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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

High-Temperature Selective Emitter Design and Materials: Titanium Aluminum Nitride Alloys for Thermophotovoltaics

The efficiency of a thermophotovoltaic (TPV) system depends critically upon the spectral selectivity and stability of an emitter, which may operate most effectively at temperatures in excess of 1000 °C. Here, we computationally design and experimentally demonstrate a novel selective emitter design based on multilayer nanostructures, robust to off-normal emission angles. A computational search of the material and temperature compatibility space of simple emitter designs motivates new material classes and identifies several promising multilayer nanostructure designs for both TPV absorber and emitter applications. One such structure, comprising a thin (<100 nm) tunable Ti x Al 1-x N (TiAlN) absorber and refractory oxide Bragg reflector is grown on W metal foil. In agreement with simulations, the emitter achieves record spectral efficiency (43.4%) and power density (3.6 W/cm 2 ) for an emitter with at least 1 h of high temperature (>800 °C) operation.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Characterizing Ion Profiles in Dynamic Junction Light-Emitting Electrochemical Cells

Organic semiconductors have the unique ability to conduct both ionic and electronic charge carriers in thin films, an emerging advantage in applications such as light-emitting devices, transistors, and electrochromic devices, among others. Evidence suggests that the profiles of ions and electrochemical doping in the polymer film during operation significantly impact the performance and stability of the device. However, few studies have directly characterized ion profiles within LECs. Here, we present profiles of ion distributions in LECs following application of voltage, via time-of-flight secondary ion mass spectrometry. Ion distributions were characterized with regard to film thickness, salt concentration, applied voltage, and relaxation over time. Results provide insight into the correlation between ion profiles and device performance, as well as potential approaches to tuning electrochemical doping processes in LECs.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2020

Highly selective electrocatalytic CO 2 reduction to ethanol by metallic clusters dynamically formed from atomically dispersed copper

Direct electrochemical conversion of CO 2 to ethanol offers a promising strategy of lowering CO 2 emission while storing energy from renewable electricity. However, current electrocatalysts offer only limited selectivity toward ethanol. Here we report a copper catalyst synthesized by a unique Cu-Li amalgm method over a commercial carbon support that achieved Faradaic efficiency (FE) higher than 91% at -0.7 V (RHE) and the active potential as low as -0.4 V (RHE) during direct electrocatalytic CO 2 -to-ethanol conversion. The catalyst also demonstrated stability over an extended period of operation. A strong correlation between the catalytic selectivity and the initial Cu atoms dispersion was found and Operando X-ray absorption spectroscopy identified a dynamic and reversible transformation from atomically dispersed copper atoms to Cu n (n = 3 and 4) under the electrochemical reaction. Frist-principles calculations further elucidate the possible catalytic mechanism of CO 2 reduction over Cu n .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

The Vital Function of Fe3O4@Au nanocomposites for Hydrolase Biosensor Design and Its Application in Detection of Methyl Parathion

A nanocomposite of gold nanoparticles (AuNPs) decorating a magnetic Fe3O4 core was synthesized using cysteamine (SH–NH2) as linker, and characterized by TEM, XPS, UV and electrochemistry. Then a hydrolase biosensor, based on self-assembly of methyl parathion hydrolase (MPH) on the Fe3O4@Au nanocomposite, was developed for sensitive and selective detection of the organophosphorus pesticide (OP) methyl parathion. The magnetic nanocomposite provides an easy way to construct the enzyme biosensor by simply exerting an external magnetic field, and also provides a simple way to renew the electrode surface by removing the magnet. Unlike inhibition-based enzyme biosensors, the hydrolase is not poisoned by OPs and thus is reusable for continuous measurement. AuNPs not only provide a large surface area, high loading efficiency and fast electron transfer, but also stabilize the enzyme through electrostatic interactions. The MPH biosensor shows rapid response and high selectivity for detection of methyl parathion, with a linear range from 0.5 to 1000 ng/mL and a detection limit of 0.1 ng/mL. It also shows acceptable reproducibility and stability. The simplicity and ease of operation of the proposed method has great potential for on-site detection of P–S containing pesticides and provides a promising strategy to construct a robust biosensor.

Au nanoparticles↗
DOE OSTI2024

Efficient electrosynthesis of hydrogen peroxide in neutral media using boron and nitrogen doped carbon catalysts

The two-electron electrocatalytic oxygen reduction reaction (2e - ORR) is a promising, sustainable, and efficient route for on-site and small-scale production of hydrogen peroxide (H 2 O 2 ) compared to the conventional anthraquinone oxidation process. Although heteroatom doped carbon materials are widely studied for the 2e - ORR, few studies have been conducted on the synergistic relationship between multiple doping elements on H 2 O 2 performance. Moreover, there is a lack of efficient and stable catalysts for H 2 O 2 electrosynthesis in neutral media. In this work, a series of boron and nitrogen co-doped carbon (BNC) catalysts are synthesized and assessed for the 2e - ORR in neutral pH electrolyte. Through X-ray photoelectron and absorption spectroscopy analyses, we characterize B–N–C moieties and correlate them with H 2 O 2 production performance. In rotating ring disk electrode measurements, BNC catalysts pyrolyzed at 900 °C exhibit H 2 O 2 Faradaic efficiency of ~70% and demonstrate excellent long-term stability over 10 hours of continuous operation. In a three-electrode flow cell, this catalyst achieves ~78% H 2 O 2 Faradaic efficiency and 0.9 mmol cm -2 h -1 productivity at 0.20 V vs. RHE, surpassing most previously reported carbon-based catalysts in neutral media. This work contributes fundamental insights into the role of boron and nitrogen heteroatom dopants toward 2e - ORR and highlights the practical viability of these catalysts for real world applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Thick-wall effects in the theory of resistive wall modes

Magnetic interaction of the plasma perturbations with the nearby resistive wall is considered as a resistive wall mode (RWM) problem, but with two essential differences from the traditional thin-wall approach. First, the wall is treated as magnetically thick, which means that the skin depth is not assumed larger than the wall thickness. Second, the plasma is allowed to enter the region where the RWM must be deeply unstable without rotation. The latter corresponds to the plasma operation above the no-wall stability limit demonstrated in the DIII-D tokamak [E. J. Strait et al., Phys. Plasmas 11, 2505 (2004)]. It is shown that the rotational stabilization observed in these experiments can be reproduced in this model if the mode is forced to rotate with a frequency above a critical level. The analytical estimates show that this effect (absent in the model based on the thin-wall approximation) is strong at realistic parameters. The model also predicts that the locking of the rotationally stabilized mode gives rise to instability with a growth rate much larger than its thin-wall estimate.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Hard magnetohydrodynamic limit in 1/3 sawtooth like activity in LHD

The optimization of LHD discharges in inward-shifted configurations with 1/3 sawtooth like activity is an open issue. These relaxation events limit the LHD performance driving a periodic plasma deconfinement. The aim of this study is to analyze the 1/3 sawtooth like activity in plasmas with different stability properties to foreseen the best operation conditions and minimize its undesired effects. We summarize the results of several MHD simulations for plasmas with Lundquist numbers between 10{sup 5} and 10{sup 6} in the slow reconnection regime, studying the equilibria properties during the onset of a chain of 1/3 sawtooth like events. The research conclusions point out that the hard MHD limit can be reached in the inner plasma region after the onset of a strong 1/3 resonant sawtooth like event and trigger a plasma collapse. The collapse can be avoided if the system remains in the soft MHD limit, namely, in a regime with a pressure gradient and a magnetic turbulence below the critical values to drive the soft-hard MHD transition. In the soft MHD limit the system relaxations are the non resonant 1/3 sawtooth like events or a weak version of the 1/3 resonant sawtooth like events. A system relaxation in the soft MHD regime drives a minor plasma deconfinement that does not limit the LHD performance if the event periodicity is not very high.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Operation of an ungated diamond field-emission array cathode in a L-band radiofrequency electron source

We report on the operation of a field-emitter-array cathode in a conventional L-band radio-frequency electron source. The cathode consisted of an array of ∼10{sup 6} diamond tips on pyramids. Maximum current on the order of 15 mA was reached and the cathode did not show appreciable signs of fatigue after weeks of operation. The measured Fowler-Nordheim characteristics, transverse beam density, and current stability are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Solid optical ring interferometer for high-throughput feedback-free spectral analysis and filtering

We describe a simple and inexpensive optical ring interferometer for use in high-resolution spectral analysis and filtering. It consists of a solid cuboid, reflection-coated on two opposite sides, in which constructive interference occurs for waves in a rhombic trajectory. Due to its monolithic design, the interferometer’s resonance frequencies are insensitive to environmental disturbances over time. Additional advantages are its simplicity of alignment, high-throughput, and feedback-free operation. If desired, it can be stabilized with a secondary laser without disturbance of the primary signal. We illustrate the use of the interferometer for the measurement of the spectral Mollow triplet from a quantum dot and characterize its long-term stability for filtering applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Stable random lasing in CdSSe micropowders

The random lasing in CdS micropowder in the green region (near 520 nm) at room temperature under optical pumping by pulsed Nd{sup 3+} : YAG and N{sub 2} lasers at wavelengths of 355 and 337 nm, respectively, is studied. The influence of fluctuations of pump pulse output energy on the random lasing action in CdS micropowder is determined. It is shown that the use of a pump laser with highly stable output power and high spatial beam uniformity (in particular, an N{sub 2} laser) provides stable random lasing in CdSSe micropowders. The lasing is characterised by the presence of a clear structure of narrow lines in the spectrum and stability of their position during pulsed operation at a repetition rate of 700 Hz at wavelengths of 525, 570, 600, and 650 nm with thresholds in the range of 1100 – 1600 kW cm{sup −2}. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Three-dimensional mesostructures as high-temperature growth templates, electronic cellular scaffolds, and self-propelled microrobots

Recent work demonstrates that processes of stress release in prestrained elastomeric substrates can guide the assembly of sophisticated 3D micro/nanostructures in advanced materials. Reported application examples include soft electronic components, tunable electromagnetic and optical devices, vibrational metrology platforms, and other unusual technologies, each enabled by uniquely engineered 3D architectures. A vast disadvantage of these systems is that the elastomeric substrates, while essential to the assembly process, can impose significant engineering constraints in terms of operating temperatures and levels of dimensional stability; they also prevent the realization of 3D structures in freestanding forms. In this work, we introduce concepts in interfacial photopolymerization, nonlinear mechanics, and physical transfer that bypass these limitations. The results enable 3D mesostructures in fully or partially freestanding forms, with additional capabilities in integration onto nearly any class of substrate, from planar, hard inorganic materials to textured, soft biological tissues, all via mechanisms quantitatively described by theoretical modeling. Illustrations of these ideas include their use in 3D structures as frameworks for templated growth of organized lamellae from AgCl–KCl eutectics and of atomic layers of WSe 2 from vapor-phase precursors, as open-architecture electronic scaffolds for formation of dorsal root ganglion (DRG) neural networks, and as catalyst supports for propulsive systems in 3D microswimmers with geometrically controlled dynamics. Taken together, these methodologies establish a set of enabling options in 3D micro/nanomanufacturing that lie outside of the scope of existing alternatives.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Experimental observation of electron-scale turbulence evolution across the L–H transition in the National Spherical Torus Experiment

Electron-scale turbulence (for $3$ $\lesssim$ $k⟂ρ_s$ $\lesssim$ $12$) ) was measured during the L–H transition in the National Spherical Torus Experiment (NSTX) (Ono et al 2000 Nucl. Fusion 40 557) using a coherent microwave scattering system. The measurements were carried out at a radial region adjacent to the edge transport barrier (ETB) (at smaller radius than ETB). The observed L–H transition occurred during current flattop, which facilitated the measurement of electron-scale turbulence. The measured electron-scale turbulence is observed to be quasi-stationary before the L–H transition, and an intermittent phase for electron-scale turbulence is observed after the start of the L–H transition with a gradual decrease in overall turbulence density fluctuation spectral power with intermittent large relative variations (on ~0.5–1 ms time scale) in the total spectral power. A turbulence-quiescent phase is observed following the intermittent phase, and a significant reduction in the electron-scale turbulence spectral power is only observed at lower wavenumbers, namely $k⟂ρ_s$ $\leqslant$ $9$ –10, which is also seen in different operational NSTX scenarios due to different stabilization mechanisms. A recovery phase is seen after the quiescent phase, where the electron-scale density fluctuation power starts to gradually increase. Simultaneous ion-scale turbulence measurements at larger radius than the electron-scale turbulence measurement location show similar temporal behavior in ion-scale turbulence as in the measured electron-scale turbulence. These observations demonstrate that the suppression of turbulence during the L–H transition is not just limited to the ETB region. None of the measured electron-scale turbulence and ion-scale turbulence from edge into core is found to be obviously leading in the response to the L–H transition, and the overall turbulence suppression after the start of the L–H transition at different radii seems to start at the same time and is a gradual process happening on a tens-of-ms time scale. The trend of decrease in electron-scale turbulence during the L–H transition is found to be consistent with a decrease in the maximum electron-temperature-gradient linear growth rate from linear gyrokinetic stability analysis. Interestingly, the observed intermittency in electron-scale turbulence during the intermittent phase cannot be explained by the linear analysis.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Isotope effects and Alfvén eigenmode stability in JET H, D, T, DT, and He plasmas

While much about Alfvén eigenmode (AE) stability has been explored in previous and current tokamaks, open questions remain for future burning plasma experiments, especially regarding exact stability threshold conditions and related isotope effects; the latter, of course, requiring good knowledge of the plasma ion composition. In the JET tokamak, eight in-vessel antennas actively excite stable AEs, from which their frequencies, toroidal mode numbers, and net damping rates are assessed. The effective ion mass can also be inferred using measurements of the plasma density and magnetic geometry. Thousands of AE stability measurements have been collected by the Alfvén Eigenmode Active Diagnostic in hundreds of JET plasmas during the recent Hydrogen, Deuterium, Tritium, DT, and Helium-4 campaigns. In this novel AE stability database, spanning all four main ion species, damping is observed to decrease with increasing Hydrogenic mass, but increase for Helium, a trend consistent with radiative damping as the dominant damping mechanism. These data are important for confident predictions of AE stability in both non-nuclear (H/He) and nuclear (D/T) operations in future devices. In particular, if radiative damping plays a significant role in overall stability, some AEs could be more easily destabilized in D/T plasmas than their H/He reference pulses, even before considering fast ion and alpha particle drive. Active MHD spectroscopy is also employed on select HD, HT, and DT plasmas to infer the effective ion mass, thereby closing the loop on isotope analysis and demonstrating a complementary method to typical diagnosis of the isotope ratio.

Alfvén eigenmodes↗
DOE OSTI2023

Calibration strategy of the PROSPECT-II detector with external and intrinsic sources

This paper presents an energy calibration scheme for an upgraded reactor antineutrino detector for the Precision Reactor Oscillation and Spectrum Experiment (PROSPECT). The PROSPECT collaboration is preparing an upgraded detector, PROSPECT-II (P-II), to advance capabilities for the investigation of fundamental neutrino physics, fission processes and associated reactor neutrino flux, and nuclear security applications. P-II will expand the statistical power of the original PROSPECT (P-I) dataset by at least an order of magnitude. The new design builds upon previous P-I design and focuses on improving the detector robustness and long-term stability to enable multi-year operation at one or more sites. The new design optimizes the fiducial volume by elimination of dead space previously occupied by internal calibration channels, which in turn necessitates the external deployment. In this paper, we describe a calibration strategy for P-II. Here, the expected performance of externally deployed calibration sources is evaluated using P-I data and a well-benchmarked simulation package by varying detector segmentation configurations in the analysis. The proposed external calibration scheme delivers a compatible energy scale model and achieves comparable performance with the inclusion of an additional AmBe neutron source, in comparison to the previous internal arrangement. Most importantly, the estimated uncertainty contribution from the external energy scale calibration model meets the precision requirements of the P-II experiment.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Advancing Cross-Sectional Scanning Electron Microscopy of Perovskite Solar Cells

Organic–inorganic perovskites are an emerging class of photovoltaic materials. Despite achieving power conversion efficiencies surpassing 26%, the challenge of perovskite stability including degradation during exposure to operational conditions such as light, heat, humidity, water, oxygen, and electric fields is well known. Related, perovskite instability has limited high-resolution electron imaging and characterization techniques that can be used for understanding degradation mechanisms. Furthermore, we demonstrate perovskite device cross-section preparation using mechanical polishing in a water-free environment with cryogenic Ar ion milling. Scanning electron microscopy was then used in both backscattered electron and secondary electron imaging modes to obtain information about layer structure, grain aggregate structure, and compositional heterogeneity. Monte Carlo CASINO simulations inform optimum beam conditions and image acquisition parameters and the effects of accelerating voltage, dwell times, and frame averaging for practical image acquisition are reported.

14 SOLAR ENERGY↗
DOE OSTI2024

Composite octet baryons in a relativistic mean field description of nuclear and neutron star matter

Here, we examine the properties of composite octet baryons in the nuclear medium and neutron-star matter. The internal quark-diquark structure of the octet baryons and the equations of state of nuclear matter and neutron-star matter in the mean field approximation are described by using the three-flavor Nambu-Jona-Lasinio (NJL) model as an effective quark theory of quantum chromodynamics. After introducing our model, we first discuss the properties of single baryons and their effective meson exchange interactions in symmetric nuclear matter by using concepts of Fermi-liquid theory. Several model-independent implications of this description are derived and illustrated by numerical results obtained in our model. Second, we extend the model description to high baryon densities and investigate the equation of state of neutron-star matter and the resulting star masses. We find that the so-called hyperon puzzle persists also for the case of composite hadrons. To get more information on this point, we also investigate the role of 6-Fermi and 8-Fermi interactions, in addition to the standard 4-Fermi interactions. The strengths of those higher-order Fermi interactions is determined so as not to spoil the saturation properties of nuclear matter. Among them, an interaction characterized by a product of four-quark current operators plays a special role to stabilize the stars over a large region of central baryon densities, although it has little effect on the maximum star masses.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Coordinated Optimal Control of Constrained DERs

In this paper, a coordinated optimal control is designed to simultaneously satisfy multiple power system objectives at the distribution network level. With high penetration of renewables, traditional generation and control may not be enough to compensate for intermittent changes in net load. Dynamic coordination of battery storage devices and demand response at aggregated distributed energy resource (DER) sites becomes necessary to maintain power system operation, however, each dynamic power component operates at different time scales. Frequency stabilization can be achieved by designing optimal controls for traditional generation, storage devices and demand response. The proposed optimal controls naturally render frequency separation of these load balancing mechanisms. Given a 24-hour net load forecast, optimal tracking control inputs are designed subject to constraints of selected system elements to ensure optimal performance of the power system. Simulation results are presented and discussed.

Harvey, Roland↗
DOE OSTI2015

A fully integrated oven controlled microelectromechanical oscillator – Part II. Characterization and measurement

Our paper reports the measurement and characterization of a fully integrated oven controlled microelectromechanical oscillator (OCMO). The OCMO takes advantage of high thermal isolation and monolithic integration of both aluminum nitride (AlN) micromechanical resonators and electronic circuitry to thermally stabilize or ovenize all the components that comprise an oscillator. Operation at microscale sizes allows implementation of high thermal resistance platform supports that enable thermal stabilization at very low-power levels when compared with the state-of-the-art oven controlled crystal oscillators. A prototype OCMO has been demonstrated with a measured temperature stability of -1.2 ppb/°C, over the commercial temperature range while using tens of milliwatts of supply power and with a volume of 2.3 mm 3 (not including the printed circuit board-based thermal control loop). Additionally, due to its small thermal time constant, the thermal compensation loop can maintain stability during fast thermal transients (>10 °C/min). This new technology has resulted in a new paradigm in terms of power, size, and warm up time for high thermal stability oscillators.

42 ENGINEERING↗