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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Determination of the mean energy of fast electron losses and anisotropies through thick-target emission on WEST

Abstract A new method to obtain the mean energy of fast electron losses in fusion plasmas using a versatile multi-energy hard x-ray (HXR) detector is presented. The method is based on measuring the thick-target emission of tungsten in the divertor region produced by fast electron losses interacting with the target and modeling the tungsten spectra by a Monte Carlo code which simulates the interaction between a beam of electrons and a solid target. The mean energy of the fast electron losses is determined through the comparison between the experimental and synthetic emission. The results show that fast electron losses during lower hybrid current drive discharges at WEST have a mean energy of 90–140 keV and represent only 2% of the total heat flux at the target. Additionally, anisotropic HXR emission has been detected for the first time at the WEST core and edge plasma, with opposite directions. It is due to the forward-peak emission of two distinctive populations of fast electrons: co-current fast electrons in the core and counter-current fast electron losses at the inner strike point. In view of future experiments like ITER where electron cyclotron current drive will generate a fast electron population, this technique could serve as a real-time monitor of fast electron losses and eventually feed an actuator on the current drive generation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Understanding the formation of a low-pressure pedestal in the presence of a strong internal transport barrier in DIII-D high β p plasmas

As a promising scenario for fusion reactors, the high poloidal-beta (β P ) scenario is characterized by a strong large radius internal transport barrier (ITB), which significantly enhances the overall confinement quality and the bootstrap current fraction for fully non-inductive operation. It is frequently observed that in the presence of a strong ITB, the pedestal height is lower and is accompanied by small edge localized modes (ELMs), which further improves the compatibility of a high performance core with an edge solution. A mechanism for the formation of the low pedestal is proposed in this paper. It is found that the strong ITB creates an off-axis bootstrap current to clamp the local safety factor q, and thus the magnetic shear in the outer core/pedestal region is increased. Gyrokinetic simulations with the CGYRO code show that the higher magnetic shear brings the experimental profiles into the range where the growth rate of drift-wave instabilities and thus transport is higher, and therefore a lower pedestal gradient is expected. Here, the combination of low pedestal and high magnetic shear further enhances the turbulent transport across the whole pedestal, consistent with power balance analysis. Such a positive feedback mechanism ultimately results in a lower pressure pedestal as observed in experiments. Under such a low pedestal, linear simulations with BOUT++ predict the growth rates of peeling–ballooning modes to be lower across the whole toroidal mode number spectra, and the nonlinear BOUT++ simulation exhibits lower saturated fluctuation intensity as well, consistent with the experimentally observed lower ELM size.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Stable electrospray signal on a microfabricated glass chip with three-dimensional open edge and tiered depth geometries

This paper presents the microfabrication and performance of a three-dimensional electrospray ionization (ESI) emitter tip made from glass, which achieves stable current signals important for chemical analysis. Our novel microfabrication process and custom-built signal conditioning hardware provides the advantage of providing accurate features and steady signals. The fabrication process relies on standard microfabrication techniques (i.e., deposition, photolithography, and wet etching). This fabrication method involves the novel application of two layers of positive and negative photoresists in addition to Parafilm® wax tape. Open edge and tiered depth details were successfully created from a multilayer planar mask. This is a benefit for integrated miniaturized and microfluidic systems that often require micro features for their functionality but relatively large millimeter size features for their physical periphery. We demonstrate the fundamental performance of electrospray with this microfluidic chip. The emitter tip was fixed on a linear axis stage with high resolution (10 μm) to finely control the tip distance from a metal counter electrode plate. Further, a custom printed circuit board system was built to safely control four voltages applied to the microchip ports from a single high voltage power supply. To readily form the electrospray, non-aqueous solvents were used for their low viscosity and a constant voltage of +2.7 kV was applied to the sheath electrospray microchannel. The liquid being sprayed was 80/20 (v/v) methanol/acetonitrile with 0.1% acetic acid in the sheath microchannel and with ammonium acetate (10–40 mM) in its remaining microchannels. The electrospray signal was measured in response to varying the distance (1.4 to 1.6mm) between the electrospray emitter tip and a metal counter electrode plate in addition to the varying concentration of the background electrolyte, ammonium acetate. Stable and repeatable electrospray signal showed linear relationships with emitter tip distance and concentration (r 2 ≥ 0.95).

42 ENGINEERING↗
DOE OSTI2023

Fluctuation-driven excess noise near superconducting phase transition

We discuss intrinsic mechanisms of nonequilibrium excess noise in superconducting devices and transition edge sensors. In particular, we present an overview of fluctuation-driven contributions to the current noise in the vicinity of the superconducting transition. We argue that sufficiently close to the critical temperature fluctuations of conductivity may become correlated provided that the rate of quasiparticle relaxation is slow as compared to dynamics of superconducting fluctuations. In this regime, fluctuations of conductivity adiabatically follow the fluctuations of the electron distribution. This leads to a substantial enhancement of current noise. Here, the corresponding spectral power density of noise has a Lorentzian shape in the frequency domain while its magnitude scales proportionally to the inelastic relaxation time. It also sensitively depends on the dephasing and Ginzburg–Landau timescales. Further estimates suggest that this mechanism dominates over the conventional temperature fluctuations in the same range of parameters. To describe these effects microscopically, we use the nonequilibrium Keldysh technique in the semiclassical approximation of superconductivity with Boltzmann–Langevin random forces to account for correlations of fluctuations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Role of deep levels and barrier height lowering in current-flow mechanism in 150 μ m thick epitaxial n-type 4H–SiC Schottky barrier radiation detectors

Schottky barrier detectors (SBDs) require larger surface areas than conventional electronics to increase the detection efficiency although such SBDs manifest large diode ideality factors due to inhomogeneous areal distribution of surface barrier height (SBH). Inhomogeneous SBH distributions lead to various current flow mechanisms in SBDs, which need to be identified to optimize detector performance. In this Letter, we identify the current flow mechanism in large area Schottky barrier diodes for radiation detection fabricated on 150 μm thick n-4H–SiC epitaxial layers. The analysis of temperature-dependent forward current–voltage (I–V–T) characteristics of SBDs revealed two linear regions in current–voltage curves up to 450 K, one corresponding to the current flow through a low barrier patch, while the other corresponds to that of average barrier distribution. Applying a SBH distribution model to the reverse I–V–T characteristics, an activation energy of 0.76 eV for the current flow over the Schottky barrier was calculated. Additionally, the activation energy did not directly correspond to any of the defect levels observed from the deep level transient spectroscopy (DLTS). Above 450 K, a Schottky type barrier lowering suggested a current flow through a low barrier patch of ≈ 0.8 eV. The absence of any SBH lowering below 450 K indicated that the current corresponded to a neutrally charged trap level at ≈ 0.6 eV below the conduction band edge, which was consistent with DLTS measurements revealing the presence of an electron trap level Z1/2 at 0.59 eV below the conduction band edge.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Surrogate models for plasma displacement and current in 3D perturbed magnetohydrodynamic equilibria in tokamaks

Abstract A numerical database of over one thousand perturbed three-dimensional (3D) equilibria has been generated, constructed based on the MARS-F (Liu et al 2000 Phys. Plasmas 7 3681) computed plasma response to the externally applied 3D field sources in multiple tokamak devices. Perturbed 3D equilibria with the n = 1–4 ( n is the toroidal mode number) toroidal periodicity are computed. Surrogate models are created for the computed perturbed 3D equilibrium utilizing model order reduction (MOR) techniques. In particular, retaining the first few eigenstates from the singular value decomposition (SVD) of the data is found to produce reasonably accurate MOR-representations for the key perturbed quantities, such as the perturbed parallel plasma current density and the plasma radial displacement. SVD also helps to reveal the core versus edge plasma response to the applied 3D field. For the database covering the conventional aspect ratio devices, about 95% of data can be represented by the truncated SVD-series with inclusion of only the first five eigenstates, achieving a relative error (RE) below 20%. The MOR-data is further utilized to train neural networks (NNs) to enable fast reconstruction of perturbed 3D equilibria, based on the two-dimensional equilibrium input and the 3D source field. The best NN-training is achieved for the MOR-data obtained with a global SVD approach, where the full set of samples used for NN training and testing are stretched and form a large matrix which is then subject to SVD. The fully connected multi-layer perceptron, with one or two hidden layers, can be trained to predict the MOR-data with less than 10% RE. As a key insight, a better strategy is to train separate NNs for the plasma response fields with different toroidal mode numbers. It is also better to apply MOR and to subsequently train NNs separately for conventional and low aspect ratio devices, due to enhanced toroidal coupling of Fourier spectra in the plasma response in the latter case.

3D equilibrium↗
DOE OSTI2024

The State of the Art in Root System Architecture Image Analysis Using Artificial Intelligence: A Review

Roots are essential for acquiring water and nutrients to sustain and support plant growth and anchorage. However, they have been studied less than the aboveground traits in phenotyping and plant breeding until recent decades. In modern times, root properties such as morphology and root system architecture (RSA) have been recognized as increasingly important traits for creating more and higher quality food in the “Second Green Revolution”. To address the paucity in RSA and other root research, new technologies are being investigated to fill the increasing demand to improve plants via root traits and overcome currently stagnated genetic progress in stable yields. Artificial intelligence (AI) is now a cutting-edge technology proving to be highly successful in many applications, such as crop science and genetic research to improve crop traits. A burgeoning field in crop science is the application of AI to high-resolution imagery in analyses that aim to answer questions related to crops and to better and more speedily breed desired plant traits such as RSA into new cultivars. This review is a synopsis concerning the origins, applications, challenges, and future directions of RSA research regarding image analyses using AI.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1972

Changes in magnetospheric configuration during the substorm growth phase.

Investigation of various changes in the configuration of the geomagnetic tail that occur during the growth phase of magnetospheric substorms. A flaring-tail model indicates that the observed increases in geomagnetic tail field are explained if the dayside magnetopause shrinks by 1 to 2 earth radii. Increased tail flaring also requires that the tail current sheet approach near the earth during the growth phase. The motion of the inner edge of the plasma sheet, and consequently an equatorward shift of the nightside auroral oval, is consistent with the structural modifications mentioned above.

Coroniti, F. V.↗
NASA NTRS1987

Transonic flow visualization using holographic interferometry

An account is made of some of the applications of holographic interferometry to the visualization of transonic flows. In the case of the compressor shock visualization, the method is used regularly and has moved from being a research department invention to a design test tool. With the implementation of automatic processing and simple digitization systems, holographic vibrational analysis has also moved into routine nondestructive testing. The code verification interferograms were instructive, but the main turbomachinery interest is now in 3 dimensional flows. A major data interpretation effort will be required to compute tomographically the 3 dimensional flow around the leading or the trailing edges of a rotating blade row. The bolt on approach shows the potential application to current unsteady flows of interest. In particular that of the rotor passing and vortex interaction effects is experienced by the new generation of unducted fans. The turbocharger tests presents a new area for the application of holography.

Bryanston-Cross, Peter J.↗
NASA NTRS1988

Application of the V(R) resistance curve method to fracture of various crack configurations

The fracture resistance curve method of Newman (1985), based on the crack-tip-opening displacement, V(R), for a 'stationary' crack, was applied to various crack configurations in 2024-T351 and 7075-T651 aluminum alloys tested at room temperature. Using a stationary crack solution, the crack-tip-displacement was calculated at the current crack length for the crack configurations which included compact, middle-crack, single-edge-crack, and three-hole-crack tension specimens. The results showed that the V(R) resistance curves are insensitive to crack length, specimen width, and specimen type up to maximum load. After the maximum load is reached, the V(R) remains nearly constant; this constant depends only on specimen type, specimen width, and crack length. The V(R) resistance curve method can be used with the strip-yield analyses to accurately predict stable crack growth and instability of cracked metallic materials.

Newman, J. C., Jr.↗
NASA NTRS2004

Exploration of Geometric Noise Suppression in Transition Edge Sensors

We present noise data on Mo/Au superconducting transition edge sensors featuring the noise suppression geometry using normal metal bars transverse to the bias current. The effectiveness of the bars in far-infrared bolometers and x-ray microcalorimeters is evaluated. We have examined the effect of the resistivity of the superconducting bilayer on excess noise in bolometer devices. We have also studied the effect of bar density on energy resolution in x-ray devices. We address the question of whether the reduction is noise is necessarily coupled to a reduction in the effective transition sharpness. We propose a fabrication technique experiment to examine the dependence of alpha and noise suppression in similar transverse bar densities.

Chervenak, J. A.↗
NASA NTRS2007

Lessons Learned JSC Micro-Wireless Instrumentation Systems on Space Shuttle and International Space Station CANEUS 2006

A viewgraph presentation on lessons learned from NASA Johnson Space Center's micro-wireless instrumentation is shown. The topics include: 1) Background, Rationale and Vision; 2) NASA JSC/Structural Engineering Approach & History; 3) Orbiter Wing Leading Edge Impact Detection System; 4) WLEIDS Confidence and Micro-WIS Lessons Learned; and 5) Current Projects and Recommendations.

Studor, George↗
NASA NTRS2012

Fabrication of Compact Superconducting Lowpass Filters for Ultrasensitive Detectors

It is extremely important for current and future far-infrared and sub-millimeter ultrasensitive detectors, which include transition edge sensors (TES) and microwave kinetic inductance detectors, to be adequately filtered from stray electromagnetic radiation in order to achieve their optimal performance. One means of filtering stray radiation is to block leakage associated with electrical connections in the detector environment. Here we discuss a fabrication methodology for realizing non-dissipative planar filters imbedded in the wall of the detector enclosure to limit wave propagation modes up to far-infrared frequencies. Our methodology consists of fabricating a boxed stripline transmission line, in which a superconducting (Nb, Mo, or Al) transmission line is encased in a silicon dioxide dielectric insulator coated with a metallic shell. We report on achieved attenuation and return loss and find that it replicates the simulated data to a high degree.

Brown, Ari↗
NASA NTRSDate not supplied

Cross-Government Development of Space-Based Quantum Sensors for Earth and Space Science

Quantum sensing technologies promise advantages over their traditional counterparts in terms of sensitivity and accuracy, including higher signal-to-noise ratios, better measurement resolution and sensitivity, and accuracies that can be tied to fundamental constants. As a result of the potentially promising advantages of quantum sensing technologies, the multi-agency Space Science and Technology Partnership Forum (S&T Forum), consisting of NASA, NRO, and USSF, conducted a 2023 study to identify the current state of space-based quantum sensing technology development that will enable cutting-edge Earth and space science. The findings contained within this work provide insight into quantum sensing and quantum enabling technology work across the S&T Forum to inform technology development and identify potential government, industry, and academic coordination and collaboration opportunities in quantum sensing within the Earth and space science community. The results herein focus on the collation of quantum sensing technologies, facilities, and developers captured from the participants of the study to provide a broad overview of quantum sensor development for the Earth and space science community; specifically highlighting how five particular areas of quantum sensing technology (listed in alphabetical order) are of near-term interest to all three S&T Forum agencies: atomic clocks, atom interferometers, quantum magnetometers, Rydberg sensors, and single photon detectors. The findings in this work point to the intent of the S&T Forum agencies to lean into the development of quantum sensing technology in which the three agencies have mutual near-term interest, including cross-cutting enabling component technologies. The information presented provides points of entry in terms of people, facilities, and quantum sensing technology work within the government as well as increased transparency into the five quantum sensing technology areas of mutual interest of the S&T Forum agencies to remove barriers and encourage participation and partnership with the Earth and space science community.

Quantum↗
DOE OSTI2021

Inter-ELM pedestal evolution and the role of edge fluctuations in the C-Mod and DIII-D tokamaks

Edge localized modes (ELMs) lead to a cyclical behaviour of the H-mode pedestal density, temperature and pressure. Substantial evidence exists associating the ELM crash with violation of ideal MHD stability, via current driven kink/peeling modes and/or pressure gradient driven ballooning modes. Recovery from ELM crashes and buildup to the next ELM crash is an active and critical area of edge physics research for ITER projections. In one set of theories, the pedestal pressure profile in H-mode discharges is predicted to be limited by micro-instabilities. One such micro-instability is the kinetic ballooning mode (KBM), which is hypothesized to provide a ‘soft’ limit that regulates the edge transport, thereby restricting the local pressure gradient. In this picture, e.g. in the EPED model, the pedestal width expands slowly until the ideal MHD stability limit is reached. Experiments were recently performed on the C-Mod and DIII-D devices to search for instabilities correlated with the pedestal evolution between ELMs. The results show correlations between the onset of quasi-coherent fluctuations between type I ELMs and a critical temperature gradient. Linear gyrokinetic calculations have shown that these fluctuations have characteristics similar to those expected for KBMs. These results provide additional data toward validation of the EPED model, increasing confidence in ITER projections.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1995

Micrometeoroids and debris on LDEF comparison with MIR data

Part of the LDEF tray allocated to French experiments (FRECOPA) has been devoted to the study of dust particles. The tray was located on the face of LDEF directly opposed to the velocity vector. Crater size distributions have made possible the evaluation of the incident microparticle flux in the near-Earth environment. Comparisons are made with measurements obtained on the other faces of LDEF (tray clamps), on the leading edge (MAP) and with results of a similar experiment flown on the MIR space station. The geometry of impact craters, depth in particular, provides useful information on the nature of impacting particles and the correlation of geometry with the chemical analysis of projectile remnants inside craters make possible a discrimination between meteoroids and orbital debris. Emphasis has been laid on the size distribution of small craters in order to assess a cut-off in the distribution of particles in LEO. Special attention has been paid to the phenomenon of secondary impacts. A comparison of flight data with current models of meteoroids and space debris shows a fair agreement for LDEF, except for the smaller particles: the possible contribution of orbital debris in GTO orbits to the LDEF trailing edge flux is discussed. For MIR, flight results show differences with current modeling: the possible enhancement of orbital debris could be due to the contaminating presence of a permanently manned space station.

Mandeville, Jean-Claude↗
NASA NTRS2004

Evaluation of Droplet Splashing Algorithm in LEWICE 3.0

The Icing Branch at NASA Glenn Research has developed a computer program to simulate ice formation on the leading edge of an aircraft wing during flight through cold, moist air. As part of the branch's current research, members have developed software known as LEWICE. This program is capable of predicting the formation of ice under designated weather conditions. The success of LEWICE is an asset to airplane manufacturers, ice protection system manufacturers, and the airline industry. Simulations of ice formation conducted in the tunnel and in flight is costly and time consuming. However, the danger of in-flight icing continues to be a concern for both commercial and military pilots. The LEWICE software is a step towards inexpensive and time efficient prediction of ice collection. In the most recent version of the program, LEWICE contains an algorithm for droplet splashing. Droplet splashing is a natural occurrence that causes accumulation of ice on aircraft surfaces. At impingement water droplets lose a portion of their mass to splashing. With part of each droplet joining the airflow and failing to freeze, early versions of LEWICE without the splashing algorithm over-predicted the collection of ice on the leading edge. The objective of my project was to determine whether the revised version of LEWICE accurately reflected the ice collection data obtained from the Icing Research Tunnel (IRT). The experimental data from the IRT was collected by Mark Potapczuk in January, March and July of 2001 and April and December of 2002. Experimental data points were the result of ice tracings conducted shortly after testing in the tunnel. Run sheets, which included a record of velocity, temperature, liquid water content and droplet diameter, served as the input of the LEWICE computer program. Parameters identical to the tunnel conditions were used to run LEWICE 2.0 and LEWICE 3.0. The results from IRT and versions of LEWICE were compared graphically. After entering the raw experimental data and computer output into a spread sheet, I mapped each ice formation onto a clean airfoil. The LEWICE output provided the data points to graphically depict ice formations developed by the program. weather conditions of runs conducted in January 2001, it was evident that the splashing algorithm of LEWICE 3.0 predicts ice formations more accurately than LEWICE 2.0. Especially at conditions with droplet size between 80 and 160 microns, the splashing algorithm of the new LEWICE version compensated for the loss of droplet mass as a result of splashing. In contrast, LEWICE 2.0 consistently over-predicted the mass of the ice in conditions with droplet size exceeding 80 microns. This evidence confirms that changes made to algorithms of LEWICE 3.0 have increased the accuracy of predicting ice collection.

Homenko, Hilary N.↗
DOE OSTI2022

Proximity Effects and Topological Spin Currents in van der Waals Heterostructures (Final Report)

The major goal of this grant has been to study spin-polarized topological edge states. The original proposal was focused specifically on those of the quantum anomalous Hall (QAH) effect, which was proposed to be realizable via a (simultaneous) magnetic and spin-orbit proximity effect in graphene. En route to realizing the QAH effect, the goal was also to study the newly-discovered 2D magnetic insulators, which have finally been isolated in the single-to-few atomic layers from compounds whose bulk properties have known since the 1970s, and the extent to which magnetic effects could be seen in graphene via proximity coupling. Since the original proposal, the scope of the work has expanded to include study of the topological edge states of the quantum spin Hall (QSH) effect and how they are modified by proximity effects and in twisted bilayers. The broader scientific context of the experiments in this proposal is to understand the physical mechanisms behind proximity effects in van der Waals heterostructures. Perhaps the ultimate scientific and technological goal of realizing topological states through proximity effects is the creation of Majorana zero modes in solid-state devices, which has been identified as a major priority in condensed-matter physics and quantum information because of the potential use of Majorana zero modes in topological quantum computing. Van der Waals materials offer advantages in this area because of the diversity of materials that can potentially be used and the unique device architectures that are possible using the van der Waals assembly techniques.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗