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NASA NTRS1987

Observations and theory of the AMPTE magnetotail barium releases

The barium releases in the magnetotail during the Active Magnetospheric Particle Tracer Explorers (AMPTE) operation were monitored by ground-based imagers and by instruments on the Ion Release Module. After each release, the data show the formation of a structured diamagnetic cavity. The cavity grows until the dynamic pressure of the expanding ions balances the magnetic pressure on its surface. The magnetic field inside the cavity is zero. The barium ions collect on the surface of the cavity, producing a shell. Plasma irregularities form along magnetic field lines draped over the surface of the cavity. The scale size of the irregularities is nearly equal to the thickness of the shell. The evolution and structuring of the diamagnetic cavity are modeled using magnetohydrodynamics theory.

Bernhardt, P. A.↗

NASA NTRS1987

Observation of nonlinear wave decay processes in the solar wind by the AMPTE IRM plasma wave experiment

Nonlinear wave decay processes have been detected in the solar wind by the plasma wave experiment aboard the Active Magnetospheric Particle Tracer Explorers (AMPTE) IRM spacecraft. The main process is the generation of ultralow-frequency ion acoustic waves from the decay of Langmuir waves near the electron plasma frequency. Frequently, this is accompanied by an enhancement of emissions near twice the plasma frequency. This enhancement is most likely due to the generation of electromagnetic waves from the coalescence of two Langmuir waves. These processes occur within the electron foreshock in front of the earth's bow shock.

Koons, H. C.↗

NASA NTRS1987

Simultaneous observation of Pc 3-4 pulsations in the solar wind and in the earth's magnetosphere

The equatorially orbiting Active Magnetospheric Particle Tracer Explorers CCE and IRM satellites have made numerous observations of Pc 3-4 magnetic field pulsations (10-s to 100-s period) simultaneously at locations upstream of the earth's bow shock and inside the magnetosphere. These observations show solar wind/IMF control of two categories of dayside magnetospheric pulsations. Harmonically structured, azimuthally polarized pulsations are commonly observed from L = 4 to 9 in association with upstream waves. More monochromatic compressional pulsations are clearly evident on occasion, with periods identical to those observed simultaneously in the solar wind. The observations reported here are consistent with a high-latitude (cusp) entry mechanism for wave energy related to harmonically structured pulsations.

Engebretson, M. J.↗

NASA NTRS1987

Nuclear techniques in studies of condensed matter

Nuclear techniques have played an important role in the studies of materials over the past several decades. For example, X-ray diffraction, neutron diffraction, neutron activation, and particle- or photon-induced X-ray emission techniques have been used extensively for the elucidation of structural and compositional details of materials. Several new techniques have been developed recently. Four such techniques are briefly reviewed which have great potential in the study and development of new materials. Of these four, Mossbauer spectroscopy, muon spin rotation, and positron annihilation spectroscopy techniques exploit their great sensitivity to the local atomic environments in the test materials. Interest in synchrotron radiation, on the other hand, stems from its special properties, such as high intensity, high degree of polarization, and high monochromaticity. It is hoped that this brief review will stimulate interest in the exploitation of these newer techniques for the development of improved materials.

Singh, Jag J.↗

NASA NTRS1988

The role of high energy photons and particles in accretion flows in active nuclei

The creation of high energy pairs and photons in the conversion of gravitational to thermal energy is a process common to most accretion models for active galactic nuclei. These are two observational methods designed to explore this process: direct observations of the hot photons, through hard X-ray and gamma-ray data, and indirect observations of the energetic pairs, through their polarized, nonthermal low frequency radiation. However, interpretation of these observations in terms of the conditions in the inner accretion flow requires understanding of the various processes which modify the pair and photon distributions within the hot, dense core. These processes include opacity effects within the pair/photon plasma, Compton losses on external photons, further acceleration of the pairs and further radiation by the pairs, and the dynamic interaction of the pair/photon plasma with the surrounding gas. Current observational and theoretical work is reviewed and new directions are considered in a search for constraints on or tests of accretion models of active nuclei.

Eilek, Jean A.↗

NASA NTRS1988

Nature and the nonlinear evolution of electrostatic waves associated with the AMPTE solar wind releases

The nonlinear evolution of the electrostatic waves observed during the AMPTE (Active Magnetosphere Particle Tracer Explorers) solar wind releases is investigated. Previous linear studies indicate two distinct sets of instabilities may be responsible for the generation. One set consists of ion-acoustic type instabilities which are insensitive to the presence of a background magnetic field, while the other group corresponds to the modified two stream instabilities and requires the solar wind flow to be across the ambient magnetic field. To establish which set of instabilities is more viable a detailed linear Vlasov theory has been conducted by numerically solving the full electromagnetic dispersion relation. In addition both the plasma wave as well as the magnetic field measurements by the IRM (Ion Release Module) spacecraft were used to correlate the frequency and the power of the observed waves with the magnitude and the direction of the solar wind magnetic field. The results of these analyses indicate that the ion-acoustic type instabilities have growth rates that are an order of magnitude or more larger than those of the modified two stream instabilities. Results show that both the solar wind protons and the released ions may be heated and accelerated in the directions oblique to the solar wind flow velocity.

Omidi, N.↗

NASA NTRS1988

A comparison of the plasma wave spectra for the eight AMPTE chemical releases

The Active Magnetospheric Particle Tracer Explorers (AMPTE) IRM spacecraft performed a series of eight chemical releases in essentially comparable pairs. There were two lithium releases in the solar wind, two lithium and two barium releases in the near-Earth magnetotail, and two barium releases to simulate artificial comets, one in the solar wind and the other in the magnetosheath. A variety of plasma waves were observed in conjunction with each of the releases. Although there were unique features associated with some of the individual releases, the comparable releases generally produced similar wave emissions. This paper discusses the similarities and differences among the releases.

Koons, H. C.↗

NASA NTRS1989

The equilibrium dayside magnetosphere

A method is presented of computing the dayside global earth magnetic field which is in equilibrium with the plasma pressure, based on satellite observations at a local region of the magnetosphere. The method, which utilizes a perturbation around a dipole magnetic field, involves computation of the global plasma pressure profile based on the equatorial (anisotropic) pressure data, derivation of the current profile which satisfies the equilibrium condition, and computation of the magnetic field using the current profile and the boundary current produced by the solar wind. The method is applied for the Active Magnetospheric Particle Tracer Explorers data, and the result of the computation is found to compare reasonably well with the observed magnetic field profile near the geomagnetic equator.

Zavriyev, Anton↗

NASA NTRS1989

High-frequency electrostatic waves near earth's bow shock

Electrostatic wave measurements from the Active Magnetospheric Particle Tracer Explorer Ion Release Module have been used to investigate the wave modes and their possible generation mechanisms in the earth's bow shock and magnetosheath. It is demonstrated that electrostatic waves are present in the bow shock and magnetosheath with frequencies above the maximum frequency for Doppler-shifted ion acoustic waves, yet below the plasma frequency. Waves in this frequency range are tentatively identified as electron beam mode waves. Data from 45 bow shock crossings are then used to investigate possible correlations between the electrostatic wave properties and the near-shock plasma parameters. The most significant relationships found are anticorrelations with Alfven Mach number and electron beta. Mechanisms which might produce electron beams in the shock and magnetosheath are discussed in terms of the correlation study results. These mechanisms include acceleration by the cross-shock electric field and by lower hybrid frequency waves. A magnetosheath 'time of flight' mechanism, in analogy to the electron foreshock region, is introduced as another possible beam generation mechanism.

Onsager, T. G.↗

NASA NTRS1990

Images of the AMPTE artificial comets

Ground-based low-light-level CCD image observations were conducted of both Active Magnetospheric Particle Tracer Explorer artificial comet experiments. Preliminary image processing and gridding into absolute astronomical coordinates are presented to illustrate the dynamical features of the effects. In both cases, the neutral gas expanded at about 1.4 km/sec. The resultant plasma structures corresponding to the comet's head drifted perpendicularly to the direction of the solar wind at speeds of about 3 km/sec and about 1 km/sec, respectively. For the second comet, B(+) ejection speeds of about 10 km/sec preceded the recoil effect, and downstream accelerations of about 90 m/sec-squared were observed.

Mendillo, Michael↗

NASA NTRS1990

Titanium oxide Magneli phases in four chondritic porous interplanetary dust particles

Detailed analytical electron microscope analyses of four fine-grained chondritic porous interplanetary dust particles (IDPs) reveal the presence of titanium oxide Magneli phases, Ti(n)O(2n-1) (n = 4, 5, 6), and rare Ti-metal. The association of Magneli phases, Ti-metal, and carbonaceous material in chondritic IDPs, along with the grain size distributions of Ti-metal and Magneli phases and equilibrium dissociation pressures for these oxygen-deficient Ti-oxides, support in situ solid carbon gasification in these extraterrestrial particles. The active catalyst in this process is titanium metal that may be of interstellar origin. A model is proposed that explains the higher solid carbon content of chondritic IDPs relative to bulk carbon abundances typical for carbonaceous chondrite matrices that represent another type of more metamorphosed undifferentiated solar system bodies.

Rietmeijer, E. J. M.↗

NASA NTRS1991

Gamma ray spectrometry of LDEF samples at SRS

A total of 31 samples from Long Duration Exposure Facility (LDEF), including materials of Al, V, and steel trunnions were analyzed by ultralow level gamma spectrometry. The study quantified particle induced activations of Na-22, Sc-46, Cr-51, Mn-54, Co-56, Co-57, Co-58, and Co-60. The samples of trunnion sections exhibited increasing activity toward the outer end of the trunnion and decreasing activity toward its radial center. The trunnion sections did not include an end piece that collects noticeable Be-7 on its leading surface. No significant Be-7 was detected in the samples analyzed. The most sensitive analyses were performed with a 90 pct. efficient HPGe gamma ray detector, which is enclosed in a purged active/passive active shield.

Winn, Willard G.↗

NASA NTRS1990

The AMPTE program's contribution to studies of the solar wind-magnetosphere-ionosphere interaction

The Active Magnetospheric Particle Tracer Explorers (AMPTE) program provided important information on the behavior of clouds of plasma artificially injected into the solar wind and the earth's magnetosphere. Now that the releases are over, data from the satellites are being analyzed to investigate the processes by which the ambient solar wind mass, momentum, and energy are transferred to the magnetosphere. Work in progress at APL indicates that the solar wind is much more inhomogeneous than previously believed, that the solar wind constantly buffets the magnetosphere, and that ground observers may remotely sense these interactions as geomagnetic pulsations.

Sibeck, David G.↗

NASA NTRS1990

Collisionless coupling processes in AMPTE releases

An evaluation is made of results obtained to date by in situ measurements, numerical simulations, and theoretical considerations of Active Magnetospheric Particle Tracer Explorer chemical releases bearing on the nature of collisionless coupling processes. It is noted that both laminar and turbulent forces act to couple the solar wind momentum and energy to the release cloud; the magnetic field compression formed in this interaction plays an important intermediary role in coupling the two plasmas, and the intense electrostatic turbulence generated enhances the interaction. A scenario accounting for several features in the observed evolution of the December 27, 1984 artificial comet release is presented.

Lui, A. T. Y.↗

NASA NTRS1992

The swelling mechanism of cathodes in Li/(CFx)(sub n) cells

Active material particles spatial arrangement in combination with the nature of the electrochemical reduction mechanism were found to be the major cause of excessive swelling in cathodes in Li/(CF(x))n cells. A better understanding of the chemical reaction mechanism, a possible new role for the carbon, and a model for cathode growth are discussed.

Margalit, Nehemiah↗

NASA NTRS1992

Gamma ray spectrometry of LDEF samples at SRL

A total of 31 samples from the Long Duration Exposure Facility (LDEF), including materials of aluminum, vanadium, and steel trunnions were analyzed by ultra-low-level gamma spectrometry. The study quantified particle induced activations of Na-22, Sc-46, Cr-51, Mn-54, Co-56, Co-57, Co-58, and Co-60. The samples of trunnion sections exhibited increasing activity toward the outer end of the trunnion and decreasing activity toward its radial center. The trunnion sections did not include end pieces, which were reported to collect noticeable Be-7 on their leading surfaces. No significant Be-7 was detected in the samples analyzed.

Winn, Willard G.↗

NASA NTRS1992

Origins of Energetic Ions in the Earth's Magnetosheath

The analysis and interpretation of the combined scientific data from the Hot Plasma Composition Experiment (HPCE) and the Charge Energy Mass (CHEM) spectrometer on the Active Mesospheric Particle Tracer Experiment (AMPTE) Charge Composition Explorer (CCE) spacecraft are discussed. These combined data sets have and will be used to survey the energetic ion environment in the Earth's magnetosheath to determine the origins and relative strengths of the energetic ion populations found there. A computer code was developed to analyze and interpret the data sets. The focus of the first year was on the determination of the contribution of leaked magnetospheric protons to the total energetic proton population. Emphasis was placed on intervals when the AMPTE spacecraft was in the plasma depletion layer because it was argued that in this region, only the leaked population contributes to the energetic ion population. Manipulation of the CHEM data and comparison of the CHEM and HPCE data over their common energy range near the magnetopause also contributed directly to a second study of that region.

Fuselter, S. A.↗

NASA NTRS1994

A comparison of energetic ions in the plasma depletion layer and the quasi-parallel magnetosheath

Energetic ion spectra measured by the Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer (AMPTE/CCE) downstream from the Earth's quasi-parallel bow shock (in the quasi-parallel magnetosheath) and in the plasma depletion layer are compared. In the latter region, energetic ions are from a single source, leakage of magnetospheric ions across the magnetopause and into the plasma depletion layer. In the former region, both the magnetospheric source and shock acceleration of the thermal solar wind population at the quasi-parallel shock can contribute to the energetic ion spectra. The relative strengths of these two energetic ion sources are determined through the comparison of spectra from the two regions. It is found that magnetospheric leakage can provide an upper limit of 35% of the total energetic H(+) population in the quasi-parallel magnetosheath near the magnetopause in the energy range from approximately 10 to approximately 80 keV/e and substantially less than this limit for the energetic He(2+) population. The rest of the energetic H(+) population and nearly all of the energetic He(2+) population are accelerated out of the thermal solar wind population through shock acceleration processes. By comparing the energetic and thermal He(2+) and H(+) populations in the quasi-parallel magnetosheath, it is found that the quasi-parallel bow shock is 2 to 3 times more efficient at accelerating He(2+) than H(+). This result is consistent with previous estimates from shock acceleration theory and simulati ons.

Fuselier, Stephen A.↗