Vladimir P. Pavlenko

Ionospheric Alfvén resonator revisited: Feedback instability

The theory of ionospheric Alfven resonator (IAR) and IAR feedback instability is reconsidered. Using a simplified model of the topside ionosphere, we have reanalyzed the physical properties of the IAR interaction with magnetospheric convective flow. It is found that in the absence of the convective flow the IAR eigenmodes exhibit a strong damping due to the leakage of the wave energy through the resonator upper wall and Joule dissipation in the conductive ionosphere. It is found that maximum of the dissipation rate appears when the ionospheric conductivity approaches the “IAR wave conductivity” and becomes infinite. However, the presence of Hall dispersion, associated with the coupling of Alfven wave modes with the compressional perturbations, reduces the infinite damping of the IAR eigenmodes in this region and makes it dependent on the wavelength. The increase in the convection electric field leads to a substantial modification of the IAR eigenmode frequencies and to reduction of the eigenmode damping rates. For a given perpendicular wavelength the position of maximum damping rate shifts to the region with lower ionospheric conductivity. When the convection electric field approaches a certain critical value, the resonator becomes unstable. This results in the IAR feedback instability. A new type of the IAR feedback instability with the lowest threshold value of convection velocity is found. The physical mechanism of this instability is similar to the Cerenkov radiation in collisionless plasmas. The favorable conditions for the instability onset are realized when the ionospheric conductivity is low, i.e., for the nighttime conditions. We found that the lowest value of the marginal electric field which is capable to trigger the feedback instability turns out to be nearly twice smaller than that predicted by the previous analysis. This effect may result in the decrease of the critical value of the electric field of the magnetospheric convection that is necessary for the formation of the turbulent Alfven boundary layer and appearance of the anomalous conductivity in the IAR region.

Linear theory of the mirror instability in non‐Maxwellian space plasmas

[1] A unified theory of the mirror instability in space plasmas is developed. In the standard quasi-hydrodynamic approach, the most general mirror-mode dispersion relation is derived and the growth rate of the mirror instability is obtained in terms of arbitrary electron and ion velocity distribution functions. Finite electron temperature effects and arbitrary electron temperature anisotropies are included. The new dispersion relation allows the treatment of more general space plasma equilibria such as the Dory-Guest-Harris (DGH) or Kennel-Ashour-Abdalla (KA) loss cone equilibria, as well as distributions with power law velocity dependence that are modeled by the family of κ-distributions. Under these conditions, we derive the general kinetic mirror instability growth rate including finite electron temperature effects. As for an example of equilibrium particle distribution, we analyze a large class of κ to suprathermal loss cone distributions in view of application to a variety of space plasmas like the solar wind, magnetosheath, ring current plasma, and the magnetospheres of other planets.

Drift mirror instability revisited, 1, Cold electron temperature limit

Linear theory of the drift-mirror instability in high-β plasma is reconsidered referring to basic principles for the two cases of a one- and a two-component ion plasma in presence of a cold electron background. In both cases the cold electrons serve to shortcut the parallel electric field component which imposes the condition of vanishing the field-aligned current. The corresponding low-frequency dispersion relation is derived in the fluid approximation as well as from kinetic theory including nonvanishing gradients in the density. The free energy of the unstable mode is taken from two sources: the pressure anisotropy and the spatial inhomogeneity of the plasma. The dispersion relation contains a correction which originates from the inclusion of the bending of the magnetic field that is caused by the reaction of the field to the total pressure force. It is shown that the mirror force substantially reduces the phase velocity which is in favour of instability since this requires phase velocities less than the drift speed. The direction of phase velocity becomes antiparallel to that of the pure density-gradient drift velocity. Even for a mirror-stable plasma an instability arises which is solely due to inhomogeneity. We analyze the transition to the classical mirror instability. Application to ring current (hot ring current ions plus cold plasmasphere ions) and magnetosheath (hot sheath ions only) conditions is presented and is in agreement with observational indication of the apparent stability of the pure mirror mode in the ring current.

Magnetic vortices in nonuniform plasmas

A localized generation of magnetic fields is found to occur in an unmagnetized nonuniform plasma. The process is described in terms of dipole and monopole vortex solutions of the equations governing the electron motion.

Excitation, conversion and damping of waves in a helicon plasma source driven by an m = 0 antenna

The excitation of a helicon plasma source by an azimuthally symmetric antenna is considered in comparison with anti-symmetric excitation. The resonances and anti-resonances at the wave excitation, as well as the peculiarities of the power absorption, are shown to be very similar for symmetric and anti-symmetric excitation. The plasma resistance turns out to be higher in the case of symmetric excitation for very short devices. The non-monotonic variation of plasma resistance with density is found to be intrinsic for both methods of excitation as a result of decreasing the power absorption at anti-resonances. This is shown to give rise to abrupt density jumps at varying input power.

Drift mirror instability in space plasmas, 2, Nonzero electron temperature effects

A linear theory of drift mirror instability accounting for the nonzero electron temperature effects is developed. Generalizing our previous approach to the analysis of this instability by accounting for a nonvanishing parallel electric field, we have derived the expressions for the mode frequency and instability growth rate. The origin of the electric field is due to the electron pressure gradient which builds up in a plasma with nonzero electron temperature, because the electrons are dragged by mirror-accelerated protons as they pass from regions of high magnetic flux into those of lower magnetic flux. The electrostatic force drag associated with the parallel electric field provides a substantial reduction of the wave phase velocity and increases the drift mirror instability threshold. It is shown that in a plasma with nonzero electron temperature the drift mirror mode is accompanied by the field-aligned current which varies in phase with the compressional changes in the magnetic field. The transition to the cold electron temperature limit is discussed.

Stationary propagating magnetic electron vortices

The nonlinear theory of the magnetic electron mode is developed. It is shown that the model equations describing this mode has stationary localized solutions of the monopole vortex type. The vortices travel in the direction perpendicular to the inhomogeneities of the plasma with a velocity determined by the ratio between the temperature perturbation and the magnetic field of the vortex. For the vortex to be stationary and localized, this velocity must be larger than the phase velocity of the linear waves.

Turbulent generation of large-scale flows and nonlinear dynamics of flute modes

Generation of large-scale flows (zonal flows and streamers) by flute mode turbulence is examined. The evolution equations for mean flow generation are obtained by averaging the model equations over fast small scales. For a system containing both drift-type waves and large-scale structures, small scales are modulated by larger scale shear flows so that energy in the small-scale component is not conserved. A WKB-type wave kinetic equation that describes the conservation (along the rays) of an action-like invariant of the flute mode turbulence with slowly varying parameters due to the mean sheared flow is formulated. The relevant action-like integral is shown to correspond to the quantity conserved for the small-scale component alone. The structure of the action integral is determined by the structure of the matrix element describing the interaction of the small-scale and large-scale component. The k-space diffusion coefficient for the zonal flows and streamers are calculated.

Effects of ion temperature gradients on the formation of drift-Alfvén vortex structures in dusty plasmas

A set of equations describing the nonlinear dynamics of drift-Alfven waves in a dusty plasma accounting for the nonzero ion temperature gradients is derived. It is shown that these new equations yield a solution in the form of two-scale dipolar vortex structures propagating with velocities close to the ion-drift velocity in a narrow cone centered around the direction perpendicular to both the external magnetic field and the plasma gradient directions. The typical scales, characteristic vortex velocities as well as the relevant conditions for their existence are discussed. It is shown that nonzero ion temperature gradients substantially enlarge the range of possible propagation directions and characteristic scales of the vortex structures.

Modification of Kolmogorov spectra of weakly turbulent shear Alfvén waves by dust grains

Decay instabilities and Kolmogorov-type spectra of weakly turbulent shear-Alfven waves in dusty plasmas are analyzed in the limit when the wave dispersion is produced solely by the dust grain density inhomogeneity. It is shown that the reduced equations for weakly nonlinear and dispersive waves possess two conservation laws for the wave energy and generalized enstrophy. It turns out that the weakly turbulent plasma Kolmogorov spectra associated with these conservation laws are nonlocal. It is found that the presence of a dust grain inhomogeneity leads to the formation of an Iroshnikov–Kraichnan type energy spectrum related to the energy conservation law. The possibility of the existence of such spectra in space plasmas is discussed. The specific features of the obtained energy spectra can be used for the identification of dust grains in the Earth’s ionosphere, the solar wind and the interstellar medium using the data collected by magnetometers onboard satellites.