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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Hydrogen-like atoms on the surface of neutron stars - Intense magnetic field effects

It is known that very strong (greater than 1-TG) magnetic fields exist on the surface of some neutron stars. The properties of atoms in fields of this nature are considerably different from those of atoms in field-free regions. Because of the mixing of spherical and cylindrical symmetries, the analytical solution to the problem of a hydrogen atom in a uniform magnetic field is impossible to obtain. In this work, a variational wave function is used to describe the properties of hydrogen like atoms in intense magnetic fields including first-order relativistic effects. Special attention is given to the transition matrix elements for the 2p(0) - 1s(0) transition in Fe XXVI.

Williams, A. C.↗
NASA NTRS1981

An electrodynamic model of electric currents and magnetic fields in the dayside ionosphere of Venus

The electric current configuration induced in the ionosphere of Venus by the interaction of the solar wind has been calculated in previous papers (Cloutier and Daniell, 1973; Daniell and Cloutier, 1977; Cloutier and Daniell, 1979) for average steady-state solar wind conditions and interplanetary magnetic field. This model is generalized to include the effects of (1) plasma depletion and magnetic field enhancement near the ionopause, (2) velocity-shear-induced MHD instabilities of the Kelvin-Helmholtz type within the ionosphere, and (3) variations in solar wind parameters and interplanetary magnetic field. It is shown that the magnetic field configuration resulting from the model varies in response to changes in solar wind and interplanetary field conditions, and that these variations produce magnetic field profiles in excellent agreement with those seen by the Pioneer-Venus Orbiter. The formation of flux-ropes by the Kelving-Helmholtz instability is shown to be a natural consequence of the model, with the spatial distribution and size of the flux-ropes determined by the magnetic Reynolds number.

Cloutier, P. A.↗
NASA NTRS1994

Analysis of magnetic field levels at KSC

The scope of this work is to evaluate the magnetic field levels of distribution systems and other equipment at Kennedy Space Center (KSC). Magnetic fields levels in several operational areas and various facilities are investigated. Three dimensional mappings and contour are provided along with the measured data. Furthermore, the portion of magnetic fields generated by the 60 Hz fundamental frequency and the portion generated by harmonics are examined. Finally, possible mitigation techniques for attenuating fields from electric panels are discussed.

Christodoulou, Christos G.↗
NASA NTRS1983

Pair Production near Threshold in Pulsar Magnetic Fields

In pulsar polar cap models, curvature radiation gamma rays produce e(+)e(-) pairs in the strong magnetic fields near the surface of the neutron star. While these gamma rays have energies E sub gamma mc(2), they also propagate at very small angles to the fields, such that the threshold condition, E gamma 2mc(2)/sin theta is just barely satisfied when they pair produce. Threshold effects on the pair production attenuation coefficient, which are due to the discreteness of the e(+)e(-) Landau states, must therefore be considered when computing the mean free paths of curvature radiation photons in pulsar magnetic fields. These effects, which are not incorporated in the asymptotic expression for the attenuation coefficient, have some interesting consequences for pulsar models. Since pair production is suppressed near threshold, the photon mean free paths are longer than previously thought. In magnetic fields approximately 6x10 approximately G, the pairs tend to be produced in the ground state Landau level and will not synchrotron radiate. Since synchrotron radiation is an essential ingredient in the electromagnetic cascades which produce low energy pairs above the acceleration region, pulsars with very high magnetic fields may not produce many pairs.

Harding, A. K.↗
NASA NTRS1972

Inferring the interplanetary magnetic field by observing the polar geomagnetic field.

Svalgaard (1968, 1972) and Mansurov (1969) have shown that it is possible to infer the polarity of the interplanetary magnetic field quite reliably from observations of the diurnal variation of polar geomagnetic fields. The effect is most prominent in the vertical component of geomagnetic observatories near the geomagnetic poles during several hours near noon. The interplanetary magnetic field observed with spacecraft near the earth is very similar to the mean solar magnetic field (i.e., the sun observed as though it were a star); thus the fact that observations of the polar geomagnetic field have existed without interruption since 1926 at the Danish Meteorological Institute station at Godhavn, Greenland, means that in effect the inferred solar magnetic field during five sunspot cycles is available for analysis.-

Wilcox, J. M.↗
NASA NTRS1996

Plasma Properties and Magnetic Field Structure of the Solar Corona, Based on Coordinated Max 1991 Observations from SERTS, the VLA, and Magnetographs

The purposes of this investigation are to determine the plasma properties and magnetic field structure of the solar corona using coordinated observations obtained with NASA/GSFC's Solar EUV Rocket Telescope and Spectrograph (SERTS), the Very Large Array (VLA), and magnetographs. The observations were obtained under the auspices of NASA's Max '91 program. The methods of achieving the stated purposes are to use SERTS spectra and spectroheliograms to determine coronal plasma properties such as temperature, density, and emission measure. These properties are subsequently used to calculate the intensity of the thermal bremsstrahlung microwave emission from the coronal plasma (the minimum microwave intensity expected from the emitting plasma). This, in turn, can be used to establish which emission mechanism(s) contribute to the observed microwave emission. Because both mechanisms that may contribute to quiescent active region microwave emission (thermal bremsstrahlung and thermal gyroemission) depend upon the coronal magnetic field in known ways, this information can ultimately be used to derive the coronal magnetic field. Ideally, three-dimensional models of the coronal plasma and magnetic field which are consistent with all of the EUV spectra and spectroheliograms, as well as with the intensity and polarization maps at all of the microwave observing frequencies, can be derived. For completeness, the coronal magnetic field derived from the coordinated multiwaveband observations must be compared with extrapolations from photospheric magnetograms.

Brosius, Jeffrey W.↗
NASA NTRS1991

The magnitude of the magnetic field near the surface of a high-T(sub c) superconductor with a trapped flux

In 1986, much excitement was caused by the discovery of a class of materials that conducted electricity with zero resistance at temperatures above the boiling temperature of liquid nitrogen. This excitement was checked by the difficulties of manufacturing ceramics and the usefulness of high temperature superconductors that were restricted by their becoming high resistive conductors at small current densities. A lack of pinning of the magnetic field flux caused the return of high resistance as the current was increased in these materials. A study of the magnetic field near the surface of a high temperature superconductor is the first step in the search for a means of pinning the flux lines and increasing their critical current densities. The author found that a comparison between the defects in the surface of the superconductor and the magnetic field showed only a change in the field near the notch and the edge. No correlation was found between the surface grain or structure and the oscillations in the magnetic field. The observed changes in the magnetic field show resonances which may give an indication of the non-flux pinning in these superconductors. A flux pinning mechanism will increase the critical current densities; therefore, other methods of determining this field should be tried. The author proposes using a flux gate magnetometer with a detector wound on a ferrite core to measure the magnitude and direction of the magnetic field.

Overcash, Dan R.↗
NASA NTRS1985

Measurements of Solar Vector Magnetic Fields

Various aspects of the measurement of solar magnetic fields are presented. The four major subdivisions of the study are: (1) theoretical understanding of solar vector magnetic fields; (3) techniques for interpretation of observational data; and (4) techniques for data display.

Hagyard, M. J.↗
NASA NTRS1976

The large-scale magnetic field in the solar wind

A literature review is presented of theoretical models of the interaction of the solar wind and interplanetary magnetic fields. Observations of interplanetary magnetic fields by the IMP and OSO spacecraft are discussed. The causes for cosmic ray variations (Forbush decreases) by the solar wind are examined. The model of Parker is emphasized. This model shows the three dimensional magnetic field lines of the solar wind to have the form of spirals wrapped on cones. It is concluded that an out-of-the-ecliptic solar probe mission would allow the testing and verification of the various theoretical models examined. Diagrams of the various models are shown.

Burlaga, L. F.↗
NASA NTRS1996

Flow Transitions in a Rotating Magnetic Field

Critical Rayleigh numbers have been measured in a liquid metal cylinder of finite height in the presence of a rotating magnetic field. Several different stability regimes were observed, which were determined by the values of the Rayleigh and Hartmann numbers. For weak rotating magnetic fields and small Rayleigh numbers, the experimental observations can be explained by the existence of a single non-axisymmetric meridional roll rotating around the cylinder, driven by the azimuthal component of the magnetic field. The measured dependence of rotational velocity on magnetic field strength is consistent with the existence of laminar flow in this regime.

Volz, M. P.↗
NASA NTRS1978

On the apparent source depth of planetary magnetic fields

Two simple assumptions regarding the ratios of the strengths of the field contributions of the multipole moments of the terrestrial magnetic field at its effective source depth are used to examine the consistency between the apparent source depths for the magnetic fields of Mercury and Jupiter and the present understanding of their interior structure. Both fields are consistent with the present understanding. However, the comparison would be facilitated by further measurements of the magnetic fields at both planets, especially at Mercury.

Elphic, R. C.↗
NASA NTRS1991

Radiative widths and splitting of cyclotron lines in superstrong magnetic fields

The radiative line widths of the Landau levels in a superstrong magnetic field are calculated and simple analytic expressions and fits are given for these which are valid over a wide range of the principal quantum number and the magnetic field strength. If QED corrections are not taken into account, all levels but the first are doubly degenerate, corresponding to the two possible spin projections. However, the interaction with the QED vacuum removes this degeneracy, leading to an energy splitting of each level which exceeds the radiative linewidth for low Landau levels if the magnetic field is not too large (B is less than approximately 10 exp 13 G). Estimations are presented of the splitting in various limits as a function of field strength and Landau number. The possibility of observing this splitting in accreting X-ray pulsars and in gamma-ray bursters is discussed.

Pavlov, G. G.↗
NASA NTRS2003

Qualifying the Sunpower M-87N Cryocooler for Operation in the AMS-02 Magnetic Field

The Alpha Magnetic Spectrometer-02 (AMs-02) experiment consists of a superfluid helium dewar. The outer vapor cooled shields of the dewar are to be held at 77 K by four Sunpower M87N cryocoolers. These cryocoolers have magnetic components that might interact with the external applied field generated by the superconducting magnet, thereby degrading the cryocoolers' performance. Engineering models of the Sunpower M87N are being tested at NASA Goddard Space Flight in order to qualify them to operate in a magnetic environment similar to the AMS-02 magnetic environment. AMS-02 will be a space station based particle detector studying the properties and origin of cosmic particles including antimatter and dark matter. It uses a superconducting magnet that is cooled by the superfluid helium dewar. Highly sensitive detector plates inside the magnet will measure a particle's momentum and charge.

Mustafi, Shuvo↗
NASA NTRS1997

Current Collection in a Magnetic Field

It is found that the upper-bound limit for current collection in the case of strong magnetic field from the current is close to that given by the Parker-Murphy formula. This conclusion is consistent with the results obtained in laboratory experiments. This limit weakly depends on the shape of the wire. The adiabatic limit in this case will be easily surpassed due to strong magnetic field gradients near the separatrix. The calculations can be done using the kinetic equation in the drift approximation. Analytical results are obtained for the region where the Earth's magnetic field is dominant. The current collection can be calculated (neglecting scattering) using a particle simulation code. Dr. Singh has agreed to collaborate, allowing the use of his particle code. The code can be adapted for the case when the current magnetic field is strong. The needed dm for these modifications is 3-4 months. The analytical description and essential part of the program is prepared for the calculation of the current in the region where the adiabatic description can be used. This was completed with the collaboration of Drs. Khazanov and Liemohn. A scheme of measuring the end body position is also proposed. The scheme was discussed in the laboratory (with Dr. Stone) and it was concluded that it can be proposed for engineering analysis.

Krivorutsky, E. N.↗
NASA NTRS1974

Electron motion in a helically perturbed magnetic field

Exact solutions have been obtained for the equations of an electron subjected to a transverse rotating magnetic field superimposed on a homogeneous axial magnetic field. The solutions show that complete transfer of the axial energy into transverse energy is possible for a range of values of the injection velocity and the transverse magnetic field.

Singh, A.↗
NASA NTRS1991

Dynamo magnetic field modes in thin astrophysical disks - An adiabatic computational approximation

An adiabatic approximation is applied to the calculation of turbulent MHD dynamo magnetic fields in thin disks. The adiabatic method is employed to investigate conditions under which magnetic fields generated by disk dynamos permeate the entire disk or are localized to restricted regions of a disk. Two specific cases of Keplerian disks are considered. In the first, magnetic field diffusion is assumed to be dominated by turbulent mixing leading to a dynamo number independent of distance from the center of the disk. In the second, the dynamo number is allowed to vary with distance from the disk's center. Localization of dynamo magnetic field structures is found to be a general feature of disk dynamos, except in the special case of stationary modes in dynamos with constant dynamo number. The implications for the dynamical behavior of dynamo magnetized accretion disks are discussed and the results of these exploratory calculations are examined in the context of the protosolar nebula and accretion disks around compact objects.

Stepinski, T. F.↗
NASA NTRS1985

Magnetic field in the wake of Venus and the formation of ionospheric holes

Magnetic field structures are analyzed for both the ionospheric hole region and the magnetosheath/ionosphere interaction region of the nightside of Venus, in search of possible coupling between these two regimes. A magnetic coordinate system based on the directions of the solar wind and the interplanetary magnetic field is found to order the data reasonably well, allowing consistent superposition of observational data from individual passes of the Pioneer Venus orbiter. The results indicate that the magnetosheath plasma flow in the wake region plays an important role in forming the ionospheric holes through deformation of the nightside ionopause. The results are combined in a model of the three-dimensional magnetic field structure around the ionosphere of Venus.

Marubashi, K.↗