R. S. Schneider

Electromagnetic cyclotron-loss-cone instability associated with weakly relativistic electrons

The amplification of fast extraordinary mode waves with frequencies very close to the electron cyclotron frequency is investigated for a plasma which consists of a weakly relativistic electron component with a loss-cone type distribution and a cold background electron component. The basic mechanism of the amplification is attributed to a relativistic cyclotron resonance between the wave and the energetic electrons. The method employed in the present analysis enables us to solve the dispersion relation in a self-consistent manner for arbitrary ratio of the densities of the energetic and background electrons. It is found that the maximum growth rates occur at certain values of ω 2 pe /Ω 2 e and the angular dependence of the growth rate is sensitive to the ratios ω 2 pe /Ω 2 e and n e / n b . Here ω pe and Ω e are the electron plasma frequency and the electron cyclotron frequency, respectively, and n e and n b denote the number densities of the energetic and background electrons, respectively.

The dielectric tensor for dusty magnetized plasmas with variable charge on dust particles

We derive the dielectric tensor for multicomponent magnetized dusty plasmas, including the effect of capture of plasma electrons and ions by the dust particles. For propagation perpendicular to the external magnetic field and Maxwellian distributions of electrons and ions, we obtain compact expressions for the components of the dielectric tensor, which can be used to analyse wave propagation. An application to the magnetosonic wave is presented.

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.

Spatial absorption of a magnetosonic wave in a dusty magnetized plasma

The dielectric tensor for a multicomponent magnetized dusty plasma, including the eect of capture of plasma electrons and ions by the dust particles, is rewritten in order to provide expressions more suitable for applications. We use this tensor to study the spatial absorption of a magnetosonic wave, including eects up to second order in the Larmor radius. We analyse the absorption of the wave due to the presence of dust particles with variable charge and the modification of this absorption due to finite-Larmor- radius eects.

Propagation and amplification of auroral kilometric radiation in finite width auroral cavities

We investigate amplification of the auroral kilometric radiation over the geomagnetic poles. The physical parameters needed for the calculation are obtained from a particular model that approximately reproduces the conditions in the auroral zone, taking into account density gradients perpendicular to the geomagnetic field and also the parallel magnetic field gradient. The components of the dielectric tensor are calculated in the locally homogeneous plasma approximation, and the dispersion relation is exactly solved with all harmonics and powers of the Larmor radius needed for the convergency of the solution. We also make a ray tracing study in the geometrical optics approximation, using the method of Poeverlein. The ray tracing study shows that the spatial scale of inhomogeneity, perpendicular to the magnetic field, is a very important factor in the amplification and that the distance to obtain a given amplification can be substantially reduced when the density gradient is increased.

Temperature effects on ion acoustic solitons in plasmas with near critical density of negative ions

The authors establish a Korteweg-de Vries type equation to describe ion acoustic solitons in a plasma made up of electrons, positive and negative ions near the critical density. It is shown that the amplitudes and widths of compressive and rarefactive solitons are dependent on the ion temperatures and that this dependence is strongly asymmetric when the positive and negative ion temperatures are unequal. As an application, they analyse results of an experiment.

Ray tracing studies on auroral kilometric radiation in finite width auroral cavities

We investigate propagation and amplification of the auroral kilometric radiation over the geomagnetic poles using a particular model for the physical parameters in the auroral zone, which takes into account density gradients perpendicular to the geomagnetic field. The propagation of the waves is investigated with the canonical set of equations of the geometrical optics, taking into account thermal effects and considering both the energetic and the background electron populations, with the components of the dielectric tensor calculated in the locally homogeneous plasma approximation. It is shown that the spatial scale of inhomogeneity perpendicular to the magnetic field is an important factor in the amplification, although less favorable than indicated by previous studies using the method of Poeverlein to obtain the trajectory of the radiation.

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.