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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 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A pathway to desired functionalities in vertically aligned nanocomposites and related architectures

Epitaxial vertically aligned nanocomposites (VANs) and their related architectures have shown many intriguing features that are not available from conventional two-dimensional planar multilayers and heterostructures. The ability to control constituent, interface, microstructure, strain, and defects based on VANs has enabled the multiple degrees of freedom to manipulate the optical, magnetic, electrochemical, electronic, ionic, and superconducting properties for specific applications. This field has rapidly expanded from the interest in oxide:oxide to oxide:metal, metal:nitride and nitride:nitride systems. To achieve unparalleled properties of the materials, three-dimensional super-nanocomposites based on a hybrid of VAN and multilayer architectures have been recently explored as well. The challenges and opportunities of VAN films are also discussed in this article.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Interlaminar Fracture Toughness Testing of Nb3Sn Insulation Systems

Epoxy cracking has been the main suspected contributor to training in Nb3Sn magnets for some time, as it leads to energy release and magnet quenching. Cracking in a superconducting composite can occur from several modes, and the likelihood of these modes is not well understood. Failure has been observed between insulation systems and the superconducting cable itself rather than within the cable or insulation. To target the behavior at the interface, samples have been fabricated and tested for mode I fracture toughness in an adapted version of ASTM D5528. This work seeks to better characterize the fracture toughness of this interface to better understand how to model and design insulation systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

X-ray Studies of the CDW Ground State and Excitations in High- T C Cuprates

We report charge density wave (CDW) in high-T C cuprates has drawn a lot of attention in the field. In this article, we review some of our recent x-ray studies about the ground state and the excitation spectrum of the CDW. Using high magnetic field to suppress the superconductivity, a three-dimensionally-ordered charge stripe state emerges in YBa 2 Cu 3 O 6+x at low temperatures, which arguably bears the characteristics of the CDW ground state. Regarding excitation spectrum, we utilized the state-of-the-art soft x-ray resonant inelastic scattering (RIXS) and found signatures of dispersive CDW excitations which manifest as some form of interference with the RIXS phonon excitations. This observation provides a new perspective to study the relationship between the CDW, the superconductivity and the putative quantum criticality inside the superconducting dome of the cuprate phase diagram. Within this context, relevant recent experimental studies are also briefly discussed.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Magnets with stabilized conductors

Method fabricates stabilized composite conductor, for use in construction of magnets, using equal amounts of superconducting and metal materials, thus reducing weight, cost and size.

Jones, C. K.↗
NASA NTRS1973

Initial results from the NASA Lewis Bumpy Torus experiment

Initial results are given for low power operation of the NASA Lewis Bumpy Torus experiment in which a steady-state ion heating method based on a modified Penning discharge is applied to a bumpy torus confinement geometry. The magnet facility consists of 12 superconducting coils capable of 3.0 T each and equally spaced in a toroidal array 1.52 m in major diameter. A 18 cm i.d. anode ring is located at each of the 12 midplanes and is maintained at high positive potentials by a dc power supply. Initial observations indicate electron temperatures from 10 to 150 eV, and ion kinetic temperatures from 200 eV to 1200 eV. Two modes of operation with different radial density profiles can be achieved, depending on the background pressure applied.

Roth, J. R.↗
NASA NTRS1989

Progress in kinetic inductance thermometers for X-ray calorimeters

Conventional X-ray microcalorimeters have so far used ionimplanted resistors for thermometers. Recently, however, several new methods for sensing small temperature changes have been suggested that are nondissipative. Such devices may have intrinsically better energy resolution by eliminating the Johnson noise present in resistive devices. The use of kinetic inductance thermometers for X-ray microcalorimeters is being investigated. This technique exploits the strong temperature dependence of magnetic penetration depth of thin superconducting films. The prototype system, designed for operation at 1.5 K, uses films of aluminum and tin. Once the expected temperature sensitivity and alpha particle detection have been demonstrated, aluminum will be replaced with titanium or another material with a suitable critical temperature and the device will be operated at 0.3 K. At this temperature, the energy resolution from thermal noise should be sufficiently good to allow X-ray detection.

Rawley, G. L.↗
NASA NTRS1992

Optimization of niobium tunnel junctions as X-ray detectors

We report on our ongoing work using Nb/Al/AlO(x)/Nb junctions for the detection of X-rays. Detectors based on superconducting tunneling junctions offer the prospect of resolution over an order of magnitude higher than is obtainable with the current generation of semiconductor-based detectors. Results of measurements taken at 1.85 K (a temperature achievable with current space flight technology) include the current-voltage (I-V) curve, subgap current vs temperature, the dependence of the superconducting current on the applied magnetic field (Fraunhofer pattern), X-ray pulses, and the spectra from a 6 keV X-ray source which gave an intrinsic device resolution of approximately 700 eV. The collection of more than 10 exp 5 electrons per 6 keV photon is established.

Saulnier, Gregory G.↗
NASA NTRS2009

Gradiometer Using Middle Loops as Sensing Elements in a Low-Field SQUID MRI System

A new gradiometer scheme uses middle loops as sensing elements in lowfield superconducting quantum interference device (SQUID) magnetic resonance imaging (MRI). This design of a second order gradiometer increases its sensitivity and makes it more uniform, compared to the conventional side loop sensing scheme with a comparable matching SQUID. The space between the two middle loops becomes the imaging volume with the enclosing cryostat built accordingly.

Penanen, Konstantin↗
DOE OSTI2023

AUP first Pre-Series Cold Mass Installation into the Cryostat

For the HiLumi LHC Upgrade (HL-LHC), new high field and large-aperture quadrupole magnets for the low-beta inner triplets (Q1, Q2, Q3) are being built. These new quadrupole magnets are based on Nb3Sn superconducting technology. As part of the US-HiLumi Accelerator Upgrade Project (AUP), ten Cryostat Assemblies (LQXFA) for Q1 and Q3 replacement will be built, tested, and delivered to CERN. The first LQXFA was assembled and tested at Fermi National Accelerator Laboratory (FNAL) during fall 2022 and spring/summer 2023, respectively. This paper summarizes the assembly process and experience of the first LQXFA Cryostat Assembly at FNAL.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

AMR Magnetic Sensors in Flux Expulsion Studies

Magnetic flux expulsion properties of the superconducting material such as bulk niobium, widely used for the radio-frequency cavity fabrication, substantially affect the performance characteristics of the cavities. The quality factor of the SRF resonators can be significantly compromised due to the presence of the trapped flux vortices causing additional RF energy losses in the material. Large number of experiments have been carried out by different research groups to establish the correlation of the flux trapping in niobium cavities with the presence of impurities in niobium as well as various surface treatment methods. Majority of these experiments utilize commercially available cryogenic fluxgate magnetic sensors to measure the field before and after the niobium transition to the superconducting state to quantify the amount of flux trapped. One disadvantage of the typically used fluxgates is the size of the sensing volume. As an example, the Barting-ton F and G type cryogenic fluxgates have a sensing core length of about 30mm, which is comparable to the curvature radius of the cavity walls and hence the magnetic field lines curvature radius after the expulsion. Thus, the measured field value needs to be corrected to account for the sensor effective averaging over the sensing volume. In case of the sharper geometries, for instance if the flux expulsion to be measured on the edge of the rectangular niobium flat sheet with a thickness of ~5mm, the use of the fluxgate would be impractical.

Netepenko, A.↗
DOE OSTI2023

Voltage-controlled magnetic anisotropy enabled by resistive switching

The discovery of new mechanisms of controlling magnetic properties by electric fields or currents furthers the fundamental understanding of magnetism and has important implications for practical use. Here, we present an approach of utilizing resistive switching to control magnetic anisotropy. We study a ferromagnetic oxide that exhibits an electrically triggered metal-to-insulator phase transition producing a volatile resistive switching. The switching occurs in a characteristic spatial pattern, the formation of an insulating barrier perpendicular to the current flow, which results in an unusual ferromagnetic/paramagnetic/ferromagnetic configuration. Further, the formation of this voltage-driven paramagnetic insulating barrier is accompanied by the emergence of a strong uniaxial magnetic anisotropy that overpowers the intrinsic material anisotropy. Our results demonstrate that resistive switching is an effective tool for manipulating magnetic properties. Because resistive switching can be induced in a broad range of materials, our findings could enable a new class of voltage-controlled magnetism systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Insights into ε - Fe 2 O 3 interactions via Cr doping

We report innovative materials, particularly multiferroics, have the potential to transform technology. Full optimization of their usage will require an in-depth understanding of the underlying electronic and magnetic interactions. One such material is ε-Fe 2 O 3 . However, because this hard ferrimagnet with strong magnetoelectric coupling is composed of only Fe 3+ , distinguishing the role of the various sites is incredibly challenging. To overcome this challenge, Cr 3+ ions were doped into the DOh1 sites of ε-Fe 2 O 3 nanoparticles, effectively creating electron deficient defects. The ε-(Fe 1-x Cr x ) 2 O 3 (x = 0.01 to 0.12) nanoparticles have reduced μ 0 H C (T) and M S (T) as the Cr concentration increases. The impact of Cr doping on the local electronic and magnetic structure is characterized. At 10 K, subtle changes are measured, with the T d site electrons becoming increasingly localized as the concentration of electron-deficient DOh1 sites increases. Far more dramatic changes occur at 300 K, when the T d site of the ε-(Fe 1-x Cr x ) 2 O 3 splits into two distinct local environments with Fe 2+ and Fe 4+ character. The nature of this splitting suggests that dynamic electron interactions play a significant role in ε-Fe 2 O 3 ’s magnetic anisotropy and magnetoelectric properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1975

Energy storage and subharmonic oscillations in Josephson junctions

The energy stored in the magnetic and electric field near a superconducting point contact is typically the same magnitude as the coupling energy which produces the Josephson effect in the weakly coupled superconductors. One consequence of energy storage in both the electric and magnetic field is that the junction can oscillate at a fundamental frequency. The dynamics of these subharmonic oscillations have been studied for a model in which the magnetic and electric energies are represented as being stored in an inductance and a capacitance respectively. The model was studied numerically for various biasing conditions, and the behavior compared to experimental data. A simple analytic approximation was developed that gives physical insight into the mechanism that creates the subharmonic oscillations.

Dempsey, D. G.↗
DOE OSTI2022

High-Temperature Superconductivity in Hydrides: Experimental Evidence and Details

Abstract Since the discovery of superconductivity at ~ 200 K in H 3 S [1], similar or higher transition temperatures, T c s, have been reported for various hydrogen-rich compounds under ultra-high pressures [2]. Superconductivity was experimentally proved by different methods, including electrical resistance, magnetic susceptibility, optical infrared, and nuclear resonant scattering measurements. The crystal structures of superconducting phases were determined by X-ray diffraction. Numerous electrical transport measurements demonstrate the typical behavior of a conventional phonon-mediated superconductor: zero resistance below T c , shift of T c to lower temperatures under external magnetic fields, and pronounced isotope effect. Remarkably, the results are in good agreement with the theoretical predictions, which describe superconductivity in hydrides within the framework of the conventional BCS theory. However, despite this acknowledgement, experimental evidences for the superconducting state in these compounds have recently been treated with criticism [3–7], which apparently stems from misunderstanding and misinterpretation of complicated experiments performed under very high pressures. Here, we describe in greater detail the experiments revealing high-temperature superconductivity in hydrides under high pressures. We show that the arguments against superconductivity [3–7] can be either refuted or explained. The experiments on the high-temperature superconductivity in hydrides clearly contradict the theory of hole superconductivity [8] and eliminate it [3].

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Crossover from Conventional to Unconventional Superconductivity in 2M-WS 2

Leveraging the reciprocal-space proximity effect between superconducting bulk and topological surface states (TSSs) offers a promising way to topological superconductivity. However, elucidating the mutual influence of bulk and TSSs on topological superconductivity remains a challenge. Here, we report pioneering transport evidence of a thickness-dependent transition from conventional to unconventional superconductivity in 2M-phase WS 2 (2M-WS 2 ). As the sample thickness reduces, we see clear changes in key superconducting metrics, including critical temperature, critical current, and carrier density. Notably, while thick 2M-WS 2 samples show conventional superconductivity, with an in-plane (IP) upper critical field constrained by the Pauli limit, samples under 20 nm exhibit a pronounced IP critical field enhancement, inversely correlated with 2D carrier density. This marks a distinct crossover to unconventional superconductivity with strong spin-orbit-parity coupling. Furthermore, our findings underscore the crucial role of sample thickness in accessing topological states in 2D topological superconductors, offering pivotal insights into future studies of topological superconductivity.

2D topological superconductor↗
DOE OSTI2021

Nematicity and competing orders in superconducting magic-angle graphene

Strongly interacting electrons in solid-state systems often display multiple broken symmetries in the ground state. The interplay between different order parameters can give rise to a rich phase diagram. We report on the identification of intertwined phases with broken rotational symmetry in magic-angle twisted bilayer graphene (TBG). Using transverse resistance measurements, we find a strongly anisotropic phase located in a “wedge” above the underdoped region of the superconducting dome. Upon its crossing with the superconducting dome, a reduction of the critical temperature is observed. Furthermore, the superconducting state exhibits an anisotropic response to a direction-dependent in-plane magnetic field, revealing nematic ordering across the entire superconducting dome. These results indicate that nematic fluctuations might play an important role in the low-temperature phases of magic-angle TBG.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗