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At least 1,441 records · Page 80
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NASA NTRS1977

The Viking magnetic properties experiment - Primary mission results

Three permanent magnet arrays were mounted on each Viking lander: a strong array fixed on a photometric reference test chart on top of the landers; and two arrays, one strong and one weak, incorporated into the backhoe of the surface sampler. Some or all of the magnetic particles detected could be highly magnetic unoxidized mineral grains (metallic Fe, magnetite, pyrrhotite) forming the core beneath a reddish coating of limonite or hematite; or grains composed of gamma-Fe2O3, with and without other iron oxides; or igneous rock (or mineral particles) which consist of an admixture of unweathered silicate material or minerals with a significant fraction of highly magnetic phase, again with a reddish coating; they could be also igneous rock or mineral particles, intrinsically nonmagnetic, but having a reddish coating containing gamma-Fe2O3; or clay mineral particles which contain and/or are coated with Fe2O3, of which a substantial fraction is in the gamma-Fe2O3 form.

Hargraves, R. B.↗
NASA NTRS1977

Bright X-ray arcs and the emergence of solar magnetic flux

The Skylab S-056 and S-082A experiments and ground-based magnetograms have been used to study the role of bright X-ray arcs and the emergence of solar magnetic flux in the McMath region 12476. The S-056 X-ray images show a system of one or sometimes two bright arcs within a diffuse emitting region. The arcs seem to directly connect regions of opposite magnetic polarity in the photosphere. Magnetograms suggest the possible emergence of a magnetic flux. The width of the main arc is approximately 6 arcsec when most clearly defined, and the length is approximately 30-50 arcsec. Although the arc system is observed to vary in brightness over a period exceeding 24 hours, it remains fixed in orientation. The temperature of the main arc is approximately 3 x 10 to the 6th K. It is suggested that merging magnetic fields may provide the primary energy source, perhaps accompanied by resistive heating from a force-free current.

Chapman, G. A.↗
NASA NTRS1978

Boundary-value problem for a counterrotating electrical discharge in an axial magnetic field

An electrical discharge between two ring electrodes embedded in the mantle of a cylindrical chamber is considered, in which the plasma in the anode and cathode regions rotates in opposite directions under the influence of an external axial magnetic field. The associated boundary-value problem for the coupled partial differential equations describing the azimuthal velocity and radial current-density fields is solved in closed form. The velocity, current density, induced magnetic induction, and electric fields are presented for typical Hartmann numbers, magnetic Reynolds numbers, and geometry parameters. The discharge is shown to produce anodic and cathodic plasma sections rotating at speeds of the order 1,000,000 cm/sec for conventional magnetic field intensities. Possible application of the magnetoactive discharge as a plasma centrifuge for isotope separation is discussed.

Hong, S. H.↗
NASA NTRS1977

Crystal field and magnetic properties of ErH3

Magnetization and magnetic susceptibility measurements have been made in the temperature range 1.3 to 4.2 K on powdered samples of ErH3. The susceptibility exhibits Curie-Weiss behavior from 4.2 to 2 K, and intercepts the negative temperature axis at 1.05 + or - 0.05 K, indicating that the material is antiferromagnetic. The low field effective moment is 6.77 + or - 0.27 Bohr magnetons per ion. The magnetization exhibits a temperature independent contribution, the slope of which is (5 + or - 1.2) times 10 to the minus 6 Weber m/kg Tesla. The saturation moment is 3.84 + or - 0.15 Bohr magnetons per ion. The results can be qualitatively explained by the effects of crystal fields on the magnetic ions. No definitive assignment of a crystal field ground state can be given, nor can a clear choice between cubically or hexagonally symmetric crystal fields be made. For hexagonal symmetry, the first excited state is estimated to be 86 to 100 K above the ground state. For cubic symmetry, the splitting is of the order of 160 to 180 K.

Flood, D. J.↗
NASA NTRS1978

Ultra-low magnetic field apparatus for a cryogenic gyroscope

An ultralow magnetic field apparatus for earth-based testing of a cryogenic gyroscope system designed for a satellite test of general relativity is described. The magnetic field apparatus makes use of a superconducting lead shield while also maintaining sufficient mechanical stability to obtain a gyroscope readout sensitivity of one arcsec over a limited range. A gyroscope environment of 2.3 times 10 to the minus seventh power gauss has been attained with the magnetic field shielding technique. The magnetic field apparatus is to be used with a three-axis London moment readout system.

Cabrera, B.↗
NASA NTRS1978

Equatorial irregularity belt and its movement during a magnetic storm

Evidence for an equatorial irregularity belt and its movement during a magnetic storm has been obtained from Faraday rotation measurements at a chain of 140-MHz radio beacons receiving from the ATS-6 satellite. The stations covered a latitude region from the magnetic equator to the 45 deg N dip on the Indian subcontinent. An irregularity belt extending from the magnetic equator to about 27 deg N latitude was observed during the main phase of the magnetic storm of 10 January, 1976.

Vats, H. O.↗
NASA NTRS1978

The statistical magnetic signature of magnetospheric substorms

Daily magnetograms from a midlatitude network of geomagnetic observatories were used in the analysis of approximately 1800 substorm events, and the characteristic magnetic signatures of magnetospheric substorms both on the ground and in space were determined. Auroral electrojet (AE) indices and individual magnetograms at different local times in the auroral zone and at midlatitudes were analyzed with reference to onsets, and superposed epoch averages of individual magnetograms and AE indices confirm the local time magnetic substorm signatures. Superposed epoch averages of the interplanetary magnetic field (IMF) associated with the onsets demonstrates both a distinct southward component prior to the onsets and a dependence of the substorm amplitude on the integrated preceding southward IMF flux. Superposed epoch averages of the tail lobe magnetic field magnitude and vector components are discussed.

Caan, M. N.↗
NASA NTRS1978

The mutual attraction of magnetic knots

It is observed that the magnetic knots associated with active regions on the sun have an attraction for each other during the formative period of the active regions, when new magnetic flux is coming to the surface. The attraction disappears when new flux ceases to rise through the surface. Then the magnetic spots and knots tend to come apart, leading to disintegration of the sunspots previously formed. The dissolution of the fields is to be expected, as a consequence of the magnetic repulsion of knots of like polarity and as a consequence of the hydromagnetic exchange instability. The purpose of this paper is to show that the mutual attraction of knots during the formative stages of a sunspot region may be understood as the mutual hydrodynamic attraction of the rising flux tubes. Two rising tubes attract each other, as a consequence of the wake of the leading tube when one is moving behind the other, and as a consequence of the Bernoulli effect when rising side by side.

Parker, E. N.↗
NASA NTRS1977

Global lunar crust - Electrical conductivity and thermoelectric origin of remanent magnetism

An upper limit is placed on the average crustal conductivity from an investigation of toroidal (V x B) induction in the moon, using ten-minute data intervals of simultaneous lunar orbiting and surface magnetometer data. Crustal conductivity is determined as a function of crust thickness. For an average global crust thickness of about 80 km, the crust surface electrical conductivity is of the order of 1 hundred millionth mho/m. The toroidal-induction results lower the surface-conductivity limit obtained from poloidal-induction results by approximately four orders of magnitude. In addition, a thermoelectric (Seebeck effect) generator model is presented as a magnetic-field source for thermoremanent magnetization of the lunar crust during its solidification and cooling. Magnetic fields from 1000 to 10,000 gammas are calculated for various crater and crustal geometries. Solidified crustal material cooling through the iron Curie temperature in the presence of such ancient lunar fields could have received thermoremanent magnetization consistent with that measured in most returned lunar samples.

Dyal, P.↗
NASA NTRS1977

Spontaneous magnetic field generation in hypervelocity impacts

Hypervelocity impacts of meteoroids onto early planetary surfaces may have generated short-lived magnetic fields. The high specific power densities of the impacts, plasma production in the ejecta clouds, and the chemically layered targets of the meteoroids are analyzed in describing the evolution of the magnetic fields. Durations from about one millionth of a minute to one minute, as well as strengths up to 100 tesla, are posited for the impact-generated magnetic fields. The analogy of magnetic-field generation in laser-target experiments is also mentioned. The acquisition of shock remanence and thermoremanence by the ejecta and nearby rock following impact is discussed.

Srnka, L. J.↗
NASA NTRS1977

Remanent magnetization stratigraphy of lunar cores

Depth dependent fluctuations have been observed in the natural remanent magnetizations (NRM) of drive cores and drill strings from Apollo 16 and 17 missions. Partial demagnetization of unstable secondary magnetizations and identification of characteristic error signals from a core which is known to have been recently disturbed allow us to identify and isolate the stable NRM stratigraphy in double drive core 60010/60009 and drill strings 60002-60004. The observed magnetization fluctuations persist after normalization to take into account depth dependent variations in the carriers of stable NRM. We tentatively ascribe the stable NRM stratigraphy to instantaneous records of past magnetic fields at the lunar surface and suggest that the stable NRM stratigraphy technique could develop as a new relative time-stratigraphic tool, to be used with other physical measurements such as relative intensity of ferromagnetic resonance and charged particle track density to study the evolution of the lunar regolith.

Banerjee, S. K.↗
NASA NTRS1978

Mercury - Magnetic field and interior

Present-day knowledge about the planetary magnetic field and interior of Mercury is reviewed. Radar observations are discussed which delineated the correct rotation rate of Mercury (58.646 days) and the planet's 3:2 spin-orbit resonance. The data obtained in Mariner 10 magnetic-field observations during the first and third encounters with Mercury are examined in detail, and theoretical studies of the planet's interior are summarized, including both steady-state models and those describing the thermal evolution of the planet. Two possible source mechanisms for the observed intrinsic planetary magnetic field are evaluated: an active dynamo and a passive paleomagnetic field frozen into the planet's outer layers at an earlier epoch. It is noted that neither the available magnetic-field data nor models of the planetary interior permit one to distinguish uniquely between the two mechanisms. The spin-orbit commensurability of Mercury is explained in the framework of the solar tides induced in the body of the planet, a nonaxisymmetric moment of inertia, and the highly eccentric orbit of the planet.

Ness, N. F.↗
NASA NTRS1975

The fine-scale lunar magnetic field

Measurements conducted with the aid of the Apollo 15 subsatellite reported by Coleman et al. (1972) showed that the lunar field was detectable at an altitude of 100 km. Since that time there has been much activity in mapping the lunar magnetic field from orbit. A review is presented of the mapping procedure used in producing lunar field maps and an investigation is conducted of the altitude dependence of the lunar magnetic field which significantly affects these maps. Attention is also given to the history of lunar magnetic field maps, the fine-scale maps, low-altitude Apollo 16 maps, the altitude dependence, and the source of the magnetization of the lunar crust. It is found that the strong altitude dependence evident in the records is different for the three components.

Russell, C. T.↗
NASA NTRS1978

Mariner 10 magnetic field observations of the Venus wake

The paper reports on an analysis of magnetic field observations by the Mariner 10 spacecraft during approximately a one-day period ending a few hours beyond Venus encounter on February 5, 1974. The magnetic field measurements are used to study the downstream region of the solar wind-Venus interaction over a distance of about 100 Venus radii. The study characterizes the various magnetic field regions encountered behind and near the planet; presents an argument that the magnetic field signatures observed are consistent with observation of either a steady or a transient wake, or at least the boundary region of such a wake, interior to a common sheath-like region; examines in detail the fluctuation and discontinuity features of these regions and compares them with those of the interplanetary medium; and summarizes how these new features contribute to the understanding of the solar wind-Venus interaction.

Lepping, R. P.↗
NASA NTRS1967

Stable superconducting magnet

Operation of a superconducting magnet is considered. A method is described for; (1) obtaining a relatively high current in a superconducting magnet positioned in a bath of a gas refrigerant; (2) operating a superconducting magnet at a relatively high current level without training; and (3) operating a superconducting magnet containing a plurality of turns of a niobium zirconium wire at a relatively high current level without training.

Boom, R. W.↗
NASA NTRS1979

The Moho as a magnetic boundary

Magnetic data are presented for mantle derived rocks: peridtites from St. Pauls rocks, dunite xenoliths from the kaupulehu flow in Hawaii, as well as peridolite, dunite and eclogite xenoliths from Roberts Victor, Dutoitspan, Kilbourne Hole, and San Carlos diatremes. The rocks are paramagnetic or very weakly ferromagnetic at room temperature. Saturation magnetization values range from 0.013 emu/gm to less than 0.001 emu/gm. A review of pertinent literature dealing with analysis of the minerals in mantle xenoliths provides evidence that metals and primary Fe3O4 are absent, and that complex CR, Mg, Al, and Fe spinels dominate the oxide mineralogy. All of the available evidence supports the magnetic results, indicating that the seismic MOHO is a magnetic boundary.

Wasilewski, P. J.↗
NASA NTRS1979

Design of high-perveance confined-flow guns for periodic-permanent-magnet-focused tubes

An approach to the design of high perveance, low compression guns is described in which confinement is used to stabilize the beam for subsequent periodic-permanent-magnet focusing. The computed results for two cases are presented. A magnetic boundary value problem was solved for the scalar potential from which the axial magnetic field was computed. A solution was found by iterating between Poisson's equation and the electron trajectory calculations. Magnetic field values were varied in magnitude until a laminar beam with minimum scalloping was produced.

Stankiewicz, N.↗
NASA NTRS1979

Magnetic field studies at Jupiter by Voyager 1: Preliminary results

Results obtained by the Goddard Space Flight Center magnetometers on Voyager 1 concerning the large scale configuration of the Jovian bow shock and magnetopause, and the magnetic field in both the inner and outer magnetosphere are highlighted. There is evidence that a magnetic tail extending away from the planet on the nightside is formed by the solar wind-Jovian field interaction. This is much like Earth's magnetosphere but is a new configuration for Jupiter's magnetosphere not previously considered from earlier Pioneer data. Magnetic field perturbations associated with intense electrical currents (approximately 5 x 10 to the 6th power amps) flowing near or in the magnetic flux tube linking Jupiter with the satellite Io and induced by the relative motion between Io and the co-rotating Jovian magnetosphere are analyzed and interpreted. These currents may be an important source of heating the ionosphere and interior of Io through Joule dissipation.

Ness, N. F.↗