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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

The Noncollinear Path to Two-Dimensional Topological Superconductivity

Two-dimensional magnet-superconductor hybrids (2D-MSH) are promising candidates to realize devices for topology-based quantum technologies and superconducting spintronics. So far, studies have focused on 2D-MSH systems with collinear ferro- or antiferromagnetic layers. Here, we present the discovery of topological superconductivity in a noncollinear MSH system where a magnetic spiral is realized in an Fe monolayer proximity coupled to a superconducting Ta(110) substrate. By combining low-temperature spin-polarized scanning tunneling spectroscopy with an in-depth theoretical study, we can conclude that the system is in a topological nodal-point superconducting phase with low-energy edge modes. Furthermore, we reveal that for this noncollinear spin texture, these edge modes exhibit a magnetization direction-dependent dispersion. This means that a spatial shift of the magnetic spiral could be used to reverse the chirality of an edge mode in future MSH-based devices.

chiral edge modes↗
NASA NTRS1980

Oscillating two-stream and parametric decay instabilities in a weakly magnetized plasma

The paper considers the effects of a weak ambient magnetic field on the oscillating two-stream and parametric decay instabilities with emphasis on the dependence of the angular variation of the instability thresholds and growth rates on the magnetic field. A dispersion relation is derived in the limit in which the electron plasma frequency is much greater than the cyclotron frequency, and is solved for dipole and monochromatic pump spectra. The analysis shows that the presence of a magnetic field can substantially enhance thresholds and reduce growth rates for waves propagating at an oblique angle with respect to the ambient magnetic field, so that the magnetic field has a stabilizing influence on the off-parallel propagating modes.

Freund, H. P.↗
NASA NTRS1983

Doubly diffusive magnetic buoyancy instability in the solar interior

An investigation of the buoyancy of diffuse magnetic fields has shown that in the presence of rotation, static equilibrium configurations of the toroidal magnetic field and ambient plasma can exist. In that case, the escape of toroidal magnetic flux from the solar interior may be determined by the growth of instabilities which the equilibrium configuration may be subject to. In connection with the present investigation, it is assumed that in the region of toroidal magnetic flux amplification, the magnetic field has not as yet filamented into flux ropes, and is therefore 'diffuse'. A study is conducted of the MHD stability of an electrically conducting and differentially rotating gas in the presence of a toroidal magnetic field, an external constant gravitational field, and radiance pressure. The full dispersion relation for the magnetic buoyancy problem is developed, and the solutions of the dispersion relation are discussed.

Schmitt, J. H. M. M.↗
NASA NTRS1973

X-ray observations of characteristic structures and time variations from the solar corona - Preliminary results from Skylab.

Examples taken from the S-054 X-ray telescope observations made during the first Skylab mission show the hot coronal plasma tracing the configuration of the magnetic fields. The high spectral resolution and sensitivity of the instrument has enabled the following two facts to be more firmly established: (1) that the 'quiet homogeneous corona' is in fact highly structured and that the structures observed appear to be the results of dispersed active region magnetic fields; and (2) that numerous bright points are distributed randomly on the disk. Their presence at high latitudes may play a role in solar cycle models. In addition, the capability of Skylab for studying time evolution has enabled the restructuring of coronal features to be seen at times of high activity, indicating a restructuring of the coronal magnetic fields.

Vaiana, G. S.↗
DOE OSTI2025

Properties of Lower Hybrid Drift Waves and Energy Transfer Near and Inside the Magnetic Reconnection Electron Diffusion Regions

Here, we investigate properties of lower hybrid drift waves (LHDWs) near and inside the electron diffusion regions in 17 magnetopause and 9 magnetotail reconnection events using Magnetospheric MultiScale (MMS) mission observations. Our analysis show that LHDW type depend on the electron beta, as electron beta increases LHDWs become more electromagnetic in nature. The energy transfer from electromagnetic fields to particles is higher in electrostatic LHDWs and it is largely in parallel direction with respect to the local magnetic field. Linear dispersion analysis shows that electrostatic LHDWs are perpendicular propagating while electromagnetic waves propagate in oblique directions and the normalized wavenumber of all LHDW types falls within 0.5–0.8 range. A simple estimate on the LHDW nonlinear saturation suggests a possibly important roles played by these waves in supporting the reconnection electric field.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1967

Study of ferromagnetic liquid

Synthesis and modification of stable colloidal dispersions with strong magnetic responses and Newtonian viscosity

Kaiser, R.↗
NASA NTRS1971

Plasma clouds in the magnetosphere

Magnetospheric plasma clouds equatorial observation by ATS 5 satellite, revealing plasma injection during substorms and dispersion by earth magnetic and electric fields

Deforest, S. E.↗
NASA NTRS1991

Magnetic flux transport and the sun's dipole moment - New twists to the Babcock-Leighton model

The mechanisms that give rise to the sun's large-scale poloidal magnetic field are explored in the framework of the Babcock-Leighton (BL) model. It is shown that there are in general two quite distinct contributions to the generation of the 'alpha effect': the first is associated with the axial tilts of the bipolar magnetic regions as they erupt at the surface, while the second arises through the interaction between diffusion and flow as the magnetic flux is dispersed over the surface. The general relationship between flux transport and the BL dynamo is discussed.

Wang, Y.-M.↗
NASA NTRS1991

Finite Difference Time Domain Electromagnetic Scattering from Frequency-Dependent Lossy Materials

During this effort the tasks specified in the Statement of Work have been successfully completed. The extension of Finite Difference Time Domain (FDTD) to more complicated materials has been made. A three-dimensional FDTD code capable of modeling interactions with both dispersive dielectric and magnetic materials has been written, validated, and documented. This code is efficient and is capable of modeling interesting targets using a modest computer work station platform. However, in addition to the tasks in the Statement of Work, a significant number of other FDTD extensions and calculations have been made. RCS results for two different plate geometries have been reported. The FDTD method has been extended to computing far zone time domain results in two dimensions. Finally, the capability to model nonlinear materials has been incorporated into FDTD and validated. The FDTD computer codes developed have been supplied, along with documentation, and preprints describing the other FDTD advances have been included with this report as attachments.

Luebbers, Raymond J.↗
NASA NTRS2007

Delta-Doped CCDs as Detector Arrays in Mass Spectrometers

In a conventional mass spectrometer, charged particles (ions) are dispersed through a magnetic sector onto an MCP at an output (focal) plane. In the MCP, the impinging charged particles excite electron cascades that afford signal gain. Electrons leaving the MCP can be read out by any of a variety of means; most commonly, they are post-accelerated onto a solid-state detector array, wherein the electron pulses are converted to photons, which, in turn, are converted to measurable electric-current pulses by photodetectors. Each step in the conversion from the impinging charged particles to the output 26 NASA Tech Briefs, February 2007 current pulses reduces spatial resolution and increases noise, thereby reducing the overall sensitivity and performance of the mass spectrometer. Hence, it would be preferable to make a direct measurement of the spatial distribution of charged particles impinging on the focal plane. The utility of delta-doped CCDs as detectors of charged particles was reported in two articles in NASA Tech Briefs, Vol. 22, No. 7 (July 1998): "Delta-Doped CCDs as Low-Energy-Particle Detectors" (NPO-20178) on page 48 and "Delta- Doped CCDs for Measuring Energies of Positive Ions" (NPO-20253) on page 50. In the present developmental miniature mass spectrometers, the above mentioned miniaturization and performance advantages contributed by the use of delta-doped CCDs are combined with the advantages afforded by the Mattauch-Herzog design. The Mattauch- Herzog design is a double-focusing spectrometer design involving an electric and a magnetic sector, where the ions of different masses are spatially separated along the focal plane of magnetic sector. A delta-doped CCD at the focal plane measures the signals of all the charged-particle species simultaneously at high sensitivity and high resolution, thereby nearly instantaneously providing a complete, high-quality mass spectrum. The simultaneous nature of the measurement of ions stands in contrast to that of a scanning mass spectrometer, in which abundances of different masses are measured at successive times.

Nikzad, Shouleh↗
NASA NTRS2017

Electric Field Activated Shape Memory Polymer Composite

Provided is an electrically activated shape memory polymer composite capable of thermal shape reformation using electric power to heat the composite through its matrix glass transition temperature. The composite includes an adaptable polymer matrix component using a diglycidyl ether resin, at least one substantially well-dispersed conductive or magnetic nano-filler component, and at least one elastic, laminated layer. Also provided are methods of preparing the composite and methods of activating the composite. A shape reformation of the composite is triggered by applying an electric field at DC and/or at a frequency above about 1.mu.Hz for a sufficient time.

Kang, Jin Ho↗
DOE OSTI2025

Connection between f -electron correlations and magnetic excitations in UTe 2

The detailed anisotropic dispersion of the low-temperature, low-energy magnetic excitations of the candidate spin-triplet superconductor UTe 2 is revealed using inelastic neutron scattering. The magnetic excitations emerge from the Brillouin zone boundary at the high symmetry Y and T points and disperse along the crystallographic $\hat{b}$ -axis. In applied magnetic fields to at least μ 0 H = 11 T along the $\hat{c}-{\rm{axis}}$ , the magnetism is found to be field-independent in the (hk0) plane. The scattering intensity is consistent with that expected from U 3+ /U 4+ f-electron spins with preferential orientation along the crystallographic $\hat{a}$ -axis, and a fluctuating magnetic moment of μ eff =1.7(5) μ B . We propose interband spin excitons arising from f-electron hybridization as a possible origin of the magnetic excitations in UTe 2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1985

The dispersive evolution of charged-particle bunches in random magnetic fields

Shortly after a strongly anisotropic beam of charged particles is injected along a guiding magnetic field on which is superimposed a small random conponent, the particle density can be represented by a Gaussian profile whose center moves with the coherent velocity and whose width increases with time at a rate controlled by the coefficient of dispersion. Both parameters depend upon the mean free path, which characterizes scattering by the random fields, and the focusing length, which characterizes spatial variations of the guiding field. These dependencies are known explicitly for the coherent velocity. Formulae for coefficient of dispersion are available only in the limits of very weak and very strong focusing. A new expression for coefficient of dispersion, which spans this gap, is presented.

Earl, J. A.↗
DOE OSTI2025

Kelvin–Helmholtz instability under stabilizing parallel magnetic field in nonhomogeneous compressible MHD flows

We study the Kelvin–Helmholtz instability (KHI) for the general case of a compressible, nonhomogeneous, magnetized plasma flow. The study is limited to a vortex sheet interface with an imposed parallel magnetic field. We introduce a new formalism based on a convective Mach number M c , a convective Alfvénic Mach number M Ac , and a total convective Mach number that combines the two. We derive an analytic expression of the KHI growth rate for a homogeneous flow (i.e., zero Atwood number, A=0) that converges toward both the expression for unmagnetized compressible flow and Chandrasekhar's expression for magnetized incompressible flow. Otherwise, the dispersion relation is solved numerically and allows deriving general stability diagrams of magnetized KHI for the triplet (A, M c , β −plasma) parameters. We show these parameters uniquely define all configurations for a parallel magnetic field. We also construct diagrams with respect to the convective Alfvénic Mach number, the β − plasma parameter, or the magnetic field showing which magnetic field strength is required for stabilizing a given shear flow. The theoretical growth rates are compared with 18 simulations made with the GAMERA code, currently used for 3D magnetospheric simulations. Finally, we apply our results to the analysis of a past KHI experiment performed at the OMEGA laser facility, showing linear theory succeeds to provide accurate estimates of the growth rate at early times. We further discuss how our results can inform future experiments in the high-Mach magnetized regime at the National Ignition Facility. Possible limitations of the study due to resistive, mixing, or turbulence effects are discussed.

compressible flows↗
NASA NTRS1992

Faraday anomalous dispersion optical filters

The present calculations of the performance of Faraday anomalous dispersion optical filters (FADOF) on IR transitions indicate that such filters may furnish high transmission, narrow-pass bandwidth, and low equivalent noise bandwidth under optimum operating conditions. A FADOF consists of an atomic vapor cell between crossed polarizers that are subject to a dc magnetic field along the optical path; when linearly polarized light travels along the direction of the magnetic field through the dispersive atomic vapor, a polarization rotation occurs. If FADOF conditions are suitably adjusted, a maximum transmission with very narrow bandwidth is obtained.

Shay, T. M.↗