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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Design of toroidal transformers for maximum efficiency

The design of the most efficient toroidal transformer that can be built given the frequency, volt-ampere rating, magnetic flux density, window fill factor, and materials is described. With the above all held constant and only the dimensions of the magnetic core varied, the most efficient design occurs when the copper losses equal 60 percent of the iron losses. When this criterion is followed, efficiency is only slightly dependent on design frequency and fill factor. The ratios of inside diameter to outside diameter and height to build of the magnetic core that result in transformers of maximum efficiency are computed.

Dayton, J. A., Jr.↗
DOE OSTI2013

Kinetic simulations of plasmoid chain dynamics

The dynamics of a plasmoid chain is studied with three dimensional Particle-in-Cell simulations. The evolution of the system with and without a uniform guide field, whose strength is 1/3 the asymptotic magnetic field, is investigated. The plasmoid chain forms by spontaneous magnetic reconnection: the tearing instability rapidly disrupts the initial current sheet generating several small-scale plasmoids that rapidly grow in size coalescing and kinking. The plasmoid kink is mainly driven by the coalescence process. It is found that the presence of guide field strongly influences the evolution of the plasmoid chain. Without a guide field, a main reconnection site dominates and smaller reconnection regions are included in larger ones, leading to an hierarchical structure of the plasmoid-dominated current sheet. On the contrary in presence of a guide field, plasmoids have approximately the same size and the hierarchical structure does not emerge, a strong core magnetic field develops in the center of the plasmoid in the direction of the existing guide field, and bump-on-tail instability, leading to the formation of electron holes, is detected in proximity of the plasmoids.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1975

Table-aided design of the energy-storage reactor in dc-to-dc converters

A new procedure for the selection of magnetic cores for use in energy-storage dc-to-dc power converters which eliminates the need for an automated computer search algorithm and stored data file is presented. The converter configurations included in the procedure are the three commonly encountered single-winding converters for voltage step-up, for current step-up and for voltage step-up/current step-up, and for the two-winding converter for voltage step-up/current step-up. For each converter configuration, three types of controllers are considered - constant-frequency, constant on-time and constant off-time. Using concepts developed from analyses of these converters by considering the transfer of energy by means of an energy-storage inductor or transformer, a special table of parameters calculated from magnetic core data is constructed and leads to a considerably simplified design procedure.

Owen, H. A., Jr.↗
DOE OSTI2023

Transformer Leakage Inductance Design Methodology

The leakage inductance exhibited by a transformer depends on its winding geometry, which generally involves the selection of several key design parameters in addition to the winding structure and the interleaving configuration. With few resources explaining the effects of these design choices on the observed leakage inductance, numerous trial-and-error iterations become necessary to realize the desired leakage inductance. This paper explores more than a hundred winding geometries feasible in a 2-winding transformer comprising the same magnetic core, number of turns, and wire gauge, and finds the leakage inductance for each unique design using 2-D finite element method (FEM) simulations in association with the semi-analytical double- 2-D model. These leakage inductances are plotted and further analyzed to understand the effects of different design parameters on the effective leakage inductance. The results presented herein and the conclusions drawn from this research can serve as a valuable resource for future design practitioners from both industry and academia.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2014

Low-amplitude magnetic vortex core reversal by non-linear interaction between azimuthal spin waves and the vortex gyromode

We show, by experiments and micromagnetic simulations in vortex structures, that an active “dual frequency” excitation of both the sub-GHz vortex gyromode and multi-GHz spin waves considerably changes the frequency response of spin wave mediated vortex core reversal. Besides additional minima in the switching threshold, a significant broadband reduction of the switching amplitudes is observed, which can be explained by non-linear interaction between the vortex gyromode and the spin waves. We conclude that the well known frequency spectra of azimuthal spin waves in vortex structures are altered substantially, when the vortex gyromode is actively excited simultaneously.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Fabrication and characterization of net-shaped iron nitride-amine-epoxy soft magnetic composites

Soft magnetic composites (SMCs) offer a promising alternative to electrical steels and soft ferrites in high performance motors and power electronics. They are ideal for incorporation into passive electronic components such as inductors and transformers, which require a non-permanent magnetic core to rapidly switch magnetization. As a result, there is a need for materials with the right combination of low coercivity, low magnetic remanence, high relative permeability, and high saturation magnetization to achieve these goals. Iron nitride is an attractive soft magnetic material for incorporation into an amine/epoxy resin matrix. This permits the synthesis of net-shaped SMCs using a “bottom-up” approach for overcoming the limitations of current state-of-the-art SMCs made via conventional powder metal processing techniques. In this work we present the fabrication of various net-shaped, iron nitride-based SMCs using two different amine/epoxy resin systems and their magnetic characterization. The maximum volume loading of iron nitride reached was ~77% via hot pressing, which produced SMCs with a saturation magnetic polarization (J s ) of ~0.9 T, roughly 2–3 times the J s of soft ferrites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

The Phase Diagram and Exotic Magnetostrictive Behaviors in Spinel Oxide Co(Fe1−xAlx)2O4 System

We report the magnetic and magnetostrictive behaviors of the pseudobinary ferrimagnetic spinel oxide system (1−x)CoFe2O4–xCoAl2O4 [Co(Fe1−xAlx)2O4], with one end-member being the ferrimagnetic CoFe2O4 and the other end-member being CoAl2O4 that is paramagnetic above 9.8 K. The temperature spectra of magnetization and magnetic susceptibility were employed to detect the magnetic transition temperatures and to determine the phase diagram of this system. Composition dependent and temperature dependent magnetostrictive behaviors reveal an exotic phase boundary that separates two ferrimagnetic states: At room temperature and under small magnetic fields (∼500 Oe), Fe-rich compositions exhibit negative magnetostriction while the Al-rich compositions exhibit positive magnetostriction though the values are small (<10 ppm). Moreover, the compositions around this phase boundary at room temperature (x = 0.35, 0.4, 0.45, 0.5) exhibit near-zero magnetostriction and enhanced magnetic susceptibility, which may be promising in the applications for magnetic cores, current sensors, or magnetic shielding materials.

36 MATERIALS SCIENCE↗
NASA NTRS1994

Core Losses In Three Alloys

Report describes experimental investigation of core losses and dynamic magnetic flux densities as functions of magnetomotive force of three soft magnetic materials under sine-wave voltage excitation at frequencies from 1 to 50 kHz and at temperatures from 23 to 300 degrees C. Prompted by need for data to design magnetic cores for efficient, lightweight power supplies operating in harsh environments.

Schwarze, G. E.↗
DOE OSTI2017

SYNTHETIC OBSERVATIONS OF MAGNETIC FIELDS IN PROTOSTELLAR CORES

The role of magnetic fields in the early stages of star formation is not well constrained. In order to discriminate between different star formation models, we analyze 3D magnetohydrodynamic simulations of low-mass cores and explore the correlation between magnetic field orientation and outflow orientation over time. We produce synthetic observations of dust polarization at resolutions comparable to millimeter-wave dust polarization maps observed by the Combined Array for Research in Millimeter-wave Astronomy and compare these with 2D visualizations of projected magnetic field and column density. Cumulative distribution functions of the projected angle between the magnetic field and outflow show different degrees of alignment in simulations with differing mass-to-flux ratios. The distribution function for the less magnetized core agrees with observations finding random alignment between outflow and field orientations, while the more magnetized core exhibits stronger alignment. We find that fractional polarization increases when the system is viewed such that the magnetic field is close to the plane of the sky, and the values of fractional polarization are consistent with observational measurements. The simulation outflow, which reflects the underlying angular momentum of the accreted gas, changes direction significantly over over the first ∼0.1 Myr of evolution. This movement could lead to the observed random alignment between outflows and the magnetic fields in protostellar cores.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Magnetic core/shell-type composites composed of coarse FePt particles coated with finely powdered iron nitride

Highlights: • Magnetic core/shell-type composites were prepared on α″-Fe{sub 16}N{sub 2}-like compound with FePt core. • α″-Fe{sub 16}N{sub 2}-like compound grew epitaxially on the FePt core. • Magnetic coupling increased the magnetic coercivity of α″-Fe{sub 16}N{sub 2}-like compound. - Abstract: Although α″-Fe{sub 16}N{sub 2}-like compounds exhibit enhanced magnetization compared to α-Fe, it is important to increase their magnetic coercivity to obtain new hard magnetic materials for electric vehicle application. In the present work, coarse FePt particles were coated with finely powdered Fe{sub 3}O{sub 4} produced by the hydrolysis of Fe(acac){sub 3} in benzyl alcohol. This Fe{sub 3}O{sub 4} coating layer was subsequently reduced under hydrogen and then nitrided by ammonolysis at 150 °C to obtain a dual-phase mixture of an α″-Fe{sub 16}N{sub 2}-like compound (referred to herein as “α″-Fe{sub 16}N{sub 2}”) and residual α-Fe. The (“α″-Fe{sub 16}N{sub 2}” + α-Fe){sub 1-x}/(FePt){sub x} composite particles for which x = 0.2, 0.4 or 0.6 generated smooth magnetization hysteresis curves, and the magnetic coercivity of these materials increased with increases in the proportion of FePt. Magnetic coupling was clearly evident between the core and shell regions in the composite powder for which x = 0.6, as demonstrated by a plot of the Wohlfarth interaction against the magnetic field. Transmission electron microscopy images confirmed magnetic coupling between the coarse FePt particles (several hundred nm in diameter) and the coating of fine mixed particles (several tens of nm in diameter) of “α″-Fe{sub 16}N{sub 2}” and α-Fe. The “α″-Fe{sub 16}N{sub 2}” crystals forming the particle shell were found to grow epitaxially, aligning their c-axes parallel to that of the tetragonal FePt.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Gapless core reactor

A gapless core reactor includes a saturable magnetic core having reactor legs without air gaps and multiple windings. The windings are each wound around a common leg, spaced apart from each other and connected in counter series. The windings are configured such that a magnetic flux generated from an alternating current flowing through the windings generates a plurality of substantially equal and counter magnetic fluxes flowing through two or more separate magnetic circuits.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS2003

Performance of the NASA Digitizing Core-Loss Instrumentation

The standard method of magnetic core loss measurement was implemented on a high frequency digitizing oscilloscope in order to explore the limits to accuracy when characterizing high Q cores at frequencies up to 1 MHz. This method computes core loss from the cycle mean of the product of the exciting current in a primary winding and induced voltage in a separate flux sensing winding. It is pointed out that just 20 percent accuracy for a Q of 100 core material requires a phase angle accuracy of 0.1 between the voltage and current measurements. Experiment shows that at 1 MHz, even high quality, high frequency current sensing transformers can introduce phase errors of a degree or more. Due to the fact that the Q of some quasilinear core materials can exceed 300 at frequencies below 100 kHz, phase angle errors can be a problem even at 50 kHz. Hence great care is necessary with current sensing and ground loops when measuring high Q cores. Best high frequency current sensing accuracy was obtained from a fabricated 0.1-ohm coaxial resistor, differentially sensed. Sample high frequency core loss data taken with the setup for a permeability-14 MPP core is presented.

Schwarze, Gene E.↗
DOE OSTI2018

Verification of 5D continuum gyrokinetic code COGENT: Studies of kinetic drift wave instability

COGENT (Continuum Gyrokinetic Edge New Technology) is a kinetic plasma simulation code that is being developed by the edge simulation laboratory (ESL) collaboration. The original version of the code has been developed in a 4D phase space (2D configuration space and 2D velocity space) to address kinetic plasma phenomena in a complex magnetic field geometry including the core, magnetic separatrix, and scrape-off layer regions. This paper is focused on extending the original 4D phase space to a 5D phase space (3D2V) to address full kinetic turbulences in a tokamak edge region. Here, we report on the current status of 5D COGENT, which presently operates in a shear-less, simple slab geometry. As a verification study, we use the problems of collision-less drift wave instability (universal instability) including its modification in the presence of collisional effects. The simulation model includes the gyrokinetic equations for ion and electron species coupled to the long-wavelength limit of the gyro-Poisson equation. Collisional effects are represented by the Krook collision model. Linear analytical results for the drift mode growth rate and real frequency are recovered, and the non-linear stage is modelled and analysed as well. In addition, extensive 5D runs have been performed to address the effects of the drift wave instability on blob/filamentary structures characteristic of a tokamak edge. Finally, a helical-shaped potential perturbation is observed to grow exponentially in time while spinning around the filament axis with electron drift frequency.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗