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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Synthesis and Magnetic Properties of Soft Magnetic Composites Based on Silicone Resin-Coated Iron Powders

Iron-based soft magnetic composites with silicone resin coating have been designed to reduce the core loss and improve the magnetic properties of cores. The silicone resin serving as electrical insulating layer was modified by 3-glycidoxypropyltrimethoxy silane, and the effect of silicone resin content, coupling agent, annealing treatment, and thermal cycling on the magnetic properties of composites was investigated in the frequency range from DC to 150 kHz. The coated silicone resin insulating layer was characterized by scanning electron microscopy and energy dispersive spectroscopy. The results showed that the optimum coating content of silicone resin to attain the acceptable permeability and the minimum magnetic loss for the prepared composites is 4 wt%. The sample with silicone resin coat exhibited better DC-bias superposition characteristics compared to the uncoated sample, 6 wt% silicone resin coating sample have excellent percentage effective permeability (84.8%) under 50 Oe applied field. AC magnetic properties evaluated at 1 and 100 kHz do not vary with a 95% confidence interval with the number of thermal cycles; therefore, the properties of the silicone resin-insulating composites are stable under thermal cycling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Organophilic, Superparamagnetic, and Reversibly Thermoresponsive Silica-Polypeptide Core–Shell Particles

Particles with a superparamagnetic cobalt inner core, silica outer core, and covalently bound homopolypeptide shell were investigated under thermal and magnetic stimuli. The homopolypeptide was poly(ε-carbobenzyloxy- l -lysine), PCBL, which is known to exhibit a thermoreversible coil ⇔ helix transition when dissolved as a pure polymer in m- cresol. Tethering to a core particle did not prevent PCBL from undergoing this conformational transition, as confirmed by dynamic light scattering and optical rotation, but the transition was broadened compared to that of the untethered polymer. The Co@SiO 2 -PCBL hybrid particles retained the superparamagnetic properties of the cobalt inner nougat. Indeed, some response remains even after aging for >5 years. The aged PCBL shell also preserved its responsiveness to temperature, although differences in the shape of the size vs temperature transition curve were determined compared to the freshly made particles. A reversible coil ⇔ helix transition for a particle-bound polypeptide in a pure organic solvent is rare. Further to providing a convenient tool for characterizing coil ⇔ helix transitions for surface-bound polypeptides without interference from pH or the strong ionic forces that dominate behavior in aqueous systems, the Co@SiO 2 -PCBL/ m -cresol system may prove useful in studies of the effect of shell polymer conformation on colloid interactions. The stability of the magnetic core and polypeptide shell suggest a long shelf life for Co@SiO 2 -PCBL, which can, in principle, be deprotected to yield positively charged Co@SiO 2 -poly( l -lysine) particles for possible transfection or antimicrobial applications or chained magnetically to produce responsive poly(colloids).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1987

Multiple wavelength microwave observations of the RS Canum Venaticorum stars UX Arietis, HR 1099, HR 5110, and II Pegasi

The variabilities, core size and magnetic field of the RS CVn star UX Arietis was measured with the VLA at pairs of frequencies near 1415 MHz and 4835 MHz on June 10, 1985. Data were also gathered on HR 1099, HR 5110 and II Peg. UX Arietis exhibited variability on time scales ranging from 30 sec to 1 hr at 4835 MHz, but no detectable variations at 1415 MHz. An upper limit of 900 billion cm was placed on the size of the core emitting region, which is estimated to have a magnetic field strength of 15 G. The 30 sec variations are attributed to absorption by thermal plasma between the G5 and K1 companions of the UX Arietis system.

Willson, Robert F.↗
DOE OSTI2013

MULTI-DIMENSIONAL RADIATIVE TRANSFER TO ANALYZE HANLE EFFECT IN Ca II K LINE AT 3933 A

Radiative transfer (RT) studies of the linearly polarized spectrum of the Sun (the second solar spectrum) have generally focused on line formation, with an aim to understand the vertical structure of the solar atmosphere using one-dimensional (1D) model atmospheres. Modeling spatial structuring in the observations of the linearly polarized line profiles requires the solution of multi-dimensional (multi-D) polarized RT equation and a model solar atmosphere obtained by magnetohydrodynamical (MHD) simulations of the solar atmosphere. Our aim in this paper is to analyze the chromospheric resonance line Ca II K at 3933 A using multi-D polarized RT with the Hanle effect and partial frequency redistribution (PRD) in line scattering. We use an atmosphere that is constructed by a two-dimensional snapshot of the three-dimensional MHD simulations of the solar photosphere, combined with columns of a 1D atmosphere in the chromosphere. This paper represents the first application of polarized multi-D RT to explore the chromospheric lines using multi-D MHD atmospheres, with PRD as the line scattering mechanism. We find that the horizontal inhomogeneities caused by MHD in the lower layers of the atmosphere are responsible for strong spatial inhomogeneities in the wings of the linear polarization profiles, while the use of horizontally homogeneous chromosphere (FALC) produces spatially homogeneous linear polarization in the line core. The introduction of different magnetic field configurations modifies the line core polarization through the Hanle effect and can cause spatial inhomogeneities in the line core. A comparison of our theoretical profiles with the observations of this line shows that the MHD structuring in the photosphere is sufficient to reproduce the line wings and in the line core, but only line center polarization can be reproduced using the Hanle effect. For a simultaneous modeling of the line wings and the line core (including the line center), MHD atmospheres with inhomogeneities in the chromosphere are required.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Comprehensive Efficiency Analysis of Current Source Inverter Based SPM Machine Drive System for Traction Applications

A current-source inverter (CSI) has the natural capability of boosting the output voltage which is a notable advantage over voltage source inverter (VSI) in traction drive applications. This paper investigates the voltage boosting feature of the CSI to improve the overall efficiency of the CSI-based surface permanent magnet (SPM) machine drive system in the constant power region. The effects of the boost function on the total system losses, including the machine copper loss, core loss, and magnet loss, as well as the device conduction and switching loss in the CSI and dc/dc converter, are described using analytical models. The operating characteristics of the machine and CSI are validated by 2-D finite-element analysis (FEA) and simulations. Based on the loss model, the effects of the modulation index on the overall drive system losses and power factor have been analyzed. A genetic algorithm has been used to optimize the CSI's boost ratio, demonstrating that the drive system efficiency can be increased by 1% to 2.5% along the constant-power regime envelope by using the boost function.

current source inverter, genetic algorithm, SPM ma↗
DOE OSTI2021

Pearl vortices in anisotropic superconducting films

The magnetic field of vortices in anisotropic superconducting films is considered in the framework of anisotropic London approach. It is found that at distances large relative to the core size, the magnetic field normal to the film surface may change sign. Here, we find that the magnetic field attenuates at large distances as 1/r 3 as it does in isotropic films, but the anisotropy induces an angular dependence to the supercurrents which causes the sign of the field to change for anisotropy parameters γ = λ 2 /λ 1 > $\sqrt{2}$ in some parts of the (x, y) plane.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Hybride magnetic nanostructure based on amino acids functionalized polypyrrole

Conducting polypyrrole is especially promising for many commercial applications because of its unique optical, electric, thermal and mechanical properties. We report the synthesis and characterization of novel pyrrole functionalized monomers and core-shell hybrid nanostructures, consisting of a conjugated polymer layer (amino acids functionalized pyrrole copolymers) and a magnetic nanoparticle core. For functionalization of the pyrrole monomer we used several amino acids: tryptophan, leucine, phenylalanine, serine and tyrosine. These amino acids were linked via different types of hydrophobic linkers to the nitrogen atom of the pyrrole monomer. The magnetic core-shell hybrid nanostructures are characterized by various methods such as FTIR spectroscopy, transmission electron microscopy (TEM) and magnetic measurements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Size dependent structural, vibrational and magnetic properties of BiFeO{sub 3} and core-shell structured BiFeO{sub 3}@SiO{sub 2} nanoparticles

Bulk BiFeO{sub 3}, BiFeO{sub 3} nanoparticles and core-shell structured BiFeO{sub 3}@SiO{sub 2} nanoparticles were synthesized by solid state reaction method, sol-gel and Stöber process (SiO{sub 2} shell) respectively. Transmission electron microscopy image confirmed the core-shell structure of BiFeO{sub 3}@SiO{sub 2} nanoparticles with BiFeO3 core ∼50-90 nm and SiO{sub 2} shell ∼16 nm. X-ray diffraction and FTIR spectroscopy results showed the presence of distorted rhombohedral structure with R3c space group in all three samples. The magnetic measurement indicated the existence of room-temperature weak ferromagnetism in core-shell BiFeO{sub 3}@SiO{sub 2} nanoparticles and BiFeO3 nanoparticles, whereas bulk BiFeO{sub 3} showed antiferromagnteic nature. Electron Spin Resonance results confirmed the enhancement in magnetic properties of coreshell structured BiFeO{sub 3}@SiO{sub 2} nanoparticles in comparison with BiFeO{sub 3} nanoparticles and bulk BiFeO{sub 3}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1970

Constant-voltage drive current-steering switch

Two-element voltage control system regulates a magnetic switch consisting of dual ferrite-core shift registers. The system has a magnetic, two-core-per-bit, voltage-controlled shift register.

Caplette, R. K.↗
NASA NTRS1993

Nulling Hall-Effect Current-Measuring Circuit

Circuit measures electrical current via combination of Hall-effect-sensing and magnetic-field-nulling techniques. Known current generated by feedback circuit adjusted until it causes cancellation or near cancellation of magnetic field produced in toroidal ferrite core by current measured. Remaining magnetic field measured by Hall-effect sensor. Circuit puts out analog signal and digital signal proportional to current measured. Accuracy of measurement does not depend on linearity of sensing components.

Sullender, Craig C.↗
DOE OSTI2021

Ribbon Wrinkling Origin and Its Effect on Tape-Wound Core Shape

Improved understanding of advanced manufacturing techniques is needed to fabricate next- generation soft magnetic tape-wound cores. These utilize metal amorphous nano-composites (MANCs) in the form of long thin ribbons. MANCs exhibit attractive soft magnetic properties for use in high frequency and high power density magnetic components. Of particular interest here, the permeability and hysteresis of MANC ribbons can be tuned in a strain annealing process. An unexpected consequence is that wider ribbons develop longitudinal wrinkle patterns. This can substantially reduce the tape-wound core stacking factor. However, when winding a wrinkled ribbon into a toroidal core, the wrinkles can completely flatten, or crinkle. By this phenomenon, the stacking factor can be recovered. To understand the crinkling effect we have developed analytical and finite element analysis (FEA) models. Experiments with known boundary conditions demonstrate the transition from wrinkled to crinkled versus winding curvature. The models utilize an elastic modulus measured via ribbon tensile testing and a ribbon thickness value measurement made by profilometry. The analytical model provides insight into the crinkling effect but cannot explain the length of the transition region from wrinkling to crinkling. With FEA, we successfully predict the transition region and depending on wrinkling amplitude can determine when a ribbon will wind into a useable core. Such mechanics-based insight provides critical feedback for allowable processing parameters in the strain annealing process.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2026

On FIRE mode in KSTAR

We report on the status of Fast Ion Regulated Enhancement (FIRE) mode experiments in the Korea Superconducting Tokamak Advanced Research. This regime is being developed for high-performance, steady-state operation which features a stationary ion internal transport barrier, enabling a central ion temperature approaching 10 keV to be sustained for up to 50 s, without the need for delicate profile control and with no significant impurity accumulation. As its key novelty lies in the significant contribution of fast ions that stabilize core turbulence, the regime has been named FIRE mode. To achieve this regime, neutral beam injection is applied at moderate power levels near the L–H power threshold, while maintaining low plasma density to avoid the L–H transition. The scenario is typically established in diverted magnetic configurations. The core features of FIRE mode were investigated through power balance analysis and fluctuation measurements, revealing a clear transport bifurcation in the ion channel. At the plasma edge, FIRE mode occasionally exhibits I-mode characteristics, particularly in unfavorable magnetic null configurations with q 95 ∼ 4, including the presence of weakly coherent modes. In terms of MHD activity, sawtooth oscillations are observed but appear to be stabilized during the high-performance phase. Fast ion-driven Alfvénic eigenmodes (AEs), indicated by strong frequency chirping near 200 kHz, are also observed. Additionally, lower-frequency MHD activities, distinct from the fast ion-driven AEs, are present and have some influence on plasma performance. The enhancement of core confinement is primarily attributed to fast ion effects, which were evaluated with respect to dilution, alpha stabilization, and resonant interactions with turbulence using gyrokinetic analyses. Among these, the dilution effect was found to be the most dominant. The characteristics of FIRE mode were compared with those of other hot ion plasma scenarios, such as supershot and hot ion mode. While they share many similarities, FIRE mode is distinguished by the accessibility to conditions with T i ≈ T e , presence of I-mode edge features, and its long-duration sustainment. Predictive simulations of FIRE mode were performed using integrated transport modeling with TRIASSIC, employing the TGLF anomalous transport model. These simulations confirmed the critical role of fast ions in achieving this regime. The future prospect of FIRE mode for application in fusion reactors is discussed, with an emphasis on possibly extending the regime to higher density operation.

FIRE mode↗
DOE OSTI2014

DARHT Axis II Magnet Models

There are known errors in the magnetic fields used to model the Axis II accelerator in the optics codes, XTR and LAMDA. These are due to the changes in the cell geometry and the proximity of the Metglas cores to the magnet coils. These were initially investigated by Houck [1] prior to the design change which resulted in adding 1.0 inch to the length of the accelerator cells. The interaction with the Metglas results in a shift and asymmetry in the magnetic field in addition to some field enhancement. Magnet models for the DARHT Axis II accelerator magnets were developed prior to modifications of the cells to improve the voltage standoff. New models have been developed representing the present cell configuration. The original and extended intercell magnets have also been modeled in the presence of nearby cells. Prior models did not consider the effect of the Metglas in the nearby cells for the extended intercell magnets. The resulting magnet models differ slightly from the original models. All magnet models were made on the basis of the nominal accelerator cell layout. The actual positions of each cell will vary from this nominal position. In addition, there is evidence that every time maintenance (cell cleaning and/or replacement) is performed on the accelerator, the location and alignment of the accelerator solenoids will shift.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Magnetically self-assembled SrFe12O19/Fe-Co core/shell particles

Epitaxial growth to synthesize core/shell-structured materials is limited because large lattice mismatches are common between materials. Magnetically hard/soft, core/shell-structured materials can be potentially used for rare-earth free permanent magnets, but their synthesis presents a challenge. We report a wet chemistry method to synthesize core/shell structured particles consisting of a magnetically hard SrFe12O19 core and a soft Fe-Co shell, with a lattice mismatch of similar to 100%, which cannot be achieved by conventional epitaxial growth or other alternative methods. When decreasing the size of the magnetically soft Fe-Co nanoclusters to below 5 nm, we show that they can be magnetically attracted by the hard SrFe12O19 to form core/shell structured particles. An AC demagnetization experiment demonstrates the formation mechanism of the core/shell particles, and their magnetic hysteresis loop shows potential for use as rare-earth free permanent magnets. Published by Elsevier B.V.

Xu, X↗
DOE OSTI2013

ALIGNMENT BETWEEN FLATTENED PROTOSTELLAR INFALL ENVELOPES AND AMBIENT MAGNETIC FIELDS

We present 350 {mu}m polarization observations of four low-mass cores containing Class 0 protostars: L483, L1157, L1448-IRS2, and Serp-FIR1. This is the second paper in a larger survey aimed at testing magnetically regulated models for core-collapse. One key prediction of these models is that the mean magnetic field in a core should be aligned with the symmetry axis (minor axis) of the flattened young stellar object inner envelope (aka pseudodisk). Furthermore, the field should exhibit a pinched or hourglass-shaped morphology as gravity drags the field inward toward the central protostar. We combine our results for the four cores with results for three similar cores that were published in the first paper from our survey. An analysis of the 350 {mu}m polarization data for the seven cores yields evidence of a positive correlation between mean field direction and pseudodisk symmetry axis. Our rough estimate for the probability of obtaining by pure chance a correlation as strong as the one we found is about 5%. In addition, we combine together data for multiple cores to create a source-averaged magnetic field map having improved signal-to-noise ratio, and this map shows good agreement between mean field direction and pseudodisk axis (they are within 15 Degree-Sign ). We also see hints of a magnetic pinch in the source-averaged map. We conclude that core-scale magnetic fields appear to be strong enough to guide gas infall, as predicted by the magnetically regulated models. Finally, we find evidence of a positive correlation between core magnetic field direction and bipolar outflow axis.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

ASTEROSEISMIC SIGNATURES OF EVOLVING INTERNAL STELLAR MAGNETIC FIELDS

Recent asteroseismic analyses indicate the presence of strong ( B ≳ 10{sup 5} G) magnetic fields in the cores of many red giant stars. Here, we examine the implications of these results for the evolution of stellar magnetic fields, and we make predictions for future observations. Those stars with suppressed dipole modes indicative of strong core fields should exhibit moderate but detectable quadrupole mode suppression. The long magnetic diffusion times within stellar cores ensure that dynamo-generated fields are confined to mass coordinates within the main-sequence (MS) convective core, and the observed sharp increase in dipole mode suppression rates above 1.5 M {sub ⊙} is likely explained by the larger convective core masses and faster rotation of these more massive stars. In clump stars, core fields of ∼10{sup 5} G can suppress dipole modes, whose visibility should be equal to or less than the visibility of suppressed modes in ascending red giants. High dipole mode suppression rates in low-mass ( M ≲ 2 M {sub ⊙}) clump stars would indicate that magnetic fields generated during the MS can withstand subsequent convective phases and survive into the compact remnant phase. Finally, we discuss implications for observed magnetic fields in white dwarfs and neutron stars, as well as the effects of magnetic fields in various types of pulsating stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Modeling of the Interstellar Pickup Protons, Alfvenic Turbulence, and Solar Wind in the Outer Heliosphere

A self-consistent model of the interstellar pickup protons, slab component of the Alfvénic turbulence (the wave vector is parallel/antiparallel to the mean magnetic field), and core solar wind protons is presented for the heliocentric distances r ≥ 1 AU. The model results show that energy in the slab turbulence agrees very well with the Voyager 2 observations of the total transverse magnetic fluctuations starting from about 8 AU. This indicates that the slab component of turbulence makes up a majority of the transverse magnetic fluctuations at low-latitudes beyond 8 – 10 AU.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

GLOBAL SIMULATIONS OF MAGNETOROTATIONAL INSTABILITY IN THE COLLAPSED CORE OF A MASSIVE STAR

We performed the first global numerical simulations of magnetorotational instability from a sub-magnetar-class seed magnetic field in core-collapse supernovae. As a result of axisymmetric ideal MHD simulations, we found that the magnetic field is greatly amplified to magnetar-class strength. In the saturation phase, a substantial part of the core is dominated by turbulence, and the magnetic field possesses dominant large-scale components, comparable to the size of a proto-neutron star. A pattern of coherent channel flows, which generally appears during the exponential growth phase in previous local simulations, is not observed in our global simulations. While the approximate convergence in the exponential growth rate is attained by increasing spatial resolution, that of the saturation magnetic field is not achieved due to still large numerical diffusion. Although the effect of the magnetic field on the dynamics is found to be mild, a simulation with a high enough resolution might result in a larger impact.

79 ASTRONOMY AND ASTROPHYSICS↗