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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Magnetic heat pumping near room temperature

It is shown that magnetic heat pumping can be made practical at room temperature by using a ferromagnetic material with a Curie point at or near operating temperature and an appropriate regenerative thermodynamic cycle. Measurements are performed which show that gadolinium is a resonable working material and it is found that the application of a 7-T magnetic field to gadolinium at the Curie point (293 K) causes a heat release of 4 kJ/kg under isothermal conditions or a temperature rise of 14 K under adiabatic conditions. A regeneration technique can be used to lift the load of the lattice and electronic heat capacities off the magnetic system in order to span a reasonable temperature difference and to pump as much entropy per cycle as possible

Brown, G. V.↗
DOE OSTI2024

A tunable dielectric resonator for axion searches at 11 GHz

In the context of axion search with haloscopes, tunable cavity resonators with high quality factor and high effective volume at frequencies above about 8 GHz are central for probing the axion-photon coupling with the required sensitivity to reach the QCD axion models. Higher order modes in dielectrically-loaded cavities allow for higher effective volumes and larger quality factors compared to basic cylindrical cavities, but a proper cavity frequency tuning mechanism to probe broad axion mass ranges is yet not available. In this work, we report about the design and construction of a tunable prototype of a single-shell dielectric resonator with its axion-sensitive pseudo-TM$_{030}$ high-order mode at about 11 GHz frequency. A clamshell tuning method previously tested for empty cylindrical resonators has been perfected for this geometry through simulations and in situ tests conducted at cryogenic temperature. Tuning is accomplished in a range of about 2 $\%$ the central frequency, without significantly impacting the quality factor of about 175000. The experimental results presented in this work demonstrate the tunability of this type of resonator, definitely confirming its applicability to high frequency axion searches.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1995

Average power effects in parametric oscillators and amplifiers

Average power effects relative to the operation of parametric oscillators and amplifiers have been calculated. Temperature gradients have been calculated for both radial and longitudinal heat extraction. In many instances, the thermal load on a parametric oscillator is higher than the thermal load on a parametric amplifier with the same pump power. Having one or both these wavelengths resonant increases the chances that a generated photon will be absorbed by the nonlinear crystal. Temperature profiles and thermal diffusion time constants have been calculated for Gaussian beams, given the heat-deposition rate. With radical heat extraction the temperature profile can be expressed in a power series or approximated by a Gaussian distribution function.

Barnes, Norman P.↗
NASA NTRS1991

Cyclotron resonant scattering and absorption

The relativistic cross-sections for first-order absorption and second-order scattering are compared to determine the conditions under which the absorption cross-section is a good approximation to the much more complex scattering cross-section for purposes of modeling cyclotron lines in gamma-ray bursts. Differences in both the cross-sections and the line profiles are presented for a range of field strengths, angles, and electron temperatures. The relative difference of the cross-sections at one line width from resonance was found to increase with field strength and harmonic number. The difference is also strongly dependent on the photon angle to the magnetic field. For the field strength, 1.7 x 10 to the 12th G, and the angle inferred from the Ginga burst features, absorption is an excellent approximation for the profiles at the first and second harmonics.

Harding, Alice K.↗
DOE OSTI2021

Magnetism dynamics driven by phase separation in Pr-doped manganite thin films: A ferromagnetic resonance study

In this work, we performed ferromagnetic resonance measurements of a (La 1–x Pr x ) 1–y Ca y MnO 3–δ with x = 0.52 ± 0.05, y = 0.23 ± 0.04, and δ = 0.14 ± 0.10 thin single crystalline film which, in combination with micromagnetic simulations, reveal three temperature regions consistent with (i) a ferromagnetic-paramagnetic transition in which ferromagnetic domains nucleate and grow, (ii) followed by a filamentary fluidlike percolation of magnetic domains exhibiting dynamic processes and finally, iii) the existence of a blocking temperature below which the magnetism is a metastable glassy-like state with strong decoherence of the uniform resonance mode. Our results suggest a strain-liquid to strain-glass spin order transition in which the magnetism and fluidlike dynamics of the separated phases freeze at low temperatures. We show the magnetism dynamics depend strongly on the phase-separated state and morphology of the magnetic domains suggesting a route to control of phase separation and realization of spintronic and magnonic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Terahertz electric-field-driven dynamical multiferroicity in SrTiO 3

The emergence of collective order in matter is among the most fundamental and intriguing phenomena in physics. In recent years, the dynamical control and creation of novel ordered states of matter not accessible in thermodynamic equilibrium is receiving much attention. The theoretical concept of dynamical multiferroicity has been introduced to describe the emergence of magnetization due to time-dependent electric polarization in non-ferromagnetic materials. In simple terms, the coherent rotating motion of the ions in a crystal induces a magnetic moment along the axis of rotation. Here we provide experimental evidence of room-temperature magnetization in the archetypal paraelectric perovskite SrTiO 3 due to this mechanism. We resonantly drive the infrared-active soft phonon mode with an intense circularly polarized terahertz electric field and detect the time-resolved magneto-optical Kerr effect. A simple model, which includes two coupled nonlinear oscillators whose forces and couplings are derived with ab initio calculations using self-consistent phonon theory at a finite temperature, reproduces qualitatively our experimental observations. A quantitatively correct magnitude was obtained for the effect by also considering the phonon analogue of the reciprocal of the Einstein–de Haas effect, which is also called the Barnett effect, in which the total angular momentum from the phonon order is transferred to the electronic one. Our findings show a new path for the control of magnetism, for example, for ultrafast magnetic switches, by coherently controlling the lattice vibrations with light.

36 MATERIALS SCIENCE↗
NASA NTRS1980

Measurements of coronal kinetic temperatures from 1.5 to 3 solar radii

A rocket-borne Lyman-alpha coronagraph has been used to make the first measurements of the spectral line profile of resonantly scattered hydrogen Lyman-alpha coronal radiation between 1.5 and 3 solar radii. These data provide, for the first time, direct measurements of coronal temperatures above 1.5 solar radii. Data were obtained in a coronal hole, quiet region, and streamer. The widths of the profiles from the quiet region decrease with height and correspond to a steady decrease in hydrogen kinetic temperature, with increasing radius, from about 2.5 million K at r = 2 solar radii to about 1 million K at r = 9 solar radii. In the coronal hole the measured line widths indicate a kinetic temperature of 1.8 million K at r = 2.5 solar radii.

Kohl, J. L.↗
DOE OSTI2024

Strength measurement of the $E^{lab}_α = 830$ keV resonance in the 22 Ne (α,n) 25 Mg reaction using a stilbene detector

The interplay between the 22 Ne (α,γ) 26 Mg reaction and the competing 22 Ne ⁢(α,n) 25 Mg reaction determines the efficiency of the latter as a neutron source at the temperatures of stellar helium burning. In both cases, the rates are dominated by the α-cluster resonance at 830 keV. This resonance plays a particularly important role in determining the strength of the neutron flux for both the weak and main s process as well as the n process. Recent experimental studies based on transfer reactions suggest that the neutron and γ-ray strengths for this resonance are approximately equal. In this study, the 22 Ne (α,n) 25 Mg resonance strength has been remeasured and found to be similar to the previous direct studies. Finally, this reinforces an 830 keV resonance strength that is approximately a factor of 3 larger for the 22 Ne ⁢(α,n) 25 Mg reaction than for the 22 Ne (α,γ) 26 Mg reaction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1995

Optically-Switched Resonant Tunneling Diodes for Space-Based Optical Communication Applications

We are developing a new type of digital photo-receiver that has the potential to perform high speed optical-to-electronic conversion with a factor of 10 reduction in component count and power dissipation. In this paper, we describe the room-temperature photo-induced switching of this InP-based device which consists of an InGaAs/AlAs resonant tunneling diode integrated with an InGaAs absorber layer. When illuminated at an irradiance of greater than 5 Wcm(exp -2) using 1.3 micromillimeter radiation, the resonant tunneling diode switches from a high-conductance to a low-conductance electrical state and exhibits a voltage swing of up to 800 mV.

Moise, T. S.↗
DOE OSTI2023

Phase Heterogeneity in Cholesterol-Containing Ternary Phospholipid Lamellar Phases

Pseudo-ternary mixtures of lamellar phase phospholipids (DPPC and brain sphingomyelin with cholesterol) were studied below T m while comparing the influence of cholesterol content, temperature, and the presence of small quantities of vitamin D binding protein (DBP) or vitamin D receptor (VDR). The measurements, conducted by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR), cover a range of cholesterol concentrations (20% mol. wt to 40% mol. wt.) and physiologically relevant temperature range (294–314 K). In addition to rich intraphase behavior, data and modeling are used to approximate the lipids’ headgroup location variations under the abovementioned experimental conditions.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Study, selection, and preparation of solid cationic conductors

Crystal chemical principles and transport theory were used to predict structures and specific compounds which might find application as solid electrolytes in rechargeable high energy and high power density batteries operating at temperatures less than 200 C. More than twenty compounds were synthesized or obtained and screened by nuclear magnetic resonance and conductivity. Many were densified by sintering or hot pressing. Encouraging results were obtained for nine of these materials but none have yet been good ionic conductors at low temperature.

Roth, W. L.↗
DOE OSTI2020

Localized-to-itinerant transition preceding antiferromagnetic quantum critical point and gapless superconductivity in CeRh 0.5 Ir 0.5 In 5

A fundamental problem posed from the study of correlated electron compounds, of which heavy-fermion systems are prototypes, is the need to understand the physics of states near a quantum critical point (QCP). At a QCP, magnetic order is suppressed continuously to zero temperature and unconventional superconductivity often appears. Here, we report pressure ( P )-dependent 115 In nuclear quadrupole resonance (NQR) measurements on heavy-fermion antiferromagnet CeRh 0.5 Ir 0.5 In 5 . These experiments reveal an antiferromagnetic (AF) QCP at \({P}_{{\rm{c}}}^{{\rm{AF}}}=1.2\) GPa where a dome of superconductivity reaches a maximum transition temperature T c . Preceding \({P}_{{\rm{c}}}^{{\rm{AF}}}\) , however, the NQR frequency ν Q undergoes an abrupt increase at \({P}_{{\rm{c}}}^{{\rm{* }}}\) = 0.8 GPa in the zero-temperature limit, indicating a change from localized to itinerant character of cerium’s f -electron and associated small-to-large change in the Fermi surface. At \({P}_{{\rm{c}}}^{{\rm{AF}}}\) where T c is optimized, there is an unusually large fraction of gapless excitations well below T c that implicates spin-singlet, odd-frequency pairing symmetry.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Mg/2+/-Fe/2+/ order-disorder in cummingtonite, /Mg, Fe/7Si8O22/OH/2 - A new geothermometer.

Determination of the temperature dependence of the Mg(2+)-Fe(2+) distribution between the M4 site and the M1, M2 and M3 sites in magnesium-rich cummingtonites by Fe-57 Mossbauer resonance spectroscopy. For the basic reversible ion-exchange reaction involved, the Gibbs free energy is estimated to be 3.6 to 4.1 kcal/mole, assuming an ideal solution model at each set of sites. The crystallization temperatures of two cummingtonite-bearing metamorphosed ultrabasic rocks are estimated to be 265 and 290 deg C. The Mossbauer resonance spectra are found to be an effective basis for detecting changes in site occupancies as a function of temperature.

Ghose, S.↗
DOE OSTI2024

Oblique instability of quasi-parallel whistler waves in the presence of cold and warm electron populations

Whistler waves propagating nearly parallel to the ambient magnetic field experience a nonlinear instability due to transverse currents when the background plasma has a population of sufficiently low energy electrons. Intriguingly, this nonlinear process may generate oblique electrostatic waves, including whistlers near the resonance cone with properties resembling oblique chorus waves in the Earth’s magnetosphere. Focusing on the generation of oblique whistlers, earlier analysis of the instability is extended here to the case where low-energy background plasma consists of both a “cold” population with energy of a few eV and a “warm” electron component with energy of the order of 100 eV. This is motivated by spacecraft observations in the Earth’s magnetosphere where oblique chorus waves were shown to interact resonantly with the warm electrons. The main new results are: 1) the instability producing oblique electrostatic waves is sensitive to the shape of the electron distribution at low energies. In the whistler range of frequencies, two distinct peaks in the growth rate are typically present for the model considered: a peak associated with the warm electron population at relatively low wavenumbers and a peak associated with the cold electron population at relatively high wavenumbers; 2) overall, the instability producing oblique whistler waves near the resonance cone persists (with a reduced growth rate) even in the cases where the temperature of the cold population is relatively high, including cases where cold population is absent and only the warm population is included; 3) particle-in-cell simulations show that the instability leads to heating of the background plasma and formation of characteristic plateau and beam features in the parallel electron distribution function in the range of energies resonant with the instability. The plateau/beam features have been previously detected in spacecraft observations of oblique chorus waves. However, they have been attributed to external sources and have been proposed to be the mechanism generating oblique chorus. In the present scenario, the causality link is reversed and the instability generating oblique whistler waves is shown to be a possible mechanism for formation of the plateau and beam features.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2024

Oblique Instability of Quasi-Parallel Whistler Waves in the Presence of Cold and Warm Electron Populations

Whistler waves propagating nearly parallel to the ambient magnetic field experience a nonlinear instability due to transverse currents when the background plasma has a population of sufficiently low energy electrons. Intriguingly, this nonlinear process may generate oblique electrostatic waves, including whistlers near the resonance cone with properties resembling oblique chorus waves in the Earth’s magnetosphere. Focusing on the generation of oblique whistlers, earlier analysis of the instability is extended here to the case where low-energy background plasma consists of both a “cold” population with energy of a few eV and a “warm” electron component with energy of the order of 100 eV. This is motivated by spacecraft observations in the Earth’s magnetosphere where oblique chorus waves were shown to interact resonantly with the warm electrons. The main new results are: 1) the instability producing oblique electrostatic waves is sensitive to the shape of the electron distribution at low energies. In the whistler range of frequencies, two distinct peaks in the growth rate are typically present for the model considered: a peak associated with the warm electron population at relatively low wavenumbers and a peak associated with the cold electron population at relatively high wavenumbers; 2) overall, the instability producing oblique whistler waves near the resonance cone persists (with a reduced growth rate) even in the cases where the temperature of the cold population is relatively high, including cases where cold population is absent and only the warm population is included; 3) particle-in-cell simulations show that the instability leads to heating of the background plasma and formation of characteristic plateau and beam features in the parallel electron distribution function in the range of energies resonant with the instability. The plateau/beam features have been previously detected in spacecraft observations of oblique chorus waves. However, they have been attributed to external sources and have been proposed to be the mechanism generating oblique chorus. In the present scenario, the causality link is reversed and the instability generating oblique whistler waves is shown to be a possible mechanism for formation of the plateau and beam features.

Vadim Roytershteyn↗
DOE OSTI2020

The influence of phonon softening on the superconducting critical temperature of Sn nanostructures

Abstract The increase in superconducting transition temperature (T C ) of Sn nanostructures in comparison to bulk, was studied. Changes in the phonon density of states (PDOS) of the weakly coupled superconductor Sn were analyzed and correlated with the increase in T C measured by magnetometry. The PDOS of all nanostructured samples shows a slightly increased number of low-energy phonon modes and a strong decrease in the number of high-energy phonon modes in comparison to the bulk Sn PDOS. The phonon densities of states, which were determined previously using nuclear resonant inelastic X-ray scattering, were used to calculate the superconducting transition temperature using the Allen-Dynes-McMillan (ADMM) formalism. Both the calculated as well as the experimentally determined values of T C show an increase compared to the bulk superconducting transition temperature. The good agreement between these values indicates that phonon softening has a major influence on the superconducting transition temperature of Sn nanostructures. The influence of electron confinement effects appears to be minor in these systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Upper critical magnetic field and multiband superconductivity in artificial high-𝑇 𝑐 superlattices of nano quantum wells

Artificial high-T c superlattices (AHTS) composed of quantum building blocks with tunable superconducting critical temperature have been synthesized by engineering their nanoscale geometry using the Bianconi-Perali Valletta (BPV) two-gap superconductivity theory. These quantum heterostructures consist of quantum wells made of superconducting, modulation-doped Mott insulators (S), confined by a metallic (N) potential barrier. The lattice geometry has been carefully engineered to induce the predicted Fano-Feshbach shape resonance between the gaps, near a topological Lifshitz transition. Here, we validate the BPV theory by providing compelling experimental evidence that AHTS samples, at the peak of the superconducting dome, exhibit resonant two-band, two-gap superconductivity. This is demonstrated by measuring the temperature dependence of the upper critical magnetic field, μ 0 H c2 , in samples with superlattice periods 3.3 < d < 5.28 nm and L/d ratios close to the magic value 2/3 (where L is the thickness of the superconducting La 2 CuO 4 layer and d is the superlattice period). Here, the data reveal the predicted upward concavity in H c2 (T) and a characteristic kink in the coherence length as a function of temperature, confirming the predicted two-band superconductivity with Fermi velocity ratio ≈ 0.25 and significant pair-exchange term among the two condensates.

Heterostructures↗