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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

ULF magnetic signatures at the earth surface due to ground water flow - A possible precursor to earthquakes

Magnetic field fluctuations at the earth's surface at less than 1 Hz are shown to result from motion with a peak velocity of about 4 cm/s of ground water (about 4 S/m) at about 5 km depth. Surface field changes can occur due to either divergence free fluid motion with transverse spatial wavelengths of a few tens of km, and/or homogeneous flow which displaces local inhomogeneities in the earth magnetic field.

Draganov, A. B.↗
NASA NTRS2011

What Supergranule Flow Models Tell Us About the Sun's Surface Shear Layer and Magnetic Flux Transport

Models of the photospheric flows due to supergranulation are generated using an evolving spectrum of vector spherical harmonics up to spherical harmonic wavenumber l~1500. Doppler velocity data generated from these models are compared to direct Doppler observations from SOHO/MDI and SDO/HMI. The models are adjusted to match the observed spatial power spectrum as well as the wavenumber dependence of the cell lifetimes, differential rotation velocities, meridional flow velocities, and relative strength of radial vs. horizontal flows. The equatorial rotation rate as a function of wavelength matches the rotation rate as a function of depth as determined by global helioseismology. This leads to the conclusions that the cellular structures are anchored at depths equal to their widths, that the surface shear layer extends to at least 70 degrees latitude, and that the poleward meridional flow decreases in amplitude and reverses direction at the base of the surface shear layer (approx.35 Mm below the surface). Using the modeled flows to passively transport magnetic flux indicates that the observed differential rotation and meridional flow of the magnetic elements are directly related to the differential rotation and meridional flow of the convective pattern itself. The magnetic elements are transported by the evolving boundaries of the supergranule pattern (where the convective flows converge) and are unaffected by the weaker flows associated with the differential rotation or meridional flow of the photospheric plasma.

Hathaway, David↗
NASA NTRS1969

Surveyor results.

Surveyor lunar scientific payload and results, discussing TV camera, soil mechanics and surface sampler, alpha scattering instrument, small magnets and surface analysis

Hibbs, A. R.↗
NASA NTRS1981

Stellar chromospheric and coronal heating by magnetohydrodynamic waves

An investigation is presented on the way in which the generation of magnetohydrodynamic waves by turbulent motions in stellar convection zones depends on the star's effective temperature, surface gravity, and magnetic field strength. It is shown that the emitted Alfven wave flux (and acoustic slow wave flux in a very strong magnetic field) is in reasonable agreement with the general trend of observed chromospheric radiative losses in stars, and with the observations of three stars for which magnetic field strength, surface area covered by strong fields, and radiative losses have all been measured.

Stein, R. F.↗
NASA NTRS1986

Development of ultrastable filters and lasers for solar seismology

The Stable Solar Analyzer is a recently developed instrument for the measurement of solar magnetic fields and surface velocities that is being employed at the U.S. National Solar Observatory to study the subsurface convection cells of the sun and the structure of surface and subsurface magnetic fields. The Analyzer is expected to ultimately be flown aboard such spacecraft as the ESA/NASA Solar and Heliospheric Observatory. This instrument is based on a crystalline lithium niobate Fabry-Perot filter that is used in conjunction with a stabilized laser that furnishes an absolute wavelength reference; this laser Fabry-Perot combination has achieved wavelength stabilities of the order of 2 parts in 10 to the 10th, over a six-hour interval.

Rust, D. M.↗
NASA NTRS2000

Magnetism of Carbonados

Origin of Carbonado is not clear. Magnetism of Carbonado comes from the surface, indicating contemporary formation of both the surface and magnetic carriers. The interior of carbonado is relatively free of magnetic phases.

Kletetschka, G.↗
NASA NTRS2000

Spectral and Timing Investigations of Dwarf Novae Selected in Hard X-Rays

There are 9 dwarf novae (DN) among the 43 cataclysmic variables (accreting white dwarfs in close binary systems) that were detected during the HEAO-1 all-sky X-ray survey (1977-1979). On the other hand, there are roughly one hundred dwarf novae that are closer and/or optically brighter and yet they were not detected as hard X-ray sources. Two of the HEAO-1 DN show evidence for X-ray pulsations that imply strong magnetic fields on the white dwarf surface, and magnetic CVs are known to be strong X-ray sources. However, substantial flux in hard X-rays may be caused by non-magnetic effects, such as an optically thin boundary layer near a massive white dwarf. We proposed RXTE observations to measure plasma temperatures and to search for X-ray pulsations. The observations would distinguish whether these DN belong to one of (rare) magnetic subclasses. For those that do not show pulsations, the observations support efforts to define empirical relations between X-ray temperature, the accretion rate, and the mass of the white dwarf. The latter is determined via optical studies of the dynamics of the binary constituents.

Thorstensen, John↗
DOE OSTI2022

Magnetic undulator shim

A magnetic undulator shim having three interconnected sections arranged one after the other in a direction substantially parallel to the beam axis. The first section is adapted to magnetically engage a magnet having a horizontal surface and configured to extend partially onto the horizontal surface of the magnet. The magnet is adjacent to a pole and the magnet and the pole form a boundary. The second third sections are interconnected to form a shape. The shape corresponds to the boundary. The third section is adapted to magnetically engage a surface of the pole.

Xu, Joseph Z.↗
NASA NTRS1973

Magnetic sheath adjacent to absorbing surfaces.

Major attention is given to the existence and structure of a 'magnetic sheath' adjacent to perfectly absorbing solid surfaces. The basic equations for a two-field continuum model are presented, and the quasi-neutral approximation and Bohm's criterion are briefly reviewed. The infinite conductivity MHD equations are recovered by invoking the small magnetic Debye length approximation. This approximation is relaxed, and the appropriate 'boundary layer' equation for the magnetic sheath is presented. The first magnetic sheath criterion is derived, which states that the conditions at the edge of the sheath, as characterized by a point in the Friedrichs diagram, must be located in certain restricted regions in order for a magnetic sheath to exist. The second magnetic sheath criterion is discussed.

Lam, S. H.↗
NASA NTRS1994

Effect of surface conductivity on the peak magnetic field radiated by first return strokes in cloud-to-ground lightning

The effect of surface conductivity on the peak magnetic field radiated by the first return stroke in cloud-to-ground lightning was investigated by comparing the peak magnetic fields from return strokes that struck water with those that struck land. The data were obtained from a network of three gated, wideband magnetic direction finders (DFs) at the NASA Kennedy Space Center during the summer of 1985. Two geographical areas that were equidistant from two of the direction finders were compared where the flash distances ranged from approximately 40 to 60 km. An unbiased data set was obtained by correcting site errors, equalizing differences in sensor gain, eliminating directional biases in DF triggering, and keeping differences in signal attenuation over the two surfaces to a minimum. When a statistical analysis was performed on the frequency distributions of the signal amplitudes, there was no statistically significant difference in the peak amplitudes of first return strokes over land (lambda = 8.2 x 10(exp -3) mho/m) and over water (lambda = 4 mho/m). Therefore we infer that the conductivity of the underlying surface does not significantly affect the magnitude of the peak magnetic field, and hence the peak current, in the first return stroke of a cloud-to-ground lightning flash.

Tyahla, Lori J.↗
DOE OSTI2022

Observation of Reentrant Correlated Insulators and Interaction-Driven Fermi-Surface Reconstructions at One Magnetic Flux Quantum per Moiré Unit Cell in Magic-Angle Twisted Bilayer Graphene

The discovery of flat bands with nontrivial band topology in magic-angle twisted bilayer graphene (MATBG) has provided a unique platform to study strongly correlated phenomena including superconductivity, correlated insulators, Chern insulators, and magnetism. A fundamental feature of the MATBG, so far unexplored, is its high magnetic field Hofstadter spectrum. Here, we report on a detailed magnetotransport study of a MATBG device in external magnetic fields of up to B = 3 1 T , corresponding to one magnetic flux quantum per moiré unit cell Φ 0 . At Φ 0 , we observe reentrant correlated insulators at a flat band filling factors of ν = + 2 and of ν = + 3 , and interaction-driven Fermi-surface reconstructions at other fillings, which are identified by new sets of Landau levels originating from these. These experimental observations are supplemented by theoretical work that predicts a new set of eight well-isolated flat bands at Φ 0 , of comparable band width, but with different topology than in zero field. Overall, our magnetotransport data reveal a qualitatively new Hofstadter spectrum in MATBG, which arises due to the strong electronic correlations in the reentrant flat bands.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

The interaction of the ITER first wall with magnetic perturbations

Mitigation of the multiple risks associated with disruptions and runaway electrons in tokamaks involves competing demands. Success requires that each risk be understood sufficiently that appropriate compromises can be made. Here the focus is on the interaction of short timescale magnetic-perturbations with the structure in ITER that is closest to the plasma, blanket modules covered by separated beryllium tiles. The effect of this tiled surface on the perturbations and on the forces on structures is subtle. Indeterminacy can be introduced by tile-to-tile shorting. A determinate subtlety is introduced because electrically separated tiles can act as a conducting surface for magnetic perturbations that have a normal component to the surface. A practical method for including this determinate subtlety into plasma simulations is developed. The shorter the timescales and the greater the localization, particularly in the toroidal direction, the more important the magnetic effects of the tiles become.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Magnetic Field Penetration Technique to Study High Field Shielding of Multilayered Superconductors

The SIS structure which consists of alternative thin layers of superconductors and insulators on a bulk niobium has been proposed to shield niobium cavity surface from high magnetic field and hence increase the accelerating gradient. The study of the behavior of multilayer super-conductors in an external magnetic field is essential to optimize their SRF performance. In this work we report the development of a simple and efficient technique to measure penetration of magnetic field into bulk, thin film and multilayer superconductors. Experimental setup contains a small superconducting solenoid which can produce a parallel surface magnetic field up to 0.5 T and Hall probes to detect penetrated magnetic field across the superconducting sample. This system was calibrated and used to study the effect of niobium sample thickness on the field of full magnetic flux penetration. We determined the optimum thickness of the niobium substrate to fabricate the multilayer structure for the measurements in our setup. This technique was used to measure penetration fields of Nb₃Sn thin films and Nb₃Sn/Al₂O₃ multi-layers deposited on Al₂O₃ wafers.

Senevirathne, I. H.↗
DOE OSTI2023

Power flow in magnetically insulated transmission lines with ion backscatter effects

Ion backscattering off of surfaces in magnetically insulated transmission lines (MITLs) is often ignored in kinetic simulations of MITL power flow. Backscattering reduces ion current losses and the surface impact heating, which dictates the rate at which surface-adsorbed contaminants are liberated into the anode–cathode gap. Backscatter probabilities are difficult to implement in a kinetic code because there are limited data for incident ion energies less than a few keV. This paper presents an analytic model based on the Rutherford scattering formula that reproduces the measured backscatter probabilities at high incident energies and transitions to the highly reflective behavior expected at low incident energies. The backscatter model is implemented in power flow simulations, which are validated with current loss experiments conducted on the 0.4 TW Mykonos accelerator at Sandia National Laboratories. This simulation setup is then used in a high-current Z-machine shot. In conclusion, backscatter effects are found to be unimportant in the low-current Mykonos regime but significantly reduce current losses at the Z-machine scale.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Signatures of a Majorana-Fermi surface in the Kitaev magnet Ag 3 LiIr 2 O 6

Detecting Majorana fermions in experimental realizations of the Kitaev honeycomb model is often complicated by non-trivial interactions inherent to potential spin liquid candidates. In this work, we identify several distinct thermodynamic signatures of massive, itinerant Majorana fermions within the well-established analytical paradigm of Landau-Fermi liquid theory. We find a qualitative and quantitative agreement between the salient features of our Landau-Majorana liquid theory and the Kitaev spin liquid candidate Ag 3 LiIr 2 O 6 . Our study presents strong evidence for a Fermi liquid-like ground state in the fundamental excitations of a honeycomb iridate, and opens new experimental avenues to detect itinerant Majorana fermions in condensed matter systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2022

Universal Scaling Laws for Solar and Stellar Atmospheric Heating: Catalog of Power-law Index between Solar Activity Proxies and Various Spectral Irradiances

The formation of extremely hot outer atmospheres is one of the most prominent manifestations of magnetic activity common to late-type dwarf stars, including the Sun. It is widely believed that these atmospheric layers, the corona, transition region, and chromosphere, are heated by the dissipation of energy transported upwards from the stellar surface by the magnetic field. This is signified by the spectral line fluxes at various wavelengths, scaled with power-law relationships against the surface magnetic flux over a wide range of formation temperatures, which are universal to the Sun and Sunlike stars of different ages and activity levels. This study describes a catalog of power-law indices between solar activity proxies and various spectral line fluxes. Compared to previous studies, we expanded the number of proxies, which now includes the total magnetic flux, total sunspot number, total sunspot area, and the F10.7 cm radio flux, and further enhanced the number of spectral lines by a factor of 2. This provides the data to study in detail the flux–flux scaling laws from the regions specified by the temperatures of the corona (log(T/K) = 6–7) to those of the chromosphere (log(T/K) ∼ 4), as well as the reconstruction of various spectral line fluxes of the Sun in the past, F-, G-, and K-type dwarfs, and the modeled stars.

Stellar coronae↗