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Results for “MAGNETIC FLUX”

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 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

The origin of rigidly rotating magnetic field patterns on the sun

Using analytical calculations and numerical simulations, it is shown that a meridional component of magnetic-flux transport will offset the shearing effect of differential rotation and give rise to rigidly rotating patterns of large-scale magnetic field. The nonaxisymmetric field attains a striped polarity pattern which rotates rigidly like a barber pole while its individual small-scale flux elements rotate at the differential rate of the latitudes they are crossing. On the sun, the meridional transport is provided by supergranular diffusion possibly assisted by a small poleward flow. New sources of flux retard this process and exclude the rigid rotation from the sunspot belts until well into the declining phase of the sunspot cycle. This mechanism accounts for a number of heretofore unexplained phenomena including the tendency for coronal holes to rotate rigidly during the declining phase of the sunspot cycle.

Sheeley, N. R., Jr.↗
DOE OSTI2020

DESC: A stellarator equilibrium solver

In this paper, the new code DESC is presented to solve for fixed-boundary ideal magnetohydrodynamic equilibria in stellarators. The approach directly solves the equilibrium force balance as a system of nonlinear equations in the form f(x) = 0. The independent variables x represent nested magnetic flux surfaces expressed in the inverse representation with toroidal flux coordinates, and the equations f(x) quantify equilibrium force balance errors at discrete points in real space. Discretizing with global Fourier–Zernike basis functions properly treats the magnetic axis and minimizes the number of coefficients needed to describe the flux surfaces. The pseudospectral method provides great flexibility in where the errors are evaluated, and the system of equations is efficiently solved with a Newton–Raphson iteration. Equilibria are computed and compared against VMEC for both axisymmetric and non-axisymmetric examples. The results show fast convergence rates and solutions with low errors throughout the plasma volume.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Enhancing Fundamental Understanding of Magnetic Confinement in the Presence of Flows, Non-Conservative Forces, Dynamics, Collisions, Relaxation and Kinetic Effects

Pulsed high-power technology is used to create MHD-governed, dynamically-evolving, plasma-filled magnetic flux tubes. Advanced diagnostics measure the dynamical evolution and the measurements are then related to theoretical models. The dynamics are relevant to solar coronal plasma loops, astrophysical jets, and other situations where magnetic field lines intercept a boundary and current flows from the boundary into the plasma along the field lines. The morphology is time-dependent and determined by complex physics involving magnetic forces, hydrodynamic forces, and boundary conditions. Unlike magnetic fusion plasma experiments which are in approximate MHD equilibrium, fast accelerated plasma flows are a dominant feature. Typical parameters are: electric current 50-150 kA, applied voltage 3-6 kV, magnetic field 0.3 to 3 kG, experiment duration 10 μs, jet velocity 10’s of km/s, flux tube dimensions a few cm in radius and 10’s of cm in length. A scheme for measuring the wavelength of a quasi-neutral magnetic plasma wave using a single point of measurement was demonstrated both by an actual spacecraft (MMS) and in the lab. The experimental work is supported by a strong theoretical component. Theoretical activities included proposing a model for driving astrophysical jets (model motivated by lab experiments), and providing new insights into fast collisionless magnetic reconnection by demonstration of a new, more fundamental parameter than previously used.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

MnP Films with Desired Magnetic, Magnetocaloric, and Thermoelectric Properties for a Perspective Magneto-Thermo-Electric Cooling Device

A new magneto-thermo-electric cooling device (MTECD) comprising a central magnetocaloric (MC) material (e.g., Gd) sandwiched by two thermoelectric (TE) materials (e.g., MnP) is proposed. The presence of the TE materials in the MTECD guides the heat flow direction and enhances heat pulsation. Here in this case, the usage of a ferromagnetic TE material that combines large TE with small MC properties within a similar temperature region can enhance the magnetic flux density and heat exchange efficiency. Herein, it is shown that MnP nanorod-structured films with desired magnetic, MC, and TE properties are very promising for use in MTECDs. The films are grown on Si substrates at 300, 400, and 500 °C using molecular beam epitaxy. The 400 °C sample shows a desired TE and MC combination. A large power factor of 24.06 μW m -1 K -2 is achieved at room temperature. In this temperature region, the film exhibits a small MC effect (-ΔS M ≈0.64 J kg -1 K and ΔT ad ≈0.3 K at μ 0 H = 2 T) but ferromagnetism that gives rise to the enhanced MC effect of the central MC material. These properties can enable the MTECD to operate at high frequency.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Quantum spin liquid in the semiclassical regime

Quantum spin liquids (QSLs) have been at the forefront of correlated electron research ever since their proposal in 1973, and the realization that they belong to the broader class of intrinsic topological orders. According to received wisdom, QSLs can arise in frustrated magnets with low spin S, where strong quantum fluctuations act to destabilize conventional, magnetically ordered states. In this work, we present a Z 2 QSL ground state that appears already in the semiclassical, large-S limit. This state has both topological and symmetry-related ground-state degeneracy, and two types of gaps, a “magnetic flux” gap that scales linearly with S and an “electric charge” gap that drops exponentially in S. The magnet is the spin-S version of the spin-1/2 Kitaev honeycomb model, which has been the subject of intense studies in correlated electron systems with strong spin–orbit coupling, and in optical lattice realizations with ultracold atoms.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Evidence for 4e charge of Cooper quartets in a biased multi-terminal graphene-based Josephson junction

Abstract In a Josephson junction (JJ) at zero bias, Cooper pairs are transported between two superconducting contacts via the Andreev bound states (ABSs) formed in the Josephson channel. Extending JJs to multiple superconducting contacts, the ABSs in the Josephson channel can coherently hybridize Cooper pairs among different superconducting electrodes. Biasing three-terminal JJs with antisymmetric voltages, for example, results in a direct current (DC) of Cooper quartet (CQ), which involves a four-fermion entanglement. Here, we report half a flux periodicity in the interference of CQ formed in graphene based multi-terminal (MT) JJs with a magnetic flux loop. We observe that the quartet differential conductance associated with supercurrent exhibits magneto-oscillations associated with a charge of 4 e , thereby presenting evidence for interference between different CQ processes. The CQ critical current shows non-monotonic bias dependent behavior, which can be modeled by transitions between Floquet-ABSs. Our experimental observation for voltage-tunable non-equilibrium CQ-ABS in flux-loop-JJs significantly extends our understanding of MT-JJs, enabling future design of topologically unique ABS spectrum.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Non-invertible symmetries in finite-group gauge theory

We investigate the invertible and non-invertible symmetries of topological finite-group gauge theories in general spacetime dimensions, where the gauge group can be abelian or non-abelian. We focus in particular on the 0-form symmetry. The gapped domain walls that generate these symmetries are specified by boundary conditions for the gauge fields on either side of the wall. We investigate the fusion rules of these symmetries and their action on other topological defects including the Wilson lines, magnetic fluxes, and gapped boundaries. We illustrate these constructions with various novel examples, including non-invertible electric-magnetic duality symmetry in 3+1d \mathbb{Z}_2 ℤ 2 gauge theory, and non-invertible analogs of electric-magnetic duality symmetry in non-abelian finite-group gauge theories. In particular, we discover topological domain walls that obey Fibonacci fusion rules in 2+1d gauge theory with dihedral gauge group of order 8. We also generalize the Cheshire string defect to analogous defects of general codimensions and gauge groups and show that they form a closed fusion algebra.

Córdova, Clay↗
NASA NTRS1986

Constraints on geomagnetic secular variation modeling from electromagnetism and fluid dynamics of the Earth's core

A spherical harmonic representation of the geomagnetic field and its secular variation for epoch 1980, designated GSFC(9/84), is derived and evaluated. At three epochs (1977.5, 1980.0, 1982.5) this model incorporates conservation of magnetic flux through five selected patches of area on the core/mantle boundary bounded by the zero contours of vertical magnetic field. These fifteen nonlinear constraints are included like data in an iterative least squares parameter estimation procedure that starts with the recently derived unconstrained field model GSFC (12/83). Convergence is approached within three iterations. The constrained model is evaluated by comparing its predictive capability outside the time span of its data, in terms of residuals at magnetic observatories, with that for the unconstrained model.

Benton, E. R.↗
NASA NTRS1989

Steady hydromagnetic flows in open magnetic fields. II - Global flows with static zones

A theoretical study of an axisymmetric steady stellar wind with a static zone is presented, with emphasis on the situation where the global magnetic field is symmetrical about the stellar equator and is partially open. In this scenario, the wind escapes in open magnetic fluxes originating from a region at the star pole and a region at an equatorial belt of closed magnetic field in static equilibrium. The two-dimensional balance of the pressure gradient and the inertial, gravitational, and Lorentz forces in different parts of the flow are studied, along with the static interplay between external sources of energy (heating and/or cooling) distributed in the flow and the pressure distribution.

Tsinganos, K.↗
NASA NTRS1989

The association of flares to cancelling magnetic features on the sun

Previous work relating flares to evolutionary changes of photospheric solar magnetic fields are reviewed and reinterpreted in the light of recent observations of canceling magnetic fields. The results show that cancelation happens with fields spanning a wide range of magnetic field strengths. Flares of all magnitudes begin adjacent to cancelation sites, whether the associated active region as a whole is developing or decaying. Both small and big flares are initiated near canceling sites, from the microflares associated with ephemeral regions to the kernels of the great flares. Canceling magnetic flux is observed or deduced to be the common denominator among all observed associations of flares to changing magnetic fields. It is proposed that canceling magnetic fields are a necessary evolutionary condition for the initiation of solar flares.

Livi, Silvia H. B.↗
NASA NTRS1992

Ionospheric models for Venus and Mars

The ways in which different models employ the multifluid continuity, momentum, and energy equations to characterize the ionospheres of Mars and Venus on the basis of in situ neutral and ion compositions are discussed. The Venus ionosphere is permeated by large-scale magnetic fields when the solar wind dynamic pressure is high, but is free from such fields under conditions of low solar wind dynamic pressure. Large-scale magnetic fields are nearly always present in the Mars ionosphere. Plasma moves downward on both planets for magnetized conditions, and magnetic flux is carried from the magnetosheath down into the ionosphere. Ohmic dissipation of the currents responsible for the magnetic field takes place deep in the ionospheres of both planets.

Cravens, T. E.↗
NASA NTRS1994

Magnetic mapping and Birkeland currents in the Toffoletto-Hill and Tsyganenko magnetosphere models

We investigate the mapping of magnetic flux tubes between the high-latitude ionosphere and the equatorial magnetosphere, using the Toffoletto and Hill (1989) theoretical model and the Tsyganenko (1987, 1989) empirical models. In all models, strong distortion of flux tubes occurs near the magnetopause and in the distant tail. These effects are illustrated for various interplanetary magnetic field directions in the Toffoletto and Hill (1989) model and for various Kp values in the Tsyganenko (1987, 1989) model. We calculate the Birkeland current that is actually present in each model (from Ampere's law), as well as the Birkeland current that would be implied if the model were in magnetostatic equilibrium with isotropic plasma pressure (from the Vasyliunas equation). Comparison of the actual and implied Birkeland currents indicates that no physically significant Birkeland current is included in any of the models tested. Each model contains a 'noise' component of Birkeland current that is, however, much smaller in magnitude than the 'real' Birkeland currents that remain to be included.

Ding, Cheng↗
DOE OSTI2017

Hysteretic Superconducting Heat-Flux Quantum Modulator

In this work, we discuss heat transport in a thermally biased superconducting quantum-interference device (SQUID) in the presence of an external magnetic flux, when a non-negligible inductance of the SQUID ring is taken into account. A properly sweeping driving flux causes the thermal current to modulate and behave hysteretically. The response of this device is analyzed as a function of both the hysteresis parameter and the degree of asymmetry of the SQUID, highlighting the parameter range over which hysteretic behavior is observable. Markedly, the temperature of the SQUID also shows hysteretic evolution, with sharp transitions characterized by temperature jumps up to, e.g., approximately 0.02 K for a realistic Al-based setup. In view of these results, the proposed device can effectively find an application as a temperature-based superconducting memory element, working even at gigahertz frequencies by suitably choosing the superconductor on which the device is based.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Disordered vortex matter out of equilibrium: a Langevin molecular dynamics study

We discuss the use of Langevin molecular dynamics in the investigation of the non-equilibrium properties of disordered vortex matter. Here, our special focus is set on values of system parameters that are realistic for disordered high-T c superconductors such as YBCO. Using a discretised elastic line model, we study different aspects of vortices far from thermal equilibrium. On the one hand, we investigate steady-state properties of driven magnetic flux lines in a disordered environment, namely the current–voltage characteristics, the gyration radius and the pinning time statistics. On the other hand, we study the complex relaxation processes and glassy-like dynamics that emerge in type-II superconductors due to the intricate competition between the long-range vortex–vortex repulsion and flux pinning due to randomly placed point defects. To this end, we consider different types of sudden perturbations: temperature, magnetic field and external current quenches.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Dynamics of Dirac strings and monopolelike excitations in chiral magnets under a current drive

Skyrmion lines in metallic chiral magnets carry an emergent magnetic field experienced by the conduction electrons. The inflow and outflow of this field across a closed surface is not necessarily equal, thus it allows for the existence of emergent monopoles. One example is a segment of skyrmion line inside a crystal, where a monopole and antimonopole pair is connected by the emergent magnetic flux line. This is a realization of Dirac stringlike excitations. Here we study the dynamics of monopoles in chiral magnets under an electric current. We show that in the process of creation of skyrmion lines, skyrmion line segments are first created via the proliferation of monopoles and antimonopoles. Then these line segments join and span the whole system through the annihilation of monopoles. The skyrmion lines are destroyed via the proliferation of monopoles and antimonopoles at high currents, resulting in a chiral liquid phase. We also propose to create the monopoles in a controlled way by applying an inhomogeneous current to a crystal. Remarkably, an electric field component in the magnetic field direction proportional to the current squared in the low current region is induced by the motion of distorted skyrmion lines, in addition to the Hall and longitudinal voltage. As a result, the existence of monopoles can be inferred from transport or imaging measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High Pressure Synthesis of New Magnets, Featuring Diamagnetic Sources of Anisotropy

Permanent magnets are the functional component of electric motors and generators found in numerous renewable energy applications spanning from regenerative brakes to wind turbines. Magnets that generate higher magnetic flux per volume are central to improved energy generation in these applications. To develop a new class of permanent magnets while retaining the properties conferred by rare-earth elements, a fundamentally different approach is required. We hypothesize that by engendering a covalent interaction between two elements, it will be possible to interact the two components of a magnetic moment—spin and orbital angular momentum—from two separate atoms to form a complete magnetic moment. This seed project focuses on the scale up of the compound FeBi 2 , which was initially synthesized in our laboratory. Scale up approaches include slow decompression, alternate synthetic routes, and using fabrication approaches to more intimately mix the precursor elements. We also pursued the synthesis of new phases in the Mn-Bi system targeted to create new magnetic materials. In our initial experiments we decompressed FeBi 2 down to 2.9 GPa, demonstrating a kinetic stability to the phase that enabled it to be recovered to an order of magnitude lower pressure than that needed to synthesize it (30 GPa). Our goal is to recover this exciting material to ambient pressures so that we can isolate samples for detailed physical properties measurements. We have undertaken three distinct approaches toward that goal, which we summarize below. Our two most notable results are the formation of a quenchable phase through antimony doping of FeBi 2 , and the development of a new approach to preparing samples for diamond anvil cell syntheses.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Eddy current studies for the beam screen of the Electron-Ion Collider hadron storage ring superconducting magnets

A copper-clad stainless steel beam screen will be installed in each of the Relativistic Heavy Ion Collider (RHIC) superconducting (SC) magnets used for making the Electron-Ion Collider (EIC) Hadron Storage Ring (HSR). Eddy currents are induced within conductors to oppose a changing magnetic flux. Eddy currents will appear on the EIC HSR beam screens during ramp up and ramp down, after a magnet quenches and when reversing the polarity of the γ transition jump quadrupoles during γ transition crossing. This study evaluates the magnitude of the eddy currents, the temperature increase due to Joule heating and the stress at the beam screens from the eddy-current induced force.

43 PARTICLE ACCELERATORS↗