust Charge Fluctuation and Particles Collisions on Dust-Acoustic Solitary Waves in Three-Dimensional Magnetized Dusty Plasmas

Taking into account the combined effects of the external magnetic field, adiabatic dust charge fluctuation and collisions occurring between the charged dust grains and neutral gas particles (dust-neutral collisions), the dust-acoustic solitary waves in three-dimensional uniform dusty plasmas are investigated analytically. By using the reductive perturbation method, the Korteweg–de Vries (KdV) equation governing the dust-acoustic solitary waves is obtained. The present analytical results show that only rarefactive solitary waves exist in this system. It is also found that the effects of the wave vector along the z-direction, dust charge variation, collisional frequency, the plasma density, and temperature ratio can significantly influence the characteristics of low-frequency wave modes. Moreover, for the collisional dusty plasmas, there is a certain critical value μc of the plasma density ratio μ, if μ < μc, the width of the waves increases with μ, otherwise the width of waves decreases with μ.

Effect of dust–neutral collisions on the dust characteristics in a magnetized plasma sheath

The characteristics of dust in a plasma sheath are investigated in the presence of an external magnetic field and taking into account the dust–neutral collision force. The continuity and momentum equations of ions and dust particles are solved numerically with various magnitudes of collision force by using the fluid model. The numerical results have revealed that the collision force reduces the dust gyro radius, changes the positions of the extrema of the dust density and the velocity in the depth direction. It is shown that the collision force reduces the dust kinetic energy which has no fluctuation even in a strong external magnetic field.

“Damped Dust Lattice Shock Wave in a Strongly Coupled Complex (Dusty) Plasma,”

Taking into account “hydrodynamic damping” due to irreversible processes that occur within the system and the neutral drag due to the dust-neutral collision, a Burgers’ equation with a linear damping term is derived for a 1D nonlinear longitudinal dust lattice wave (LDLW) in homogeneous strongly coupled complex (dusty) plasma. The hydrodynamic damping generated-dissipative effect causes the generation of a shock wave in a dusty plasma crystal, whereas the neutral drag-induced dissipative effect causes the decay of the shock intensity with time. The width of the observed compressive shock increases (decreases) with an increase in shielding parameter κ (characteristic length L). Its implication in a glow-discharge plasma is briefly discussed.

Multidimensional nonlinear dust acoustic shock waves in nonuniform magnetized dusty plasmas with nonadiabatic dust charge fluctuation

The propagation of multidimensional nonlinear dust acoustic shock waves in inhomogeneous dusty plasmas due to spatial gradients of dust charge and plasma densities is investigated. A modified variable coefficients Korteweg–de Vries Burgers equation is derived with the nonadiabatic dust charge fluctuation, the nonthermally distributed ions, dust-neutral collision, and the external magnetic field. The numerical results show that the inhomogeneity, the nonthermal ions and the nonadiabatic dust charge fluctuation have strong influence on the nonlinear properties of dust acoustic shock waves.

“Damped Dust Lattice Shock Wave in a Strongly Coupled Complex (Dusty) Plasma”

Taking into account “hydrodynamic damping” due to irreversible processes that occur within the system and the neutral drag due to the dust-neutral collision, a Burgers’ equation with a linear damping term is derived for a 1D nonlinear longitudinal dust lattice wave (LDLW) in homogeneous strongly coupled complex (dusty) plasma. The hydrodynamic damping generated-dissipative effect causes the generation of a shock wave in a dusty plasma crystal, whereas the neutral drag-induced dissipative effect causes the decay of the shock intensity with time. The width of the observed compressive shock increases (decreases) with an increase in shielding parameter κ (characteristic length L). Its implication in a glow-discharge plasma is briefly discussed.

Shielding of N×M projectiles in a collisional, self-gravitating, generalized Lorentzian dusty plasma

The shielding potential of N×M projectiles passing through a collisional, self-gravitating dust contaminated plasma is studied by mean of linearized dielectric theory for a generalized Lorentzian plasma. The correlation and interference effects of projectiles on the shielded potential as well as on the energy loss are presented. The amplitude of the shielded potential is enhanced with the increase of dust Jeans frequency for separation less than the effective Debye length. The dust charge fluctuations produce a potential well for slow charge relaxation rate and the energy is gained by the test charge projectiles. However, for fast charge relaxation rate with a fixed value of Jeans frequency, the energy loss is enhanced. The dust neutral collisions also enhance the energy loss for the test charge velocities greater than the dust acoustic speeds.

Experimental observation of strong coupling effects on the dispersion of dust acoustic waves in a plasma

The dispersion properties of low frequency dust acoustic waves in the strong coupling regime are investigated experimentally in an argon plasma embedded with a mixture of kaolin and $MnO_2$ dust particles. The neutral pressure is varied over a wide range to change the collisional properties of the dusty plasma. In the low collisional regime the turnover of the dispersion curve at higher wave numbers and the resultant region of $\partial\omega/\partial k < 0$ are identified as signatures of dust-dust correlations. In the high collisional regime dust neutral collisions produce a similar effect and prevent an unambiguous identification of strong coupling effects.

Effect of self-gravitation and dust-charge fluctuations on the shielding and energy loss of N×M projectiles in a collisional dusty plasma

A simple derivation of the electrostatic potential and energy loss of N×M test charge projectiles traveling through dusty plasma has been presented. The effect of dust-charge fluctuations, dust neutral collisions, and self-gravitation on the shielded potential and energy loss of charge projectiles has been investigated both analytically as well as numerically. An interference contribution of these projectiles to the shielded potential and energy loss has been observed, which depends upon their relative orientation and separation distance. A comparison has been made for correlated and uncorrelated motion of the two projectiles. The amplitude of the shielded potential is enhanced with the increase of dust Jeans frequency for separation less than the effective Debye length. The dust-charge fluctuations produce a potential well for a slow charge relaxation rate and energy is gained, not lost, by the test charge projectiles. However, a fast charge relaxation rate with a fixed value of Jeans frequency enhances the energy loss. The dust neutral collisions are also found to enhance the energy loss for the test charge velocities greater than the dust acoustic speeds. The present investigation might be useful to explain the coagulation of dust particles such as those in molecular clouds, the interstellar medium, comet tails, planetary rings, etc.

Dust-acoustic solitary waves in an inhomogeneous magnetized hot dusty plasma with dust charge fluctuations

Using a standard reductive perturbation theory, a Zakharov-Kuznnetsov (ZK) equation is derived in an inhomogeneous dusty plasma comprised of negatively charged dust grains of equal radii, Boltzmann distributed electrons and positive ions. The effects of dust thermal pressure, dust charge variation, dust-neutral collision, and the external magnetic field are taken into account. Either compressive or rarefective solitons are shown to exist depending on the critical value of the phase velocity which in turn, depends on the dust temperature and pressure. An analytic soliton solution is obtained and discussed. The behaviors of the soliton amplitude, width, and the Mach number are investigated numerically for different plasma parameters.

Charging-delay effect on longitudinal dust acoustic shock wave in strongly coupled dusty plasma

Taking into account the charging-delay effect, the nonlinear propagation characteristics of longitudinal dust acoustic wave in strongly coupled collisional dusty plasma described by generalized hydrodynamic model have been investigated. In the “hydrodynamic limit,” a Korteweg–de Vries Burger (KdVB) equation with a damping term arising due to dust-neutral collision is derived in which the Burger term is proportional to the dissipation due to dust viscosity through dust-dust correlation and charging-delay-induced anomalous dissipation. On the other hand, in the “kinetic limit,” a KdVB equation with a damping term and a nonlocal nonlinear forcing term arising due to memory-dependent strong correlation effect of dust fluid is derived in which the Burger term depends only on the charging-delay-induced dissipation. Numerical solution of integrodifferential equations reveals that (i) dissipation due to dust viscosity and principally due to charging delay causes excitation of the longitudinal dust acoustic shock wave in strongly coupled dusty plasma and (ii) dust-neutral collision does not appear to play any direct role in shock formation. The condition for the generation of shock is also discussed briefly.

Effect of charge fluctuations and collisions on the energy loss of N×M projectiles for a generalized Lorentzian dusty plasma

The shielded potential and the energy loss by N×M projectiles passing through a collisional dust-contaminated plasma with dust-charge fluctuations and grain-size distribution are presented. Analytical general expressions are obtained for the shielded potential and for the energy loss by considering two-body correlation effects. An interference contribution of these projectiles to the potential and energy loss is observed which depends upon their orientation and separation distance. The dust-charge fluctuation produces a potential well instead of Coulomb-type potential for a slowly moving test charge with slow charge relaxation rate and energy is gained by the charged projectiles. However, fast charge relaxation enhances the energy loss and some peaks are observed showing the excitation of some electrostatic modes. On the other hand, the dust neutral collisions also enhance the energy loss for projectile velocities greater than the dust acoustic speed for a Maxwellian plasma (for a large value of the spectral index κ).