Engineering topics

Khazanov, G. V.

Publications and source records attributed to Khazanov, G. V..

104 records · Page 6

NASA NTRS1997

Generalized Kinetic Description of Steady-State Collisionless Plasmas

We present a general solution to the collisionless Boltzmann (Vlasov) equation for a free-flowing plasma along a magnetic field line using Liouville's theorem, allowing for an arbitrary potential structure including non-monotonicities. The constraints of the existing collisionless kinetic transport models are explored, and the need for a more general approach to the problem of self- consistent potential energy calculations is described. Then a technique that handles an arbitrary potential energy distribution along the field line is presented and discussed. For precipitation of magnetospherically trapped hot plasma, this model yields moment calculations that vary by up to a factor of two for various potential energy structures with the same total potential drop. The differences are much greater for the high-latitude outflow scenario, giving order of magnitude variations depending on the shape of the potential energy distribution.

Khazanov, G. V.↗

NASA NTRS1997

Ponderomotive Force and Lower Hybrid Turbulence Effects in Space Plasmas Subjected to Large-Amplitude Low-Frequency Waves

In the auroral region, simultaneous occurrences of upward-flowing ions and field-aligned electrons have been observed by the Viking satellite. The occurrence is strongly correlated with large amplitude low frequency fluctuations of the electric field. Large-amplitude shear Alfven waves have also been observed by sounding rockets in the auroral ionosphere. When such LF waves are propagating in a plasma, a ponderomotive force and other types of waves are produced which may lead to significant effects on the plasma. This force is directed toward decreasing density, providing the electromagnetic lift of the background plasma and an increase of collisionless plasma expansion. We find that even for modest wave strengths, the influence on the outflowing oxygen ions can be dramatic, increasing the high-altitude density by orders of magnitude. It is also demonstrated that large-amplitude low-frequency waves (LFW) may generate lower hybrid waves (LHW) in the auroral zone. The excitation of LHW by a LF wave may lead to the appearance of an additional channel of energy transfer from, for example, Alfven or fast magnetosonic waves, to particles. This process then influences the formation of the plasma distribution function at the expense of acceleration in the tail of the distribution during the collapse of the LHW. The ion energization due to the LHW can be comparable with that produced by the ponderomotive force of the LFW. It is shown that the LH turbulence leads to equalization of the ponderomotive acceleration of the different ion species. The mechanism of LHW excitation due to the oxygen ion relative drift in a plasma subjected to low-frequency waves is used for analysis of Viking satellite data for events in the cusp/cleft region. It is found that, in some cases, such a mechanism leads to LHW energy densities and ion distribution functions close to those observed.

Khazanov, G. V.↗

NASA NTRS1997

Global Kinetic Modeling of Banded Electron Structures in the Plasmasphere

Significant fluxes of 10 eV to 30 keV electrons have been detected in the plasmasphere, appearing as banded structures in energy with broad spatial extents and slowly evolving over several days. It is thought that these populations are decaying plasma sheet electrons injected into the corotating region of near-Earth space. This capture can occur when the convective electric field drops rapidly and the Alfven boundary suddenly outward, trapping the inner edge of the plasma sheet along closed drift paths. Our bounce-averaged kinetic model of superthermal electron transport is able to simulate this capture and the subsequent drift, diffusion, and decay of the plasma cloud. Results of this simulation will be shown and discussed, from the initial injection during the elevated convection to the final loss of the particles. It is thought that not only Coulomb collisions but also wave-particle interactions play a significant role in altering the plasma cloud. Quasilinear diffusion is currently being incorporated into the model and the importance of this mechanism will be examined. Also, the high anisotropy of the trapped population could be unstable and generate plasma waves. These and other processes will be investigated to determine the final fate of the cloud and to quantify where, how, and when the energy of the plasma cloud is deposited. Comparisons with CRRES observations of these events are shown to verify the model and explain the data.

Liemohn, M. W.↗

NASA NTRS1997

Banded Electron Structure Formation in the Inner Magnetosphere

Banded electron structures in energy-time spectrograms have been observed in the inner magnetosphere concurrent with a sudden relaxation of geomagnetic activity. In this study, the formation of these banded structures is considered with a global, bounce-averaged model of electron transport, and it is concluded that this structure is a natural occurrence when plasma sheet electrons are captured on closed drift paths near the Earth. These bands do not appear unless there is capture of plasma sheet electrons; convection along open drift paths making open pass around the Earth do not have time to develop this feature. The separation of high-energy bands from the injection population due to the preferential advection of the gradient-curvature drift creates spikes in the energy distribution, which overlap to form a series of bands in the energy spectrograms. The lowest band is the bulk of the injected population in the sub-key energy range. Using the Kp history for an observed banded structure event, a cloud of plasma sheet electrons is captured and the development of their distribution function is examined and discussed.

Liemohn, M. W.↗

NASA NTRS1996

Global, Collisional Model of High-Energy Photoelectrons

A previously-developed colissional, interhemispheric flux tube model for photoelectrons (PE) has been extended to three dimensions by including transport due to vector E x vector B and magnetic gradient-curvature drifts. Using this model, initial calculations of the high-energy (greater then 50 eV) PE distribution as a function of time, energy, pitch angle, and spatial location in the equatorial plane, are reported for conditions of low geomagnetic activity. To explore both the dynamic and steady behaviors of the model, the simulation starts with the abrupt onset of photoelectron excitation, and is followed to steady state conditions. The results illustrate several features of the interaction of photoelectrons with typical magnetospheric plasmas and fields, including collisional diffusion of photoelectrons in pitch angle with flux tube filling, diurnal intensity and pitch angle asymmetries introduced by directional sunlight, and energization of the photoelectron distribution in the evening sector. Cross-field drift is shown to have a long time scale, taking 12 to 24 hours to reach a steady state distribution. Future applications of the model are briefly outlined.

Khazanov, G. V.↗

NASA NTRS1994

A bounce-averaged kinetic model of the ring current ion population

A bounced-averaged ring current kinetic model for arbitrary pitch angle, including losses due to charge exchange and Coulomb collisions along ion drift paths, is developed and solved numerically. Results from simplifield model runs, intended to illustrate the effects of adiabatic drifts and collisional losses on the proton population, are presented. The processes of: (1) particle acceleration under the conditions of time-independent magnetospheric electric fields; (2) a predominant loss of particles with small pitch angles due to charge exchange; and (3) a buildup of a low-energy population caused by the Coulomb drag energy degradation, are discussed.

Jordanova, V. K.↗

NASA NTRS1994

Thermodynamic effect of the ion sound instability in the ionosphere

During geomagnetic disturbances when the ring current interacts intensely with the plasmasphere, the plasma of this region undergoes a strong heating due to an ion cyclotron instability. This is followed by the transfer of heat along geomagnetic field lines from the heating region to the ionosphere. One of the results of this process is the formation of non-isothermal region (in which T(sub e) greater than 3.4 T(sub i) at ionospheric heights) caused by a rapid cooling the H(+) ions due to their resonant charge exchange with neutral hydrogen. Heat transfer from the top of the flux tube to the ionosphere is investigated using a hydrodynamic model for the ionosphere-plasmasphere coupling. Field-aligned currents, present in the topside ionosphere, are often accompanied by ion sound turbulence. The turbulence scatters electrons, increasing the total electron collision frequency through wave-particle effects. The influence of wave-particle interactions introduces an anomalous component to the total collision frequency, which modifies substantially the heat conduction coefficient of the plasma. As a result, the plasma is heated more intensely above than below this region of ion sound turbulence.

Khazanov, G. V.↗

NASA NTRS1994

Effect of magnetospheric convection on thermal plasma in the inner magnetosphere

The effects of E x B convection on the distribution of plasma parameters in the inner magnetosphere have been examined. Analytical solutions describing density distributions along convective trajectories in the equatorial plane have been found. These solutions suggest the following dependence of plasma concentration n on the magnetic field B along convective trajectories: n proportional to B(exp alpha), where the parameter alpha varies between alpha is less than or = between 4/3 and 2. The alpha = 2 case corresponds to disregarding transport parallel to B. The lower bound alpha = 4/3 describes the situation when parallel transport dominates over convective motions perpendicular to B. A solution has also been obtained describing the effect of convection on diffusive equilibrium profiles in the dayside plasmasphere. In addition, ion temperature variations due to adiabatic effects associated with plasma convection have been analyzed in detail. Convective drifts lead to ion temperature anisotropies with the value and sign of the anisotropy contingent on density and temperature variations, local time, and the location of the convective trajectory with respect to the location of the plasmapause. We have also found that convective motions lead to a substantial exchange of energy between the ionosphere and the plasmasphere through electron heat fluxes.

Khazanov, G. V.↗

NASA NTRS1993

Decay of equatorial ring current ions and associated aeronomical consequences

The decay of the major ion species which constitute the ring current is studied by solving the time evolution of their distribution functions during the recovery phase of a moderate geomagnetic storm. In this work, only equatorially mirroring particles are considered. Particles are assumed to move subject to E x B and gradient drifts. They also experience loses along their drift paths. Two loss mechanisms are considered: charge exchange with neutral hydrogen atoms and Coulomb collisions with thermal plasma in the plasmasphere. Thermal plasma densities are calculated with a plasmaspheric model employing a time-dependent convection electric field model. The drift-loss model successfully reproduces a number of important and observable features in the distribution function. Charge exchange is found to be the major loss mechanism for the ring current ions; however the important effects of Coulomb collisions on both the ring current and thermal populations are also presented. The model predicts the formation of a low-energy (less than 500 eV) ion population as a result of energy degradation caused by Coulomb collision of the ring current ions with the plasmaspheric electrons; this population may be one source of the low-energy ions observed during active and quiet periods in the inner magnetosphere. The energy transferred to plasmaspheric electrons through Coulomb collisions with ring current ions is believed to be the energy source for the electron temperature enhancement and the associated 6300 A (stable auroral red (SAR) arc) emission in the subauroral region. The calculated energy deposition rate is sufficient to produce a subauroral electron temperature enhancement and SAR arc emissions that are consistent with observations of these quantities during moderate magnetic activity levels.

Fok, M.-C.↗

NASA NTRS1993

Double layer propagation in experiments with electron beam injection

Electron beam injection into a plasma is investigated using the analytical inverted Bernstein-Green-Kruskal method. Particle number and momentum conservation laws are applied to evaluate the propagation velocity and potential drop on the leading edge of the beam. Electric potential is supposed to be monotonic, thus the leading front has a double-layer-like structure. For the case of cold particles, analytical expressions for the double layer velocity and potential drop are obtained. It is pointed out that double layer velocity differs from the initial electron speed: even for weak beams a noticeable deceleration takes place. Strong beams are found incapable of penetrating into plasma - their propagation velocity is very small. Ambient electrons undergo a considerable acceleration forming a return current which neutralizes the injector. Possible instability of the distribution functions is discussed.

Bruskin, L. G.↗

NASA NTRS1993

Plasma hydrodynamics in view of quasilinear effects

We have obtained expressions for the moments of the quasi-linear integral of anisotropic plasma collisions. Resonant and adiabatic interactions of particles with an arbitrary wave mode are considered. Expressions for the moments describing the interactions of ion-cyclotron waves with ring current and magnetospheric helium ions have been derived as an example, using the obtained results.

Gamaiunov, K. V.↗

NASA NTRS1992

Anisotropic ion heating and parallel O(+) acceleration in regions of rapid E x B convection

A numerical solution to the 20-moment set of transport equations has been found in order to study subauroral ionospheric outflows during periods of enhanced perpendicular ion drifts. The numerical model solves the time-dependent O(+) density, momentum, and both the parallel and perpendicular energy and heat flow equations in the 200-6000 km altitude range. Assuming perpendicular drifts of 3 km/s relative to the neutral atmosphere, we have found that anisotropic heating of O(+) (a result of ion-neutral collisions) leads to a temperature anisotropy, with perpendicular temperatures exceeding 8000 K and parallel temperatures greater than 5000 K (near 200 km altitude). Above approximately 2000 km, transport processes dominate the effects of collisions and wavelike oscillations in O(+) velocity, temperature and heat flux were noted.

Korosmezey, A.↗

NASA NTRS1992

Analytic description of the electron temperature behavior in the upper ionosphere and plasmasphere

Approximate analytic solutions to the well-known and commonly used time-dependent electron energy balance equation for the upper ionosphere and plasmasphere have been obtained and are discussed. The various potential heating sources for the terrestrial plasmasphere are summarized and the corresponding electron temperatures and related characteristic heating and cooling times are calculated. A comparison between the analytic expressions for the temperature variations and relevant measurements shows excellent agreement.

Khazanov, G. V.↗

NASA NTRS1992

An analytic model of the neutral cloud evolution in the earth's atmosphere

An analytic model for the expansion of a chemically reacting gas in the upper atmosphere is discussed. The spatial-temporal distribution of released particles in the initial regime is described on the basis of self-similar solutions of Euler's equations. In the case of transition to the diffusion regime an approximate solution of the kinetic equation with the collision integral in the form of BGK is performed. Gravitation and the atmospheric inhomogeneity are taken into account, The diffusion regime is described by an analytic solution of the diffusion equation in an exponential atmosphere taking account of possible losses of the gas due to chemical reactions. Some peculiarities of the expansion of various gases as well as the possibility of applying the model for describing ionospheric 'holes' are discussed.

Bruskin, L. G.↗