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At least 343 records · Page 19

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NASA NTRS1976

Studies of solar magnetic fields. IV - The effects of angular resolution

In order to provide a smooth transition to a smaller aperture for the Mount Wilson daily magnetograms, a two-step change was made, with two daily observations performed using two different apertures covering an interval of several months. A comparison of these observations has made possible a check on the zero-level and calibration errors of the Mount Wilson magnetograph in recent years, and it has shown that an interval of low measured total magnetic flux resulted at least in part from an increase in the mixing of magnetic elements of the two polarities on a scale comparable with the aperture size.

Howard, R.↗

NASA NTRS1981

Magnetic fields and charged particles around major planets and their satellites

It is noted that whereas Jupiter and Saturn have magnetospheres whose large-scale structure can be understood by analogy with earth, the ways in which the magnetospheres differ are of great interest. At earth, large-scale processes are dominated by convective flows of plasma driven by the solar wind. At Jupiter, centrifugal effects that are driven by planetary rotation are critical. Magnetic particle sources include not only the ionosphere and solar wind (as at earth) but also satellites and rings. The internal planetary magnetic moments controlling the scale of the magnetosphere differ by orders of magnitude between Jupiter and earth. It is pointed out that where the magnetic moments have been modeled from spacecraft data, the restricted spatial sampling has biased the results and limited confidence in details of the models. Voyager data suggest that Io may itself be magnetized and surrounded by an entirely unfamiliar type of magnetosphere.

Kivelson, M. G.↗

NASA NTRS1984

Geopotential Research Mission (GRM)

Two spacecraft, one following the other with a separation of a few hundred kilometers and orbiting at an altitude of 160 kilometers in a 90-degree polar orbit, are used to detect the minute variations in the earth's gravitational field. One spacecraft, equipped with magnetometers, will measure the vector and scalar components of the earth's magnetic field. The scientific data obtained will provide an order-of-magnitude increase beyond the present knowledge of the earth's gravitational and magnetic fields.

Keating, T.↗

NASA NTRS1974

Further analysis of field effects on liquids and solidification. Study of the liquid-solid transition for materials processing in space

Expressions for diffusion coefficient, D, and solidification rate, Uc, from the free volume model of liquids developed by Turnbull and Cohen have been used to estimate the effects which microgravity and magnetic fields will have on these quantities. The mathematical formalism describing changes in D and Uc is the same for both the microgravity and magnetic field cases, but the difference between the magnitudes of the two effects is quite large. The change in D and Uc is found to be less than 0.0001% for the microgravity case and on the order of 0.1 to 1.1% for the magnetic field case for four representative materials. D and Uc are found to increase under the influence of an applied magnetic field, and this is in agreement with experimental observations.

Seiler, R. F.↗

NASA NTRS1975

External field effects on diffusion and solidification derived from the free-volume model

Expressions for the diffusion coefficient and the solidification rate from the free-volume model of liquids developed by Turnbull and Cohen have been used to estimate the effects which microgravity and magnetic fields will have on these quantities. The mathematical formalism describing changes of the diffusion coefficient and the solidification rate is the same for both the microgravity and magnetic field cases, but the difference between the magnitudes of the two effects is quite large. The change in the two parameters is found to be less than .0001% for the microgravity case and on the order of 0.1 to 1.1% for the magnetic field case for four representative materials. The diffusion coefficient and the solidification rate are found to increase under the influence of an applied magnetic field, and this is in agreement with experimental observations.

Miller, R. I.↗

NASA NTRS1976

Evidence for opposed currents in active region loops

EUV and X-ray images of the sun are used as tracers of the magnetic-field structure in the solar atmosphere in order to study the existence of currents in active regions. Criteria are suggested for comparing the data with theoretical extrapolations of magnetic-field lines above the level of magnetograph observations. Analysis of the data presented in conjunction with force-free field calculations suggests the existence of currents flowing in opposite directions in nearby sets of loops in the active regions considered. Some simple qualitative implications of opposed current structures are suggested.

Levine, R. H.↗

NASA NTRS1993

Alignment of dust grains in ionized regions

The rate at which charged dust grains in a plasma are torqued by passing ions and electrons is calculated. When photo-emission of electrons is not important, attraction of ions by the grain monopole potential increases the rate at which the grains' spins are dealigned by nearly an order of magnitude. Consequently, the energy density of the magnetic field required to align grains in an H II region may be increased by about an order of magnitude. In contrast, electric dipole and quadrupole moments are unlikely to produce large dealignment rates for grains of modest length-to-width ratio. Nonetheless, for positively charged grains these higher-order moments likely prevent monopole repulsion of ions from reducing the dealignment rate far below that for neutral grains. The presence of positive grain charge therefore does not greatly facilitate grain alignment in an H II region.

Anderson, Nels↗

NASA NTRS1996

Design and Performance Improvements of the Prototype Open Core Flywheel Energy Storage System

A prototype magnetically suspended composite flywheel energy storage (FES) system is operating at the University of Maryland. This system, designed for spacecraft applications, incorporates recent advances in the technologies of composite materials, magnetic suspension, and permanent magnet brushless motor/generator. The current system is referred to as an Open Core Composite Flywheel (OCCF) energy storage system. This paper will present design improvements for enhanced and robust performance. Initially, when the OCCF prototype was spun above its first critical frequency of 4,500 RPM, the rotor movement would exceed the space available in the magnetic suspension gap and touchdown on the backup mechanical bearings would occur. On some occasions it was observed that, after touchdown, the rotor was unable to re-suspend as the speed decreased. Additionally, it was observed that the rotor would exhibit unstable oscillations when the control system was initially turned on. Our analysis suggested that the following problems existed: (1) The linear operating range of the magnetic bearings was limited due to electrical and magnetic saturation; (2) The inductance of the magnetic bearings was affecting the transient response of the system; (3) The flywheel was confined to a small movement because mechanical components could not be held to a tight tolerance; and (4) The location of the touchdown bearing magnifies the motion at the pole faces of the magnetic bearings when the linear range is crucial. In order to correct these problems an improved design of the flywheel energy storage system was undertaken. The magnetic bearings were re-designed to achieve a large linear operating range and to withstand load disturbances of at least 1 g. The external position transducers were replaced by a unique design which were resistant to magnetic field noise and allowed cancellation of the radial growth of the flywheel at high speeds. A central rod was utilized to ensure the concentricity of the magnetic bearings, the motor/generator, and the mechanical touchdown bearings. In addition, the mechanical touchdown bearings were placed at two ends of the magnetic bearing stack to restrict the motion at pole faces. A composite flywheel was made using a multi-ring interference assembled design for a high specific energy density. To achieve a higher speed and better efficiency, a permanent magnet DC brushless motor was specially designed and fabricated. A vacuum enclosure was constructed to eliminate windage losses for testing at high speeds. With the new improvements the OCCF system was tested to 20,000 RPM with a total stored energy of 15.9 WH and an angular momentum of 54.8 N-m-s (40.4 lb-ft-s). Motor current limitation, caused by power loss in the magnetic bearings, was identified as causing the limit in upper operating speed.

Pang, D.↗

NASA NTRS1973

Convection and magnetic fields in an atmosphere with constant temperature gradient. I - Hydrodynamic flows

In order to deduce the fluid and field conditions deep in the supergranules from the fluid motions and magnetic fields observed in the solar photosphere, it is necessary to have some idea of the depth to which the supergranules extend and the form of their internal fluid velocities. Toward this end a number of analytic solutions of the Navier-Stokes equations are given for circumstances possessing various facets of the supergranule environment in the sun. These solutions, together with the earlier work by others, shows that the granules extend to depths in excess of their mean diameters, that the convective velocities probably do not diminish much, if any, with depth, and that across the tops of the supergranules at the photosphere the horizontal velocity is more or less independent of depth.

Parker, E. N.↗

NASA NTRS1980

Magnetic clouds in the solar wind

Two interplanetary magnetic clouds, characterized by anomalous magnetic field directions and unusually high magnetic field strengths with a scale of the order of 0.25 AU, are identified and described. As the clouds moved past a spacecraft located in the solar wind near Earth, the magnetic field direction changed by rotating approximately 180 deg nearly parallel to a plane which was essentially perpendicular to the ecliptic. The configuration of the magnetic field in the clouds might be that of a tightly wound cylindrical helix or a series of closed circular loops. One of the magnetic clouds was in a cold stream preceded by a shock, and it caused both a geomagnetic storm and a depression in the galactic cosmic ray intensity. No stream, geomagnetic storm, or large cosmic ray decrease was associated with the other magnetic cloud.

Burlaga, L. F.↗

NASA NTRS2001

Magnetic Field, Force, and Inductance Computations for an Axially Symmetric Solenoid

The pumping of liquid oxygen (LOX) by magnetic fields (B field), using an array of electromagnets, is a current topic of research and development at Kennedy Space Center, FL. Oxygen is paramagnetic so that LOX, like a ferrofluid, can be forced in the direction of a B field gradient. It is well known that liquid oxygen has a sufficient magnetic susceptibility that a strong magnetic gradient can lift it in the earth's gravitational field. It has been proposed that this phenomenon can be utilized in transporting (i.e., pumping) LOX not only on earth, but on Mars and in the weightlessness of space. In order to design and evaluate such a magnetic pumping system, it is essential to compute the magnetic and force fields, as well as inductance, of various types of electromagnets (solenoids). In this application, it is assumed that the solenoids are air wrapped, and that the current is essentially time independent.

Lane, John E.↗

NASA NTRS1972

Heat conduction in a turbulent magnetic field, with application to solar-wind electrons.

Consideration of random, long-wavelength fluctuations in a turbulent magnetic field, showing that they can appreciably decrease the heat conductivity of a plasma along the magnetic field. In simple cases of interest, the reduction along the average field is approximately by the factor (cos delta theta) squared, where delta theta is the angle of the local magnetic field relative to the average field. Application to solar-wind electrons indicates that this reduction in heat conductivity due to observed fluctuations in the interplanetary magnetic field may be of the order of a factor of 2. This may help to explain recent measurements which indicate a rather low electron heat flux in the solar wind.

Hollweg, J. V.↗

NASA NTRS1980

Magnetic pumping of particles in the outer Jovian magnetosphere

The mechanism of magnetic pumping consists of two processes, the adiabatic motion of charged particles in a time varying magnetic field and their pitch-angle diffusion. The result is a systematic increase in the energy of charged particles trapped in mirror (and particularly, magnetospheric) magnetic fields. A numerical model of the mechanism is constructed, compared with analytic theory where possible, and, through elementary exercises, is used to predict the consequences of the process for cases that are not tractable by analytical means. For energy dependent pitch angle diffusion rates, characteristic 'two temperature' distributions are produced. Application of the model to the outer Jovian magnetosphere shows that beyond 20 Jupiter radii in the outer magnetosphere, particles may be magnetically pumped to energies of the order of 1 - 2 MeV. Two temperature distribution functions with "break points" at 1 - 4 KeV for electrons and 8 - 35 KeV for ions are predicted.

Borovsky, J. E.↗

NASA NTRS1980

Pioneer Venus Sounder Probe Neutral Gas Mass Spectrometer

A neutral gas mass spectrometer was flown to Venus as part of the Pioneer Venus Multiprobe to measure the composition of its lower atmosphere. The instrument, mounted in the Sounder Probe, was activated after the probe entered the top of the atmosphere, and it obtained data during the descent from 62 km to the surface. Atmospheric gases were sampled through a pair of microleaks, the effluent from which was pumped by a combination of ion and getter pumping. A pneumatically operated valve, controlled by the ambient atmospheric pressure, maintained the ion source pressure at a nearly constant value during descent while the atmospheric pressure varied by three orders of magnitude. A single focusing magnetic sector field mass spectrometer with mass resolution sufficient to reasonably separate argon from C3H4 at 40 amu provided the mass analysis and relative abundance measurements. A microprocessor controlled the operation of the mass spectrometer through a highly efficient peak-tip stepping routine and data compression algorithm that effected a scan of the mass spectrum from 1 to 208 amu in 64 sec while requiring an information rate of only 40 bits/sec to return the data to earth. A subscale height altitude resolution was thus obtained. Weight, size, and power requirements were minimized to be consistent with interplanetary flight contraints.

Hoffman, J. H.↗

NASA NTRS1980

New advances in thermal plasma research

Recent measurements obtained of the cold or thermal plasma of the earth's magnetosphere, which is believed to originate in the ionosphere, are reviewed. Consideration is given to the results of ATS 6 measurements which indicated unexpectedly high plasma temperatures and varied pitch-angle distributions, and the data from the low-energy plasma experiments on board GEOS 1 and 2 and ISEE 1, which were intended to clarify the ATS 6 results. These later measurements of ion composition, plasma energy and plasma distribution are noted to have confirmed earlier data and discovered new plasma components (D(+) or He(+2)), an intermixing of cold ionospheric plasma and hot magnetospheric plasma, the ordering of the plasma by the magnetic field rather than the ram direction in the outer magnetosphere, and wave phenomena. Questions remaining concerning the temperature and composition distributions of the plasmasphere and plasma trough, the relative densities of the cold and warmer components of the magnetosphere, plasma energization mechanisms, and the relative mix of the various plasma distributions are indicated.

Chappell, C. R.↗

NASA NTRS1981

Magnetic pumping of particles in the outer Jovian magnetosphere

The mechanism of magnetic pumping consists of two processes, the adiabatic motion of charged particles in a time-varying magnetic field and their pitch angle diffusion. The result is a systematic increase in the energy of charged particles trapped in mirror (and particularly, magnetospheric) magnetic fields. A numerical model of the mechanism is constructed, compared with analytic theory where possible, and, is used to predict the consequences of the process for cases that are not tractable by analytical means. The model is applied to the outer Jovian magnetosphere for two purposes; to find magnetospheric regions in which the mechanism may energize trapped particles, and to generate distribution functions involving pitch angle diffusion caused by wave-particle interactions. Beyond 20 Jupiter radii in the outer magnetosphere particles may be magnetically pumped to energies of the order of 1-2 MeV and two-temperature distribution functions with 'break points' at 1-4 keV for electrons and 8-35 keV for ions are predicted.

Borovsky, J. E.↗

NASA NTRS1982

Magnetohydrodynamic equilibrium. II - General integrals of the equations with one ignorable coordinate

The steady equations of hydromagnetics for the isentropic or nonisentropic flow of an inviscid magnetofluid of high electrical conductivity, with one ignorable coordinate in a general orthogonal system, are treated. Several integrals of the equations are established thereafter reducing them to a scalar, quasi-linear, second order, partial differential equation for the magnetic potential. Simple solutions of this final equation are presented. The result, together with a similar treatment of helically symmetric hydromagnetic flows presented in a subsequent paper, allows a unified and systematic approach to the solution of problems involving steady hydromagnetic fields with a topological invariance in various curvilinear coordinates.

Tsinganos, K. C.↗

NASA NTRS1983

On scaling the magnetic field strength in interstellar clouds Resolution of the 'B versus n dilemma'

Attention is given to the 'B versus n dilemma' associated with the near constancy of magnetic field strength based on H I Zeeman data over a range of gas densities. The problem is examined in terms of preferential mass flow along magnetic field lines resulting from the low thermal energy of these regions. Approximate relations have been found to scale the magnetic field strength in interstellar clouds. It is noted that the fiducial gas density for scaling the increasing magnetic field strength is 2-3 orders of magnitude above the average interstellar density often used to estimate B.

Fleck, R. C., Jr.↗