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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Demagnetization effects on forward and reverse thresholds of M-R memory elements

A refinement in the way hard-axis demagnetizing effects are treated in multilayer M-R memory elements brings experimental and calculated results into agreement for both the forward and reverse switching thresholds. In the improved model, the nonuniform rotation of the magnetization in the elements because of edge pinning is taken into account. The demagnetizing fields are treated as corrections to the hard-axis word field rather than an addition to the anisotropy constant.

Pohm, A. V.↗
NASA NTRS1988

Adiabatic demagnetization refrigerator for use in zero gravity

In this effort, a new design concept for an adiabatic demagnetization refrigerator (ADR) that is capable of operation in zero gravity has been developed. The design uses a vortex precooler to lower the initial temperature of magnetic salt from the initial space superfluid helium dewar of 1.8 K to 1.1 K. This reduces the required maximum magnetic field from 4 Tesla to 2 Tesla. The laboratory prototype vortex precooler reached a minimum temperature of 0.78 K, and had a cooling power of 1 mW at 1.1 K. A study was conducted to determine the dependence of vortex cooler performance on system element configuration. A superfluid filled capillary heat switch was used in the design. The laboratory prototype ADR reached a minimum temperature of 0.107 K, and maintained temperatures below 0.125 K for 90 minutes. Demagnetization was carried out from a maximum field of 2 T. A soft iron shield was developed that reduced the radial central field to 1 gauss at 0.25 meters.

Dingus, Michael L.↗
NASA NTRS2005

Support of NASA ADR/ Cross-Enterprise NRA Advanced Adiabatic Demagnetization Refrigerators for Continuous Cooling from 10K to 50mK, Development of a Heat Switch

Mechanical heat switches are used in conjunction with sorption refrigerators, adiabatic demagnetization refrigerators and for other cryogenic tasks including the pre-cooling cryogenic systems. They use a mechanical actuator which closes Au plated Cu jaws on an Au plated Cu bar. The thermal conductance in the closed position is essentially independent of the area of the jaws and proportional to the force applied. It varies linearly with T. It is approximately 10mW/K for 200 N at 1.5K. In some applications, the heat switch can be driven from outside the cryostat by a rotating rod and a screw. Such heat switches are available commercially from several sources. In other applications, including systems for space, it is desirable to drive the switch using a cold linear motor, or solenoid. Superconducting windings are used at temperatures s 4.2K to minimize power dissipation, but are not appropriate for pre-cooling a system at higher temperatures. This project was intended to improve the design of solenoid activated mechanical heat switches and to provide such switches as required to support the development of Advanced Adiabatic Demagnetization Refrigerators for Continuous Cooling from 10 K to 50 mK at GSFC. By the time funding began in 5/1/01, the immediate need for mechanical heat switches at GSFC had subsided but, at the same time, the opportunity had arisen to improve the design of mechanical heat switching by incorporating a "latching solenoid". In this device, the solenoid current is required only for changing the state of the switch and not during the whole time that the switch is closed.

Richards, Paul L.↗
NASA NTRS2011

Demagnetization Tests Performed on a Linear Alternator for a Stirling Power Convertor

Demagnetization temperature of a linear alternator (LA) can be accurately predicted through an analytical Maxwell model. The M-H characteristics of the alternator magnets must be known. Vendor data are given for cube-shaped magnets, and the shape of a LA magnet may affect its magnetic properties. At GRC, M-H data are directly measured for each LA magnet. This method was validated using TDC alternator tests on the Alternator Test Rig. The analytical Maxwell modeling was utilized on a different style linear alternator to predict demagnetization temperatures for the Advanced Stirling Convertor.

Geng, Steven M.↗
NASA NTRS2016

Cold Ion Demagnetization near the X-line of Magnetic Reconnection

Although the effects of magnetic reconnection in magnetospheres can be observed at planetary scales, reconnection is initiated at electron scales in a plasma. Surrounding the electron diffusion region, there is an Ion-Decoupling Region (IDR) of the size of the ion length scales (inertial length and gyroradius). Reconnection at the Earths magnetopause often includes cold magnetospheric (few tens of eV), hot magnetospheric (10 keV), and magnetosheath (1 keV) ions, with different gyroradius length scales. We report observations of a subregion inside the IDR of the size of the cold ion population gyroradius (approx. 15 km) where the cold ions are demagnetized and accelerated parallel to the Hall electric field. Outside the subregion, cold ions follow the E x B motion together with electrons, while hot ions are demagnetized. We observe a sharp cold ion density gradient separating the two regions, which we identify as the cold and hot IDRs.

Toledo-Redondo, Serio↗
NASA NTRSDate not supplied

Development of an Ultra-Low-Temperature 5-Stage Continuous Adiabatic Demagnetization Refrigerator That Provides Cooling at Two Unique Temperatures

The cryogenics group at NASA-Goddard has built several adiabatic demagnetization refrigerators (ADRs) for cooling detectors to sub-Kelvin temperatures in a lab, balloon, or space environment. The effort presented here describes the development of a new 5-stage adiabatic demagnetization refrigerator capable of providing continuous cooling at 35 mK with a cooling power double that previously demonstrated at this temperature. It will also provide a separate continuous temperature platform near 1 K. This system will be qualified using flight-like conditions, culminating in an ADR that is ready for the rigors of spaceflight by the end of the effort.

ADR↗
NASA NTRSDate not supplied

Design and Performance of the Hitomi/XRISM Adiabatic Demagnetization Refrigerator Controller

The Resolve instrument in the recently launched X-ray Imaging and Spectroscopy Mission (XRISM) is a rebuild of the Soft X-ray Spectrometer (SXS) in Hitomi (aka Astro-H which had an unfortunately brief mission life in 2016). It is a high-resolution non-dispersive soft x-ray spectrometer from nominally 0.3 keV to 12 keV based on a calorimeter detector array operating at 50 mK with a resolution better than 7 eV FWHM at 6 keV. For such sensitive cryogenic instruments, temperature stability has a strong impact on the detector’s performance. The Adiabatic Demagnetization Refrigerator Controller (ADRC) in the XRISM Resolve instrument is an electronics box responsible for high-precision sub-K temperature readout and control of the multi-stage adiabatic demagnetization refrigerator subsystem to achieve a thermal stability better than 2.5 uK RMS (over a 10-minute interval) for the calorimeter detectors in both cryogen (liquid helium) and cryo-free modes. It has direct telemetry/command and power interfaces with the spacecraft. It also provides sensor read-out and heater circuits for decontamination of the filters in the cold aperture. As a part of the discussion on the design and performance of the ADRC, this paper will also include an overall view of the 50 mK temperature control, plus monitor and control of the aperture filter temperature for de-contamination purpose.

ADRC↗
NASA NTRSDate not supplied

Design and Performance of the Hitomi/XRISM Adiabatic Demagnetization Refrigerator Controller

The Resolve instrument in the recently launched X-ray Imaging and Spectroscopy Mission (XRISM) is a rebuild of the Soft X-ray Spectrometer (SXS) in Hitomi (aka Astro-H which had an unfortunately brief mission life in 2016). It is a high-resolution non-dispersive soft x-ray spectrometer from nominally 0.3 keV to 12 keV based on a calorimeter detector array operating at 50 mK with a resolution better than 7 eV FWHM at 6 keV. For such sensitive cryogenic instruments, temperature stability has a strong impact on the detector’s performance. The Adiabatic Demagnetization Refrigerator Controller (ADRC) in the XRISM Resolve instrument is an electronics box responsible for high-precision sub-K temperature readout and control of the multi-stage adiabatic demagnetization refrigerator subsystem to achieve a thermal stability better than 2.5 uK RMS (over a 10-minute interval) for the calorimeter detectors in both cryogen (liquid helium) and cryo-free modes. It has direct telemetry/command and power interfaces with the spacecraft. It also provides sensor read-out and heater circuits for decontamination of the filters in the cold aperture. As a part of the discussion on the design and performance of the ADRC, this paper will also include an overall view of the 50 mK temperature control, plus monitor and control of the aperture filter temperature for de-contamination purpose.

ADRC↗
DOE OSTI2026

Ultrafast local demagnetization in 𝑑 6 systems via driven Jahn-Teller distortions

Ultrafast control of spin orientations without relying on highly nonequilibrium electron distributions offers a new pathway for femtosecond spintronics. It is shown that excitation of specific vibronic modes can drive a substantial demagnetization of a local moment relative to the magnetization axis, while preserving its total spin quantum number. Using a fully quantum many-body treatment of a local 𝑆=2 (𝑑 6 ) many-body spin coupled to a driven Jahn-Teller mode with quantum dissipation, we find that the projected spin can be strongly reduced via a Jahn-Teller-induced 𝑥⁢𝑦↑→𝑦⁢𝑧/𝑧⁢𝑥↓ transition, which occurs without additional Coulomb exchange cost. The excited state subsequently relaxes back to its original electronic configuration with a rotated spin direction, enabling spin reorientation without generating a large net angular momentum in the electronic subsystem.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2012

Design of the PIXIE Adiabatic Demagnetization Refrigerators

The Primordial Inflation Explorer (PIXIE) is a proposed mission to densely map the polarization of the cosmic microwave background. It will operate in a scanning mode from a sun-synchronous orbit, using low temperature detectors (at 0.1 K) and located inside a teslescope that is cooled to approximately 2.73 K - to match the background temperature. A mechanical cryocooler operating at 4.5 K establishes a low base temperature from which two adiabatic demagnetization refrigerator (ADR) assemblies will cool the telescope and detectors. To achieve continuous scanning capability, the ADRs must operate continuously. Complicating the design are two factors: 1) the need to systematically vary the temperature of various telescope components in order to separate the small polarization signal variations from those that may arise from temperature drifts and changing gradients within the telescope, and 2) the orbital and monthly variations in lunar irradiance into the telescope barrels. These factors require the telescope ADR to reject quasi-continuous heat loads of 2-3 millwatts, while maintaining a peak heat reject rate of less than 12 milliwatts. The detector heat load at 0.1 K is comparatively small at 1-2 microwatts. This paper will describe the 3-stage and 2-stage continuous ADRs that will be used to meet the cooling power and temperature stability requirements of the PIXIE detectors and telescope.

adiabatic demagnetization refrigerator↗
NASA NTRS2014

Salt Pill Design and Fabrication for Adiabatic Demagnetization Refrigerators

The performance of an adiabatic demagnetization refrigerator (ADR) is critically dependent on the design and construction of the salt pills that produce cooling. In most cases, the primary goal is to obtain the largest cooling capacity at the low temperature end of the operating range. The realizable cooling capacity depends on a number of factors, including refrigerant mass, and how efficiently it absorbs heat from the various instrument loads. The design and optimization of "salt pills" for ADR systems depend not only on the mechanical, chemical and thermal properties of the refrigerant, but also on the range of heat fluxes that the salt pill must accommodate. Despite the fairly wide variety of refrigerants available, those used at very low temperature tend to be hydrated salts that require a dedicated thermal bus and must be hermetically sealed, while those used at higher temperature - greater than about 0.5 K - tend to be single-­‐ or poly-­‐crystals that have much simpler requirements for thermal and mechanical packaging. This paper presents a summary of strategies and techniques for designing, optimizing and fabricating salt pills for both low-­‐ and mid-­‐temperature applications.

sub-kelvin cooling↗
NASA NTRS2016

On-Orbit Operation of the Adiabatic Demagnetization Refrigerator on the Astro-H/Hitomi Soft X-ray Spectrometer Instrument

The Soft X-ray Spectrometer instrument on the Astro-H observatory contains a 6x6 array of x-ray microcalorimeters, which is cooled to 50 mK by an adiabatic demagnetization refrigerator (ADR). The ADR consists of three stages in order to provide stable detector cooling using either a 1.2 K superfluid helium bath or a 4.5 K Joule-Thomson (JT) cryocooler as its heat sink. When liquid helium is present, two of the ADRs stages are used to single-shot cool the detectors while rejecting heat to the helium. After the helium is depleted, all three stages are used to cool both the helium tank (to about 1.5 K) and the detectors (to 50 mK) using the JT cryocooler as its heat sink. The Astro-H observatory, renamed Hitomi after its successful launch in February 2016, carried approximately 36 liters of helium into orbit. On day 5, the helium had cooled sufficiently (1.4 K) to allow operation of the ADR. This paper describes the design, operation and on-orbit performance of the ADR.

sub-kelvin refrigeration↗
NASA NTRS2018

Design and On-Orbit Operation of the Adiabatic Demagnetization Refrigerator on the Hitomi Soft X-Ray Spectrometer Instrument

The Soft X-ray Spectrometer instrument on the Astro-H observatory contains a 6x6 array of x-ray microcalorimeters that is cooled to 50 mK by an adiabatic demagnetization refrigerator (ADR). The ADR consists of three stages in order to provide stable detector cooling using either a 1.2 K superfluid helium bath or a 4.5 K Joule-Thomson (JT) cryocooler as its heat sink. When liquid helium is present, two of the ADR's stages are used to single-shot cool the detectors while rejecting heat to the helium. After the helium is depleted, all three stages are used to continuously cool the helium tank (to about 1.5 K) and single-shot cool the detectors (to 50 mK), using the JT cryocooler as its heat sink. The Astro-H observatory, renamed Hitomi after its successful launch in February 2016, carried approximately 36 liters of helium into orbit. On day 5, the helium had cooled sufficiently (<1.4 K) to allow operation of the ADR. This paper describes the design, operation and on-orbit performance of the ADR, and the use of the ADR's heat rejection as a tool for mass gauging the helium tank.

adiabatic demagnetization refrigerator↗
NASA NTRS2019

Development of a Flight-Worthy 10 to 4 K Continuous Adiabatic Demagnetization Refrigerator

The cryogenics and fluids branch at NASA's Goddard Space Flight Center is currently developing a high-efficiency, vibration-free, flight-worthy Continuous Adiabatic Demagnetization Refrigerator (CADR) that consist of two modular units: one that lifts ~6 microW at 50 mK while rejecting its heat to a 4 K thermal sink, and another unit that provides a constant 4 K cooling stage while rejecting its heat to a thermal sink at 10 K. The two units are linked together via a 4 K common platform. This paper discusses the status report on the thermodynamic performance of the 4 -10 K ADR. This ADR utilizes an Nb3Sn superconducting magnet and Gadolinium Gallium Garnet (GGG) as its refrigerant. Results show that an idealized cycle, one where its hold time at 4 K is equal to the recycle time, can lift 13 mW at 4 K with a hold time of 132 seconds.

CADR↗
DOE OSTI2022

Formation of Complex Spin Textures in Thermally Demagnetized La 0.7 Sr 0.3 Mn O 3 Artificial-Spin-Ice Structures

Artificial spin ices (ASIs) have traditionally been designed such that each nanomagnet possesses a single-domain magnetic configuration that is assumed to be minimally perturbed by interisland dipolar interactions. Using x-ray photoemission electron microscopy to perform magnetic domain imaging, we study thermally demagnetized La 0.7 Sr 0.3 MnO 3 -based brickwork ASI arrays and showed that complex spin textures (CSTs) can be stabilized through an appropriate selection of nanoisland width and interisland spacing. While the width dependence can be explained through the dominance of shape anisotropy in isolated nanoislands, the ASIs we investigate demonstrate a complex dependence on both the nanoisland width and interisland spacing. Micromagnetic simulations reveal that interisland dipolar interactions play a role in the formation of CSTs, which are composed of single- and double-vortex states. Furthermore, energy analysis of the simulations provides an understanding of the system energetics that arises from a delicate balance between intraisland effects (i.e., shape anisotropy and exchange energy) and interisland effects (i.e., dipolar interactions between nearest-neighbor nanoislands).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1981

An adiabatic demagnetization refrigerator for infrared bolometers

Adiabatic demagnetization refrigerators have been built and installed in small portable liquid helium cryostats to test the feasibility of this method of cooling infrared bolometric detectors to temperatures below 0.3 K. Performance has been achieved which suggests that bolometer temperatures of 0.2 K can be maintained for periods of approximately 60 hours. Applications to sensitive infrared detection from ground-based telescopes and space satellites are discussed. Design data are given which permit the evaluation of refrigerator performance for a variety of design parameters.

Britt, R. D.↗