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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Ferromagnetic behavior and exchange bias effect in akaganeite nanorods

We report ferromagnetic-like properties and exchange bias effect in akaganeite (β-FeOOH) nanorods. They exhibit a Néel temperature T{sub N} = 259 K and ferromagnetic-like hysteresis behavior both below and above T{sub N}. An exchange bias effect is observed below T{sub N} and represents an interesting behavior for akaganeite nanorods. These results are explained on the basis of a core-shell structure in which the core has bulk akaganeite magnetic properties (i.e., antiferromagnetic ordering) while the shell exhibits a disordered spin state. Thus, the nanorods show ferromagnetic properties and an exchange bias effect at the same time, increasing their potential for use in practical applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Mode spectrum characteristics and onset of the low-shear MHD stability regime

Equilibria with extended regions of weak magnetic shear, including some tokamak scenarios and stellarators, can be susceptible to pressure-driven internal MHD instabilities even though there is no mode rational surface in the plasma. Nonresonant modes, in particular, can have properties that are unattractive for confinement, including displacing substantial volumes of the plasma and leading to more efficient pressure gradient flattening in the nonlinear regime. The onset and linear properties of the low shear stability regime are examined using the initial-value, extended-MHD code M3D-C. For monotonic q-profiles, we demonstrate a clear correlation between the convergents associated with the continued fraction representation of q 0 and the spectrum of unstable modes. Nonresonant modes are observed to be destabilized preferentially to any other resonant instability with the same toroidal mode number when n > 1. Using the observed connection between the spectrum associated with q 0 and the overall equilibrium stability properties, we suggest a technique for reducing the uncertainty on both q 0 and magnetic shear in the core region, obtained either via measurement or through the analysis and reconstruction of experimental results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Effects of drifts on scrape-off layer transport in W7-X

Abstract Drifts affect particle, momentum, and energy transport in the scrape-off layer (SOL) of tokamaks and stellarators, altering plasma flows and creating asymmetries between divertors. To understand how drifts affect SOL transport in the W7-X island divertor, an experiment was performed to compare plasmas with matched core parameters but opposite magnetic field directions, and therefore opposite drift transport directions. Parallel flow measurements made with coherence imaging spectroscopy are interpreted with the aid of a diagnostic forward model and a 1D simple SOL model that includes the E × B drift. In low-density plasmas ( n ‾ e < 2 × 10 19 m −3 ), the poloidal E × B drift induces a large poloidal density asymmetry within the island SOL, as measured by divertor Langmuir probes. This in turn causes the parallel flow stagnation point to shift from the position halfway between targets to the X-point in the drift direction, leading to near-unidirectional flow throughout the SOL. As density increases, the effects of the poloidal E × B drift decrease substantially, resulting in a smaller density asymmetry and the development of a counter-streaming flow pattern. For the entire density range probed in this experiment ( n ‾ e = 1.5 − 6 × 10 19 m −3 ), the experimental observations are more consistent with the effects of the poloidal E × B drift than the radial E × B drift.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Magnetic Amplifier-Based Power-Flow Controller

The concept of the magnetic amplifier, a common electromagnetic device in electronic applications in the past, has seldom been used in power systems. In this paper, we introduce the magnetic amplifier-based power-flow controller (MAPFC), an innovative low-cost device that adopts the idea of the magnetic amplifier for power-flow control applications. The uniqueness of MAPFC is in the use of the magnetization of the ferromagnetic core, shared by an ac and a dc winding, as the medium to control the ac winding reactance inserted in series with the transmission line to be controlled. Large power flow in the line can be regulated by the small dc input to the dc winding. Moreover, a project on the R&D of an MAPFC has been funded by the U.S. Department of Energy (DOE) and conducted by the Oak Ridge National Laboratory (ORNL), the University of Tennessee-Knoxville, and Waukesha Electric Systems, Inc. since early 2012. Findings from the project are presented along with some results obtained in a laboratory environment.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2022

Topological Materials with Complex Long-Range Order

The overarching vision of this proposal is to understand exotic metallic behavior in frustrated quantum magnets. This problem is at the core of understanding a number of mysteries in the study of itinerant magnetism, and of high temperature superconductivity. The central challenge is that magnetic order is generally understood by localized magnetic moments. In these systems the mobile electrons form an ordered magnetic state, sometime breaking sharp symmetry, sometimes forming incommensurate order, and other times forming a spin liquid. The present research focuses on finding complex magnets that are in close proximity to a sea of metallic, itinerant electrons.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Measurement of Magnetic Field using Doppler-Free Saturation Spectroscopy (DFSS) in C-2W FRC Plasma

The Cooperative Research and Development Agreement (CRADA) between Oak Ridge National Laboratory (ORNL) and TAE Technologies (TAE) focused on implementing an existing mobile Doppler-free saturation spectroscopy (DFSS) diagnostic to determine the direction of the equilibrium magnetic field within TAE’s C-2W field-reversed configuration (FRC) fusion device. Non-perturbative measurements of magnetic fields in the core of FRCs can provide critical information needed to constrain equilibrium models and for the continued advancement of the fusion research program at TAE. DFSS is a well-established, laser-based absorption spectroscopy technique used to suppress inhomogeneous (Doppler) broadening and reveal the Zeeman fine structure of the target emission lines. The collaboration involved the use of ORNL’s recently constructed mobile DFSS diagnostic. The DFSS diagnostic was shipped and installed on C- 2W in February 2023. TAE’s expertise was used to design and construct the mechanic support structures required to mount the optical hardware on C-2W. Additionally TAE provide critical input to minimize the noise imposed on the DFSS signal by vibrations of the mechanic support structure during operations. DFSS data was obtained for over 500 C-2W shots and will continue until the expiration of this CRADA on September 30 th 2023. Over the course of this work, significant progress was made to maximize the signal to noise (SNR) ratio. Analysis of recently acquired data is on-going, however, initial indications are highly suggestive that a DFSS signal above background has been successfully acquired in C-2W.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Final Technical Report for the SciDAC Center for the Study of Plasma Microturbulence

This final technical report for the SciDAC Center for the Study of Plasma Microturbulence documents contributions from MIT to the project over the period of the award (February 15, 2011 to February 14, 2020). This project focused on the development of neoclassical and gyrokinetic simulation capabilities relevant for the description of particle, momentum and energy transport in tokamak fusion plasmas. Extensive validation against experimental results from Alcator C-Mod and DIII-D experiments was performed. Overall areas of emphasis included gyrokinetic simulations, experiments, and observation of density gradient driven Trapped Electron Mode (TEM) turbulence relevant to burning plasmas; theory and gyrokinetic simulations of the parametric variation of the nonlinear upshift of the TEM critical density gradient; identification of a new mechanism for the isotope effect due to density gradient driven TEM turbulence; new synthetic diagnostics based on full-wave simulations which enabled unprecedented agreement between gyrokinetic simulations and measured fluctuation spectra with and without strong electron heating; development of new continuum pedestal neoclassical and turbulence codes; formulation and implementation of the first gyrokinetic exact Fokker-Planck collision operator in gyrokinetic turbulence simulations; development of new spectral approaches in velocity space for highly efficient treatments of collisions; new model collision operators implemented in the discontinuous Galerkin gyrokinetic edge turbulence code GKEYLL; and a new model and spectral code to study the interaction of ion- and electron-scale turbulence, which will serve as an efficient test-bed for multi-rate and multi-scale methods. These fundamental advances contribute to the development of a validated, predictive capability for turbulent and collisional particle, momentum and energy transport in both the core and edge of magnetically confined fusion plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

A nonmagnetic differentiated early planetary body

Paleomagnetic studies of meteorites have shown that the solar nebula was likely magnetized and that many early planetary bodies generated dynamo magnetic fields in their advecting metallic cores. The surface fields on these bodies were recorded by a diversity of chondrites and achondrites, ranging in intensity from several μT to several hundred μT. In fact, an achondrite parent body without evidence for paleomagnetic fields has yet to be confidently identified, hinting that early solar system field generation and the dynamo process in particular may have been common. Here we present paleomagnetic measurements of the ungrouped achondrite NWA 7325 indicating that it last cooled in a near-zero field (<~1.7μT), estimated to have occurred at 4563.09 ± 0.26 million years ago (Ma) from Al–Mg chronometry. Because NWA 7325 is highly depleted in siderophile elements, its parent body nevertheless underwent large-scale metal-silicate differentiation and likely formed a metallic core. This makes NWA 7325 the first recognized example of an essentially unmagnetized igneous rock from a differentiated early solar system body. These results indicate that all magnetic fields, including those from any core dynamo on the NWA 7325 parent body, the solar nebula, young Sun, and solar wind, were <1.7 μT at the location of NWA 7325 at 4563 Ma. Finally, this supports a recent conclusion that the solar nebula had dissipated by ~4 million years after solar system formation. NWA 7325 also serves as an experimental control that gives greater confidence in the positive identification of remanent magnetization in other achondrites.

36 MATERIALS SCIENCE↗
DOE OSTI2015

OBSERVED VARIABILITY OF THE SOLAR Mg II h SPECTRAL LINE

The Mg ii h and k doublet are two of the primary spectral lines observed by the Sun-pointing Interface Region Imaging Spectrograph (IRIS). These lines are tracers of the magnetic and thermal environment that spans from the photosphere to the upper chromosphere. We use a double-Gaussian model to fit the Mg ii h profile for a full-Sun mosaic data set taken on 2014 August 24. We use the ensemble of high-quality profile fits to conduct a statistical study on the variability of the line profile as it relates the magnetic structure, dynamics, and center-to-limb viewing angle. The average internetwork profile contains a deeply reversed core and is weakly asymmetric at h2. In the internetwork, we find a strong correlation between h3 wavelength and profile asymmetry as well as h1 width and h2 width. The average reversal depth of the h3 core is inversely related to the magnetic field. Plage and sunspots exhibit many profiles that do not contain a reversal. These profiles also occur infrequently in the internetwork. We see indications of magnetically aligned structures in plage and network in statistics associated with the line core, but these structures are not clear or extended in the internetwork. The center-to-limb variations are compared to predictions of semi-empirical model atmospheres. We measure a pronounced limb darkening in the line core that is not predicted by the model. The aim of this work is to provide a comprehensive measurement baseline and preliminary analysis on the observed structure and formation of the Mg ii profiles observed by IRIS.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

METGLAS 2605-SA1 core

The amorphous tape wound core is manufactured with iron-based 2605-SA1 amorphous foil. The 2605-SA1 amorphous foil is provided by METGLAS, Inc. and the core is manufactured by MK Magnetics. The 2605-SA1 amorphous foil is made up of mainly Iron, with small percentages of Silicon and Boron. Applications include transformers, pulse power cores, motors, and high frequency inductors.

36 MATERIALS SCIENCE↗
DOE OSTI2015

ZFSP Proposal: Understanding the Physics and Chemistry of Iron Alloys relevant to the Conditions of Planetary Cores

Recent research results by the deep-Earth geoscience and astronomy communities have revealed a wealth of interesting and outstanding fundamental science questions about the interiors of terrestrial planets and exoplanets including the origin of the magnetic field in the iron core and its impact on the evolution of life, the alloying of light elements on physics and chemistry of the planet’s dynamic processes, and the discovery of super-rotation and heterogeneous behavior of the inner core. Resolving these questions requires a first-hand experimental database at relevant pressure-temperature (P-T) conditions, but is technically challenging using static diamond anvil cell (DAC) and dynamic shock wave efforts alone, due to their limited P-T conditions and analytical capabilities. However, the recent advent of new capabilities of Sandia’s Z-Machine, coupled with our recent developments in in-situ ellipsometry at the UT Austin and Sandia National Laboratory and first-principles calculations and geodynamic modelling capabilities at UC Berkeley, motivates the joint collaborative effort presented here. In this collaborative research, we will use the capabilities of Sandia’s Z-Machine to investigate the elastic, thermal transport and melting properties of material relevant to both Earth and exoplanets at their relative P-T conditions. Our long-term research goal is to better understand the physics and dynamics of planetary interiors through interdisciplinary collaborations between physicists, mineral physicists, theorists, geodynamicists, and astrophysicists. The conditions in the Earth and super-Earth can range up to ~300-500 GPa and ~5000-8000 K. We will couple these experiments with a unique set of diagnostics, to include a new ellipsometry capability, in order to sensitively measure conductivity of these materials, and phase changes, including melting. Specifically, the newly demonstrated capability of Z to shock materials to a given P-T along the Hugoniot, and then to apply a pressure ramp taking the material along an isentrope, provides a unique opportunity to obtain P-T conditions not accessible by traditional DAC technology, or through shocks simply along the Hugoniot. Our physics team will perform experiments and analyze results to determine the physics underlying iron alloys as high-energy planetary impactors, classic transition metal alloys, and iron-bearing periclase relevant to the interiors of rocky planets, including exoplanets. The experimental results so analyzed will provide data that our collaborative team of mineral physicists, geodynamics, seismologists, and astrophysicists will apply toward obtaining a fundamental understanding of the physical and chemical states of the terrestrial planets and exoplanets, including their chemical compositions, thermal transport behavior, origin of magnetic fields, and dynamic evolution of the planet.

58 GEOSCIENCES↗
DOE OSTI2018

Geometries of edge and mixed dislocations in bcc Fe from first principles calculations

We use density functional theory (DFT) to compute the core structures of $a_0[100](010)$ edge, $a_0[100](011)$ edge, $a_0/2[\bar{1}\bar{1}1](1\bar{1}0)$ edge, and $a_0/2[111](1\bar{1}0)$ $71^{\circ}$ mixed dislocations in body-centered cubic (bcc) Fe. The calculations are performed using flexible boundary conditions (FBC), which effectively allow the dislocations to relax as isolated defects by coupling the DFT core to an infinite harmonic lattice through the lattice Green function (LGF). We use the LGFs of the dislocated geometries in contrast to most previous FBC-based dislocation calculations that use the LGF of the bulk crystal. The dislocation LGFs account for changes in the topology of the crystal in the core as well as local strain throughout the crystal lattice. A simple bulk-like approximation for the force constants in a dislocated geometry leads to dislocation LGFs that optimize the core structures of the $a_0[100](010)$ edge, $a_0[100](011)$ edge, and $a_0/2[111](1\bar{1}0)$ $71^{\circ}$ mixed dislocations. This approximation fails for the $a_0/2[\bar{1}\bar{1}1](1\bar{1}0)$ dislocation however, so in this case we derive the LGF from more accurate force constants computed using a Gaussian approximation potential. The standard deviations of the dislocation Nye tensor distributions quantify the widths of the dislocation cores. The relaxed cores are compact, and the local magnetic moments on the Fe atoms closely follow the volumetric strain distributions in the cores. We also compute the core structures of these dislocations using eight different classical interatomic potentials, and quantify symmetry differences between the cores using the Fourier coefficients of their Nye tensor distributions. Most of the core structures computed using the classical potentials agree well with the DFT results. Furthermore the DFT core geometries provide benchmarking for classical potential studies of work-hardening, as well as substitutional and interstitial sites for computing solute-dislocation interactions that serve as inputs for mesoscale models of solute strengthening and solute diffusion near dislocations.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Magnetars and axion-like particles: probes with the hard X-ray spectrum

Quiescent hard X-ray and soft gamma-ray emission from neutron stars constitute a promising frontier to explore axion-like-particles (ALPs). ALP production in the core peaks at energies of a few keV to a few hundreds of keV; subsequently, the ALPs escape and convert to photons in the magnetosphere. The emissivity goes as ~T 6 while the conversion probability is enhanced for large magnetic fields, making magnetars, with their high core temperatures and strong magnetic fields, ideal targets for probing ALPs. We compute the energy spectrum of photons resulting from conversion of ALPs in the magnetosphere and then compare it against hard X-ray data from NuSTAR, INTEGRAL, and XMM-Newton, for a set of eight magnetars for which such data exists. Upper limits are placed on the product of the ALP-nucleon and ALP-photon couplings. For the production in the core, we perform a calculation of the ALP emissivity in degenerate nuclear matter modeled by a relativistic mean field theory. The reduction of the emissivity due to improvements to the one-pion exchange approximation is incorporated, as is the suppression of the emissivity due to proton superfluidity in the neutron star core. A range of core temperatures is considered, corresponding to different models of the steady heat transfer from the core to the stellar surface. For the subsequent conversion, we solve the coupled differential equations mixing ALPs and photons in the magnetosphere. The conversion occurs due to a competition between the dipolar magnetic field and the photon refractive index induced by the external magnetic field. Semi-analytic expressions are provided alongside the full numerical results. Furthermore, we also present an analysis of the uncertainty on the axion limits we derive due to the uncertainties in the magnetar masses, nuclear matter equation of state, and the proton superfluid critical temperature.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Magnetic susceptibility of (Bi{sub 2-x}Sb{sub x})Te{sub 3} (0 < x < 1) alloys in the temperature range 2 to 50 K

The superconducting quantum interferometer device with Josephson junctions (SQUID magnetometer) is used to study the temperature dependences of the magnetic susceptibility of (Bi{sub 2-x}Sb{sub x})Te{sub 3} (0 < x < 1) alloy crystals in the temperature range 2 to 50 K, at the magnetic field vector H orientations H perpendiular C{sub 3} and H Up-Tack C{sub 3} with respect to the crystal trigonal axis C{sub 3}. It is found that the magnetic susceptibility of the ion core of the samples under study is {chi}{sup G} = -0.35 Multiplication-Sign 10{sup -6} cm{sup 3}/g, the contribution of lattice defects to magnetic susceptibility can be disregarded, and the contribution of free carriers is of a diamagnetic nature in the entire studied temperature range. It is shown that the contribution of free carriers to the resulting magnetic susceptibility and its anisotropy can be described within the Pauli and Landau-Peierls approach. In calculating the magnetic susceptibility, taking into account the constant concentration of free carriers in the state of pronounced degeneracy, it is found that the temperature dependence of the anisotropic effective masses varies with crystal chemical composition. This is possibly associated with the complex structure of the valence band and its variation as the Sb{sub 2}Te{sub 3} content in the alloy increases.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Magnetic nanostructures and composites for millimeter wave absorption

A product includes a nanostructure having a core and a shell. The core has a coercive field of at least 3 kOe and the shell has a saturation magnetization of at least 50 emu per gram. A product includes a nanostructure having a core and a shell. The shell has a coercive field of at least 3 kOe and the core has a saturation magnetization of at least 50 emu per gram. A method includes forming core/shell nanostructures and forming millimeter wave absorbers including the core/shell nanostructures and a support structure.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Neodymium-iron-boron magnet with selective surface modification, and method of producing same

A bulk high performance permanent magnet comprising a neodymium-iron-boron core having an outer surface, and a coercivity-enhancing element residing on at least a portion of said outer surface, with an interior portion of said neodymium-iron-boron core not having said coercivity-enhancing element therein. Also described herein is a method for producing the high-coercivity bulk permanent magnet, the method comprising: (i) depositing a coercivity-enhancing element on at least a portion of an outer surface of a neodymium-iron-boron core substrate to form a coated permanent magnet; and (ii) subjecting the coated permanent magnet to a pulse thermal process that heats said outer surface to a substantially higher temperature than an interior portion of said neodymium-iron-boron core substrate, wherein said substantially higher temperature is at least 200° C. higher than said interior portion and is of sufficient magnitude to induce diffusion of said coercivity-enhancing element below said outer surface but outside of said interior portion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Reverse Current Model for Coronal Mass Ejection Cavity Formation

In this work, we present a new model for explaining the three-part structure of coronal mass ejections (CMEs). The model proposes that the cavity in a CME forms because a rising electric current in the core prominence induces an oppositely directed electric current in the background plasma; this eddy current is required to satisfy the frozen-in magnetic flux condition in the background plasma. The magnetic force between the inner-core electric current and the oppositely directed induced eddy current propels the background plasma away from the core, creating a cavity and a density pileup at the cavity edge. The cavity radius saturates when an inward restoring force from magnetic and hydrodynamic pressure in the region outside the cavity edge balances the outward magnetic force. The model is supported by (i) laboratory experiments showing the development of a cavity as a result of the repulsion of an induced reverse current by a rising inner-core flux-rope current, (ii) 3D numerical magnetohydrodynamic (MHD) simulations that reproduce the laboratory experiments in quantitative detail, and (iii) an analytic model that describes cavity formation as a result of the plasma containing the induced reverse current being repelled from the inner core. This analytic model offers broad applicability because the predicted cavity widths are relatively independent of both the current injection mechanism and the injection timescale.

79 ASTRONOMY AND ASTROPHYSICS↗