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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Shielding of the azimuthal magnetic field by the anode plasma in a relativistic self-magnetic-pinch diode

In relativistic electron beam diodes, the self-generated magnetic field causes electron-beam focusing at the center of the anode. Generally, plasma is formed all over the anode surface during and after the process of the beam focusing. In this work, we use visible-light Zeeman-effect spectroscopy for the determination of the magnetic field in the anode plasma in the Sandia 10 MV, 200 kA (RITS-6) electron beam diode. The magnetic field is determined from the Zeeman-dominated shapes of the Al III 4 s –4 p and C IV 3 s –3 p doublet emissions from various radial positions. Near the anode surface, due to the high plasma density, the spectral line-shapes are Stark-dominated, and only an upper limit of the magnetic field can be determined. The line-shape analysis also yields the plasma density. The data yield quantitatively the magnetic-field shielding in the plasma. In conclusion, the magnetic-field distribution in the plasma is compared to the field-diffusion prediction and found to be consistent with the Spitzer resistivity, estimated using the electron temperature and charge-state distribution determined from line intensity ratios.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Modeling inter-particle magnetic correlations in magnetite nanoparticle assemblies using x-ray magnetic scattering data

Magnetic nanoparticles are increasingly used in nanotechnologies and biomedical applications, such as drug targeting, MRI, bio-separation. Magnetite (Fe 3 O 4 ) nanoparticles stand to be effective in these roles due to the non-toxic nature of magnetite and its ease of manufacture. To be more effective in these applications, a greater understanding of the magnetic behavior of a collection of magnetite nanoparticles is needed. This research seeks to discover the local magnetic ordering of ensembles of magnetite nanoparticles occurring under various external fields. To complete this study, we use x-ray resonant magnetic scattering (XRMS). Here we discuss the modeling of the magnetic scattering data using a one-dimensional chain of nanoparticles with a mix of ferromagnetic, anti-ferromagnetic, and random orders. By fitting the model to the experimental data, we extracted information about the magnetic correlations in the nanoparticle assembly.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Estimates of the wavenumber wavelet power spectrum of magnetic fluctuations during magnetic reconnection

Fluctuation analyses of experimental observations generally lack high temporal resolution and are in frequency-space f, contrary to theoretical efforts in wavenumber-space k. This is due to the inherent limits of the Fourier transform, though it is prominent due to the ease of diagnostic implementation. Advances in wavelet-based analysis have provided relief due to its temporal resolution, but in its common use, is still hard to compare to theoretical models. By using the two-point correlation technique in conjunction with large data sets, a wavelet power spectrum in wavenumber-space can be created. Dubbed the wavenumber wavelet power spectrum, this spectrum relates wavenumber to power in time. Further, this analysis technique more closely connects characterizations of experimentally observed fluctuations with other system parameters and theoretical predictions. In this article, we develop the wavenumber wavelet power spectrum using magnetic fluctuations caused by tearing instability driven magnetic reconnection in reproducible, high temperature laboratory plasmas. These dynamic magnetic fluctuations generated in reversed field pinch plasmas are broadband, ranging from the low frequency, 10's of kHz, up to the ion gyroradii frequencies, 100's of kHz. The dominant fluctuations have poloidal and toroidal mode numbers (m,n)=(1,6−10) and can grow to 2%–3% of the mean magnetic field. During these reconnection events, ions, and electrons are energized, magnetic fluctuation amplitudes increase, plasma flow is halted, and the toroidal magnetic flux increases, all on a semi-periodic basis. The newly developed spectrum provides better temporal resolution of spectrum characteristics to correlate with these particle energization phenomena.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Sensitivity of the magnetic axis to variations in the magnetic field

Lagrangian variational principles are used to locate the magnetic axis and to determine its sensitivity to variations in the magnetic field. Only the change in the magnetic field on axis is required to determine, to lowest order, the location of the new magnetic axis. Using a simple example, namely, the magnetic field produced by a set of current-carrying filaments (a.k.a. coils), the variation in the coil geometry that induces the largest change in the magnetic axis is determined using singular value decomposition.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Pattern formation in strongly magnetized plasmas: observations from the magnetized dusty plasma experiment (MDPX) device

The last decade has seen the development of new experimental devices to explore the physics of magnetized dusty plasmas. Because of the small charge-to-mass ratio of the charged microparticles, it is necessary to operate these experiments at high magnetic fields of several Tesla in order to observe the direct effect of the magnetic forces on the transport properties of the charged microparticles. While the study of magnetized dusty plasmas is still the ultimate goal, these experiments have also provided new opportunities to studies regimes of strongly magnetized, low temperature, laboratory plasmas that have not been extensively explored. Experiments show the formation of new types of self- and imposed-ordered structures that form in both the plasma and among the microparticles. This work summarizes recent experimental observations of plasma filamentation (in the plasma) and will discuss possible connections to 'dust gridding' phenomena that are observed in the magnetized dusty plasma experiment device.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Borderline Magnetism: How Adding Mg to Paramagnetic Ce Co 3 Makes a 450-K Ferromagnet with Large Magnetic Anisotropy

A recent experimental study [Phys. Rev. Appl. 9, 024023 (2018)] on paramagnetic CeCo 3 finds that magnesium alloying induces a ferromagnetic transition with intrinsic properties large enough for permanent magnet applications. Here we explain these surprising results via a first-principles study of the electronic structure and magnetism of magnesium-alloyed CeCo 3 . We find the origin of this magnesium-induced ferromagnetic transition to be Stoner physics—the substantial increase in the Fermi-level density of states N(E F ) with Mg alloying. Here, our calculations suggest that both Ce and Co atoms are likely to be important for generating large magnetic anisotropy suggesting the viability of Co-3d and Ce-4f interaction for the generation of magnetic anisotropy in magnetic materials. These results offer a route to the discovery of ferromagnetic materials and provide fundamental insight into the magnetic properties of these alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Single-Crystal Permanent Magnets: Extraordinary Magnetic Behavior in the Ta-,Cu-, and Fe-Substituted CeCo 5 Systems

To reduce material and processing costs of commercial permanent magnets and to attempt to fill the empty niche of energy products, 10–20 MGOe, between low-flux (ferrites, alnico) and high-flux (Nd 2 Fe 14 B- and SmCo 5 -type) magnets, we report the synthesis, structure, magnetic properties, and modeling of Ta-, Cu-, and Fe-substituted CeCo 5 . Using a self-flux technique, we grow single crystals of Ce 15.1 Ta 1.0 Co 74.4 Cu 9.5 , Ce 16.3 Ta 0.6 Co 68.9 Cu 14.2 , Ce 15.7 Ta 0.6 Co 67.8 Cu 15.9 , Ce 16.3 Ta 0.3 Co 61.7 Cu 21.7 , and Ce 14.3 Ta 1.0 Co 62.0 Fe 12.3 Cu 10.4 . X-ray-diffraction analysis shows that these materials retain a CaCu 5 substructure and incorporate small amounts of Ta in the form of “dumbbells,” filling the 2e crystallographic sites within the one-dimensional hexagonal channel with the 1a Ce site, whereas Co, Cu, and Fe are statistically distributed among the 2c and 3g crystallographic sites. Scanning-electron-microscopy, energy-dispersive-x-ray-spectroscopy, and scanning-transmission-electron-microscopy examinations provide strong evidence of the single-phase nature of the as-grown crystals, even though they readily exhibit significant magnetic coercivities of approximately 1.6 kOe to approximately 1.8 kOe caused by Co-enriched, nanosized structural defects and faults that can serve as pinning sites. Heat treatments at 1040°C for 10 h and hardening at 400°C for 4 h lead to the formation of a so-called composite crystal with a bimodal microstructure that consists of a Ta-poor matrix and Ta-rich laminal precipitates. Formation of the composite crystal during the heat treatment creates a three-dimensional array of extended defects within a primarily single-grain single crystal, which greatly improves its magnetic characteristics. Possible causes for the formation of the composite crystal may be associated with Ta atoms leaving matrix interstices at lower temperatures and/or matrix degradation induced by decreased miscibility at lower temperatures. Furthermore Fe strongly increases both the Curie temperature and magnetization of the system resulting, in ( BH ) max ≈ 13 MGOe at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Helical magnetic ordering in Sr ( Co 1 - x Ni x ) 2 As 2

SrCo 2 As 2 is a peculiar itinerant magnetic system that does not order magnetically, but inelastic neutron-scattering experiments observe the same stripe-type antiferromagnetic (AF) fluctuations found in many of the Fe-based superconductors along with evidence of magnetic frustration. Here we present results from neutron diffraction measurements on single crystals of Sr(Co 1-x Ni x ) 2 As 2 that show the development of long-range AF order with Ni doping. However, the AF order is not stripe type. Rather, the magnetic structure consists of ferromagnetically aligned (FM) layers (with moments laying in the layer) that are AF arranged along c with an incommensurate propagation vector of (0 0 τ), i.e., a helix. Using high-energy x-ray diffraction, we find no evidence for a temperature-induced structural phase transition that would indicate a collinear AF order. This finding supports a picture of competing FM and AF interactions within the square transition-metal layers due to flat-band magnetic instabilities. However, the composition dependence of the propagation vector suggests that far more subtle Fermi surface and orbital effects control the interlayer magnetic correlations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Frustrated magnetism from local moments in FeSe

We investigate properties of a spin-1 Heisenberg model with extended and biquadratic interactions, which captures crucial aspects of the low energy physics in FeSe. While we show that the model exhibits a rich phase diagram with four different magnetic ordering tendencies, we identify a parameter regime with strong competition between Néel, staggered dimer, and stripelike magnetic fluctuations, accounting for the physical properties of FeSe. We evaluate the spin and Raman responses using exact diagonalization. Through comparison with experiments we find enhanced magnetic frustration between Néel and collinear stripe ordering tendencies, which increases with increasing temperature. As a result, the explanation of these spectral behaviors with this frustrated spin model supports the idea of local spin interactions in FeSe.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Azimuthal magnetic field distribution in gas-puff Z -pinch implosions with and without external magnetic stabilization

An experimental study of the magnetic field distribution in gas-puff Z pinches with and without a preembedded axial magnetic field (B z0 ) is presented. Spatially resolved, time-gated spectroscopic measurements were made at the Weizmann Institute of Science on a 300 kA, 1.6 μs rise time pulsed-power driver. The radial distribution of the azimuthal magnetic field, B θ , during the implosion, with and without a preembedded axial magnetic field of B z0 = 0.26 T, was measured using Zeeman polarization spectroscopy. The spectroscopic measurements of B θ were consistent with the corresponding values of B θ inferred from current measurements made with a B-dot probe. One-dimensional magnetohydrodynamic simulations, performed with the code TRAC-II, showed agreement with the experimentally measured implosion trajectory, and qualitatively reproduced the experimentally measured radial B θ profiles during the implosion when B z0 = 0.26 T was applied. Simulation results of the radial profile of B θ without a preembedded axial magnetic field did not qualitatively match experimental results due to magneto-Rayleigh-Taylor (MRT) instabilities. Furthermore, our analysis emphasizes the importance of MRT instability mitigation when studying the magnetic field and current distributions in Z pinches. Discrepancies of the simulation results with experiment are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Effects of an axial magnetic field on the current distribution in a Z-pinch implosion with preembedded magnetic field

In this study, the fundamental physics of the magnetic field distribution in a plasma implosion with a pre-embedded magnetic field is investigated within a gas puff Z-pinch. Time and space resolved spectroscopy of the polarized Zeeman effect, applied for the first time, reveals the impact of a pre-embedded axial field on the evolution of the current distribution driven by a pulsed-power generator. The measurements show that the azimuthal magnetic field in the imploding plasma, even in the presence of a weak axial magnetic field, is substantially smaller than expected from the ratio of the driving current to the plasma radius. Much of the current flows at large radii through a slowly-imploding, low-density plasma. The development of a force-free current configuration is suggested to explain this phenomenon. Finally, previously unpredicted observations in higher-power imploding-magnetized-plasma experiments, including recent unexplained structures observed in the Magnetized Liner Inertial Fusion experiment, may be explained by the present discovery.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Magnetic-Field Control of Topological Electronic Response near Room Temperature in Correlated Kagome Magnets

Strongly correlated kagome magnets are promising candidates for achieving controllable topological devices owing to the rich interplay between inherent Dirac fermions and correlation-driven magnetism. Here we report tunable local magnetism and its intriguing control of topological electronic response near room temperature in the kagome magnet Fe 3 Sn 2 using small angle neutron scattering, muon spin rotation, and magnetoresistivity measurement techniques. The average bulk spin direction and magnetic domain texture can be tuned effectively by small magnetic fields. Magnetoresistivity, in response, exhibits a measurable degree of anisotropic weak localization behavior, which allows the direct control of Dirac fermions with strong electron correlations. Furthermore, our work points to a novel platform for manipulating emergent phenomena in strongly correlated topological materials relevant to future applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Electron-Only Magnetic Reconnection and Inverse Magnetic-Energy Transfer at Subion Scales

We derive, and validate numerically, an analytical model for electron-only magnetic reconnection applicable to strongly magnetized plasmas. Our model predicts subion-scale reconnection rates significantly higher than those pertaining to large-scale reconnection, aligning with recent observations and simulations. Here, we apply this reconnection model to the problem of inverse magnetic energy transfer at subion scales. We derive time-dependent scaling laws for the magnetic energy decay and the typical magnetic structure dimensions that differ from those previously found in the magnetohydrodynamics regime. These scaling laws are validated via two- and three-dimensional simulations, demonstrating that subion-scale magnetic fields can reach large, system-size scales via successive coalescence.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Evaluating the effects of structural disorder on the magnetic properties of Nd 2 Zr 2 O 7

Motivated by the variation in reported lattice parameters of floating-zone-grown Nd 2 Zr 2 O 7 crystals, we have performed a detailed study of the relationship between synthesis environment, structural disorder, and magnetic properties. Using a combination of polycrystalline standards, electron-probe microanalysis, and scattering techniques, we show that crystals grown under atmospheric conditions have a reduced lattice parameter relative to pristine polycrystalline powders due to occupation of the Nd site by excess Zr (i.e., negative stuffing). In contrast, crystals grown under high-pressure Ar are nearly stoichiometric with an average lattice parameter approaching the polycrystalline value. While minimal disorder of the oxygen sublattices is observed on the scale of the average structure, neutron pair-distribution function analysis indicates a highly local disorder of the oxygen coordination, which is only weakly dependent on growth environment. Most importantly, our magnetization, heat capacity, and single-crystal neutron scattering data show that the magnetic properties of crystals grown under high-pressure Ar match closely with those of stoichiometric powders. Neutron scattering measurements reveal that the signature of magnetic moment fragmentation—the coexistence of all-in-all-out (AIAO) magnetic Bragg peaks and diffuse pinch-point scattering due to spin-ice correlations–persists in these nearly stoichiometric crystals. However, in addition to an increased AIAO transition temperature, the diffuse signal is seemingly stabilized and remains nearly unchanged upon warming to 800 mK. This behavior indicates that both the AIAO magnetic order and spin-ice correlations are sensitive to deviations of the Nd stoichiometry.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Successive magnetic orderings in the Ising spin chain magnet DyNi 5 Ge 3

In this report, we investigated a new rare-earth-based one-dimensional Ising spin chain magnet DyNi 5 Ge 3 by means of magnetization, specific heat, and powder neutron diffraction measurements. Due to the crystalline electrical field splitting, the magnetic Dy ions share an Ising-like ground doublet state. Owning to the local point symmetry, these Ising moments form into two canted magnetic sublattices, which were further confirmed by the angle-dependent magnetization measurement. In zero fields, two successive antiferromagnetic phase transitions were found at temperatures T N1 =6K and T N2 =5K, respectively. Only part of the moments are statically ordered in this intermediate state between T N1 and T N2 . Powder neutron diffraction experiments at different temperatures were performed as well. Further, an incommensurate magnetic propagation vector of k m =(0.5,0.4,0.5) was identified. The refined spin configurations through the irreducible representation analysis confirmed that these Ising spins are canted in the crystal ab plane.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Magnetic Field Mapping Design for the MOLLER Spectrometer Magnets at Jefferson Lab

The Thomas Jefferson National Accelerator Facility (JLab) has developed a unique spectrometer system to study the weak interaction between electrons. The "Measurement of Lepton-Lepton Electroweak Reaction" (MOLLER) experiment, utilizing JLab's recent 12 GeV electron beam upgrade, is scheduled to operate for three years. Central to the MOLLER experiment are five water-cooled toroidal magnets, each with a unique geometry and seven-fold symmetry, designed to focus the particles. These magnets generate the magnetic field needed to separate incident beam electrons scattered from target electrons (Møller scattering) and protons (elastic e-p scattering) within a liquid hydrogen target. Here, this paper details the magnet field measuring technique developed to map all five MOLLER toroidal magnets at multiple locations inside and along the bore. It covers the design, mounting, and operation of the probe, along with the calibration procedure to determine the field and to prepare a field map for GEANT4 analysis. Additionally, the paper addresses the challenges of accurately measuring low magnetic fields.

Ghoshal, Probir K. [Thomas Jefferson National Acce↗
DOE OSTI2024

Design and instrumentation for permanent magnet samples exposed to a radiation environment

This work is part of a larger program to study the effects of radiation on permanent magnets in an accelerator environment. In order to be sure that the permanent magnet samples are accurately placed, measured, and catalogued we have developed a system of sample racks, holders and measuring apparatuses. We have combined these holders and measurement racks with electronics to allow a single computer to catalogue the position and intensity of the magnet measurements. We outline the design of the apparatus, the collection software, and the methodology we will use to collect the data.

Accelerator Physics↗