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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

The Co-evolution of a Magnetized Intracluster Medium and Hot Galactic Coronae: Magnetic Field Amplification and Turbulence Generation

We use adaptive-mesh magnetohydrodynamic simulations to study the effect of magnetic fields on ram pressure stripping of galaxies in the intracluster medium (ICM). Although the magnetic pressure in typical clusters is not strong enough to affect the gas mass loss rate from galaxies, magnetic fields can affect the morphology of stripped galaxies. ICM magnetic fields are draped around orbiting galaxies and aligned with their stripped tails. Magnetic fields suppress shear instabilities at the galaxy-ICM interface, and magnetized tails are smoother and narrower than tails in comparable hydrodynamic simulations in Vijayaraghavan and Ricker. Orbiting galaxies stretch and amplify ICM magnetic fields, amplifying magnetic power spectra on 10–100 kpc scales. Galaxies inject turbulent kinetic energy into the ICM via their turbulent wakes and g-waves. The magnetic energy and kinetic energy in the ICM increase up to 1.5--2 Gyr of evolution, after which galaxies are stripped of most of their gas, and do not have sufficiently large gaseous cross sections to further amplify magnetic fields and inject turbulent kinetic energy. The increase in turbulent pressure due to galaxy stripping and generation of g-waves results in an increase in the turbulent volume fraction of the ICM. This turbulent kinetic energy is not a significant contributor to the overall ICM energy budget, but greatly impacts the evolution of the ICM magnetic field. Additionally, the effect of galaxies on magnetic fields can potentially be observed in high resolution Faraday rotation measure (RM) maps as small-scale fluctuations in the RM structure.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Cluster expansion modeling and Monte Carlo simulation of alnico 5–7 permanent magnets

The concerns about the supply and resource of rare earth (RE) metals have generated a lot of interests in searching for high performance RE-free permanent magnets. Alnico alloys are traditional non-RE permanent magnets and have received much attention recently due their good performance at high temperature. In this paper, we develop an accurate and efficient cluster expansion energy model for alnico 5–7. Monte Carlo simulations using the cluster expansion method are performed to investigate the structure of alnico 5–7 at atomistic and nano scales. The alnico 5–7 master alloy is found to decompose into FeCo-rich and NiAl-rich phases at low temperature. The boundary between these two phases is quite sharp (∼2 nm) for a wide range of temperature. The compositions of the main constituents in these two phases become higher when the temperature gets lower. Both FeCo-rich and NiAl-rich phases are in B2 ordering with Fe and Al on α-site and Ni and Co on β-site. The degree of order of the NiAl-rich phase is much higher than that of the FeCo-rich phase. A small magnetic moment is also observed in NiAl-rich phase but the moment reduces as the temperature is lowered, implying that the magnetic properties of alnico 5–7 could be improved by lowering annealing temperature to diminish the magnetism in NiAl-rich phase. The results from our Monte Carlo simulations are consistent with available experimental results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Magnetic nulls in interacting dipolar fields

The prominence of nulls in reconnection theory is due to the expected singular current density and the indeterminacy of field lines at a magnetic null. Electron inertia changes the implications of both features. Magnetic field lines are distinguishable only when their distance of closest approach exceeds a distance Δ d . Electron inertia ensures Δ d ≳ c/ω pe . The lines that lie within a magnetic flux tube of radius Δ d at the place where the field strength B is strongest are fundamentally indistinguishable. If the tube, somewhere along its length, encloses a point where B = 0 vanishes, then distinguishable lines come no closer to the null than ≈ (a 2 c/ω pe ) 1/3 , where a is a characteristic spatial scale of the magnetic field. Here, the behaviour of the magnetic field lines in the presence of nulls is studied for a dipole embedded in a spatially constant magnetic field. In addition to the implications of distinguishability, a constraint on the current density at a null is obtained, and the time required for thin current sheets to arise is derived.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Alignment of magnetic particles in anisotropic Nd–Fe–B bonded magnets

High-performance anisotropic bonded magnets need a high volumetric filling fraction of magnetic powder in a polymer binder and good alignment while possessing adequate mechanical properties. The correlation between the degree of alignment (DOA) and the volumetric filling fraction of magnetic powder, the type of binder and the processing parameters have been studied using Nd–Fe–B anisotropic bonded magnets. Here, thermomagnetic analysis and differential scanning calorimetry results show that the magnetic powder can be well aligned in a bonded magnet under an external magnetic field at a temperature higher than the binders' melting point by 20–60 K, depending on the type of magnetic powder and binder. The DOA results mainly from the interplay between the Zeeman energy (E app ) and the inter-particle static energy (E stat ) in bonded magnets at the chosen alignment temperature and the magnetic fields. A good alignment can be achieved by an alignment magnetic field which is about twice its coercivity in an anisotropic Nd–Fe–B bonded magnet, which is confirmed by our experimental and modeling results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Inverse energy transfer in decaying, three-dimensional, non-helical magnetic turbulence due to magnetic reconnection

ABSTRACT It has been recently shown numerically that there exists an inverse transfer of magnetic energy in decaying, non-helical, magnetically dominated, magnetohydrodynamic turbulence in three dimensions (3D). We suggest that magnetic reconnection is the underlying physical mechanism responsible for this inverse transfer. In the two-dimensional (2D) case, the inverse transfer is easily inferred to be due to smaller magnetic islands merging to form larger ones via reconnection. We find that the scaling behaviour is similar between the 2D and 3D cases, i.e. the magnetic energy evolves as t−1, and the magnetic power spectrum follows a slope of k−2. We show that on normalizing time by the magnetic reconnection time-scale, the evolution curves of the magnetic field in systems with different Lundquist numbers collapse on to one another. Furthermore, transfer function plots show signatures of magnetic reconnection driving the inverse transfer. We also discuss the conserved quantities in the system and show that the behaviour of these quantities is similar between the 2D and 3D simulations, thus making the case that the dynamics in 3D could be approximately explained by what we understand in 2D. Lastly, we also conduct simulations where the magnetic field is subdominant to the flow. Here, too, we find an inverse transfer of magnetic energy in 3D. In these simulations, the magnetic energy evolves as t−1.4 and, interestingly, a dynamo effect is observed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Optimizing Magnetic Force Microscopy Resolution and Sensitivity to Visualize Nanoscale Magnetic Domains

Magnetic force microscopy (MFM) enables mapping local magnetic fields across a sample surface with nanoscale resolution. To perform MFM, an atomic force microscopy (AFM) probe whose tip has been magnetized vertically (i.e., perpendicular to the probe cantilever) is oscillated at a fixed height above the sample surface. The resultant shifts in the oscillation phase or frequency, which are proportional to the magnitude and sign of the vertical magnetic force gradient at each pixel location, are then tracked and mapped. Although the spatial resolution and sensitivity of the technique increases with decreasing lift height above the surface, this seemingly straightforward path to improved MFM images is complicated by considerations such as minimizing topographical artifacts due to shorter range van der Waals forces, increasing the oscillation amplitude to further improve sensitivity, and the presence of surface contaminants (in particular water due to humidity under ambient conditions). In addition, due to the orientation of the probe's magnetic dipole moment, MFM is intrinsically more sensitive to samples with an out-of-plane magnetization vector. Here, high-resolution topographical and magnetic phase images of single and bicomponent nanomagnet artificial spin-ice (ASI) arrays obtained in an inert (argon) atmosphere glovebox with <0.1 ppm O 2 and H 2 O are reported. Further, optimization of lift height and drive amplitude for high resolution and sensitivity while simultaneously avoiding the introduction of topographical artifacts is discussed, and detection of the stray magnetic fields emanating from either end of the nanoscale bar magnets (~250 nm long and <100 nm wide) aligned in the plane of the ASI sample surface is shown. Likewise, using the example of a Ni-Mn-Ga magnetic shape memory alloy (MSMA), MFM is demonstrated in an inert atmosphere with magnetic phase sensitivity capable of resolving a series of adjacent magnetic domains each ~200 nm wide.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Unitary structure having magnetic and non-magnetic phases

A magnetic component having a unitary structure, a transverse flux electric machine having the magnetic component, and a method of making the magnetic component are disclosed. The unitary structure of the magnetic component includes a magnetic region and a non-magnetic region. The magnetic region includes a magnetic phase and an electrically insulating phase. The non-magnetic region includes a non-magnetic phase. The magnetic phase includes a metallic material and the non-magnetic phase includes a nitrogenated metallic material formed by a controlled nitrogenation of the metallic material.

Johnson, Francis↗
DOE OSTI2024

Evolution of magnetism in the magnetic topological semimetal NdSb x Te 2–x+δ

Magnetic topological semimetals LnSbTe (Ln = Lanthanide) have attracted intensive attention because of the presence of interplay between magnetism, topological, and electron correlations depending on the choices of magnetic Ln elements. Recently, varying Sb-Te composition has been found to effectively control the electronic and magnetic states in LnSb x Te 2-x . Here, with this motivation, we report the evolution of magnetic properties with Sb-Te substitution in NdSb x Te 2-x+δ , (0 ≤ x ≤ 1). Our work reveals the interesting non-monotonic change in magnetic ordering temperature with varying composition stoichiometry. In addition, reducing the Sb content x drives the reorientation of moments from in-plane (ab-plane) to out-of-plane (c-axis) direction that results in the distinct magnetic structures for two end compounds NdTe 2 (x = 0) and NdSbTe (x = 1). Furthermore, the moment orientation in NdSb x Te 2-x+δ is also found to be strongly tunable upon application of weak magnetic field, leading to rich magnetic phases depending on the composition stoichiometry, temperature, and magnetic field. Such strong tuning of magnetism in this material establishes it as a promising platform for investigating tunable topological states and correlated topological physics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

SU-E-T-590: Optimizing Magnetic Field Strengths with Matlab for An Ion-Optic System in Particle Therapy Consisting of Two Quadrupole Magnets for Subsequent Simulations with the Monte-Carlo Code FLUKA

Purpose: Aim of this study was to optimize the magnetic field strengths of two quadrupole magnets in a particle therapy facility in order to obtain a beam quality suitable for spot beam scanning. Methods: The particle transport through an ion-optic system of a particle therapy facility consisting of the beam tube, two quadrupole magnets and a beam monitor system was calculated with the help of Matlab by using matrices that solve the equation of motion of a charged particle in a magnetic field and field-free region, respectively. The magnetic field strengths were optimized in order to obtain a circular and thin beam spot at the iso-center of the therapy facility. These optimized field strengths were subsequently transferred to the Monte-Carlo code FLUKA and the transport of 80 MeV/u C12-ions through this ion-optic system was calculated by using a user-routine to implement magnetic fields. The fluence along the beam-axis and at the iso-center was evaluated. Results: The magnetic field strengths could be optimized by using Matlab and transferred to the Monte-Carlo code FLUKA. The implementation via a user-routine was successful. Analyzing the fluence-pattern along the beam-axis the characteristic focusing and de-focusing effects of the quadrupole magnets could be reproduced. Furthermore the beam spot at the iso-center was circular and significantly thinner compared to an unfocused beam. Conclusion: In this study a Matlab tool was developed to optimize magnetic field strengths for an ion-optic system consisting of two quadrupole magnets as part of a particle therapy facility. These magnetic field strengths could subsequently be transferred to and implemented in the Monte-Carlo code FLUKA to simulate the particle transport through this optimized ion-optic system.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Spontaneous magnetization of a vacuum in the hot Universe and intergalactic magnetic fields

We review the spontaneous magnetization of the vacuum of non-Abelian gauge fields at high temperature. The standard model of particles is investigated as a particular example. By using both analytic methods of quantum field theory and gauge field theory on a lattice, we determine the Abelian (chromo)magnetic fields in the restored phase of the model at high temperatures T ≥ T{sub ew}. The fields are stable and temperature dependent, B = B(T). We investigate the mechanisms of the field stabilization in detail. The screening parameters for electric and magnetic fields—the Debye, m{sub D}(B, T), and magnetic, m{sub magn}(B, T), masses—are calculated. It is shown that, in the field presence, the former one is smaller than at zero field. The magnetic mass of the (chromo)magnetic fields is determined to be zero, as for usual U(1) magnetic field. We also show that the vacuum magnetization stops at temperatures below the electroweak phase transition temperature, T ≤ T{sub ew}, when a scalar condensate creates. These properties make reasonable a possibility that the intergalactic magnetic fields observed recently were spontaneously generated in the hot Universe at the reheating epoch due to vacuum polarization of non-Abelian gauge fields. We present a procedure for estimating the field strengths B(T) at different temperatures. In particular, the value of B(T{sub ew}) ∼ 10{sup 14} G, at T{sub ew} is estimated with taking into consideration the observed intergalactic magnetic field B{sub 0} ∼ 10{sup −15} G. The magnetic field scale is also estimated. Some model dependent peculiarities of the phenomena studied are briefly discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Magnetic Helicity Estimations in Models and Observations of the Solar Magnetic Field. III. Twist Number Method

We study the writhe, twist, and magnetic helicity of different magnetic flux ropes, based on models of the solar coronal magnetic field structure. These include an analytical force-free Titov–Démoulin equilibrium solution, non-force-free magnetohydrodynamic simulations, and nonlinear force-free magnetic field models. The geometrical boundary of the magnetic flux rope is determined by the quasi-separatrix layer and the bottom surface, and the axis curve of the flux rope is determined by its overall orientation. The twist is computed by the Berger–Prior formula, which is suitable for arbitrary geometry and both force-free and non-force-free models. The magnetic helicity is estimated by the twist multiplied by the square of the axial magnetic flux. We compare the obtained values with those derived by a finite volume helicity estimation method. We find that the magnetic helicity obtained with the twist method agrees with the helicity carried by the purely current-carrying part of the field within uncertainties for most test cases. It is also found that the current-carrying part of the model field is relatively significant at the very location of the magnetic flux rope. This qualitatively explains the agreement between the magnetic helicity computed by the twist method and the helicity contributed purely by the current-carrying magnetic field.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The distribution alloying elements in alnico 8 and 9 magnets: Site preference of ternary Ti, Fe, Co, and Ni additions in DO{sub 3} Fe{sub 3}Al, Co{sub 3}Al, and Ni{sub 3}Al based intermetallic phases

Recently, interest in alnico magnetic alloys has been rekindled due to their potential to substitute for rare-earth based permanent magnets provided modest improvements in their coercivity can be achieved without loss of saturation magnetization. Recent experimental studies have indicated that atomic and magnetic structure of the two phases (one AlNi-based, the other FeCo-based) that comprise these spinodally decomposed alloy is not as simple as previously thought. A key issue that arises is the distribution of Fe, Co, and Ti within the AlNi-based matrix phase. In this paper, we report the results of first-principles calculations of the site preference of ternary alloying additions in DO{sub 3} Fe{sub 3}Al, Co{sub 3}Al, and Ni{sub 3}Al alloys, as models for the aluminide phase. For compound compositions that are Al rich, which correspond to experimental situation, Ti and Fe are found to occupy the α sites, while Co and Ni prefer the γ sites of the DO{sub 3} lattice. An important finding is that the magnetic moments of transition metals in Fe{sub 3}Al and Co{sub 3}Al are ordered ferromagnetically, whereas the Ni{sub 3}Al were found to be nonmagnetic unless the Fe or Co is added as a ternary element.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Tailoring graphene magnetism by zigzag triangular holes: A first-principles thermodynamics study

In this study, we discuss the thermodynamic stability and magnetic property of zigzag triangular holes (ZTHs) in graphene based on the results of first-principles density functional theory calculations. We find that ZTHs with hydrogen-passivated edges in mixed sp 2 /sp 3 configurations (z 211 ) could be readily available at experimental thermodynamic conditions, but ZTHs with 100% sp 2 hydrogen-passivation (z 1 ) could be limitedly available at high temperature and ultra-high vacuum conditions. Graphene magnetization near the ZTHs strongly depends on the type and the size of the triangles. While metallic z 1 ZTHs exhibit characteristic edge magnetism due to the same-sublattice engineering, semiconducting z 211 ZTHs do show characteristic corner magnetism when the size is small < 2 nm. Our findings could be useful for experimentally tailoring metal-free carbon magnetism by simply fabricating triangular holes in graphene.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Effects of Magnetic Ordering in Conductivity and Magnetization of GaAs-Based Semiconductor Heterostructures upon Changing the Concentration of the Delta-Layer of Manganese Admixture

Characteristic effects of magnetic ordering and conduction in semiconductor heterostructures with a GaAs : Be/Ga{sub 0.84}In{sub 0.16}As/GaAs quantum well and manganese δ-layers of different thickness (from 0.4 to 2 monolayers) were studied based on analysis of magnetic field and temperature dependences, galvanomagnetic effects, and magnetization. An anomalous dependence of the conductivity on the manganese atoms concentration in the δ-layer was observed, which was due to a strong scattering of charge carriers in the structures with the low content of magnetic impurities. Magnetic properties of the heterostructures clearly indicated the magnetic ordering of the impurity system (saturation and hysteresis of the magnetization and fulfillment of the Curie–Weiss law at increasing temperature). Parameters of the magnetic subsystem allowed revealing different types of ordering in the systems with different concentrations of the magnetic impurity. Changing the concentration of the Mn admixture in the δ-layer was shown to influence significantly the conductivity and magnetism in the studied structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Thermal and magnetic hysteresis associated with martensitic and magnetic phase transformations in Ni 52 Mn 25 In 16 Co 7 Heusler alloy

Ni-Mn-In-Co Heusler alloys demonstrate promising magnetocaloric performance for use as refrigerants in magnetic cooling systems with the goal of replacing the lower efficiency, eco-adverse fluid-compression technology. The largest change in entropy occurs when the applied magnetic field causes a merged structural and magnetic transformation and the associated entropy changes of the two transformations works constructively. In this study, magnetic and crystalline phase transformations were each treated separately and the effects of the application of magnetic field on thermal hystereses associated with both structural and magnetic transformations of the Ni 52 Mn 25 In 16 Co 7 were studied. From the analysis of synchrotron diffraction data and thermomagnetic measurements, it was revealed that the alloy undergoes both structural (from cubic austenite to a mixture of 7M & 5M modulated martensite) and magnetic (ferromagnetic to a low-magnetization phase) phase transformations. Here, thermal hysteresis is associated with both transformations, and the variation of the thermal hystereses of the magnetic and structural transformations with applied magnetic field is significantly different. Because of the differences between the hystereses loops of the two transformations, they merge only upon heating under a certain magnetic field.

36 MATERIALS SCIENCE↗
DOE OSTI2015

EFFECTS OF THE NON-RADIAL MAGNETIC FIELD ON MEASURING MAGNETIC HELICITY TRANSPORT ACROSS THE SOLAR PHOTOSPHERE

It is generally believed that the evolution of magnetic helicity has a close relationship with solar activity. Before the launch of the Solar Dynamics Observatory (SDO), earlier studies had mostly used Michelson Doppler Imager/SOHO line of sight (LOS) magnetograms and assumed that magnetic fields are radial when calculating the magnetic helicity injection rate from photospheric magnetograms. However, this assumption is not necessarily true. Here we use the vector magnetograms and LOS magnetograms, both taken by the Helioseismic and Magnetic Imager on SDO, to estimate the effects of the non-radial magnetic field on measuring the magnetic helicity injection rate. We find that: (1) the effect of the non-radial magnetic field on estimating tangential velocity is relatively small; (2) when estimating the magnetic helicity injection rate, the effect of the non-radial magnetic field is strong when active regions are observed near the limb and is relatively weak when active regions are close to disk center; and (3) the effect of the non-radial magnetic field becomes minor if the amount of accumulated magnetic helicity is the only concern.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

A viable dipole magnet concept with REBCO CORC ® wires and further development needs for high-field magnet applications

REBCO coated conductors maintain a high engineering current density above 16 T at 4.2 K. That fact will significantly impact markets of various magnet applications including high-field magnets for high-energy physics and fusion reactors. One of the main challenges for the high-field accelerator magnet is the use of multi-tape REBCO cables with high engineering current density in magnet development. Several approaches developing high-field accelerator magnets using REBCO cables are demonstrated. In this paper, we introduce an alternative concept based on the canted cos θ (CCT) magnet design using conductor on round core (CORC®) wires that are wound from multiple REBCO tapes with a Cu core. We report the development and test of double-layer three-turn CCT dipole magnets using CORC ® wires at 77 and 4.2 K. The scalability of the CCT design allowed us to effectively develop and demonstrate important magnet technology features such as coil design, winding, joints and testing with minimum conductor lengths. The test results showed that the CCT dipole magnet using CORC ® wires was a viable option in developing a REBCO accelerator magnet. One of the critical development needs is to increase the engineering current density of the 3.7 mm diameter CORC® wire to 540 A mm -2 at 21 T, 4.2 K and to reduce the bending radius to 15 mm. Furthermore, this would enable a compact REBCO dipole insert magnet to generate a 5 T field in a background field of 16 T at 4.2 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗