Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “DIPOLE MAGNET”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Coupling-dependent antiferromagnetic-ferromagnetic ordering in a pinwheel artificial spin ice

Nanopatterned magnetic thin films offer a platform for exploration of tailored magnetic properties such as emergent long-range order. A prominent example is artificial spin ice (ASI), where an arrangement of nanoscale magnetic elements, acting as macrospins, interact via their dipolar fields. In this study, we discuss the transition from antiferromagnetic (AFM) to ferromagnetic (FM) long-range order in a square lattice ASI as the magnetic elements are gradually rotated through 45⁢° to a “pinwheel” configuration. The AFM-FM transition is observed experimentally using synchrotron radiation x-ray spectromicroscopy and occurs for a certain rotation angle of the nanomagnets, dependent on the dipolar coupling strength determined by the separation of the magnets in the lattice. Large-scale magnetic dipole simulations show that the point-dipole approximation fails to capture the correct AFM-FM transition angle. However, excellent agreement with experimental data is obtained using a dumbbell-dipole model, which better reflects the actual dipolar fields of the magnets. This model also explains the coupling dependence of the transition angle, another feature not captured by the point-dipole model. Our findings resolve a discrepancy between measurement and theory in previous work on “pinwheel” ASIs and establish the coupling dependence of the AFM-FM transition. The revised dipole model, with a more accurate representation of the stray field, offers more precise control of magnetic order in artificial spin systems.

Artificial spin ice↗
DOE OSTI2016

Relativistic Anandan quantum phase and the Aharonov–Casher effect under Lorentz symmetry breaking effects in the cosmic string spacetime

From the modified Maxwell theory coupled to gravity, we establish a possible scenario of the violation of the Lorentz symmetry and write an effective metric for the cosmic string spacetime. Then, we investigate the arising of an analogue of the Anandan quantum phase for a relativistic Dirac neutral particle with a permanent magnetic dipole moment in the cosmic string spacetime under Lorentz symmetry breaking effects. Besides, we analyse the influence of the effects of the Lorentz symmetry violation and the topology of the defect on the Aharonov–Casher geometric quantum phase in the nonrelativistic limit.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

THE ROLE OF NEWLY BORN MAGNETARS IN GAMMA-RAY BURST X-RAY AFTERGLOW EMISSION: ENERGY INJECTION AND INTERNAL EMISSION

Swift observations suggest that the central compact objects of some gamma-ray bursts (GRBs) could be newly born millisecond magnetars. Therefore, considering the spin evolution of the magnetars against r-mode instability, we investigate the role of magnetars in GRB X-ray afterglow emission. Besides modifying the conventional energy injection model, we pay particular attention to the internal X-ray afterglow emission, whose luminosity is assumed to track the magnetic dipole luminosity of the magnetars with a certain fraction. Following a comparison between the model and some selected observational samples, we suggest that some so-called canonical X-ray afterglows including the shallow decay, normal decay, and steeper-than-normal decay phases could be internally produced by the magnetars (possibly through some internal dissipations of the magnetar winds), while the (energized) external shocks are associated with another type of X-ray afterglows. If this is true, then from those internal X-ray afterglows we can further determine the magnetic field strengths and the initial spin periods of the corresponding magnetars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Signature of a spin-up magnetar from multi-band afterglow rebrightening of GRB 100814A

In recent years, more and more gamma-ray bursts (GRBs) with late rebrightenings in their multi-band afterglows have revealed the late-time activity of their central engines. GRB 100814A is a special case among the well-sampled events, with complex temporal and spectral evolution. The single power-law shallow decay index of the optical light curve observed by GROND between 640 s and 10 ks is α{sub opt}=0.57±0.02, which apparently conflicts with expectations from the simple external shock model. In particular, there is remarkable rebrightening in the optical to near-infrared bands at late times, challenging the external shock model with synchrotron emission coming from the interaction of the blast wave with the surrounding interstellar medium. In this paper, we invoke a magnetar with spin evolution to explain the complex multi-band afterglow emission of GRB 100814A. The initial shallow decay phase in the optical bands and the plateau in the X-ray can be explained as being due to energy injection from a spin-down magnetar. At late times, with materials from the fall-back disk falling onto the central object of the burster, the angular momentum of the accreted materials is transferred to the magnetar, which leads to a spin up process. As a result, the magnetic dipole radiation luminosity will increase, resulting in significant rebrightening of the optical afterglow. We show that the model can well reproduce the observed multi-band afterglow emission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

High-Energy Ions from Near-Critical Density Plasmas via Magnetic Vortex Acceleration

Ultraintense laser pulses propagating in near-critical density plasmas generate magnetic dipole vortex structures. In the region of decreasing plasma density, the vortex expands both in forward and lateral directions. The magnetic field pressure pushes electrons and ions to form a density jump along the vortex axis and induces a longitudinal electric field. This structure moves together with the expanding dipole vortex. The background ions located ahead of the electric field are accelerated to high energies. The energy scaling of ions generated by this magnetic vortex acceleration mechanism is derived and corroborated using particle-in-cell simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Comprehensive tracking study for the H-dipoles and common magnets in the splitter sections of the Cornell/Brookhaven Energy-Recovery-Linac Test Accelerator

The Cornell-Brookhaven Energy-Recovery-Linac Test Accelerator will have two splitter sections responsible for and guiding beams of 42, 78, 114, and 150 MeV energies between the Fixed-Field Alternating Gradient return loop and the Main Linac Cryomodule [6], correcting optics, and providing path length adjustments. Modeling of all 36 H-dipole magnets under contract with Elytt Energy has been completed. Four common dipoles, two of which are needed for next year’s Fractional Arc Test, will be added to the order with Elytt. The design of these magnets is underway. This report describes the findings of the tracking studies of the 36 H-dipoles and gives the status of the common dipoles.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Synthesis, Characterization and Comparative Luminescence Studies of Rare-Earth-Doped Gd{sub 2}O{sub 3} Nanoparticles

A facile direct precipitation method was used for the synthesis of luminescence nanomaterial. Gd{sub 2}O{sub 3} doped with rare earth element Eu{sup 3+} is synthesized by polyol route. The synthesized nanoparticles show their characteristic red emission. The nanoparticles are characterized by x-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and photoluminescence (PL) study. The synthesized nanoparticles are spherical particles with ~ 30 nm size. The photoluminescence studies show the characteristic Eu{sup 3+} red emission. The PL study shows the intensity of the magnetic dipole transition ({sup 5}D{sub 0}→ {sup 7}F{sub 1}) at 592 nm compared to that of the electronic dipole transition ({sup 5}D{sub 0}→ {sup 7}F{sub 2}) at 615 nm. The nanomaterials can show significant application in various display devices and biomedical applications for tracking.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Diffractive Hyperbola of a Skin Layer

Based on an analysis of physics of the phase transition from the quasistatic state field to the running wave field of elementary electric and magnetic dipoles located in absorbing media, it is concluded that the skin layer is formed at the boundary of this phase transition. The possibility is considered of obtaining the diffractive hyperbola of the skin layer and its subsequent application for sensing of objects in strongly absorbing media.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

First Detection of Sign-reversed Linear Polarization from the Forbidden [O I] 630.03 nm Line

We report on the detection of linear polarization of the forbidden [O i] 630.03 nm spectral line. The observations were carried out in the broader context of the determination of the solar oxygen abundance, an important problem in astrophysics that still remains unresolved. We obtained spectro-polarimetric data of the forbidden [O i] line at 630.03 nm as well as other neighboring permitted lines with the Solar Optical Telescope of the Hinode satellite. A novel averaging technique was used, yielding very high signal-to-noise ratios in excess of 10{sup 5}. We confirm that the linear polarization is sign-reversed compared to permitted lines as a result of the line being dominated by a magnetic dipole transition. Our observations open a new window for solar oxygen abundance studies, offering an alternative method to disentangle the Ni i blend from the [O i] line at 630.03 nm that has the advantage of simple LTE formation physics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

FINGERPRINTS OF GALACTIC LOOP I ON THE COSMIC MICROWAVE BACKGROUND

We investigate possible imprints of galactic foreground structures such as the ''radio loops'' in the derived maps of the cosmic microwave background. Surprisingly, there is evidence for these not only at radio frequencies through their synchrotron radiation, but also at microwave frequencies where emission by dust dominates. This suggests the mechanism is magnetic dipole radiation from dust grains enriched by metallic iron or ferrimagnetic molecules. This new foreground we have identified is present at high galactic latitudes, and potentially dominates over the expected B-mode polarization signal due to primordial gravitational waves from inflation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Spin polarization through axially chiral linkers: Length dependence and correlation with the dissymmetry factor

Abstract The chiral‐induced spin selectivity (CISS) effect relates to the spin‐selective electron transport through chiral molecules; therefore, the chiral molecules act as spin filters. In past studies, correlation was found between the magnitude of the spin filtering and the intensity of the circular dichroism (CD) spectrum (the first Compton peak) of the molecules. Since the intensity of the CD peak relates to both the magnitude of the electric and magnetic dipole transitions, it was not clear which of these properties correlate with the CISS effect. This work aims at addressing this question. By studying the spin‐dependent conduction and the CD spectra of the thiol‐functionalized enantiopure binaphthalene (BINAP) and ternaphthalene (TERNAP), we found that both BINAP and TERNAP exhibit a similar spin polarization of 50%, despite the first Compton peak in TERNAP being almost twice as intense as the peak in BINAP. These results can be explained by the similar values of their anisotropy (or dissymmetry) factor, g abs , which is proportional to the magnetic transition dipole moment. Hence, we concluded that the CISS effect is proportional to the transition dipole moment in chiral molecules, namely, to the dissymmetry factor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Bending of electromagnetic waves in all-dielectric particle array waveguides

We propose and demonstrate experimentally an alternative approach for realizing subwavelength photonic structures, exploiting the waveguiding properties of chains of high-index dielectric disks with both electric and magnetic dipole resonances. We reveal that the electromagnetic energy can be efficiently guided through sharp corners by means of the mode polarization conversion at waveguide bends. We confirm experimentally the guidance through a 90° bend in the microwave frequency range.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

LOOKING FOR A PULSE: A SEARCH FOR ROTATIONALLY MODULATED RADIO EMISSION FROM THE HOT JUPITER, {tau} BOOeTIS b

Hot Jupiters have been proposed as a likely population of low-frequency radio sources due to electron cyclotron maser emission of similar nature to that detected from the auroral regions of magnetized solar system planets. Such emission will likely be confined to specific ranges of orbital/rotational phase due to a narrowly beamed radiation pattern. We report on GMRT 150 MHz radio observations of the hot Jupiter {tau} Booetis b, consisting of 40 hr carefully scheduled to maximize coverage of the planet's 79.5 hr orbital/rotational period in an effort to detect such rotationally modulated emission. The resulting image is the deepest yet published at these frequencies and leads to a 3{sigma} upper limit on the flux density from the planet of 1.2 mJy, two orders of magnitude lower than predictions derived from scaling laws based on solar system planetary radio emission. This represents the most stringent upper limits for both quiescent and rotationally modulated radio emission from a hot Jupiter yet achieved and suggests that either (1) the magnetic dipole moment of {tau} Booetis b is insufficient to generate the surface field strengths of >50 G required for detection at 150 MHz or (2) Earth lies outside the beaming pattern of the radio emission from the planet.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Upper limits to the magnetic field in central stars of planetary nebulae

More than about 20 central stars of planetary nebulae (CSPNs) have been observed spectropolarimetrically, yet no clear, unambiguous signal of the presence of a magnetic field in these objects has been found. We perform a statistical (Bayesian) analysis of all the available spectropolarimetric observations of CSPN to constrain the magnetic fields in these objects. Assuming that the stellar field is dipolar and that the dipole axis of the objects is oriented randomly (isotropically), we find that the dipole magnetic field strength is smaller than 400 G with 95% probability using all available observations. The analysis introduced allows integration of future observations to further constrain the parameters of the distribution, and it is general, so that it can be easily applied to other classes of magnetic objects. We propose several ways to improve the upper limits found here.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Achromat Design for Multi-Pulse Test Line

This note describes the design of a 90° achromatic bend on DARHT Axis 2 to support multi-pulse target studies. The achromatic bend consists of two 45° dipole magnets with a focusing quadrupole centered between the dipoles. The optical design of the achromat is described followed by a discussion of the sensitivity to space charge and variations in the beam energy. The preliminary design of the magnets is then described with a description of the electro-mechanical parameters.

42 ENGINEERING↗
DOE OSTI2016

Collider study on the loop-induced dark matter mediation

Collider experiments are one of the most promising ways to constrain Dark Matter (DM) interactions. For DM couplings involving light mediators, especially for the loop-mediated interactions, a meaningful interpretation of the results requires to go beyond effective field theory. In this note we discuss the study of the magnetic dipole interacting DM, focusing on a model with anarchic dark flavor structure. By including the momentum-dependent form factors that mediate the coupling – given by the Dark Penguin – in collider processes, we study bounds from monophoton, diphoton, and non-pointing photon searches at the LHC. We also compare our results to constraints from the direct detection experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Relativistic pseudospin symmetry and shell model Hamiltonians that conserve pseudospin symmetry

Professor Akito Arima and his colleagues discovered 'pseudospin' doublets forty-one years ago in spherical nuclei. These doublets were subsequently discovered in deformed nuclei. We show that pseudospin symmetry is an SU(2) symmetry of the Dirac Hamiltonian which occurs when the scalar and vector potentials are opposite in sign but equal in magnitude. This symmetry occurs independent of the shape of the nucleus: spherical, axial deformed, triaxial, and gamma unstable. We survey some of the evidence that pseudospin symmetry is approximately conserved for a Dirac Hamiltonian with realistic scalar and vector potentials by examining the energy spectra, the lower components of the Dirac eigenfunctions, the magnetic dipole and Gamow-Teller transitions in nuclei, the upper components of the Dirac eigenfunctions, and nucleon-nucleus scattering. We shall also suggest that pseudospin symmetry may have a fundamental origin in chiral symmetry breaking by examining QCD sum rules. Finally we derive the shell model Hamiltonians which conserve pseudospin and show that they involve tensor interactions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

BINARY NEUTRON STAR MERGERS: A JET ENGINE FOR SHORT GAMMA-RAY BURSTS

We perform magnetohydrodynamic simulations in full general relativity (GRMHD) of quasi-circular, equal-mass, binary neutron stars that undergo merger. The initial stars are irrotational, n = 1 polytropes and are magnetized. We explore two types of magnetic-field geometries: one where each star is endowed with a dipole magnetic field extending from the interior into the exterior, as in a pulsar, and the other where the dipole field is initially confined to the interior. In both cases the adopted magnetic fields are initially dynamically unimportant. The merger outcome is a hypermassive neutron star that undergoes delayed collapse to a black hole (spin parameter a / M {sub BH} ∼ 0.74) immersed in a magnetized accretion disk. About 4000 M ∼ 60( M {sub NS}/1.625 M {sub ⊙}) ms following merger, the region above the black hole poles becomes strongly magnetized, and a collimated, mildly relativistic outflow—an incipient jet—is launched. The lifetime of the accretion disk, which likely equals the lifetime of the jet, is Δ t ∼ 0.1 ( M {sub NS}/1.625 M {sub ⊙}) s. In contrast to black hole–neutron star mergers, we find that incipient jets are launched even when the initial magnetic field is confined to the interior of the stars.

79 ASTRONOMY AND ASTROPHYSICS↗