Models of the earth's magnetic field
Earth geomagnetic core field model construction from land and ocean magnetometer data
MAGNETOMETER↗
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Improvements of magnetic heads through the use of new and refined core materials
A process for making ferromagnetic films with high permeability and development of the technology for fabricating a magnetic head using these films are reported. An interim head was successfully built, tested, and delivered for evaluation and a process for sputtering high permeability films has been developed. Two heads with deposited pole tips have been tested and delivered. One had a 0.0001 inch gap and the other a 0.0003 inch gap. Both heads were boned with epoxy but served to test the geometry of the head design.
Source record↗
Comparative Wide Temperature Core Loss Characteristics of Two Candidate Ferrites for the NASA/TRW 1500 W PEBB Converter
High frequency core loss and magnetization properties of commercial type MN8CX and PC40, high resistivity, MnZn based, power ferrites are presented over the temperature range of -l50 C to 150 C, at selected values of peak flux density (B (sub p)). Most of the data is at 100 kHz, with some data extended to 200 and 300 kHz for the MN8CX. Plots of the specific Core loss against temperature exhibit the minimal characteristic of such ferrites. These plots show that the MN8CX is optimized for minimum loss at about 25 C, whereas the PC40 is optimized at about 80 C. At the points of minimum loss and for the same B (sub p), the MN8CX has roughly half the losses of the PC40 at the lower flux densities. This loss ratio continues down to cryogenic temperatures. However, above about 80 C the losses are practically equal. The lowest 100 kHz loss recorded, 50 mW/cm3 for the MNGCX at a B (sub p) of 0.1T, equals that of a very low loss, Co based, transverse magnetically annealed, amorphous ribbon material. Except possibly at lower B (sub p) or much higher frequencies, these ferrites are not competitive for low losses over a wide temperature range with certain specialty amorphous materials. Permeability is computed from a linear model, plots against temperature are presented and again compared to the specialty amorphous materials.
Niedra, Janis M.↗
Elementary Theoretical Forms for the Spatial Power Spectrum of Earth's Crustal Magnetic Field
The magnetic field produced by magnetization in Earth's crust and lithosphere can be distinguished from the field produced by electric currents in Earth's core because the spatial magnetic power spectrum of the crustal field differs from that of the core field. Theoretical forms for the spectrum of the crustal field are derived by treating each magnetic domain in the crust as the point source of a dipole field. The geologic null-hypothesis that such moments are uncorrelated is used to obtain the magnetic spectrum expected from a randomly magnetized, or unstructured, spherical crust of negligible thickness. This simplest spectral form is modified to allow for uniform crustal thickness, ellipsoidality, and the polarization of domains by an periodically reversing, geocentric axial dipole field from Earth's core. Such spectra are intended to describe the background crustal field. Magnetic anomalies due to correlated magnetization within coherent geologic structures may well be superimposed upon this background; yet representing each such anomaly with a single point dipole may lead to similar spectral forms. Results from attempts to fit these forms to observational spectra, determined via spherical harmonic analysis of MAGSAT data, are summarized in terms of amplitude, source depth, and misfit. Each theoretical spectrum reduces to a source factor multiplied by the usual exponential function of spherical harmonic degree n due to geometric attenuation with attitude above the source layer. The source factors always vary with n and are approximately proportional to n(exp 3) for degrees 12 through 120. The theoretical spectra are therefore not directly proportional to an exponential function of spherical harmonic degree n. There is no radius at which these spectra are flat, level, or otherwise independent of n.
Voorhies, C.↗
The Substructure of a Flux Transfer Event Observed by the MMS Spacecraft
On 15 August 2015, MMS (Magnetospheric Multiscale mission), skimming the dusk magnetopause, detected an isolated region of an increased magnetic strength and bipolar Bn, indicating a flux transfer event (FTE). The four spacecraft in a tetrahedron allowed for investigations of the shape and motion of the FTE. In particular, high-resolution particle data facilitated our exploration of FTE substructures and their magnetic connectivity inside and surrounding the FTE. Combined field and plasma observations suggest that the core fields are open, magnetically connected to the northern magnetosphere from which high-energy particles leak; ion "D" distributions characterize the axis of flux ropes that carry old-opened field lines; counter streaming electrons superposed by parallel-heated components populate the periphery surrounding the FTE; and the interface between the core and draped regions contains a separatrix of newlyopened magnetic field lines that emanate from the X line above the FTE.
Hwang, K.-J.↗
Sensitivity of selected geomagnetic properties to truncation level of spherical harmonic expansions
The model dependence of Gauss coefficients associated with a lack of spherical harmonic orthogonality on a nonuniform Magsat data grid is shown to be minor, where the fitting level exceeds the harmonic order by a value of approximately four. The shape of the magnetic energy spectrum outside the core, and the sensitivity to truncation level of magnetic contour location and the number of their intersections on the core-mantle boundary, suggest that spherical harmonic expansions of the main geomagnetic field should be truncated at a truncation level value of not more than eight if they are to be extrapolated to the core.
Benton, E. R.↗
Open-loop characteristics of magnetic suspension systems using electromagnets mounted in a planar array
The open-loop characteristics of a Large-Gap Magnetic Suspension System (LGMSS) were studied and numerical results are presented. The LGMSS considered provides five-degree-of-freedom control. The suspended element is a cylinder that contains a core composed of permanent magnet material. The magnetic actuators are air core electromagnets mounted in a planar array. Configurations utilizing five, six, seven, and eight electromagnets were investigated and all configurations were found to be controllable from coil currents and observable from suspended element positions. Results indicate that increasing the number of coils has an insignificant effect on mode shapes and frequencies.
Groom, Nelson J.↗
Lunar magnetic permeability, magnetic fields, and electrical conductivity temperature
In the time period 1969-1972 a total of five magnetometers were deployed on the lunar surface during four Apollo missions. Data from these instruments, along with simultaneous measurements from other experiments on the moon and in lunar orbit, were used to study properties of the lunar interior and the lunar environment. The principal scientific results from analyses of the magnetic field data are discussed. The results are presented in the following main categories: (1) lunar electrical conductivity, temperature, and structure; (2) lunar magnetic permeability, iron abundance, and core size limits; (3) the local remnant magnetic fields, their interaction with the solar wind, and a thermoelectric generator model for their origin. Relevant publications and presented papers are listed.
Parkin, C. W.↗
Formation, history and energetics of cores in the terrestrial planets
The size, evolution and energetics of the earth's core and the probable central, metalic cores of Mercury, Venus, the moon and Mars are discussed. The cores of Mercury, Mars and the earth are considered likely to decrease in relative mass and volume with distance from the sun; the moon does not fit this sequence and data from Venus are insufficient. Core formation is concluded to have occurred early (prior to four billion years ago) on the earth and Mercury, while that on the moon would have occurred over a longer interval and the core of Mars would have formed much later. Of the possible energy sources in planetary cores able to maintain a molten state and drive magnetic dynamos, the energy of core formation was probably spent too early in planetary history to provide much present power, and the energy gained from freezing an inner core in the earth and Mercury are considered at best marginally able to match conductive heat loss. Future measurements proposed to improve the quantitative understanding of core properties include a better documentation of the magnetic fields of Venus and Mars and the seismometry of Mars.
Solomon, S. C.↗
Computation of flux switching in magnetic circuits.
Computation of flux switching in magnetic circuits using semiempirical models, noting ferrite core thickness effect
MAGNETIC CIRCUIT↗
Evolution of magnetized, rotating, isothermal clouds
Molecular cloud cores, in which star formation process now proceeds, are often found with elongated shape. This suggests that the core collapsed preferentially along the direction parallel to the global magnetic field and/or parallel to the cloud's initial angular momentum. Actually the magnetic field strength in the cloud has been measured recently with the Zeeman splitting (Goodman et al. 1989). The authors indicate the magnetic field of 10 to 30 mu G exists in the cloud. Further, the observation of polarization in the near IR from background stars shows that the magnetic field runs perpendicularly to the major axis of the cloud (Tamura et al. 1987). As for the angular momentum, the rotation rate of 0.2 to 6 kms s(exp -1) pc(exp -1) is reported (Goldsmith and Arquilla 1984) in 16 dark cloud regions. If the cloud collapses from the diffuse cloud with density n approx. 1 cm (exp -3) with strictly conserving the angular momentum which was shared from the galactic rotation, the rotation rate of the cloud will be x mega sub j = const approx. 3(n/1000 cm exp -3) exp 2/3 km s(exp -1) pc (exp -1) (Mouschovias 1987). The evolution of the rotating magnetized cloud is discussed here.
Tomisaka, Kohji↗
GEOMAGNETISM
Geomagnetism - role of gravitational and magnetic fields in space and earth core currents - use of satellites in electromagnetic mapping
EARTH CORE↗
Core polarization in Cr super 53.
Values for contribution of core polarization to hyperfine structure of excited states of chromium compared theoretically and experimentally, extracting core contributions to magnetic field
HYPERFINE STRUCTURE↗
Flat-band assembly for toroidal transformer cores
Toroidal transformer cores are often banded together by means of strap. Spot welds secure strap. Proper tension is obtained by use of special fixture in conjunction with winding of wire which is placed temporarily on core; winding is excited by dc current to hold core halves together magnetically during alignment.
Mclyman, W. T.↗
Multivariable frequency domain controller for magnetic suspension and balance systems
The magnetic suspension and balance system for an airplane model in a large wind tunnel is considered. In this system, superconducting coils generate magnetic forces and torques on the magnetized soft iron core of the airplane model. The control system is a position servo where the airplane model, with six degrees of feedom, follows the reference static or dynamic input commands. The controller design, based on the characteristic loci method, minimizes the effects of aerodynamic and inertial cross-couplings, and provides the specified dynamic response.
Baheti, R. S.↗
Earth's variable rotation
Recent improvements in geodetic data and practical meteorology have advanced research on fluctuations in the earth's rotation. The interpretation of these fluctuations is inextricably linked with studies of the dynamics of the earth-moon system and dynamical processes in the liquid metallic core of the earth (where the geomagnetic field originates), other parts of the earth's interior, and the hydrosphere and atmosphere. Fluctuations in the length of the day occurring on decadal time scales have implications for the topographay of the core-mantle boundary and the electrical, magnetic, ande other properties of the core and lower mantle. Investigations of more rapid fluctuations bear on meteorological studies of interannual, seasonal, and intraseasonal variations in the general circulation of the atmosphere and the response of the oceans to such variations.
Hide, Raymond↗
Polytropic relationship in interplanetary magnetic clouds
High time-resolution data from the ISEE 3 and IMP 8 spacecraft are presented for the magnetic field and the proton and electron populations of a number of magnetic clouds, in order to investigate such clouds' thermodynamics and the relationship between their magnetic and thermodynamic structures. It is judged on the basis of these data that while the magnetic flield of the cloud expands, the ions are cooled. Hot electrons are trapped by the magnetic field in the magnetic cloud's core. These conditions are favorable for the generation of ion-acoustic waves.
Osherovich, V. A.↗
Current transducer
A current transducer for rugged environments uses a solid permalloy core including a magnetic gap for a Hall effect generator and rigid mounting extensions.
McLyman, W. T.↗