Search NASA⌕ Search

SEARCH · Search NASA

Results for “Demagnetization”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Sub-Kelvin temperatures in space

It is pointed out that the use of temperatures below 1 K in space would provide a significant improvement in several areas of research. The sensitivity of bolometers, for instance, can be improvead by as much as a factor of 50, if the operating temperature is lowered from 1.5 K to 0.3 K. A decrease in temperature to 0.1 K can provide even an improvement up to three orders of magnitude. Detectors based on the utilization of such improvements could be employed for far-infrared (100-1000 microns) photometry and spectroscopy in the low-background conditions of space. The study of critical phenomena in He-3/He-4 mixtures is also of interest, taking into account investigations at the tricritical point (0.87 K), which represents the junction of a first-order and a second-order transition. Tests in space are needed because gravity-related effects make adequate tests on earth impossible. He-3 refrigeration can be used to attain temperatures below 1 K. Adiabatic demagnetization can produuce temperatures below 0.3 K.

Kittel, P.↗
NASA NTRS1982

History, status and future applications of spaceborne cryogenic systems

Cryogenic cooling is employed for an increasing number of space instruments. Cryogenic cooling is needed to provide the required detector response, reduce preamplifier noise, and/or reduce background radiation. Cryogenic cooling is required by instruments employed for applications missions, gamma-ray and X-ray astronomy, cosmic ray measurements, space surveillance, IR astronomy, relativity measurements, superconductivity devices, and basic research experiments. The cooling is provided with the aid of radiant coolers, stored solid cryogen coolers, stored liquid-helium coolers, mechanical coolers, He-3 coolers, adiabatic demagnetization, refrigeration, and higher temperature adsorption and magnetic systems. Radiant coolers will continue to find widespread application for low cooling-load/high-temperature situation. It is pointed out that a long-lifetime closed-cycle, mechanical cooler is one of the most critical space technological needs.

Sherman, A.↗
NASA NTRS1984

Integrated optical signal processing with magnetostatic waves

Magneto-optical devices based on Bragg diffraction of light by magnetostatic waves (MSW's) offer the potential of large time-bandwidth optical signal processing at microwave frequencies of 1 to 20 GHz and higher. A thin-film integrated-optical configuration, with the interacting MSW and guided-optical wave both propagating in a common ferrite layer, is necessary to avoid shape-factor demagnetization effects. The underlying theory of the MSW-optical interaction is outlined, including the development of expressions for optical diffraction efficiency as a function of MSW power and other relevant parameters. Bradd diffraction of guided-optical waves by transversely-propagating magnetostatic waves and collinear TE/TM mode conversion included by MSW's have been demonstrated in yttrium iron garnet (YIG) thin films. Diffraction levels as large as 4% (7 mm interaction length) and a modulation dynamic range of approx 30 dB have been observed. Advantages of these MSW-based devices over the analogous acousto-optical devices include: much greater operating frequencies, tunability of the MSW dispersion relation by varying either the RF frequency or the applied bias magnetic field, simple broad-band MSW transducer structures (e.g., a single stripline), and the potential for very high diffraction efficiencies.

Fisher, A. D.↗
NASA NTRS1984

He-3 cooling systems for space

The development of a space-compatible He(3) refrigerator would provide a significant improvement in several areas of research in the 0.3 to 1 K temperature range. There are several methods of achieving these temperatures on Earth: He(3) refrigeration, dilution refrigeration, and adiabatic demagnetization refrigeration. The progress of adapting He(3) refrigeration for use in space is described. Various cycles and possible embodiments of He(3) refrigerators are described. Also included is an analysis of the liquid confinement and liquid-vapor phase-separation system. A possible configuration is then analyzed. Finally, the results of ground-based experiments will be discussed.

Kittel, P.↗
NASA NTRS1984

Remanent magnetization of a 'paramagnetic' composition in the ilmenite-hematite solid solution stress

In the ilmenite-hematite solid solution series, compositions more ilmenite-rich than Ilm(73)Hem(27) are classically thought to be paramagnetic at room temperature. Ilm(80)Hem(20) samples have nevertheless been synthesized that acquire hard saturation remanent and thermoremanent moments. From analysis of AC demagnetization data, the source of the measured remanence is believed to be a single-domain (SD) like material within the IlM(80)Hem(20) grains themselves. On the basis of transmission electron microscope observations, it is suggested that transformation-induced domain boundaries, which in part are enriched in hematite component relative to the bulk composition of the grains, could act as the magnetic carrier of the SD-like remanence.

Lawson, C. A.↗
NASA NTRS1985

Reciprocating Magnetic Refrigerator

Unit cools to 4 K by adiabatic demagnetization. Two porous matrices of paramagnetic material gadolinium/gallium/garnet held in long piston called displacer, machined out of Micarta (phenol formaldehyde polymer). Holes in side of displacer allow heat-exchange fluid to flow to and through matrices within. Piston seals on displacer prevent substantial mixing of fluid in two loops. Magnetic refrigerator provides continuous rather than "one-shot" cooling.

Johnson, D. L.↗
NASA NTRS1984

Effects of thermal cycling on magnetic properties of lunar analogs

An experimental study has been performed to determine whether stresses associated with thermal cycling cracks can affect the coercivity of remanence carried by iron in lunar samples. Initially, samples were cycled up to 100 times in a refrigerator over a period of about 30 min per cycle. In a second set of experiments, samples were dipped directly into liquid nitrogen up to 100 times at about 1 min per cycle. Comparison of AF demagnetization curves of weak field anhysteretic remanent magnetization before and after cycling revealed no systematic differences. Calculations based on a model of spherical iron grains within olivine or troilite indicate that it is unlikely that the iron will crack under thermal stress. Thus, thermal cycling does not appear to provide an explanation for increasing the stability of remanence in samples from the lunar surface.

Barron, A. M.↗
NASA NTRS1985

Hydride absorption refrigerator system for ten Kelvin and below

A very long-life, lightweight and efficient hydride absorption refrigerator system was built to operate at ten Kelvin and below. The system consists of four basic stages of refrigeration. The first stage is accomplished by an active refrigeration system. The second stage is operated by a hydride absorption system, wherein a heated hydride powder drives off high pressure hydrogen through a Joule-Thomson/heat exchanger expansion loop such that the hydrogen is partially liquefied. In the third stage, the vapor pressure over the collected liquid hydrogen is lowered by absorbing the hydrogen vapor onto a different low pressure, worn hydride. With a 1.7 torr partial pressure of hydrogen gas in the hydride, liquid hydrogen is solidified and sublimes at 10 K. Long-life adiabatic demagnetization refrigerators, helium desorption, or helium diaphragm compressors are used to cool to 4 K or below. It is shown that the hydride concepts provide an extremely efficient means of refrigeration to 10 K, and that an entire sorption refrigeration process can be accomplished solely by using low grade heat energy at about 150 C.

Jones, J. A.↗
NASA NTRS1986

Carbon isotope evidence for a magmatic origin for Archaean gold-quartz vein ore deposits

Sediments from three sites in the Santa Barbara Basin were examined with a 160X power light microscope and TEM equipment to characterize the magnetostatic bacteria (MB) in the samples. Both the free magnetite and the crystals in the MB in the samples had lengths from 40-60 nm in length and increased in size from one end to the next. An intact magnetosome was also observed. Scanning the sediments with saturation isothermal remanent magnetization (SIRM) and altering field demagnetization techniques using a SQUID magnetometer yielded coercivity spectra which showed that the primary remanence carrier in the sediments was single domain magnetite. Although it is expected that the predominance of the bacterial magnetite component will decrease with depth in the open ocean basin, single-domain bacteria as old as 50 Myr have been observed in oceanic sediments.

Burrows, D. R.↗
NASA NTRS1986

MIPS - The Multiband Imaging Photometer for SIRTF

The Multiband Imaging Photometer for SIRTF (MIPS) is to be designed to reach as closely as possible the fundamental sensitivity and angular resolution limits for SIRTF over the 3 to 700 micron spectral region. It will use high performance photoconductive detectors from 3 to 200 micron with integrating JFET amplifiers. From 200 to 700 microns, the MIPS will use a bolometer cooled by an adiabatic demagnetization refrigerator. Over much of its operating range, the MIPS will make possible observations at and beyond the conventional Rayleigh diffraction limit of angular resolution.

Rieke, G. H.↗
NASA NTRS1986

MIPS - The Multiband Imaging Photometer for SIRTF

The Multiband Imaging Photometer System (MIPS) for SIRTF is to be designed to reach as closely as possible the fundamental sensitivity and angular resolution limits for SIRTF over the 3 to 700 microns spectral region. It will use high performance photoconductive detectors from 3 to 200 microns with integrating JFET amplifiers. From 200 to 700 microns, the MIPS will use a bolometer cooled by an adiabatic demagnetization refrigerator. Over much of its operating range, the MIPS will make possible observations at and beyond the conventional Rayleigh diffraction limit of angular resolution.

Rieke, G. H.↗
NASA NTRS1987

Cryogenics program overview

An overview of the cryogenics program of the Goddard Space Flight Center is given in viewgraph form. Goddard's role and the flight programs requiring cryogenics are outlined. Diagrams are given of the Cosmic Background Explorer, the Broad Band X-Ray Telescope, the Hubble Space Telescope, an adiabatic demagnetization refrigerator, a liquid cryogenic cooler for the Shuttle Glow Experiment, a liquid helium dewar, and the X-ray spectrometer on the Advanced X-Ray Astrophysics Facility.

Castles, Stephen H.↗
NASA NTRS1987

Ames Research Center cryogenics program

Viewgraphs describe the Ames Research Center's cryogenics program. Diagrams are given of a fluid management system, a centrifugal pump, a flow meter, a liquid helium test facility, an extra-vehicular activity coupler concept, a dewar support with passive orbital disconnect, a pulse tube refrigerator, a dilution refrigerator, and an adiabatic demagnetization cooler.

Kittel, Peter↗
NASA NTRS1988

Limiting depth of magnetization in cratonic lithosphere

Values of magnetic susceptibility and natural remanent magnetization (NRM) of clino-pyroxene-garnet-plagioclase granulite facies lower crustal xenoliths from a kimberlite in west Africa are correlated to bulk geochemistry and specific gravity. Thermomagnetic and alternating-field demagnetization analyses identify magnetite (Mt) and native iron as the dominant magnetic phases (totaling not more than 0.1 vol pct of the rocks) along with subsidiary sulfides. Oxidation states of the granulites are not greater than MW, observed Mt occurs as rims on coarse (about 1 micron) Fe particles, and inferred single domain-pseudosingle domain Mt may be a result of oxidation of fine-grained Fe. The deepest limit of lithospheric ferromagnetism is 95 km, but a limit of 70 km is most reasonable for the West African Craton and for modeling Magsat anomalies over exposed Precambrian shields.

Toft, Paul B.↗
NASA NTRS1988

Clockwise rotation of the western Mojave Desert

A study of paleomagnetic data from Miocene volcanic rocks in the western Mojave Desert, which suggests about 25 deg of clockwise rotation, is presented. A total of 166 oriented core samples of two types of basalt were taken from 19 sites in the region. After demagnetization to 40 or 60 mT, application of structural corrections, and inversion of reversed sites, the data yielded an average direction of 51.6 deg inclination and 15.6 deg declination. When compared with the expected direction for Miocene rocks for stable North America, the direction for these Mojave rocks shows a clockwise rotation of 23.8 deg + or - 11.3 deg and a flattening of about 2.1 deg, a rotation which agrees in direction with oroclinal bending of the southern Sierra Nevada due to right-lateral shear along the western margin of North America. Most of this rotation is constrained by other paleomagnetic and strucural information to have occurred soon after the sampled basalts were deposited (about 20 Ma) and before about 16 Ma. These clockwise declination anomalies indicate that any subsequent counterclockwise rotation is small and/or compensated by previous clockwise rotation.

Golombek, Matthew P.↗
NASA NTRS1988

Current developments in NASA cryogenic cooler technology

Cooler technologies that are being developed by NASA to meet the varying temperature and cooling power requirements of NASA instruments are described. In addition to providing the desired operating temperature and cooling power by stabilizing temperatures from room temperature down to 0.1 K or less, these coolers will have working lifetimes commensurate with the 10 to 15 year lifetime expected for major future NASA facilities. The types of coolers currently under development are discussed, including radiative coolers, solid cryogen coolers, surface tension confined liquid cryogen coolers, mechanical coolers, liquid helium dewars, He3 adsorption coolers, adiabatic demagnetization refrigerators, and dilution refrigerators.

Castles, Stephen H.↗
NASA NTRS1988

Field oriented control of an induction machine in a high frequency link power system

A field-oriented controlled induction machine drive operating with a high-frequency single-phase sinusoidal voltage link is presented. System performance is investigated by computer simulation and is verified by a test on a prototype system. A novel control loop to minimize the link voltage fluctuation is proposed. The capability of rapid demagnetization of the induction machine by current regulation is investigated. A current-modulation technique termed mode control is proposed, and its performance is compared with that of the conventional delta-modulation technique.

Sul, Seung K.↗
NASA NTRS1989

Magnetic-Flux-Compression Cooling Using Superconductors

Proposed magnetic-flux-compression refrigeration system produces final-stage temperatures below 4.2 K. More efficient than mechanical and sorption refrigerators at temperatures in this range. Weighs less than comparable liquid-helium-cooled superconducting magnetic refrigeration systems operating below 4.2 K. Magnetic-flux-compression cooling stage combines advantages of newly discovered superconductors with those of cooling by magnetization and demagnetization of paramagnetic salts.

Strayer, Donald M.↗