RUDI GAELZER

We study the dispersion relation for low frequency waves in the whistler mode propagating along
the ambient magnetic field, considering ions and electrons with product-bi-kappa (PBK) velocity
distributions and taking into account the presence of a population of dust particles. The results
obtained by numerical analysis of the dispersion relation show that the decrease in the j indexes in
the ion PBK distribution contributes to the increase in magnitude of the growth rates of the ion
firehose instability and the size of the region in wave number space where the instability occurs. It
is also shown that the decrease in the j indexes in the electron PBK distribution contribute to
decrease in the growth rates of instability, despite the fact that the instability occurs due to the
anisotropy in the ion distribution function. For most of the interval of j values which has been
investigated, the ability of the non-thermal ions to increase the instability overcomes the tendency
of decrease due to the non-thermal electron distribution, but for very small values of the kappa
indexes the deleterious effect of the non-thermal electrons tends to overcome the effect due to the
non-thermal ion distribution.

We investigate the dispersion relation for low frequency electromagnetic waves propagating parallel to the ambient magnetic field, considering that the velocity distributions of ions and electrons can be either bi-Maxwellian of product bi-kappa distributions. The effect of the anisotropy and non-thermal features associated to the product-bi-kappa distributions on the firehose instability are numerically investigated. The general conclusion to be drawn from the results obtained is that the increase in non-thermal features which is consequence of the decrease of the κ indexes in the ion distribution contributes to increase the instability in magnitude and wave number range, in comparison with bi-Maxwellian distributions with similar temperature anisotropy, and that the increase of non-thermal features in the electron distribution contributes to the quenching of the instability, which is nevertheless driven by the anisotropy in the ion distribution. Significant differences between results obtained either considering product-bi-kappa distributions or bi-kappa distributions are also reported.

This article demonstrates the generation of enhanced ion-acoustic waves by beam-plasma instability in a density cavity. The self-consistent equations of weak turbulence theory that include quasi-linear, decay, and scattering processes as well as convective and dispersive effects are numerically solved for a one-dimensional density cavity. It is shown that significant enhancements of ion-acoustic waves occur in the presence of counterstreaming electron beams and that the enhanced ion-acoustic waves are initially localized near the center of the density cavity at large wavelengths. Later in the evolution, the enhancement in the spectrum of ion-acoustic waves spreads out toward the edges of the cavity, with a shift to smaller wavelengths, while the enhancement near the center of the cavity tends to decrease in magnitude. The significance of the present findings is discussed.

The dispersion relation for parallel propagating waves in the ion-cyclotron branch is investigated
numerically by considering that the velocity distribution of the ion population is a function of type
product-bi-kappa. We investigate the effects of the non-thermal features and of the anisotropy associated with this type of distribution on the ion-cyclotron instability, as well as the influence of different forms of the electron distribution, by considering Maxwellian distributions, bi-kappa distributions, and product-bi-kappa distributions. The cases of ions described by either Maxwellian or bi-kappa distributions are also considered, for comparison. The results of the numerical analysis show that the increase in the non-thermal character associated with the anisotropic kappa distributions for ions contributes to enhance the instability as compared to that obtained in the Maxwellian case, in magnitude and in wave number range, with more significant enhancement for the case of ion product-bi-kappa distributions than for the case of ion bi-kappa distributions. It is also shown
that the ion-cyclotron instability is decreased if the electrons are described by product-bi-kappa distributions, while electrons described by bi-kappa distributions lead to growth rates which are very
similar to those obtained considering a Maxwellian distribution for the electron population.

Ion-acoustic enhancements are investigated within the context of turbulent beam-plasma interaction processes. The analysis assumes a pair of counterstreaming electron beams interacting with the background plasma. Two-dimensional velocity space and two-dimensional wave number space are assumed for the analysis, with physical parameters that characterize typical ionospheric conditions. The solutions of the electrostatic weak turbulence theory show that the ion-acoustic wave levels are significantly enhanced when the computation is initialized with a pair of counterstreaming beams in contrast to a single beam. We suggest that this finding is highly relevant for the observed ion-acoustic enhancements in the Earth's ionosphere that are known to be correlated with auroral activity.