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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 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Single-Domain Ferromagnet of Noncentrosymmetric Uniaxial Magnetic Ions and Magnetoelectric Interaction

The feasibility of a single-domain ferromagnet based on uniaxial magnetic ions was examined. For a noncentrosymmetric uniaxial magnetic ion of magnetic moment μ at a site of local electric dipole moment p , it is unknown to date whether μ prefers to be parallel or antiparallel to μ . The nature of this magnetoelectric interaction was probed in terms of analogical reasoning based on the Rashba effect and density functional theory (DFT) calculations. Here, we show that μ and p prefer an antiparallel arrangement, predict that Fe-doped CaZnOS is a single-domain ferromagnet like a bar magnet, and find the probable cause for the ferromagnetism and weak magnetization hysteresis in Fe-doped hexagonal ZnO and ZnS at very low dopant concentrations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Nb3Sn cable development for the 11 T dipole demonstation model

Fermilab (FNAL) and CERN have started the development of 11 T 11-m long Nb{sub 3}Sn dipoles to replace a number of LHC NbTi dipoles and free space for cold collimators in the LHC DS areas. An important step in the design of these magnets is the development of the high aspect ratio Nb{sub 3}Sn cable to achieve the nominal field of 11 T at the nominal LHC operating current of 11.85 kA at 1.9 K with 20% margin. Keystoned cables with 40 and 41 strands with and without a stainless steel core were made out of hard Cu wires and Nb{sub 3}Sn RRP strand of 0.7 mm nominal diameter. The cable optimization process was aimed at achieving both mechanical stability and minimal damage to the delicate internal architecture of the Restacked-Rod-Process (RRP) Nb3Sn strands with 127 restack design to be used in the magnet short models. Each cable was characterized electrically for transport properties degradation at high field and for low field stability, and metallographically for internal damage.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Emerged Metallicity in Molecular Ferromagnetic Wires

Supramolecular engineering bridges molecular assembly with macromolecular charge-transfer salts, promising the design to construct supramolecular architectures that integrate cooperative properties difficult or impossible to find in conventional lattices. Here, we report the crystal engineering design and kinetic growth of one-dimensional supramolecular wires composed of bis(ethylenedithio)tetrathiafulvalene (ET + ) cation and polymeric Cu[N(CN) 2 ] 2 – anion. A bulk ferromagnetic order is discovered for filling up the gap where strong ferromagnetism is missing in such ET molecule-based charge-transfer salts. Metallicity is induced by electric current from the semiconducting wire, which is attributed to strain effect by tuning its close molecular contact. This structural feature is evidenced through the combination of various mechanistic spectroscopic studies. Further, electric dipole is established from the close molecular contacts and is suggestive to stabilize ferromagnetic spin interaction through anions bridging spin sites. The breakthrough shown here provides a pathway to explore low-dimensional supramolecular materials exhibiting strong electron correlation, metallicity, and ferromagnetism.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Extraordinary phase transition revealed in a van der Waals antiferromagnet

While the surface-bulk correspondence has been ubiquitously shown in topological phases, the relationship between surface and bulk in Landau-like phases is much less explored. Theoretical investigations since 1970s for semi-infinite systems have predicted the possibility of the surface order emerging at a higher temperature than the bulk, clearly illustrating a counterintuitive situation and greatly enriching phase transitions. But experimental realizations of this prediction remain missing. Here, we demonstrate the higher-temperature surface and lower-temperature bulk phase transitions in CrSBr, a van der Waals (vdW) layered antiferromagnet. We leverage the surface sensitivity of electric dipole second harmonic generation (SHG) to resolve surface magnetism, the bulk nature of electric quadrupole SHG to probe bulk spin correlations, and their interference to capture the two magnetic domain states. Our density functional theory calculations show the suppression of ferromagnetic-antiferromagnetic competition at the surface is responsible for this enhanced surface magnetism. Our results not only show counterintuitive, richer phase transitions in vdW magnets, but also provide viable ways to enhance magnetism in their 2D form.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

THE BEHAVIOR OF THE 17 GHz SOLAR RADIUS AND LIMB BRIGHTENING IN THE SPOTLESS MINIMUM XXIII/XXIV

The current solar minimum has surprised the entire solar community because the spotless period is presently almost 2-3 years longer than the usual minima. To better understand this, we studied the variation of the solar radius and the polar limb brightening at 17 GHz, comparing the results from the minimum at the end of cycle XXIII with those of the previous one. Daily maps obtained by the Nobeyama Radioheliograph (NoRH) from 1992 through 2010 were analyzed. Whereas the variation of the solar radius at radio frequencies indicates the heating of the solar atmosphere due to solar activity, the limb brightening intensity depends on the organization of the polar magnetic field of the Sun, including the global dipole and the features formed around it. These features are more prominent during minima periods. As a common result, researchers have observed a decrease in both radius and limb brightness intensity at 17 GHz during the present minimum when compared with the previous one. The mean solar radius is 0.''9 {+-} 0.''6 smaller and the limb brightening reduced its intensity by around 20%. Both decrements are interpreted in terms of the weaker solar chromospheric activity of the present cycle. Measurement of the radius and limb brightening at 17 GHz can be used as an alternative solar activity index and should be included in the set of parameters used to predict future cycles.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Zeeman Spectroscopy of Ultracold Thulium Atoms

Dipolar ultracold gases are of great interest for quantum simulation experiments. The first step of such a simulation is deep cooling of atoms in a pre-specified internal state. The results of detailed studies of the formation of a spin-polarized cloud of thulium atoms in a dipole trap are presented. We have calibrated the magnetic field by means of radio-frequency Zeeman spectroscopy and measured the polarization of atoms in an optimized trap by the beam expansion method in a magnetic field gradient based on this calibration. We have obtained 1.1 × 10{sup 6} atoms at a temperature of 27 μK with polarization 〈m{sub F}〉 = –3.95 ± 0.12.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Summary of the Persistent Current Effect Measurements in Nb 3 Sn and NbTi Accelerator Magnets at Fermilab

In the past 10 years, Fermilab has been executing an intensive R&D program on accelerator magnets based on Nb 3 Sn superconductor technology. This R&D effort includes dipole and quadrupole models for different programs, such as LARP and 11 T dipoles for the LHC high-luminosity upgrade. Before the Nb 3 Sn R&D program, Fermilab was involved in the production of the low-beta quadrupole magnets for LHC based on the NbTi superconductor. Additionally, during the 2003-2005 campaign to optimize the operation of the Tevatron, a large number of Tevatron magnets were re-measured. As a result of this field analysis, a systematic study of the persistent current decay and snapback effect in these magnets was performed. This paper summarizes the result of this study and presents a comparison between Nb 3 Sn and NbTi dipoles and quadrupoles.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Interaction-induced stabilization of circular Rydberg atoms

We discuss a candidate solution for the controlled trapping and manipulation of two individual Rydberg atoms by means of a magnetic Ioffe-Pritchard trap that is superimposed by a constant electric field. In such a trap Rydberg atoms experience a permanent electric dipole moment that can be of the order of several hundred debye. The interplay of electric dipolar repulsion and three-dimensional magnetic confinement leads to a well controllable equilibrium configuration with tunable trap frequency and atomic distance. We thoroughly investigate the trapping potentials and analyze the interaction-induced stabilization of two such trapped Rydberg atoms. Possible limitations and collapse scenarios are discussed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Localized surface phonon polariton resonances in polar gallium nitride

We demonstrate the excitation of localized surface phonon polaritons in an array of sub-diffraction pucks fabricated in an epitaxial layer of gallium nitride (GaN) on a silicon carbide (SiC) substrate. The array is characterized via polarization- and angle-dependent reflection spectroscopy in the mid-infrared, and coupling to several localized modes is observed in the GaN Reststrahlen band (13.4–18.0 μm). The same structure is simulated using finite element methods and the charge density of the modes are studied; transverse dipole modes are identified for the transverse electric and magnetic polarizations and a quadrupole mode is identified for the transverse magnetic polarization. The measured mid-infrared spectrum agrees well with numerically simulated spectra. This work could enable optoelectronic structures and devices that support surface modes at mid- and far-infrared wavelengths.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

High-Field Magnets for Future Hadron Colliders

Recent strategy updates by the international particle physics community have confirmed strong interest in a next-generation energy frontier collider after completion of the High-Luminosity LHC program and construction of a e + e - Higgs factory. Both hadron and muon colliders provide a path toward the highest energies, and both require significant and sustained development to achieve technical readiness and optimize the design. For hadron colliders, the energy reach is determined by machine circumference and the strength of the guiding magnetic field. To achieve a collision energy of 100 TeV while limiting the circumference to 100 km, a dipole field of 16 T is required and is within the reach of niobium–tin magnets operating at 1.9 K. Magnets based on high-temperature superconductors may enable a range of alternatives, including a more compact footprint, a reduction of the cooling power, or a further increase of the collision energy to 150 TeV. The feasibility and cost of the magnet system will determine the possible options and optimal configurations. In this article, I review the historical milestones and recent progress in superconducting materials, design concepts, magnet fabrication, and test results and emphasize current developments that have the potential to address the most significant challenges and shape future directions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Simulations of emerging magnetic flux. II. The formation of unstable coronal flux ropes and the initiation of coronal mass ejections

We present results from three-dimensional magnetohydrodynamic simulations of the emergence of a twisted convection zone flux tube into a pre-existing coronal dipole field. As in previous simulations, following the partial emergence of the sub-surface flux into the corona, a combination of vortical motions and internal magnetic reconnection forms a coronal flux rope. Then, in the simulations presented here, external reconnection between the emerging field and the pre-existing dipole coronal field allows further expansion of the coronal flux rope into the corona. After sufficient expansion, internal reconnection occurs beneath the coronal flux rope axis, and the flux rope erupts up to the top boundary of the simulation domain (∼36 Mm above the surface). We find that the presence of a pre-existing field, orientated in a direction to facilitate reconnection with the emerging field, is vital to the fast rise of the coronal flux rope. The simulations shown in this paper are able to self-consistently create many of the surface and coronal signatures used by coronal mass ejection (CME) models. These signatures include surface shearing and rotational motions, quadrupolar geometry above the surface, central sheared arcades reconnecting with oppositely orientated overlying dipole fields, the formation of coronal flux ropes underlying potential coronal field, and internal reconnection which resembles the classical flare reconnection scenario. This suggests that proposed mechanisms for the initiation of a CME, such as 'magnetic breakout', are operating during the emergence of new active regions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Exploring Plasma Heating in the Current Sheet Region in a Three-dimensional Coronal Mass Ejection Simulation

We simulate a coronal mass ejection using a three-dimensional magnetohydrodynamic code that includes coronal heating, thermal conduction, and radiative cooling in the energy equation. The magnetic flux distribution at 1 Rs is produced by a localized subsurface dipole superimposed on a global dipole field, mimicking the presence of an active region within the global corona. Transverse electric fields are applied near the polarity inversion line to introduce a transverse magnetic field, followed by the imposition of a converging flow to form and destabilize a flux rope, producing an eruption. We examine the quantities responsible for plasma heating and cooling during the eruption, including thermal conduction, radiation, adiabatic effects, coronal heating, and ohmic heating. We find that ohmic heating is an important contributor to hot temperatures in the current sheet region early in the eruption, but in the late phase, adiabatic compression plays an important role in heating the plasma there. Thermal conduction also plays an important role in the transport of thermal energy away from the current sheet region throughout the reconnection process, producing a “thermal halo” and widening the region of high temperatures. We simulate emission from solar telescopes for this eruption and find that there is evidence for emission from heated plasma above the flare loops late in the eruption, when the adiabatic heating is the dominant heating term. These results provide an explanation for hot supra-arcade plasma sheets that are often observed in X-rays and extreme ultraviolet wavelengths during the decay phase of large flares.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Development of a Small-Aperture Cos-theta Dipole Insert Coil Based on Bi2212 Rutherford Cable and Stress Management Structure

The U.S. Magnet Development Program (US-MDP) is developing high-field accelerator magnets with magnetic fields beyond the limits of Nb3Sn technology based on high temperature superconductor Bi 2 Sr 2 CaCu 2 O 8-x (Bi2212). However, Bi2212 wires and cables are sensitive to transverse stresses and strains, which are substantial in high-field accelerator magnets. To prevent large degradation of the Bi2212 coils and achieve the required field quality, an innovative design which provides turn positioning during coil fabrication and operation and manage azimuthal and radial strains/stresses in the coil has been proposed at FNAL. This paper describes the development of a small-aperture two-layer Bi2212 dipole coil with stress management. The main parameters of the Bi2212 wire and Rutherford cable, the design of coil stress management structure and its plastic model, the coil mechanical analysis in the dipole mirror configuration are presented and discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Examination of the low-energy enhancement of the γ -ray strength function of Fe 56

A model-independent technique was used to determine the gamma-ray strength function (gamma SF) of Fe-56 down to gamma-ray energies less than 1 MeV for the first time with GRETINA using the (p, p') reaction at 16MeV. No difference was observed in the energy dependence of the gamma SF built on 2(+) and 4(+) final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. The polarization results show a small bias towards magnetic character in the region of the enhancement.

Jones, M. D.↗
DOE OSTI2016

Neutron electric dipole moment and possibilities of increasing accuracy of experiments

The paper reports the results of an experiment on searching for the neutron electric dipole moment (EDM), performed on the ILL reactor (Grenoble, France). The double-chamber magnetic resonance spectrometer (Petersburg Nuclear Physics Institute (PNPI)) with prolonged holding of ultra cold neutrons has been used. Sources of possible systematic errors are analyzed, and their influence on the measurement results is estimated. The ways and prospects of increasing accuracy of the experiment are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Structural and magnetic properties of the nanocomposite materials based on a mesoporous silicon dioxide matrix

The structural and magnetic properties of the mesoporous systems based on silicon dioxide with a regular hexagonal arrangement of pores several microns in length and several nanometers in diameter, which are filled with iron compound nanofilaments in various chemical states, are studied in detail. The studies are performed using the following mutually complementary methods: transmission electron microscopy, SQUID magnetometry, electron spin resonance, Mössbauer spectroscopy, polarized neutron small-angle diffraction, and synchrotron radiation diffraction. It is shown that the iron nanoparticles in pores are mainly in the γ phase of Fe{sub 2}O{sub 3} with a small addition of the α phase and atomic iron clusters. The effective magnetic field acting on a nanofilament from other nanofilaments is 11 mT and has a dipole nature, the ferromagnetic–paramagnetic transition temperature is in the range 76–94 K depending on the annealing temperature of the samples, and the temperature that corresponds to the change in the magnetic state of the iron oxide nanofilaments is T ≈ 50–60 K at H = 0 and T ≈ 80 K at H = 300 mT. It is also shown that the magnetization reversal of an array of nanofilaments is caused by the magnetostatic interaction between nanofilaments at the fields that are lower than the saturation field.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Superconducting focusing lenses for the SSR-1 cryomodule of PXIE test stand at Fermilab

Five solenoid-based focusing lenses designed for use inside the SSR1 cryomodule of the PXIE test stand at Fermilab have been fabricated and tested. In addition to a focusing solenoid, each lens is equipped with a set of windings that generate magnetic field in the transverse plane and can be used in the steering dipole mode or as a skew quadrupole corrector. The lenses will be installed between superconducting cavities in the cryomodule, so getting sufficiently low fringe magnetic field was one of the main design requirements. Beam dynamics simulations indicated a need for high accuracy positioning of the lenses in the cryomodule, which triggered a study towards understanding uncertainties of the magnetic axis position relative to the geometric features of the lens. Furthermore, this report summarizes the efforts towards certification of the lenses, including results of performance tests, fringe field data, and uncertainty of the magnetic axis position.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗