M. C. de Juli

Effects of dust-charge fluctuation on the damping of Alfvén waves in dusty plasmas

Using a completely kinetic description to analyze wave propagation in dusty plasmas, the case of propagation of waves exactly parallel to the external magnetic field and Maxwellian distributions for electrons and ions in the equilibrium is considered. A model for the charging process of dust particles which depends on the frequency of inelastic collisions between dust particles and electrons and ions is used. The dispersion relation and damping rates for Alfven waves are obtained. For the numerical solutions, the average value of the inelastic collision frequency is used as an approximation. The results show that the presence of dust particles with variable charge in the plasma produces significant additional damping of the Alfven wave. A novel process of mode coupling of low-frequency waves is demonstrated to occur due to the presence of dust particles.

Mode coupling of low frequency electromagnetic waves in magnetized dusty plasmas

A kinetic description is used to analyze wave propagation in dusty plasmas, taking into account the fluctuation of the charge of the dust particles due to inelastic collisions with electrons and ions. The case of propagation of waves exactly parallel to the external magnetic field and Maxwellian distributions for the electrons and ions in the equilibrium is considered, and a parametric analysis of the dispersion relation is performed. The investigation emphasizes particularly the effects of dust density, radius of dust particles, ion temperature, ratio between electron and ion temperatures, ion density, and ambient magnetic field, on the solutions of the dispersion relation. The analysis shows the possibility of occurrence of coupling between waves in the whistler branch and waves in the branch of circularly polarized waves, in the presence of the dust particles.

DUSTY MOLECULAR CLOUD COLLAPSE IN THE PRESENCE OF ALFVEN WAVES

It has been shown that magnetic fields play an important role in the stability of molecular clouds, mainly perpendicular to the field direction. However, in the parallel direction the stability is a serious problem still to be explained. Interstellar turbulence may allow the generation of Alfven waves that propagate through the clouds in the magnetic field direction. These regions also present great quantities of dust particles, which can give rise to new wave modes or modify the preexisting ones. The dust-cyclotron damping affects the Alfven wave propagation near the dust-cyclotron frequency. On the other hand, the clouds present different grain sizes, which carry different charges. In this sense, a dust particle distribution has several dust-cyclotron fre- quencies, and it will affect a broad band of wave frequencies. In this case, the energy transfer to the gas is more efficient than in the case where the ion-cyclotron damping is considered alone. This effect becomes more important if a power-law spectrum is considered for the wave energy flux, since the major part of the energy is concentrated in low-frequency waves. In this work we calculate the dust-cyclotron damping in a dusty and magnetized dwarf molecular cloud, and determine the changes in the Alfven wave flux. Then we use these results to study the gravitational stability of the cloud. We show that, considering the presence of charged dust particles, the wave flux is rapidly damped through dust-cyclotron damping. Then the wave pressure acts in a small length scale and cannot explain the observable cloud sizes, but can explain the existence of small and dense cores.

Obliquely propagating Alfvén waves in a Maxwellian dusty plasma

A kinetic formulation developed to analyze wave propagation in dusty plasmas, which takes into account the charge variation of the dust particles, is utilized to study the propagation and damping of Alfven waves propagating in oblique directions relative to the ambient magnetic field. A dusty plasma containing spherical and immobile dust grains in a homogeneous ambient magnetic field is considered. The charging process of the dust grains is assumed to be associated with the capture of electrons and ions by the dust particles during inelastic collisions between them and plasma particles. The dispersion relation and the damping rates of obliquely propagating Alfven waves are obtained assuming Maxwellian distributions for electrons and ions in equilibrium. For the numerical analysis of the dispersion relation we use the average values of the inelastic collision frequency as an approximation, instead of the momentum dependent expressions originally derived in the kinetic formulation, and study the modifications which the presence of the dust particles causes in both the propagation and the damping of the Alfven waves. In particular is discussed the competition between the different damping mechanisms, namely, the Landau damping and the damping associated with the dust charge variation, and it is shown that the inelastic collision frequency plays a pivotal role in the magnitude of the damping rates.

A new formulation for the dielectric tensor for magnetized dusty plasmas with variable charge on the dust particles

A kinetic approach to the problem of wave propagation in dusty plasmas, which takes into account the variation of the charge of the dust particles due to inelastic collisions with electrons and ions, is utilized as a starting point for the development of a new formulation, which writes the components of the dielectric tensor in terms of a finite and an infinite series, containing all effects of harmonics and Larmor radius. The formulation is quite general and valid for the whole range of frequencies above the plasma frequency of the dust particles, which were assumed motionless. The formulation is employed to the study of electrostatic waves propagating along the direction of the ambient magnetic field, in the case for which ions and electrons are described by Maxwellian distributions. The results obtained in a numerical analysis corroborate previous analysis, about the important role played by the inelastic collisions between electrons and ions and the dust particles, particularly on the imaginary part of the dispersion relation. The numerical analysis also show that additional terms in the components of the dielectric tensor, which are entirely due these inelastic collisions, play a very minor role in the case of electrostatic waves, under the conditions considered in the present analysis.

Electrostatic waves in a Maxwellian dusty plasma with variable charge on dust particles

A kinetic formulation developed to analyze wave propagation in dusty plasmas, which takes into account the variation of the charge of the dust particles due to inelastic collisions with electrons and ions, is utilized to study the propagation and damping of electrostatic waves with wave number exactly parallel to the external magnetic field and Maxwellian distributions for the electrons and ions in the equilibrium. It is shown that, due to the presence of the dust, the damping of Langmuir waves in the region of large wavelengths is increased as compared to conventional Landau damping. Langmuir waves in the occurrence of collisional charging of dust particles also feature weak damping for small wavelengths, which vanishes if the effect of collisional charging of the dust particles is neglected in the dispersion relation. It is also shown that the damping of ion-acoustic waves is modified by the presence of the dust, and that some damping effect due to the dust particles remains even if the effect of collisional charging of dust particles is neglected in the dispersion relation.

Mode-coupling of low-frequency electromagnetic waves in dusty plasmas with temperature anisotropy

This paper studies the effects of the presence of dust particles with variable charge, in fully ionized, homogeneous, magnetized plasma of electrons and ions, with the electrons and ions described by bi-Maxwellian distributions in the equilibrium. The dispersion relation and the absorption rate are obtained for low frequency waves, with frequencies much lower than the ion cyclotron frequency. Two branches are obtained, identified as the whistler branch and the branch of circularly polarized waves, featuring damping due to the Landau damping process and to the collisional charging of the dust particles. The effects of the anisotropy of temperature on the damping rate of low frequency waves, and on the mode coupling which was demonstrated to occur in the isotropic situation, are numerically investigated. The results obtained show that in the anisotropic case the point of mode coupling is displaced to different values of dust density, and that a new point of mode coupling may appear from the effect of the te...

Alfvén waves in dusty plasmas with plasma particles described by anisotropic kappa distributions

We utilize a kinetic description to study the dispersion relation of Alfven waves propagating parallelly to the ambient magnetic field in a dusty plasma, taking into account the fluctuation of the charge of the dust particles, which is due to inelastic collisions with electrons and ions. We consider a plasma in which the velocity distribution functions of the plasma particles are modelled as anisotropic kappa distributions, study the dispersion relation for several combinations of the parameters κ∥ and κ⊥, and emphasize the effect of the anisotropy of the distributions on the mode coupling which occurs in a dusty plasma, between waves in the branch of circularly polarized waves and waves in the whistler branch.

Electrostatic waves in dusty plasmas with variable charge on dust particles

In this work we present results obtained using a kinetic approach for parallel propagation of waves in a homogeneous magnetized dusty plasma. In this magnetized plasma we consider embedded spherical dust grains with constant radius and variable charge. We consider that the principal process of dust charging is by capture of electrons and ions of the plasma, and use a cross‐section derived from the orbital motion limited theory to describe this process. We concentrate on electrostatic waves and obtain the dispersion relation, which is applied to Langmuir oscillations, taking into account those effects due to charge fluctuation which do not contain terms with the derivative of the charging cross‐section, and using an approximation for the collision frequency between plasma particles and dust particles. We also analyse the competition between Landau damping and the damping that results from the electric charge variation of the dust particles.

Effects of dust charge variation on electrostatic waves in dusty plasmas with temperature anisotropy

We utilize a kinetic approach to the problem of wave propagation in dusty plasmas, taking into account the variation of the charge of the dust particles due to inelastic collisions with electrons and ions. The components of the dielectric tensor are written in terms of a finite and an infinite series, containing all effects of harmonics and Larmor radius. The formulation is quite general and valid for the whole range of frequencies above the plasma frequency of the dust particles, which are assumed motionless. The formulation is employed to the study of electrostatic waves propagating along the direction of the ambient magnetic field, in the case for which ions and electrons are described by bi-Maxwellian distributions. The results obtained in a numerical analysis corroborate previous analysis, about the important role played by the dust charge variation, particularly on the imaginary part of the dispersion relation, and about the very minor role played in the case of electrostatic waves by some additional terms appearing in the components of the dielectric tensor, which are entirely due to the occurrence of the dust charge variation.