Engineering topics

Hudson, Mary K.

Publications and source records attributed to Hudson, Mary K..

11 records

NASA NTRS2002

A Theoretical Study of the Global Geospace System Simulations

This report describes work undertaken by the principal investigator (PI) and her colleagues in three areas of research: Relativistic Electron Dynamics, Solar Energetic Particle Study, and ULF Wave Statistical Study. The researchers conducted three dimensional modeling of relativistic electron dynamics, simulated Solar Energetic Particles (SEP) trapping using a magnetohydrodynamic (MHD) code, and a study of Pc 5 magnetic pulsations.

Hudson, Mary K.↗

NASA NTRS1994

Low-frequency magnetic fluctuation spectra in the magnetosheath and plasma depletion layer

Recent observations have delineated several different kinds of enhanced magnetic fluctuation spectra below the proton cyclotron frequency in the terrestrial magnetosheath. A model is presented that represents the variation of plasma parameters across the plasma depletion layer and into the magnetosheath proper. Using this model, we find that many of the properties of the observed spectra follow directly from the predictions of linear Vlasov instability theory. The observed progression of spectral features is a natural progression from mirror mode to merged (in frequency range) proton and He(2+) cyclotron modes to bifurcated (in frequency range) cyclotron modes as plasma convects earthward in the magnetosheath. The necessary change in dispersion surface topology from separated proton and He(2+) cyclotron surfaces at low beta to merged surfaces at high beta is described.

Denton, Richard E.↗

NASA NTRS1993

Electromagnetic ion cyclotron waves in the plasma depletion layer

Results of a study of the theoretical properties of electromagnetic ion cyclotron (EMIC) waves which occur in the plasma depletion layer are presented. The analysis assumes a homogeneous plasma with the characteristics which were measured by the AMPTE/CCE satellite at 1450-1501 UT on October 5, 1984. Waves were observed in the Pc 1 frequency range below the hydrogen gyrofrequency, and these waves are identified as EMIC waves. The higher-frequency instability is driven by the temperature anisotropy of the H(+) ions, while the lower-frequency instability is driven by the temperature anisotropy of the He(2+) ions. It is argued that the higher-frequency waves will have k roughly parallel to B(0) and will be left-hand polarized, while the lower frequency wave band will have k oblique to B(0) and will be linearly polarized, in agreement with observations.

Denton, Richard E.↗

NASA NTRS1992

Acoustic double layers in multispecies plasma

The formation of acoustic double layers in the presence of two ion species is examined via a particle simulation in a 1D bounded system. The effect of having two ion components, an H(+) and an O(+) beam, on double-layer evolution from ion acoustic turbulence driven by an electron drift relative to the H(+) beam of about 0.5 u sub e, where u sub e is the electron thermal speed, is examined. It is found that acoustic double layers form in either ion species on a time scale of about 100 omega sub ps exp -1, where omega sub ps is the ion plasma frequency for species 's' and s = H or O, and for drifts relative to the electrons lower than that required for double layer formation in simulations of single ion component plasma.

Gray, Perry C.↗

NASA NTRS1992

Wave-particle interaction at the plasmasphere-ring current interface

During the plasmasphere filling process following geomagnetic storms, an outward density decrease of the cold plasma at L = 3-4 is typically observed. When this structure overlaps with the sharp inner edge of the ring current, wave activity is detected at linearly stable phase velocities. The excitation of these waves around the lower hybrid frequency and their effects on the heating of thermal ions is analyzed. It is found that lower hybrid drift waves are most effective at heating lower mass ions, e.g. plasmaspheric H(+), versus He(+), which may be heated more effectively by electromagnetic ion cyclotron waves driven unstable by the ring current loss cone.

Roth, Ilan↗

NASA NTRS1992

Loss-cone-driven ion cyclotron waves in the magnetosphere

The study examines the theoretical properties of linear ion cyclotron waves propagating in the magnetosphere at arbitrary angles to the background magnetic field. It is found that in some cases the linear wave growth of modes with oblique propagation can dominate that of the parallel propagating electromagnetic ion cyclotron (EMIC) wave. The growth rate of the loss-cone-driven mode depends strongly on the depth of the loss cone. A simple analytical theory which explains the scaling of the growth rate of the oblique mode with respect to various parameters is presented. The loss-cone-driven mode is an electromagnetic mode which is preferentially nearly linearly polarized. The wave field which results from the oblique mode in its perferentially nearly linearly polarized form are nearly perpendicular to B0 and are such that they may be difficult to distinguish from those of a linearly polarized parallel propgating EMIC wave.

Denton, Richard E.↗

NASA NTRS1990

Simulation study of ion two-stream instability in the auroral acceleration region

Particle in cell plasma simulation technique has been used to study the effect of the ion two-stream instability on hydrogen and oxygen distributions at small relative drifts. Whether heating due to parallel modes which are unstable at low drifts might be sufficient to quench oblique modes which are unstable at higher drifts is investigated. It is found that this is not the case and that the oblique modes contribute significantly to heating.

Gray, Perry C.↗

NASA NTRS1989

Excitation of linearly stable waves in a multispecies plasma

Excitation of electrostatic modes as a result of the injection of an argon beam into a multispecies plasma is investigated. It is shown that the injection of a warm artificial beam into a thermal plasma may excite waves of significant amplitude with a range of phase velocities which are linearly stable. These waves appear as a result of the correlation between motions of an individual particle in a Vlasov fluid. When the free energy is derived from a warm beam and the linear instability diminishes due to the large temperature of the beam, the competing mechanism of thermal fluctuations is responsible for the main excitation of waves. This mechanism is valid for the various modes in a multispecies plasma, with a higher enhancement at the lower-hybrid than at the ion-ion-hybrid modes.

Roth, Ilan↗

NASA NTRS1987

The excitation of the far ultraviolet electroglow emissions on Uranus, Saturn, and Jupiter

Data from Voyager 2 observations of FUV electroglow in the sunlit atmospheres of Jupiter, Saturn, and Uranus are compiled in tables and graphs and analyzed theoretically, and an excitation mechanism is proposed. This mechanism is based on local acceleration of photoelectrons and ions by the electric field (consisting of field-aligned potentials) due to an ionospheric dynamo. Anomalous resistivity and plasma instabilities induced by field-aligned currents in the ionosphere are invoked to explain the field-aligned potentials, and the processes which might give rise to such currents are further explored.

Clarke, John T.↗

NASA NTRS1987

Effect of double layers on magnetosphere-ionosphere coupling

The Earth's auroral zone contains dynamic processes occurring on scales from the length of an auroral zone field line which characterizes Alfven wave propagation to the scale of microscopic processes which occur over a few Debye lengths. These processes interact in a time-dependent fashion since the current carried by the Alfven waves can excite microscopic turbulence which can in turn provide dissipation of the Alfven wave energy. This review will first describe the dynamic aspects of auroral current structures with emphasis on consequences for models of microscopic turbulence. A number of models of microscopic turbulence will be introduced into a large-scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. In particular, the effects of a double layer electric field which scales with the plasma temperature and Debye length is compared with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is found that the double layer model is less diffusive than in the resistive model leading to the possibility of narrow, intense current structures.

Lysak, Robert L.↗

NASA NTRS1987

Effect of double layers on magnetosphere-ionosphere coupling

The dynamic aspects of auroral current structures are reviewed with emphasis on consequences for models of microscopic turbulence (MT). A number of models of MT are introduced into a large-scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. The effect of a double layer (DL) electric field which scales with the plasma temperature and the Debye length is compared with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is shown that the DL model is less diffusive than the resistive model, indicating the possibility of narrow intense current structures.

Lysak, Robert L.↗