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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

SGR 0418+5729: A SMALL INCLINATION ANGLE RESULTING IN A NOT SO LOW DIPOLE MAGNETIC FIELD?

The spin-down behaviors of SGR 0418+5729 are investigated. The pulsar spin-down model of Contopoulos and Spitkovsky is applied to SGR 0418+5729. It is shown that SGR 0418+5729 lies below the pulsar death line and its rotation-powered magnetospheric activities may therefore have stopped. The compact star is now spun down by the magnetic dipole moment perpendicular to its rotation axis. Our calculations show that under these assumptions there is the possibility of SGR 0418+5729 having a strong dipole magnetic field, if there is a small magnetic inclination angle. Its dipole magnetic field may be much higher than the characteristic magnetic field. Therefore, SGR 0418+5729 may be a normal magnetar instead of a low magnetic field magnetar.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE SUBMILLIMETER AND MILLIMETER EXCESS OF THE SMALL MAGELLANIC CLOUD: MAGNETIC DIPOLE EMISSION FROM MAGNETIC NANOPARTICLES?

The Small Magellanic Cloud (SMC) has surprisingly strong submillimeter- and millimeter-wavelength emission that is inconsistent with standard dust models, including those with emission from spinning dust. Here, we show that the emission from the SMC may be understood if the interstellar dust mixture includes magnetic nanoparticles, emitting magnetic dipole radiation resulting from thermal fluctuations in the magnetization. The magnetic grains can be metallic iron, magnetite Fe{sub 3}O{sub 4}, or maghemite {gamma}-Fe{sub 2}O{sub 3}. The required mass of iron is consistent with elemental abundance constraints. The magnetic dipole emission is predicted to be polarized orthogonally to the normal electric dipole radiation if the nanoparticles are inclusions in larger grains. We speculate that other low-metallicity galaxies may also have a large fraction of the interstellar Fe in magnetic materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Guiding center equations for the magnetic dipole

Since the discovery of Van Allen radiation belts in the 1960s, observations of energetic ions trapped in the Earth's dipole magnetic field have illustrated the remarkable confinement properties of this configuration. As such, it has been used for confining a hot plasma for nuclear fusion studies, starting from the pioneering work of Bo Lehnert and Akira Hasegawa, in the Levitated Dipole Experiment (LDX) at MIT until 2011 and in the RT-1 experiment at the University of Tokyo. More recently, the dipole has been subject to a renewed interest for fusion studies by a couple of startups and for smaller applications as a cold plasma source. While the equilibrium and magneto-hydrodynamic stability of the dipole have been investigated quite in detail, neoclassical properties of the dipole are comparatively much less known: the dipole is more known in geophysics than in fusion science. For this reason, in this paper, we propose a set of Hamiltonian, guiding-center equations to describe the motion of electrons and ions in a magnetic dipole configuration. We also developed a code, and we show the main features of particle motion, benchmarking our results with the analytical solutions for the bounce and precession motion, which are well documented in the literature. We also draw some general conclusions for the neoclassical transport in usual toroidal confinement schemes, such as the tokamak and the stellarator, pointing out the unique advantages of the dipole in confining energetic particles.

Hamiltonian mechanics↗
DOE OSTI2011

PULSAR PAIR CASCADES IN A DISTORTED MAGNETIC DIPOLE FIELD

We investigate the effect of a distorted neutron star dipole magnetic field on pulsar pair cascade multiplicity and pair death lines. Using a simple model for a distorted dipole field that produces an offset polar cap (PC), we derive the accelerating electric field above the PC in space-charge-limited flow. We find that even a modest azimuthally asymmetric distortion can significantly increase the accelerating electric field on one side of the PC and, combined with a smaller field line radius of curvature, leads to larger pair multiplicity. The death line for producing pairs by curvature radiation moves downward in the P- P-dot diagram, allowing high pair multiplicities in a larger percentage of the radio pulsar population. These results could have important implications for the radio pulsar population, high energy pulsed emission, and the pulsar contribution to cosmic ray positrons.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Splitting of magnetic dipole modes in anisotropic TiO 2 micro-spheres: Splitting of magnetic dipole modes in anisotropic TiO 2 micro-spheres

Monocrystalline titanium dioxide (TiO 2 ) micro-spheres support two orthogonal magnetic dipole modes at terahertz (THz) frequencies due to strong dielectric anisotropy. For the first time, we experimentally detected the splitting of the first Mie mode in spheres of radii inline imagem through near-field time-domain THz spectroscopy. By fitting the Fano lineshape model to the experimentally obtained spectra of the electric field detected by the sub-wavelength aperture probe, we found that the magnetic dipole resonances in TiO 2 spheres have narrow linewidths of only tens of gigahertz. Lastly, anisotropic TiO 2 micro-resonators can be used to enhance the interplay of magnetic and electric dipole resonances in the emerging THz all-dielectric metamaterial technology.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Giant Primeval Magnetic Dipoles

Macroscopic magnetic dipoles are considered cosmic dark matter. Permanent magnetism in relativistic field structures can involve some form of superconductivity, one example being current-carrying string loops (“springs”) with vanishing net tension. We derive the cross-section for free classical dipoles to collide, finding it depends weakly on orientation when mutual precession is rapid. The collision rate of “spring” loops with tension T∼10{sup −8}c{sup 4}/G in galactic halos approaches the measured rate of fast radio bursts (FRBs) if the loops compose most of the dark matter. A large superconducting dipole (LSD) with mass ∼10{sup 20} g and size ∼1 mm will form a ∼100 km magnetosphere moving through interstellar plasma. Although hydromagnetic drag is generally weak, it is strong enough to capture some LSDs into long-lived rings orbiting supermassive black holes (SMBHs) that form by the direct collapse of massive gas clouds. Repeated collisions near young SMBHs could dominate the global collision rate, thereby broadening the dipole mass spectrum. Colliding LSDs produce tiny, hot electromagnetic explosions. The accompanying paper shows that these explosions couple effectively to propagating low-frequency electromagnetic modes, with output peaking at 0.01–1 THz. We describe several constraints on, and predictions of, LSDs as cosmic dark matter. The shock formed by an infalling LSD triggers self-sustained thermonuclear burning in a C/O (ONeMg) white dwarf (WD) of mass ≳1 M {sub ⊙} (1.3 M {sub ⊙}). The spark is generally located off the center of the WD. The rate of LSD-induced explosions matches the observed rate of Type Ia supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Design of B1pF-A Large Aperture Dipole Magnet for EIC

The design of interaction region (IR) magnets for the Electron Ion Collider (EIC), demands tight boundary conditions on the magnet design given by the high field requirements and the proximity of electron and hadron beams within a common yoke and resultant crosstalk. Here, this article discusses the electromagnetic design of the superconducting collared magnet B1pF. The magnet will be built as the prototype for several collared magnets (dipoles and quadrupoles) for the hadron beam in the forward direction of the IR. The magnet design is based on a single layer coil with an inner diameter of 300 mm over a slot length of 3 m. The magnet produces an integral field of 10.34 T.m at a current of 11.9 kA to produce a nominal field of about 3.96 T at its center. Given by the common Rutherford cable parameters, the magnet will be used as a baseline for optimization of all the collared magnets. The article further discusses yoke optimizations, quench analysis, coil end design and efforts on fine tuning of field quality.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Conceptual Design of a 17 T Nb$_3$Sn Accelerator Dipole Magnet

$Nb_3Sn$ dipole magnets with a nominal field of 16 T and sufficient operation margins are being considered for the LHC energy upgrade or a future Very High Energy Hadron Collider. This paper describes the conceptual design of a 17 T dipole magnet with 60 mm aperture, 4-layer cos-theta coil and stress management techniques.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Radiation effects in a muon collider ring and dipole magnet protection

The requirements and operating conditions for a Muon Collider Storage Ring (MCSR) pose significant challenges to superconducting magnets. The dipole magnets should provide a high magnetic field to reduce the ring circumference and thus maximize the number of muon collisions during their lifetime. One third of the beam energy is continuously deposited along the lattice by the decay electrons at the rate of 0.5 kW/m for a 1.5-TeV c.o.m. and a luminosity of 10{sup 34} cm{sup -2}s{sup -1}. Unlike dipoles in proton machines, the MCSR dipoles should allow this dynamic heat load to escape the magnet helium volume in the horizontal plane, predominantly towards the ring center. This paper presents the analysis and comparison of radiation effects in MCSR based on two dipole magnets designs. Tungsten masks in the interconnect regions are used in both cases to mitigate the unprecedented dynamic heat deposition and radiation in the magnet coils.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

POLARIZATION OF MAGNETIC DIPOLE EMISSION AND SPINNING DUST EMISSION FROM MAGNETIC NANOPARTICLES

Magnetic dipole emission (MDE) from interstellar magnetic nanoparticles is potentially an important Galactic foreground in the microwave frequencies, and its polarization level may pose great challenges for achieving reliable measurements of cosmic microwave background B-mode signal. To obtain realistic predictions for the polarization of MDE, we first compute the degree of alignment of big silicate grains incorporated with magnetic inclusions. We find that thermally rotating big grains with magnetic inclusions are weakly aligned and can achieve alignment saturation when the magnetic alignment rate becomes much faster than the rotational damping rate. We then compute the degree of alignment for free-flying magnetic nanoparticles, taking into account various interaction processes of grains with the ambient gas and radiation field, including neutral collisions, ion collisions, and infrared emission. We find that the rotational damping by infrared emission can significantly decrease the degree of alignment of small particles from the saturation level, whereas the excitation by ion collisions can enhance the alignment of ultrasmall particles. Using the computed degrees of alignment, we predict the polarization level of MDE from free-flying magnetic nanoparticles to be rather low. Such a polarization level is within the upper limits measured for anomalous microwave emission (AME), which indicates that MDE from free-flying iron particles may not be ruled out as a source of AME. We also quantify rotational emission from free-flying iron nanoparticles with permanent magnetic moments and find that its emissivity is about one order of magnitude lower than that from spinning polycyclic aromatic hydrocarbons.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Low temperature superconductor and aligned high temperature superconductor magnetic dipole system and method for producing high magnetic fields

A dipole-magnet system and method for producing high-magnetic-fields, including an open-region located in a radially-central-region to allow particle-beam transport and other uses, low-temperature-superconducting-coils comprised of low-temperature-superconducting-wire located in radially-outward-regions to generate high magnetic-fields, high-temperature-superconducting-coils comprised of high-temperature-superconducting-tape located in radially-inward-regions to generate even higher magnetic-fields and to reduce erroneous fields, support-structures to support the coils against large Lorentz-forces, a liquid-helium-system to cool the coils, and electrical-contacts to allow electric-current into and out of the coils. The high-temperature-superconducting-tape may be comprised of bismuth-strontium-calcium-copper-oxide or rare-earth-metal, barium-copper-oxide (ReBCO) where the rare-earth-metal may be yttrium, samarium, neodymium, or gadolinium. Advantageously, alignment of the large-dimension of the rectangular-cross-section or curved-cross-section of the high-temperature-superconducting-tape with the high-magnetic-field minimizes unwanted erroneous magnetic fields. Alignment may be accomplished by proper positioning, tilting the high-temperature-superconducting-coils, forming the high-temperature-superconducting-coils into a curved-cross-section, placing nonconducting wedge-shaped-material between windings, placing nonconducting curved-and-wedge-shaped-material between windings, or by a combination of these techniques.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Full kinetic simulations of plasma flow interactions with meso- and microscale magnetic dipoles

We examined the plasma flow response to meso- and microscale magnetic dipoles by performing three-dimensional full particle-in-cell simulations. We particularly focused on the formation of a magnetosphere and its dependence on the intensity of the magnetic moment. The size of a magnetic dipole immersed in a plasma flow can be characterized by a distance L from the dipole center to the position where the pressure of the local magnetic field becomes equal to the dynamic pressure of the plasma flow under the magnetohydrodynamics (MHD) approximation. In this study, we are interested in a magnetic dipole whose L is smaller than the Larmor radius of ions r{sub iL} calculated with the unperturbed dipole field at the distance L from the center. In the simulation results, we confirmed the clear formation of a magnetosphere consisting of a magnetopause and a tail region in the density profile, although the spatial scale is much smaller than the MHD scale. One of the important findings in this study is that the spatial profiles of the plasma density as well as the current flows are remarkably affected by the finite Larmor radius effect of the plasma flow, which is different from the Earth's magnetosphere. The magnetopause found in the upstream region is located at a position much closer to the dipole center than L. In the equatorial plane, we also found an asymmetric density profile with respect to the plasma flow direction, which is caused by plasma gyration in the dipole field region. The ion current layers are created in the inner region of the dipole field, and the electron current also flows in the region beyond the ion current layer because ions with a large inertia can closely approach the dipole center. Unlike the ring current structure of the Earth's magnetosphere, the current layers in the microscale dipole fields are not circularly closed around the dipole center. Since the major current is caused by the particle gyrations, the current is independently determined to be in the direction of the electron and ion gyrations, which are the same in both the upstream and downstream regions. The present analysis on the formation of a magnetosphere in the regime of a microscale magnetic dipole is significant for understanding the solar wind response to the crustal magnetic anomalies on the Moon surface, such as were recently observed by spacecraft.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Control of the diocotron instability of a hollow electron beam with periodic dipole magnets

A method to control the diocotron instability of a hollow electron beam with peri-odic dipole magnetic fields has been investigated by a two-dimensional particle-in-cell simulation. At first, relations between the diocotron instability and several physical parameters such as the electron number density, current and shape of the electron beam, and the solenoidal field strength are theoretically analyzed without periodic dipole magnetic fields. Then, we study the effects of the periodic dipole magnetic fields on the diocotron instability using the two-dimensional particle-in-cell simulation. In the simulation, we considered the periodic dipole magnetic field applied along the propagation direction of the beam, as a temporally varying magnetic field in the beam frame. Lastly, a stabilizing effect is observed when the oscillating frequency of the dipole magnetic field is optimally chosen, which increases with the increasing amplitude of the dipole magnetic field.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Elliptic Aperture CCT Coils for HTS Dipole Magnets

High-temperature REBa$_{2}$Cu$_{3}$O$_{7-x}$ (REBCO) superconductors are a route to increase the field of accelerator magnets beyond the 15-16T practical limit of Nb$_{3}$Sn. REBCO cabled in a CORC geometry is a promising fit for this application, enabling the design of low inductance magnets with conductor transposition. However, the use of CORC in coils with the tight conductor bending radii typical of accelerator magnets remains a key challenge, with on-going research both on the conductor development and coil design fronts seeking to address this issue. Here, in this work we explore the tradeoffs between circular and elliptic aperture canted-cosine-theta (CCT) coils when the conductor minimum bending radius is a key consideration, concluding that aperture ellipticity is an important free parameter in the optimization of magnetically efficient CORC dipole magnets. In particular, we show that elliptic bore designs enable a regime of smaller aperture HTS coils, an important result for LTS-HTS hybrid magnets and more generally for accelerator applications benefiting from non-circular magnet apertures. To this end we present an elliptic aperture dipole design optimized for hybrid testing within the US Magnet Development Program (US-MDP) and share 77 K test results of a prototype coil which provides first experimental confirmation of the advantages.

Brouwer, L. [Lawrence Berkeley National Laboratory↗
DOE OSTI2016

Magnetic dipole interactions in crystals

The influence of magnetic dipole interactions (MDIs) on the magnetic properties of local-moment Heisenberg spin systems is investigated. A general formulation is presented for calculating the eigenvalues λ and eigenvectors μ ˆ of the MDI tensor of the magnetic dipoles in a line (one dimension, 1D), within a circle (2D) or a sphere (3D) of radius r surrounding a given moment μ → i for given magnetic propagation vectors k for collinear and coplanar noncollinear magnetic structures on both Bravais and non-Bravais spin lattices. Results are calculated for collinear ordering on 1D chains, 2D square and simple-hexagonal (triangular) Bravais lattices, 2D honeycomb and kagomé non-Bravais lattices, and 3D cubic Bravais lattices. The λ and μ ˆ values are compared with previously reported results. Calculations for collinear ordering on 3D simple tetragonal, body-centered tetragonal, and stacked triangular and honeycomb lattices are presented for c/a ratios from 0.5 to 3 in both graphical and tabular form to facilitate comparison of experimentally determined easy axes of ordering on these Bravais lattices with the predictions for MDIs. Comparisons with the easy axes measured for several illustrative collinear antiferromagnets (AFMs) are given. The calculations are extended to the cycloidal noncollinear 120 ° AFM ordering on the triangular lattice where λ is found to be the same as for collinear AFM ordering with the same k. The angular orientation of the ordered moments in the noncollinear coplanar AFM structure of GdB 4 with a distorted stacked 3D Shastry-Sutherland spin-lattice geometry is calculated and found to be in disagreement with experimental observations, indicating the presence of another source of anisotropy. Similar calculations for the undistorted 2D and stacked 3D Shastry-Sutherland lattices are reported. The thermodynamics of dipolar magnets are calculated using the Weiss molecular field theory for quantum spins, including the magnetic transition temperature T m and the ordered moment, magnetic heat capacity, and anisotropic magnetic susceptibility χ versus temperature T . The anisotropic Weiss temperature θ p in the Curie-Weiss law for T>T m is calculated. A quantitative study of the competition between FM and AFM ordering on cubic Bravais lattices versus the demagnetization factor in the absence of FM domain effects is presented. The contributions of Heisenberg exchange interactions and of the MDIs to T m and to θ p are found to be additive, which simplifies analysis of experimental data. Some properties in the magnetically-ordered state versus T are presented, including the ordered moment and magnetic heat capacity and, for AFMs, the dipolar anisotropy of the free energy and the perpendicular critical field. The anisotropic χ for dipolar AFMs is calculated both above and below the Néel temperature T N and the results are illustrated for a simple tetragonal lattice with c/a>1, c/a=1 (cubic), and c/a<1 , where a change in sign of the χ anisotropy is found at c/a=1 . Finally, following the early work of Keffer [Phys. Rev. 87, 608 (1952)], the dipolar anisotropy of χ above T N =69 K of the prototype collinear Heisenberg-exchange-coupled tetragonal compound MnF 2 is calculated and found to be in excellent agreement with experimental single-crystal literature data above 130 K, where the smoothly increasing deviation of the experimental data from the theory on cooling from 130 K to T N is deduced to arise from dynamic short-range collinear c -axis AFM ordering in this temperature range driven by the exchange interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Longitudinal Gradient Dipole Magnet Prototype for APS at ANL

We planned an upgrade of the Advanced Photon Source at Argonne National Laboratory (ANL). The main goal of the upgrade is to improve the storage ring performance based on more advanced optics. One of the key magnet system elements is bending dipole magnets having a field strength change along the electron beam path. Moreover, a prototype of one such longitudinal gradient dipole magnet has been designed, built, and measured in a collaborative effort of ANL and Fermilab. Our paper discusses various magnetic design options, the selected magnet design, and the fabrication technology. The prototype magnet has been measured by rotational coils, a stretched wire, and a Hall probe. Measurement results are discussed and compared with simulations.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

HTS Dipole Magnet With Mechanical Energy Transfer in the Magnetic Field

Several high-temperature superconducting (HTS) model magnets for particle accelerators were designed and successfully tested at Fermilab. Some worked in a persistent current mode by continuously generating magnetic fields in the iron-dominated magnet gap. This paper investigated a novel HTS dipole magnet concept with a mechanical energy transfer in the magnetic field. To pump the energy in the superconducting HTS dipole magnet, a detachable magnetizer was used. The HTS dipole magnet was built and successfully tested at a liquid nitrogen temperature. We discuss the magnet design, test results, the proposed approach limits, and efficiency.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

DETECTION OF NONPOLAR IONS IN {sup 2}{Pi}{sub 3/2} STATES BY RADIOASTRONOMY VIA MAGNETIC DIPOLE TRANSITIONS

The possibility of magnetic dipole-induced pure rotational transitions in the interstellar medium is investi- gated for symmetric Hund's case (a) linear molecules, such as H-C{identical_to}C-H{sup +} (X-tilde {sup 2}{Pi}{sub 3/2u}), CO{sub 2} {sup +} (X-tilde {sup 2}{Pi}{sub 3/2g}), H-C{identical_to}C-C{identical_to}C-H{sup +} (X-tilde {sup 2}{Pi}{sub 3/2g}), and N{sub 3} (X-tilde {sup 2}{Pi}{sub 3/2g}). These species lack an electric dipole moment and therefore cannot undergo pure rotational electric dipole transitions. These species can undergo pure rotational transitions via the parallel component of the magnetic dipole operator, however. The transition moments and Einstein A coefficients for the allowed pure rotational transitions are derived for a general Hund's case (a) linear molecule, and tabulated for the examples of H-C{identical_to}C-H{sup +} ({sup 2}{Pi}{sub 3/2u}) and H-C{identical_to}C-C{identical_to}C-H{sup +} ({sup 2}{Pi}{sub 3/2g}). It is found that the rates of emission are comparable to collision rates in interstellar clouds, suggesting that this decay mechanism may be important in simulating rotational population distributions in diffuse clouds and for detecting these molecules by radioastronomy. Expected line positions for the magnetic dipole-allowed R{sub ef} (J) and R{sub fe} (J) transitions of H-C{identical_to}C-H{sup +} ({sup 2}{Pi}{sub 3/2u}), H-C{identical_to}C-C{identical_to}C-H{sup +} ({sup 2}{Pi}{sub 3/2g}), CO{sub 2}{sup +} ({sup 2}{Pi}{sub 3/2g}), and N{sub 3} ({sup 2}{Pi}{sub 3/2g}) are tabulated to assist in their observation by radioastronomy or in the laboratory.

74 ATOMIC AND MOLECULAR PHYSICS↗