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At least 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Single-particle and dipole excitations in Co 62

An extensive study of the level structure of 62 Co has been performed following a complex multinucleon transfer reaction, 26 Mg( 48 Ca, 2α3npγ) 62 Co, at beam energies of 275, 290, and 320 MeV. The combination of the Gammasphere array, the fragment mass analyzer, and a focal-plane ionization chamber was used to identify and delineate excited levels in 62 Co. A considerable extension to the 62 Co level scheme is proposed with firm spin-parity values assigned on the basis of angular distribution and correlation analyses. Here, various level sequences built upon states of single-particle character have been observed, and an interpretation of these structures in the framework of the spherical shell model is presented. At moderate spins, two dipole bands have been observed and, based on their phenomenological study, a possible magnetic rotation character is suggested. However, theoretical calculations performed using the particle rotor model support magnetic rotation for only one of these dipole bands.

59 ≤ A ≤ 89↗
DOE OSTI2019

Interaction Region Magnets for Future Electron-Ion Collider ¿at Jefferson Lab

The Jefferson Lab Electron Ion Collider (JLEIC) is a pro-posed new machine for nuclear physics research. It uses the existing CEBAF accelerator as a full energy injector to deliver 3 to 12 GeV electrons into a new electron collider ring. An all new ion accelerator and collider complex will deliver up to 200 GeV protons. The machine has luminosity goals of 1034 cm-2 sec-1. The whole detector region including forward detection covers about 80 meters of the JLEIC complex. The interaction region design has recently been optimized to accommodate 200 GeV proton energy using conventional NbTi superconducting magnet technology. This paper will describe the requirements and preliminary designs for both the ion and electron beam magnets in the most complex 34.5 m long interaction region (IR) around the interaction point (IP). The interaction region has over thirty-four superconducting magnets operating at 4.5K; these include dipoles, quadrupoles, skew quadrupoles, solenoids, horizontal and vertical correctors and higher order multipole magnets. The paper will also dis-cuss the electromagnetic interaction between these magnets.

Rajput-Ghoshal, Renuka↗
DOE OSTI2019

Interaction Region Magnets for Future Electron-Ion Collider at Jefferson Lab

The Jefferson Lab Electron Ion Collider (JLEIC) is a pro-posed new machine for nuclear physics research. It uses the existing CEBAF accelerator as a full energy injector to deliver 3 to 12 GeV electrons into a new electron collider ring. An all new ion accelerator and collider complex will deliver up to 200 GeV protons. The machine has luminosity goals of 1034 cm-2 sec-1. The whole detector region including forward detection covers about 80 meters of the JLEIC complex. The interaction region design has recently been optimized to accommodate 200 GeV proton energy using conventional NbTi superconducting magnet technology. This paper will describe the requirements and preliminary designs for both the ion and electron beam magnets in the most complex 34.5 m long interaction region (IR) around the interaction point (IP). The interaction region has over thirty-four superconducting magnets operating at 4.5K; these include dipoles, quadrupoles, skew quadrupoles, solenoids, horizontal and vertical correctors and higher order multipole magnets. The paper will also dis-cuss the electromagnetic interaction between these magnets.

Rajput-Ghoshal, Renuka↗
DOE OSTI2013

Collective oscillations of the magnetic moments of a chain of spherical magnetic nanoparticles with uniaxial magnetic anisotropy

Magnetic particles moving freely in a fluid can organize dense phases (3D clusters or linear chains). We analyze the spectrum of magnetic oscillations of a chain of spherical magnetic particles taking into account the magnetic anisotropy of an individual particle for an arbitrary relation between the anisotropy energy and the energy of the dipole interaction of particles. For any relation between these energies, the spectrum contains three branches of collective oscillations: a high-frequency branch and a weakly split doublet of low-frequency branches. The frequency of the high-frequency branch is determined by a stronger interaction, while the frequencies of the low-frequency branches are determined by the weakest interaction. Accordingly, the dispersion is maximal for oscillations formed by the dipole-dipole interaction of particles, which have high frequencies in the case of a strong dipole interaction or low frequencies in the case of a strong anisotropy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1972

UK-4 flight spacecraft magnetic tests

Magnetic tests conducted on the UK-4 spacecraft are discussed. The objectives of the test are: (1) to determine the permanent, induced, and stray magnetic moments of the spacecraft, (2) to assess its magnetic stability, (3) to determine the dipole moment produced by energizing the magnetorquer coil, (4) to measure the despin torque due to eddy current and magnetic hysteresis, and (5) to deperm, compensate, and make other adjustments necessary to achieve satisfactory magnetic characteristics for the spacecraft.

Pruett, W. E.↗
NASA NTRS1992

Can accretion onto isolated neutron stars produce gamma-ray bursts?

It is shown here that, if slow accretion onto high-velocity neutron stars from the interstellar medium is to be the origin of gamma-ray bursts, the accretion physics is very different from what applies for local low-velocity neutron stars. For halo neutron stars with high magnetic fields and velocities, electromagnetic dipole radiation pressure prevents accretion unless the period is longer than tens of seconds; the centrifugal barrier will then prevent accretion until the period reaches several thousand seconds. For periods as long as this, accretion may proceed through Kelvin-Helmholtz instability at the magnetopause boundary. At interstellar densities and neutron-star magnetic fields of about 10 exp 12 G, the accretion rate by this process can be much larger than the Bondi-Hoyle accretion rate, but is still well below what is needed for slow-accretion burst models. It is concluded that slow accretion onto high-velocity neutron stars in the halo cannot be the origin of gamma-ray bursts.

Harding, Alice K.↗
DOE OSTI2020

Development and First Test of the 15 T Nb 3 Sn Dipole Demonstrator MDFCT1

Fermilab in the framework of the U.S. Magnet Development Pro-gram (US-MDP) has developed and fabricated a 15 T Nb 3 Sn dipole demonstrator for a post-LHC hadron collider. In June 2019 the magnet was tested and reached a world record field in the aperture of 14.1T at 4.5 K.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Development and Comparison of Mechanical Structures for FNAL 15 T Nb$_3$Sn Dipole Demonstrator

Main design challenges for 15 T accelerator magnets are large Lorentz forces at this field level. The large Lorentz forces generate high stresses in the coil and mechanical structure and, thus, need stress control to maintain them at the acceptable level for brittle Nb3Sn coils and other elements of magnet mechanical structure. To provide these conditions and achieve the design field in the FNAL 15 T dipole demonstrator, several mechanical structures have been developed and analysed. The possibilities and limitations of these designs are discussed in this paper

43 PARTICLE ACCELERATORS↗
NASA NTRS2011

Gamma-Ray Pulsar Light Curves in Vacuum and Force-Free Geometry

Recent studies have shown that gamma-ray pulsar light curves are very sensitive to the geometry of the pulsar magnetic field. Pulsar magnetic field geometries, such as the retarded vacuum dipole and force-free magnetospheres have distorted polar caps that are offset from the magnetic axis in the direction opposite to rotation. Since this effect is due to the sweepback of field lines near the light cylinder, offset polar caps are a generic property of pulsar magnetospheres and their effects should be included in gamma-ray pulsar light curve modeling. In slot gap models (having two-pole caustic geometry), the offset polar caps cause a strong azimuthal asymmetry of the particle acceleration around the magnetic axis. We have studied the effect of the offset polar caps in both retarded vacuum dipole and force-free geometry on the model high-energy pulse profiles. We find that, compared to the profiles derived from symmetric caps, the flux in the pulse peaks, which are caustics formed along the trailing magnetic field lines, increases significantly relative to the off-peak emission, formed along leading field lines. The enhanced contrast produces improved slot gap model fits to Fermi pulsar light curves like Vela, with vacuum dipole fits being more favorable.

Harding, Alice K.↗
DOE OSTI2018

Model Proposed to Calculate the Exchange Interaction in Ni/Pt Multilayers

The behavior of spin waves is mainly influenced by all parameters that characterize the magnetic material such as exchange interactions, surface and volume anisotropy effects, dipole interactions, and phase transitions and imperfections. In this article, we develop a simple calculation model based on a ferromagnetic anisotropic system that has allowed us to obtain numerical estimates for the Pt exchange interaction and the interlayer coupling force at various Ni/Pt multilayers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Numerical analysis of thermally assisted spin-transfer torque magnetization reversal in synthetic ferrimagnetic free layers

The spin transfer torque magnetization reversal of synthetic ferrimagnetic free layers under pulsed temperature rise was numerically studied by solving the Landau–Lifshitz–Gilbert equation, taking into account the stochastic random fields, the temperature dependence of magnetic parameters, and the spin torque terms. The anti-parallel magnetization configuration was retained at the elevated temperature, due to interlayer dipole coupling. A significant thermal assistance effect, resulting in a 40% reduction in the switching current, was demonstrated during a nanosecond pulsed temperature rise up to 77% of the Curie temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Performance of Superconducting Magnet Prototypes for LCLS-II Linear Accelerator

The new LCLS-II Linear Superconducting Accelerator at SLAC needs superconducting magnet packages installed inside SCRF Cryomodules to focus and steer an electron beam. Two magnet prototypes were built and successfully tested at Fermilab. Magnets have an iron dominated configuration, quadrupole and dipole NbTi superconducting coils, and splittable in the vertical plane configuration. Magnets inside the Cryomodule are conductively cooled through pure Al heat sinks. Both magnets performance was verified by magnetic measurements at room temperature, and during cold tests in liquid helium. Test results including magnetic measurements are discussed. Special attention was given to the magnet performance at low currents where the iron yoke and the superconductor hysteresis effects have large influence. Both magnet prototypes were accepted for the installation in FNAL and JLAB prototype Cryomodules.

43 PARTICLE ACCELERATORS↗
NASA NTRS1982

Modeling the thermal structure and magnetic properties of the crust of active regions with application to the Rio Grande rift

Experiments in Curie depth estimation from long wavelength magnetic anomalies are summarized. The heart of the work is equivalent-layer-type magnetization models derived by inversion of high-elevation, long wavelength magnetic anomaly data. The methodology is described in detail in the above references. A magnetization distribution in a thin equivalent layer at the Earth's surface having maximum detail while retaining physical significance, and giving rise to a synthetic anomaly field which makes a best fit to the observed field in a least squares sense is discussed. The apparent magnetization contrast in the equivalent layer is approximated using an array of dipoles distributed in equal area at the Earth's surface. The dipoles are pointed in the direction of the main magnetic field, which carries the implicit assumption that crustal magnetization is dominantly induced or viscous. The determination of the closest possible dipole spacing giving a stable inversion to a solution having physical significance is accomplished by plotting the standard deviation of the solution parameters against their spatial separation for a series of solutions.

Source record↗
NASA NTRS2003

Properties of Cusp Diamagnetic Cavities

Progress can be reported in two areas related to characterizing the properties of cusp diamagnetic cavities. Laboratory terrella experiments have been conducted for the purpose of using neutral gas excitation as a tracer of trapped electron populations in the presence of two dipoles that are used to develop a magnetic cusp topology. Figure 1 and 2 show top and side views of two configurations. Dipole trapped electron populations appear as the two luminous annular rings. Other populations are the most intense regions are shown. Interspersed between these regions are narrow regions that represent the topological cusps in these configurations. That they contain luminous gas is evidence for cusp trapping similar to what we believe exists in the terrestrial magnetosphere. The asymmetry of these cusp regions as seen in Figure 1 is the result of a relative tilt between the two dipoles suggestive of what would be expected in space. It is in these regions that particle observations were sought, so as to validate the realization of proposed and laboratory achieved trapping in a diamagnetic cusp. Figure 3 shows particle trajectories in a modeled cusp magnetic topology for three particle energies. Blue, green, and red traces correspond to increasing energies. Due to factors discussed outside of this final report, a thorough exploration of relevant satellite observations have not been achieved.

Sheldon, Robert B.↗
DOE OSTI2016

Direct imaging of coexisting ordered and frustrated sublattices in artificial ferromagnetic quasicrystals

Here, we have used scanning electron microscopy with polarization analysis and photoemission electron microscopy to image the two-dimensional magnetization of permalloy films patterned into Penrose P2 tilings (P2T). The interplay of exchange interactions in asymmetrically coordinated vertices and short-range dipole interactions among connected film segments stabilize magnetically ordered, spatially distinct sublattices that coexist with frustrated sublattices at room temperature. Numerical simulations that include long-range dipole interactions between sublattices agree with images of as-grown P2T samples and predict a magnetically ordered ground state for a two-dimensional quasicrystal lattice of classical Ising spins.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Conceptual Design of the Interaction Region Magnets for Future Electron-Ion Collider at Jefferson Lab

The Jefferson Lab Electron Ion Collider (JLEIC) is a proposed new machine for nuclear physics research. As proposed, it will deliver between 15 and 65 GeV center of mass energy collisions between electrons and nuclei. It uses the existing CEBAF accelerator as a full energy injector to deliver 3 to 10 GeV electrons into a new electron collider ring. An all new ion accelerator and collider complex will deliver up to 100 GeV protons, or 40 GeV/nucleon ions. The machine will have luminosity goals of above 1033 cm-2 sec-1 in the whole energy range with a maximum of a few 1034 cm-2 sec-1. The two collider rings use a unique figure-of eight layout to deliver a high degree of polarization in both beams. The machine will include room for two interaction regions with only one initially installed. The crossing angle in the primary interaction region will be 50 mrad. The whole detector region including forward detection covers about 80 meters of the JLEIC complex. This paper will describe the requirements and preliminary designs for both the ion and electron beam magnets in the most complex 32 m long interaction region (IR) around the interaction point (IP). The interaction region has over thirty-seven superconducting magnets operating at 4.5K; these include dipoles, quadrupoles, skew-quadrupoles, solenoids, horizontal and vertical correctors and higher order multipole magnets. The paper will also discuss the electromagnetic interaction between these magnets.

Wiseman, Mark (ORCID:0000000179110306)↗
NASA NTRS1982

Modelling the core magnetic field of the earth

It is suggested that radial off-center dipoles located within the core of the earth be used instead of spherical harmonics of the magnetic potential in modeling the core magnetic field. The off-center dipoles, in addition to more realistically modeling the physical current systems within the core, are if located deep within the core more effective at removing long wavelength signals of either potential or field. Their disadvantage is that their positions and strengths are more difficult to compute, and such effects as upward and downward continuation are more difficult to manipulate. It is nevertheless agreed with Cox (1975) and Alldredge and Hurwitz (1964) that physical realism in models is more important than mathematical convenience. A radial dipole model is presented which agrees with observations of secular variation and excursions.

Harrison, C. G. A.↗