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Results for “Magnetic Field Measurements”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Inert gas thrusters

Inert gas thrusters have continued to be of interest for space propulsion applications. Xenon is of interest in that its physical characteristics are well suited to propulsion. High atomic weight and low tankage fraction were major factors in this choice. If a large amount of propellant was required, so that cryogenic storage was practical, argon is a more economical alternative. Argon was also the preferred propellant for ground applications of thruster technology, such as sputter etching and deposition. Additional magnetic field measurements are reported. These measurements should be of use in magnetic field design. The diffusion of electrons through the magnetic field above multipole anodes was studied in detail. The data were consistent with Bohm diffusion across a magnetic field. The theory based on Bohm diffusion was simple and easily used for diffusion calculations. Limited startup data were obtained for multipole discharge chambers. These data were obtained with refractory cathodes, but should be useful in predicting the upper limits for starting with hollow cathodes.

Kaufman, H. R.↗
NASA NTRS1980

Coordinated ionospheric and magnetospheric observations from the ISIS 2 satellite by the ISIS 2 experimenters. Volume 2: Auroral optical emissions magnetic field perturbations, and plasma characteristics, measured simultaneously on the same magnetic field line

The data set consists of a selected number of passes, each comprising a format combination that is most appropriate for the particular data set. A list of ISIS 2 experimenters, with addresses and telephone numbers is included. A brief description of the ISIS 2 satellite is given, followed by more detailed instrument descriptions, format descriptions, data set descriptions, and the data themselves.

Shepherd, G. G.↗
DOE OSTI2021

Small bore magnetic measurement system, method for measuring small bore magnets

The invention provides a system for measuring magnets, the system comprising a guide tube removably received by a beam chamber tunnel, wherein said guide tube has a first end terminating at a first end of the tunnel and a second end terminating at a second end of the tunnel; a flexible substrate removably and slidably received by the tube, wherein the flexible substrate has a first end and a second end; a first rotary stage removably attached to the first end of said flexible substrate and a second rotary stage removably attached to the second end of said flexible substrate wherein the first rotary stage and the second rotary stage effects movement of the substrate through the tube; and a Hall probe supported by the flexible substrate. Also provided is a method for measuring magnetic fields, the method comprising extending a measuring probe into a magnetic core while maintaining the probe at ambient temperature and pressure.

Kasa, Matthew T.↗
NASA NTRS2003

Cluster electric current density measurements within a magnetic flux rope in the plasma sheet

On August 22, 2001 all 4 Cluster spacecraft nearly simultaneously penetrated a magnetic flux rope in the tail. The flux rope encounter took place in the central plasma sheet, Beta(sub i) approx. 1-2, near the leading edge of a bursty bulk flow. The "time-of-flight" of the flux rope across the 4 spacecraft yielded V(sub x) approx. 700 km/s and a diameter of approx.1 R(sub e). The speed at which the flux rope moved over the spacecraft is in close agreement with the Cluster plasma measurements. The magnetic field profiles measured at each spacecraft were first modeled separately using the Lepping-Burlaga force-free flux rope model. The results indicated that the center of the flux rope passed northward (above) s/c 3, but southward (below) of s/c 1, 2 and 4. The peak electric currents along the central axis of the flux rope predicted by these single-s/c models were approx.15-19 nA/sq m. The 4-spacecraft Cluster magnetic field measurements provide a second means to determine the electric current density without any assumption regarding flux rope structure. The current profile determined using the curlometer technique was qualitatively similar to those determined by modeling the individual spacecraft magnetic field observations and yielded a peak current density of 17 nA/m2 near the central axis of the rope. However, the curlometer results also showed that the flux rope was not force-free with the component of the current density perpendicular to the magnetic field exceeding the parallel component over the forward half of the rope, perhaps due to the pressure gradients generated by the collision of the BBF with the inner magnetosphere. Hence, while the single-spacecraft models are very successful in fitting flux rope magnetic field and current variations, they do not provide a stringent test of the force-free condition.

Slavin, J. A.↗
NASA NTRS1992

Hydrogen Lyman-alpha coronagraph/polarimeter

The present treatment of vector magnetic field measurement in coronas by means of the Hanle effect of the Lyman-alpha line uses data from all-reflecting imaging coronagraph/polarimeters. The polarization sensitivity, bandpass, and spatial resolution of these instruments are defined through a modeling of the Hanle-effect signature in Lyman-alpha emission from coronal magnetic loops; the line-of-sight integration through an inhomogeneous coronal medium is taken into account. The use of the Hanle effect to measure solar corona vector magnetic fields is verified.

Fineschi, Silvano↗
NASA NTRS1977

Measurement of magnetic field aligned potential differences using high resolution conjugate photoelectron energy spectra

Simultaneous high-resolution observations of a distinctive feature in the energy spectrum of conjugate photoelectrons and spacecraft potential relative to the local ionosphere have allowed the net potential difference between magnetic conjugate points at latitudes below the region of low-energy (i.e., lower than 100 eV) auroral electron precipitation to be determined. Measurements made at 300 km from Atmosphere Explorer C show that there is normally no net potential difference between hemispheres in this region, which extended up to invariant latitudes as high as 74 deg. Two types of apparently related anomalous behavior were infrequently observed at high latitudes. During these periods the incident flux of conjugate photoelectrons was either decelerated by about 3 eV or was not detected.

Peterson, W. K.↗
DOE OSTI2022

Diagnosing magnetic fields in cylindrical implosions with oblique proton radiography

Two experiments at the OMEGA Laser System used oblique proton radiography to measure magnetic fields in cylindrical implosions with and without an applied axial magnetic field. Although the goal of both experiments was to measure the magnitude of the compressed axial magnetic field in the core of the implosion, this field was obfuscated by two features in the coronal plasma produced by the compression beams: an azimuthal self-generated magnetic field and small length scale, high-amplitude structures attributed to collisionless effects. In order to understand these features, synthetic radiographs are generated using fields produced by 3D HYDRA simulations. These synthetic radiographs reproduce the features of the experimental radiographs with the exception of the small-scale structures. A direct inversion algorithm is successfully applied to a synthetic radiograph but is only partially able to invert the experimental radiographs in part because some protons are blocked by the field coils. The origins of the radiograph features and their dependence on various experimental parameters are explored. Furthermore, the results of this analysis should inform future measurements of compressed axial magnetic fields in cylindrical implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1980

Calculations of lightning return stroke electric and magnetic fields above ground

A lightning return stroke model with which the two station electric and magnetic fields measured at ground level can be reproduced is used to compute fields at altitudes up to 10 km and at ranges from 20 m to 10 km. These calculations provide the first detailed estimates of the return strokes fields that are encountered by aircraft in flight. With the advent of modern aircraft utilizing low voltage digital electronics and reduced electromagnetic shielding by way of structures containing advanced composite materials, these calculations are of considerable practical interest. Further, since airborne electric and magnetic field measurements are presently being attempted, a comparison of the calculations presented with appropriate experimental data, when they are available, will constitute a test of the return stroke model.

Uman, M. A.↗
NASA NTRS1981

Magnetic space-based field measurements

Because the near Earth magnetic field is a complex combination of fields from outside the Earth of fields from its core and of fields from its crust, measurements from space prove to be the only practical way to obtain timely, global surveys. Due to difficulty in making accurate vector measurements, early satellites such as Sputnik and Vanguard measured only the magnitude survey. The attitude accuracy was 20 arc sec. Both the Earth's core fields and the fields arising from its crust were mapped from satellite data. The standard model of the core consists of a scalar potential represented by a spherical harmonics series. Models of the crustal field are relatively new. Mathematical representation is achieved in localized areas by arrays of dipoles appropriately located in the Earth's crust. Measurements of the Earth's field are used in navigation, to map charged particles in the magnetosphere, to study fluid properties in the Earth's core, to infer conductivity of the upper mantels, and to delineate regional scale geological features.

Langel, R. A.↗
NASA NTRS2016

Suppression of Heating of Coronal Loops Rooted in Opposite Polarity Sunspot Umbrae

EUV observations of active region (AR) coronae reveal the presence of loops at different temperatures. To understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar AR, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. From AIA 193 and 94 Å images we identify many clearly discernible coronal loops that connect plage or a sunspot of one polarity to an opposite-­polarity plage region. The AIA 94 Å images show dim regions in the umbrae of the spots. To see which coronal loops are rooted in a dim umbral area, we performed a non-linear force‐free field (NLFFF) modeling using photospheric vector magnetic field measurements obtained with the Heliosesmic Magnetic Imager (HMI) onboard SDO. The NLFFF model, validated by comparison of calculated model field lines with observed loops in AIA 193 and 94 Å, specifies the photospheric roots of the model field lines. Some model coronal magnetic field lines arch from the dim umbral area of the positive-polarity sunspot to the dim umbral area of a negative-polarity sunspot. Because these coronal loops are not visible in any of the coronal EUV and X-ray images of the AR, we conclude they are the coolest loops in the AR. This result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed.

sunspots↗
NASA NTRS2016

Suppression of Heating of Coronal Loops Rooted in Opposite Polarity Sunspot Umbrae

EUV observations of active region (AR) coronae reveal the presence of loops at different temperatures. To understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar AR, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. From AIA 193 and 94 Å images we identify many clearly discernible coronal loops that connect plage or a sunspot of one polarity to an opposite-­polarity plage region. The AIA 94 Å images show dim regions in the umbrae of the spots. To see which coronal loops are rooted in a dim umbral area, we performed a non-linear force‐free field (NLFFF) modeling using photospheric vector magnetic field measurements obtained with the Heliosesmic Magnetic Imager (HMI) onboard SDO. The NLFFF model, validated by comparison of calculated model field lines with observed loops in AIA 193 and 94 Å, specifies the photospheric roots of the model field lines. Some model coronal magnetic field lines arch from the dim umbral area of the positive-polarity sunspot to the dim umbral area of a negative-polarity sunspot. Because these coronal loops are not visible in any of the coronal EUV and X-ray images of the AR, we conclude they are the coolest loops in the AR. This result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed.

sunspot↗
NASA NTRS1979

Constraints on the origins of lunar magnetism from electron reflection measurements of surface magnetic fields

The paper describes a new method of detecting lunar surface magnetic fields, summarizes electron reflection measurements and correlations of surface field anomalies to moon geologic features, and discusses the constraints on the origin of lunar magnetism. Apollo 15 and 16 measurements of lunar surface magnetic fields by the electron reflection method show patches of strong surface fields distributed over the lunar surface, and a positive statistical correlation is found in lunar mare regions between the surface field strength and the geologic age of the surface. However, there is a lack of correlation of surface field with impact craters indicating that the mare does not have a strong large-scale uniform magnetization as may be expected from an ancient lunar dynamo. Fields were found in lunar highlands which imply that the rille has a strong magnetization associated with it as intrusive, magnetized rock or as a gap in a uniformly magnetic layer of rock.

Lin, R. P.↗
NASA NTRS1975

Synchronous Meteorological Satellite spin testing

The end-to-end spin tests conducted on the Synchronous Meteorological Satellite are described in detail. It is noted that the objective of these tests was to demonstrate that the satellite performed its intended functions under spinning conditions and that all satellite functions were tested except for solar-panel illumination, pyrotechnic-device operation, VISSR infrared operation, and auxiliary propulsion-system operation. Tests discussed include antenna pointing, S-band and UHF equivalent isotropic radiated power, output-power ripple, bit error rate, synchronous electromagnetic interference, earth width measurement, and satellite magnetic-field measurement. The purpose, technique, salient results, and problems of each test are outlined.

Mcbrady, D. J.↗
NASA NTRS1980

Cryogenic systems for spacecraft

It is noted that the use of cryogenic components on spacecraft, already quite common, will likely increase in the future. Attention is given to a number of applications including earth observation, atmospheric measurements, infrared astronomy and magnetic field measurements. These applications are discussed with regard to their cryogenic requirements. Further, four cryogenic instruments provided by the United States to be launched on spacecraft in the near future are described. Finally, other missions being planned that will use cryogenic instrumentation are also considered.

Vorreiter, J. W.↗