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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 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Round-robin analysis of highly depleted lithium for Generation IV nuclear reactor applications

Lithium reference materials containing unnaturally high abundances of 7 Li are not currently available, which poses quality control problems for highly depleted lithium materials (i.e., depleted in 6 Li) required for Generation IV nuclear reactors. This study presents an interlaboratory comparison of a lithium carbonate (NIST SRM924a) containing nominally natural isotopic abundances (~92.4 % Li-7) and a highly depleted lithium hydroxide material (~99.95 % Li-7). The natural lithium isotope abundances of NIST SRM924a are confirmed, and the 6 Li/ 7 Li ratio of the lithium hydroxide ranged from 0.000399 to 0.000436 with an average of 0.000428 ± 0.000023 (2SD, n = 9). Finally, going forward this material can be used as quality control for analytical work involving highly depleted lithium.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Oxygen Distribution and Segregation at Grain Boundaries in Nb and Ta-Encapsulated Nb Thin Films for Superconducting Qubits

We report on atomic-scale analyses of oxygen distribution and segregation at grain boundaries (GBs) of Nb and Ta-encapsulated Nb (Ta/Nb) thin films for superconducting qubits using atom probe tomography (APT) and transmission electron microscopy (TEM). We observe oxygen segregation at grain boundaries (GBs) relative to the oxygen concentration within the grains for both Nb and Ta-capped Nb thin films and find that a higher oxygen concentration in the interior of Nb grains leads to greater oxygen segregation levels at GBs. This finding reveals that the formation of a local equilibrium of oxygen concentration between GBs and grain interiors of Nb is the primary driving force of the oxygen segregation behaviors in Nb and Ta-capped Nb. The enrichment factors (CGB/Cgrain) for oxygen segregation at GBs in Nb and Ta-capped Nb range from 2.4 ± 0.3 to 2.7 ± 0.4. The current results also highlight that controlling oxygen impurities in Nb during film deposition and fabrication processing is important to concomitantly reducing the level of oxygen segregation at GBs in Nb. Finally, we find that increases in the oxygen concentration in both Nb grains and GBs correlate with a suppression in the critical temperature for superconductivity (Tc). Together, our comparative chemical and charge transport property analyses provide atomic-scale insights into a potential mechanism, contributing to the decoherence in superconducting qubits.

Lee, Jaeyel [Fermilab] (ORCID:0000000185429612)↗
DOE OSTI2024

Complex Fluid‐Driven Fractures Caused by Crack‐Parallel Stress

Abstract Managing fluid‐driven fracture networks is crucial for subsurface resource utilization, yet the current understanding of the key controlling factors remains insufficient. While geologic discontinuities have been shown to significantly influence fracture network complexity, this study identifies another major contributor. We conducted a new set of experiments using a transparent true triaxial cell, which enabled video recording of the temporal evolution of fluid‐driven fracture paths. Using pseudo‐2D samples without macroscale structural discontinuities, we observed multiple occurrences of hydraulic fracture curving and branching under anisotropic boundary stresses. We proposed a theoretical model demonstrating that the stress parallel to the crack line in the solid matrix near the crack tip (i.e., the T ‐stress) accounts for the observed fracture curving behavior. This finding suggests that T ‐stress is an additional mechanism contributing to the complexity of fluid‐driven fracture networks in the subsurface, besides the geologic discontinuities.

58 GEOSCIENCES↗
DOE OSTI2023

A quinary WTaCrVHf nanocrystalline refractory high-entropy alloy withholding extreme irradiation environments

In the quest of new materials that can withstand severe irradiation and mechanical extremes for advanced applications (e.g. fission & fusion reactors, space applications, etc.), design, prediction and control of advanced materials beyond current material designs become paramount. Here, through a combined experimental and simulation methodology, we design a nanocrystalline refractory high entropy alloy (RHEA) system. Compositions assessed under extreme environments and in situ electron-microscopy reveal both high thermal stability and radiation resistance. We observe grain refinement under heavy ion irradiation and resistance to dual-beam irradiation and helium implantation in the form of low defect generation and evolution, as well as no detectable grain growth. The experimental and modeling results—showing a good agreement—can be applied to design and rapidly assess other alloys subjected to extreme environmental conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Magnetic droplet soliton pairs

We demonstrate magnetic droplet soliton pairs in all-perpendicular spin-torque nano-oscillators (STNOs), where one droplet resides in the STNO free layer (FL) and the other in the reference layer (RL). Typically, theoretical, numerical, and experimental droplet studies have focused on the FL, with any additional dynamics in the RL entirely ignored. Here we show that there is not only significant magnetodynamics in the RL, but the RL itself can host a droplet driven by, and coexisting with, the FL droplet. Both single droplets and pairs are observed experimentally as stepwise changes and sharp peaks in the dc and differential resistance, respectively. While the single FL droplet is highly stable, the coexistence state exhibits high-power broadband microwave noise. Furthermore, micromagnetic simulations reveal that the pair dynamics display periodic, quasi-periodic, and chaotic signatures controlled by applied field and current. The strongly interacting and closely spaced droplet pair offers a unique platform for fundamental studies of highly non-linear soliton pair dynamics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

A cryogenic near-field thermal diode leveraging superconducting phase transitions

Control of charge and heat transport is essential for computing and thermal management technologies. Recent work with superconducting materials has shown rectified electrical supercurrents near liquid helium temperatures. However, despite large theoretical interest and expected impact on quantum technologies, no experiments have demonstrated control of nanoscale radiative heat currents at cryogenic temperatures. Here we study photon-mediated thermal transport in nanogaps between niobium and gold. Using novel scanning calorimetric probes and nanofabricated devices, we reveal a ~20-fold suppression of radiative heat transport, when niobium transitions from the metallic to the superconducting state. Taking advantage of this effect, we also demonstrate a niobium-based cryogenic thermal diode with a heat rectification ratio of 70%. As a result, the experimental techniques and advances presented here will enable studying nanoscale thermal transport in quantum materials and advancing thermal management of superconducting devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Measurement and modeling of the radio frequency sheath impedance in a large magnetized plasma

The DC and RF properties of radio frequency (RF) driven sheaths were studied in the Large Plasma Device (LAPD) at the University of California, Los Angeles. The experiments diagnosed RF sheaths on field lines connected to a grounded plate at one end and an ion cyclotron range of frequencies (ICRF) antenna at the other end. The experimental setup permitted measurement of the RF sheath impedance at the plate as a function of DC sheath voltage, with the latter controlled by varying the RF current applied to the antenna. Here, the DC current-voltage characteristics of these sheaths and the RF sheath impedance measurements were compared with modeling. Hot electrons, present in the LAPD plasma, were inferred to contribute significantly to both the DC and RF currents and hence the RF impedance. It was postulated that at very low power hot electrons could not access the region of the plasma subject to RF waves, resulting in an increased RF impedance. Within some experimental limitations and significant assumptions, an RF sheath impedance model was verified by the experimental data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Influence of surface adsorption on MoS 2 memtransistor switching kinetics

Sulfur-deficient polycrystalline two-dimensional (2D) molybdenum disulfide (MoS 2 ) memtransistors exhibit gate-tunable memristive switching to implement emerging memory operations and neuromorphic computing paradigms. Grain boundaries and sulfur vacancies are critical for memristive switching; however, the underlying physical mechanisms are not fully understood. Furthermore, the adsorption of water and gaseous species strongly perturbs electronic transport in monolayer MoS 2 , and little work has been done to explore the influence of surface interactions on defect-related kinetics that produces memristive switching. Here, we study the switching kinetics of back-gated MoS 2 memtransistors using current transient measurements in a controlled atmosphere chamber. Here, we observe that adsorbed water molecules lead to suppression of the electronic trap-filling processes concomitant with the resistive switching process, resulting in altered kinetics of the resistive switching. Additionally, using the transient response from “bunched” drain voltage pulse trains performed as a function of temperature, we extract the energy of the affected trap state and find that it places the trap roughly midgap [E T = E C – 0.7 (±0.4) eV]. Our results highlight the importance of controlling for surface interactions that may affect switching kinetics in 2D memtransistors, synaptic transistors, and related memory devices.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Heavy ion irradiation induced failure of gallium nitride high electron mobility transistors: effects of in-situ biasing

Abstract While radiation is known to degrade AlGaN/GaN high-electron-mobility transistors (HEMTs), the question remains on the extent of damage governed by the presence of an electrical field in the device. In this study, we induced displacement damage in HEMTs in both ON and OFF states by irradiating with 2.8 MeV Au 4+ ion to fluence levels ranging from 1.72 × 10 10 to 3.745 × 10 13 ions cm −2 , or 0.001–2 displacement per atom (dpa). Electrical measurement is done in situ , and high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray (EDX), geometrical phase analysis (GPA), and micro-Raman are performed on the highest fluence of Au 4+ irradiated devices. The selected heavy ion irradiation causes cascade damage in the passivation, AlGaN, and GaN layers and at all associated interfaces. After just 0.1 dpa, the current density in the ON-mode device deteriorates by two orders of magnitude, whereas the OFF-mode device totally ceases to operate. Moreover, six orders of magnitude increase in leakage current and loss of gate control over the 2-dimensional electron gas channel are observed. GPA and Raman analysis reveal strain relaxation after a 2 dpa damage level in devices. Significant defects and intermixing of atoms near AlGaN/GaN interfaces and GaN layer are found from HRTEM and EDX analyses, which can substantially alter device characteristics and result in complete failure.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2026

Indirect tunneling enabled spontaneous time-reversal symmetry breaking and Josephson diode effect in TiN/Al 2 ⁢O 3 /Hf 0.8 ⁢Zr 0.2 ⁢O 2 /Nb tunnel junctions

Josephson diode (JD) effect in Josephson tunnel junctions (JTJs) has attracted a great deal of attention due to its importance for developing superconducting-circuitry-based quantum technologies. Even though the preparation of high-quality JTJs by techniques employed in the semiconductor industry has been demonstrated, which was an important milestone because JTJs are the building blocks of superconducting electronics even before the quantum era, the JD effect has not been accomplished in them, nor has the highly desirable electrical control of the effect. We report here the fabrication of JTJs featuring a composite tunnel barrier of Al 2 ⁢O 3 and Hf 0.8 ⁢Zr 0.2 ⁢O 2 using complementary-metal-oxide-semiconductor compatible atomic layer deposition. These JTJs were found to show the JD effect in nominally zero magnetic fields with nonreciprocity controllable via an electric training current, yielding a surprisingly large diode efficiency. The quasiparticle tunneling, through which the Josephson coupling in a JTJ is established, was found to show theoretically expected gap features but no nonreciprocity. We attribute these observations to the simultaneous presence of positive and negative local Josephson couplings in the JTJs, with the negative Josephson coupling originating from indirect tunneling, which results in spontaneous time-reversal symmetry breaking. Finally, the double-minima washboard potential for the ensemble-averaged phase difference in the resistively and capacitively shunted junction model is shown to fully account for the experimentally observed JD effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Flat Bands and Chiral Optical Response of Moiré Insulators

Here, we present a low-energy model describing the reconstruction of the electronic spectrum in twisted bilayers of honeycomb crystals with broken sublattice symmetry. The resulting moiré patterns are classified into two families with different symmetry. In both cases, flat bands appear at relatively large angles without any magic-angle condition. Transitions between them give rise to sharp resonances in the optical absorption spectrum at frequencies well below the gap of the monolayer. Owing to their chiral symmetry, twisted bilayers display circular dichroism, that is, different absorption of left and right circularly polarized light. This optical activity is a nonlocal property determined by the stacking. In hexagonal boron nitride, sensitivity to the stacking leads to strikingly different circular dichroism in the two types of moirés. Our calculations exemplify how subtle properties of the electronic wave functions, encoded in current correlations between the layers, control physical observables of moiré materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Error-Free and Current-Driven Synthetic Antiferromagnetic Domain Wall Memory Enabled by Channel Meandering

We propose a new type of energy-efficient multi-bit magnetic memory based on current-driven, field-free, controlled domain wall motion. A meandering domain wall channel with precisely interspersed pinning regions provides the multi-bit capability of a magnetic tunnel junction memory. The magnetic free layer of the memory device has perpendicular magnetic anisotropy (PMA) and interfacial Dzyaloshinskii-Moriya interaction (DMI) so that spin-orbit torques (SOTs) induce efficient domain wall motion. Using micromagnetic simulations, we find two different cell designs: two-way switching and four-way switching. The memory cell design choices and the physics of pinning mechanisms are discussed in detail. Furthermore, we show that switching reliability and speed may be significantly improved by replacing the ferromagnetic free layer with a synthetic antiferromagnetic (SAF) layer. Switching behavior and material choices will be discussed for the two memory implementations.

magnetic domain wall↗
DOE OSTI2020

Substrate quality drives fungal necromass decay and decomposer community structure under contrasting vegetation types

Fungal mycelium is increasingly recognized as a central component of soil biogeochemical cycling, yet our current understanding of the ecological controls on fungal necromass decomposition is limited to single sites and vegetation types. By deploying common fungal necromass substrates in a temperate oak savanna and hardwood forest in the midwestern USA, we assessed the generality of the rate at which high- and low-quality fungal necromass decomposes; further, we investigated how the decomposer ‘necrobiome’ varies both across and within sites under vegetation types dominated by either arbuscular or ectomycorrhizal plants. In this work, the effects of necromass quality on decay rate were robust to site and vegetation type differences, with high-quality fungal necromass decomposing, on average, 2.5 times faster during the initial stages of decay. Across vegetation types, bacterial and fungal communities present on decaying necromass differed from bulk soil microbial communities and were influenced by necromass quality. Moulds, yeasts and copiotrophic bacteria consistently dominated the necrobiome of high-quality fungal substrates. Synthesis. We show that regardless of differences in decay environments, high-quality fungal substrates decompose faster and support different types of decomposer micro-organisms when compared with low-quality fungal tissues. These findings help to refine our theoretical understanding of the dominant factors affecting fast cycling components of soil organic matter and the microbial communities associated with rapid decay.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

GATE Center of Excellence in Innovative Drivetrains in Electric Automotive Technology Education (IDEATE) (Final Report)

The IDEATE project recognized that this is a critical point in history where advanced engineering solutions are required to propel the U.S. automotive industry irrevocably to the next level: the electrified drivetrain. The existing workforce is not sufficient to this task. It is imperative that automotive engineers with traditional backgrounds focused on internal-combustion and mechanical-drivetrain technologies be retrained with the most current advanced solutions in battery controls and vehicle power electronics. For the long-term success of the U.S. automakers, it is even more important that a future workforce be developed that has both broad and deep comprehension of the issues involved and the most advanced solutions known to these problems. Two campuses of the University of Colorado system joined forces to establish the GATE Center of Excellence in Innovative Drivetrains in Electric Automotive Technology Education (IDEATE). The University of Colorado Boulder (CU-Boulder) is widely regarded as having one of the top graduate programs in power electronics in the country; the University of Colorado Colorado Springs (UCCS) has unrivaled expertise in algorithms for automotive battery control. By collaborating, IDEATE built on our team’s proven strengths to develop innovative curricula and to initiate courses and programs that have provided (and continue to provide) students with a unique opportunity for holistic and specialty education in electric drivetrain technology (part-way through the project, we invited Utah State University to join the project, adding to our strength in power electronics for battery application).

42 ENGINEERING↗
DOE OSTI2020

Evaluation of the lgnitability Hazards in Remediated Nitrate Salt Waste

The hazards associated with the characteristic of ignitability in remediated nitrate salt (RNS) waste containing nitric acid (HNO 3 ) and metal nitrate salts, currently stored at the Waste Control Specialists (WCS) facility near Andrews, Texas have been evaluated. For these waste drums there are two ignitability hazards that may apply, each separately distinguished from the other and uniquely correlated to one of two competing reaction mechanisms. One ignitability hazard, designated the autocatalytic thermal runway, is uniquely correlated to an acid/base reaction of hydrolysis of a hydrated metal nitrate salt. The other applicable ignitability hazard, designated the oxidizer property, is uniquely correlated to a redox disproportionation reaction involving an anhydrous metal nitrate salt. Which reaction mechanism pathway is accessible to a given metal nitrate, and therefore which ignitability hazard may apply, depends on the acidity of the metal ion and its corresponding capacity to maintain coordination with water.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Statistical Profiles of E1 EMP Coupling to Single Conductors

An electro-magnetic pulse (EMP) event can induce large currents and voltages on electrical conductors such as electrical power transmission lines which span many kilometers and the shorter lines typically tens of meters in length used to monitor equipment controlling the power grid. The exact current and voltage induced on a conductor depends on many factors, such as line height, diameter and length as well as ground conductivity and the location of the EMP event relative to the conductor. The current work focus on the line location and orientation relative to the EMP source. A statistical, Monte-Carlo approach is used in sampling the line configuration and then calculating the induced current and voltage. Thousands of EMP events are simulated on the region of the Earth where the EMP event can couple to a given above-ground conductor and the resulting current and voltage is then calculated on that conductor. Through the many simulations, one can assemble statistics on the insult including the peak value, rise time and pulse width.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2022

Designing a Particle Flow Control Apparatus

Flow control within a particle-based Concentrated Solar Power (CSP) system is essential in determining the heat transfer coefficient, and therefore, the power generation capability of these systems. There are three areas where particle flow control is significant: the receivers, storage tanks, and particle-sCO2 heat exchangers. The focus of this work is on designing a new mechanism to control the flow in the particle-sCO2 heat exchangers due to the simplicity and potential cost savings when compared to the other areas of interest. The goal is for this new design to have quicker response times in terms of particle flowrate than a slide gate or flow control valve, which are designs currently used. The design resembles that of a chuck mechanism within a drill where a rotation of the sleeve elicits movement of the jaws both vertically and horizontally to close the outlet area of the nozzle. Additionally, this design will utilize the current actuator that is already used within these heat exchangers to reduce the complexity of implementation. The jaws are designed to be closed at an angle of 76˚ which is just slightly steeper than the hopper leading to the mechanism. Furthermore, this design can be tuned to limit particle bridging and other particle flow phenomena that result in blockages. The prototypes were 3D printed out of polylactic acid (PLA) and scaled up to 100%, 200%, and 400% to be able to observe the velocity profiles of the mechanism more clearly. Experiments are performed with this prototype to compare the inlet and outlet mass flow rates at different configurations of the jaws. The particles used in these experiments are 0.3mm HSP 40/70 that are commonly used in particle-based CSP systems.

14 SOLAR ENERGY↗