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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

CORSICA modelling of ITER hybrid operation scenarios

The hybrid operating mode observed in several tokamaks is characterized by further enhancement over the high plasma confinement (H-mode) associated with reduced magneto-hydro-dynamic (MHD) instabilities linked to a stationary flat safety factor ($q$ ) profile in the core region. The proposed ITER hybrid operation is currently aiming at operating for a long burn duration (>1000 s) with a moderate fusion power multiplication factor, $Q$ , of at least 5. This paper presents here candidate ITER hybrid operation scenarios developed using a free-boundary transport modelling code, CORSICA, taking all relevant physics and engineering constraints into account. The ITER hybrid operation scenarios have been developed by tailoring the 15 MA baseline ITER inductive H-mode scenario. Accessible operation conditions for ITER hybrid operation and achievable range of plasma parameters have been investigated considering uncertainties on the plasma confinement and transport. ITER operation capability for avoiding the poloidal field coil current, field and force limits has been examined by applying different current ramp rates, flat-top plasma currents and densities, and pre-magnetization of the poloidal field coils. Various combinations of heating and current drive (H&CD) schemes have been applied to study several physics issues, such as the plasma current density profile tailoring, enhancement of the plasma energy confinement and fusion power generation. A parameterized edge pedestal model based on EPED1 added to the CORSICA code has been applied to hybrid operation scenarios. Finally, fully self-consistent free-boundary transport simulations have been performed to provide information on the poloidal field coil voltage demands and to study the controllability with the ITER controllers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Se diffusion in CdTe thin films for photovoltaics

Manipulating CdSeTe bandgrading to enhance photocurrent and carrier lifetime is an essential part of high-performance CdTe photovoltaics (PVs). Here, we examine Se diffusion kinetics in single-crystal and polycrystalline CdTe during deposition, thermal annealing, and CdCl 2 treatments. Se distributions are determined by dynamic secondary-ion-mass spectroscopy and Auger electron spectroscopy depth profiling and coupled with electron backscatter diffraction images of the crystalline structure. Effective bulk and grain boundary diffusion coefficients are determined by analytical models and discussed in the context of processing and film morphology. Se is found to diffuse in CdTe at much higher rates during CdCl 2 treatments than with thermal processing alone. GB diffusion also occurs at a significantly faster rate than bulk diffusion. As a result of these two effects, the near interface bulk and GB Se diffusion during CdCl 2 treatments dominates the bandgrading profiles in CdTe PVs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

High resolution density pedestal measurements during edge localized modes by short-pulse reflectometry in the TCV tokamak

Here, this publication presents high spatio-temporal resolution (mm µs -1 ) density profile measurements of the pedestal top during type I, III, and small edge localized mode (ELM) H-mode plasmas in the tokamak à configuration variable (TCV). These measurements were performed using a novel short-pulse reflectometer. Average inter-ELM density profiles are obtained via conditional averaging using the D α trace as ELM indicator. Changes to the pedestal density profile gradients prior to type-III ELMs reveal unique pedestal dynamics leading to the ELM crash which can provide important experimental data for validation of non-linear MHD ELM simulations. The small-ELM scenario is found to feature a ~25–35 kHz quasi-coherent density fluctuation near the separatrix ρ ψ 0.993–1.05 not observed during a similar type-I ELM discharge. This oscillation is also found in low-field-side magnetic pick-up probes displaying a ballooning character and n = +1 toroidal mode number. This oscillation could help explain the markedly different pedestal dynamics observed in the small-ELM regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Perturbation of soil organic carbon induced by land-use change from primary forest

Abstract The impact of land-use change (LUC) on soil organic carbon (SOC) has been a wide concern of land management policymakers because CO 2 emissions induced by LUC have been the second largest carbon source worldwide. However, due to insufficient data quality and limited biome coverage, a global big picture of the impact of LUC on SOC is still not clear. This study conducted a meta-analysis on 288 independent observations sourced from 62 peer-reviewed papers to provide a global summary of the change in SOC after the conversion of primary forests into other land-use types. The conversion of primary forest to cropland resulted in the most severe SOC loss (−33.2%), followed by conversion into plantation forests (−22.3%) and secondary forests (−19.1%). Nonetheless, SOC increased by 9.1% after a conversion from primary forests into pasture. More SOC loss was found at sites with lower precipitation for primary forests converted to cropland and plantation forests. The SOC loss decreased consistently with increasing mean annual temperature (MAT) for all four types of LUC. Moreover, the loss of SOC tended to worsen over time when primary forests are converted to cropland or plantation forests. In contrast, SOC loss recovered over time following conversion to secondary forests. The gain of SOC gradually increased over time after conversion to pastures. To conclude, the changes in SOC are related not only to the land-use type but also to precipitation, temperature and turn years after LUC. Due to limited data, this study focuses on soil profiles within 30 cm depth, and future research should explore SOC dynamics induced by LUC at greater depths. Overall, cases of SOC loss of approximately 30% following deforestation were very common (except for conversion to pasture), and the results of this study show that the loss of SOC following LUC should be carefully considered and monitored in land management.

Zhang, Zhiyuan (ORCID:0000000223407001)↗
DOE OSTI2018

Ultrafast Electric Field Pulse Control of Giant Temperature Change in Ferroelectrics

There is a surge of interest in developing environmentally friendly solid-state-based cooling technology. Here, we point out that a fast cooling rate (≈ 10 11 K/s) can be achieved by driving solid crystals to a high-temperature phase with a properly designed electric field pulse. Specifically, we predict that an ultrafast electric field pulse can cause a giant temperature decrease up to 32 K in PbTiO 3 occurring on few picosecond time scales. Here, we explain the underlying physics of this giant electric field pulse-induced temperature change with the concept of internal energy redistribution: the electric field does work on a ferroelectric crystal and redistributes its internal energy, and the way the kinetic energy is redistributed determines the temperature change and strongly depends on the electric field temporal profile. This concept is supported by our all-atom molecular dynamics simulations of PbTiO 3 and BaTiO 3 . Moreover, this internal energy redistribution concept can also be applied to understand electrocaloric effect. We further propose new strategies for inducing giant cooling effect with ultrafast electric field pulse. This Letter offers a general framework to understand electric-field-induced temperature change and highlights the opportunities of electric field engineering for controlled design of fast and efficient cooling technology.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A Simulated Evaluation of Powder Flowability Through a Partially Obstructed Consumable in Blown Powder Directed Energy Deposition Systems

Abstract In the interest of continued industrialization of metal additive manufacturing in modern production environments, cost is often referenced as a primary deterrent to new adopters. Conventional economic models for additive systems, processes, and supply chains often focus on specific process applications with little generalizability, or they neglect significant costs associated with production such as machine maintenance and consumable part replacement. Compounding the latter issue are substantial knowledge gaps in consumable part wear characterization for additive and other convergent manufacturing systems. In coaxial blown powder directed energy deposition systems, gas atomized metal powder is wasted during material deposition at a rate that is partly dependent on present wear phenomena in a consumable nozzle housed in the cladding head assembly. The price and lead time required to replace the nozzle incentivizes its reuse even when visibly worn. Often this initiates a process quality decline in the form of underbuilt geometry and internal defects due to losses in powder catchment efficiency. While depositing H13 steel using a hybrid manufacturing machine tool equipped with such a deposition system, a unique partial clog with a bridge-like structure formed at the consumable nozzle exit when supporting argon gas flows failed mid-process. To further understand coaxial multi-phase powder flow in the event of support gas failure, a computational fluid dynamics simulation is tailored to relevant process parameters, H13 powder material profile, and machine operator observations collected after the incident. The resulting differences in powder flow compared to control gas flow parameters is presented and discussed. The powder flowability and performance of the clogged nozzle is then assessed by using an optical profilometer to extract the profile of the clog and recreate the clog geometry within the simulation environment. In past work this simulation has been experimentally validated for a 316L steel powder material profile and used specifically for analyzing powder stream geometry and catchment efficiency. After the initial powder flow characterization, the clog is removed, and the nozzle is reprofiled. After removing the obstructing clog, the newly unobstructed nozzle geometry, the original off the shelf nozzle geometry, and additional nozzle profiles exploring different consumable refurbishment strategies are reevaluated in the simulation. Powder catchment efficiency for all variant nozzle geometries and relevant flow variables are compared and discussed, along with potential mitigation strategies for optimizing powder flowability with worn consumables. This work expands on the known morphology of blown powder obstructions and wear defects present in consumable coaxial nozzles while discussing pragmatic simulation driven responses to unanticipated subsystem failure in hybrid manufacturing machining platforms.

DeWitte, Lisa↗
DOE OSTI2025

Genetic_and_epigenetic_signatures_of_Populus_Trichocarpa_in_response_to_abiotic_stress

Plants respond to abiotic stresses such as drought, heat, and salinity through both shared and stress-specific regulatory pathways. However, the role of epigenetic mechanisms, particularly DNA methylation, in modulating these responses is still underexplored. Here, we integrated transcriptome profiling with whole-genome bisulfite sequencing (WGBS) to investigate the dynamic relationship between gene expression and DNA methylation in Populus trichocarpa during brief early-stage exposure to abiotic stress. Each stress elicited distinct transcriptional and methylation signatures; however, a subset of conserved stress-responsive genes was commonly regulated across treatments. Approximately 5% of differentially expressed genes also displayed differential methylation patterns, suggesting a coordinated role for DNA methylation in regulating gene expression. Motif enrichment analysis of differentially methylated regions revealed binding sites of key transcription factor families, including ERF, bHLH, and ABF, highlighting potential role for methylation in modulating transcription factor targeting. Furthermore, we identified stress-inducible molecular markers with potential applications in early stress detection and functional dissection of gene regulatory pathways. Together, these findings provide new insights into the coordinated genetic and epigenetic responses to abiotic stress and provide a foundation for developing biosensors and breeding strategies to enhance stress resilience woody plants.

CBI↗
DOE OSTI2017

Structure and Dynamics of Cool Flare Loops Observed by the Interface Region Imaging Spectrograph

Flare loops were well observed with the Interface Region Imaging Spectrograph ( IRIS ) during the gradual phase of two solar flares on 2014 March 29 and 2015 June 22. Cool flare loops are visible in various spectral lines formed at chromospheric and transition-region temperatures and exhibit large downflows which correspond to the standard scenario. The principal aim of this work is to analyze the structure and dynamics of cool flare loops observed in Mg ii lines. Synthetic profiles of the Mg ii h line are computed using the classical cloud model and assuming a uniform background intensity. In this paper, we study novel IRIS NUV observations of such loops in Mg ii h and k lines and also show the behavior of hotter lines detected in the FUV channel. We obtained the spatial evolution of the velocities: near the loop top, the flow velocities are small and they are increasing toward the loop legs. Moreover, from slit-jaw image (SJI) movies, we observe some plasma upflows into the loops, which are also detectable in Mg ii spectra. The brightness of the loops systematically decreases with increasing flow velocity, and we ascribe this to the effect of Doppler dimming, which works for Mg ii lines. Emission profiles of Mg ii were found to be extremely broad, and we explain this through the large unresolved non-thermal motions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

THE KEY ROLE OF SOLAR DYNAMICS IN THE CHROMOSPHERIC HANLE POLARIZATION

The quantum theory of polarized light allows one to model scattering in the solar atmosphere for inferring its properties. This powerful approach has revealed two key long-standing problems in solar physics: the puzzling dilemmas between theory and observations in several anomalously polarized spectral lines and the need for inferring the ubiquitous weak chromospheric magnetic fields, which requires discriminating the Hanle effect in dynamic optically thick plasmas. However, the ever-present dynamics, i.e., the temporal evolution of heatings and macroscopic motions, has been widely disregarded when modeling and interpreting the scattering polarization. This has hindered a consistent theoretical solution to the puzzle while falsifying the Hanle diagnosis. Here, we show that the dynamical evolution is a keystone for solving both problems because its systematic impact allows an explanation of the observations from “anomalous” instantaneous polarization signals. Evolution accounted for, we reproduce amplitudes and (spectral and spatial) shapes of the Ca i 4227 Å polarization at solar disk center, identifying a restrictive arrangement of magnetic fields, kinematics, heatings, and spatio-temporal resolution. We find that the joint action of dynamics, Hanle effect, and low temporal resolutions mimics Zeeman linear polarization profiles, the true weak-field Zeeman signals being negligible. Our results allow reinterpretation of many polarization signals of the solar spectra and support time-dependent scattering polarization as a powerful tool for deciphering the spatio-temporal distribution of chromospheric heatings and fields. This approach may be a key aid in developing the Hanle diagnosis for the solar atmosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

High resolution density pedestal measurements during edge localized modes by short-pulse reflectometry in the TCV tokamak

This publication presents high spatio-temporal resolution (mm/μs) density profile measurements of the pedestal top during type I, III, and small edge localized mode (ELM) H-mode plasmas in the Tokamak à Configuration Variable (TCV). These measurements were performed using a novel short-pulse reflectometer. Average inter-ELM density profiles are obtained via conditional averaging using the Dα trace as ELM indicator. Changes to the pedestal density profile gradients prior to type-III ELMs reveal unique pedestal dynamics leading to the ELM crash which can provide important experimental data for validation of non-linear MHD ELM simulations. The small-ELM scenario is found to feature a ∼25-35 kHz quasi-coherent density fluctuation near the separatrix rho_psi ∼0.993-1.05 not observed during a similar type-I ELM discharge. This oscillation is also found in low-field-side magnetic pick- up probes displaying a ballooning character and n=+1 toroidal mode number. This oscillation could help explain the markedly different pedestal dynamics observed in the small-ELM regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1977

Engine Hydraulic Stability

An analytical injector model was developed specifically to analyze combustion instability coupling between the injector hydraulics and the combustion process. This digital computer dynamic injector model will, for any imposed chamber of inlet pressure profile with a frequency ranging from 100 to 3000 Hz (minimum) accurately predict/calculate the instantaneous injector flowrates. The injector system is described in terms of which flow segments enter and leave each pressure node. For each flow segment, a resistance, line lengths, and areas are required as inputs (the line lengths and areas are used in determining inertance). For each pressure node, volume and acoustic velocity are required as inputs (volume and acoustic velocity determine capacitance). The geometric criteria for determining inertances of flow segments and capacitance of pressure nodes was set. Also, a technique was developed for analytically determining time averaged steady-state pressure drops and flowrates for every flow segment in an injector when such data is not known. These pressure drops and flowrates are then used in determining the linearized flow resistance for each line segment of flow.

Kesselring, R. C.↗
NASA NTRS1980

Algorithm for fixed-range optimal trajectories

An algorithm for synthesizing optimal aircraft trajectories for specified range was developed and implemented in a computer program written in FORTRAN IV. The algorithm, its computer implementation, and a set of example optimum trajectories for the Boeing 727-100 aircraft are described. The algorithm optimizes trajectories with respect to a cost function that is the weighted sum of fuel cost and time cost. The optimum trajectory consists at most of a three segments: climb, cruise, and descent. The climb and descent profiles are generated by integrating a simplified set of kinematic and dynamic equations wherein the total energy of the aircraft is the independent or time like variable. At each energy level the optimum airspeeds and thrust settings are obtained as the values that minimize the variational Hamiltonian. Although the emphasis is on an off-line, open-loop computation, eventually the most important application will be in an on-board flight management system.

Lee, H. Q.↗
NASA NTRS1979

Pioneer Venus infrared radiometer - Design, implementation and preliminary results

The paper discusses the Pioneer Venus infrared radiometer design and operation. Its main function is to measure the thermal emission from the atmosphere at seven pressure levels above the Venus clouds, allowing a determination of the vertical temperature structure. In addition to the temperature sounding channels, there are two channels operating in the visible and near infrared to study the structure of the upper clouds, and a far infrared channel sensitive to water vapor in and above the clouds. The instrument can operate in four modes including a calibration sequence; by utilizing the spinning action of the spacecraft and short integration times, a substantial portion of the planet can be mapped within a 90 min data taking period centered about periapsis time. Temperature profiles retrieved during the course of the mission will clarify the dynamical processes in the upper atmosphere.

Martonchik, J. V.↗
NASA NTRS1988

Winds from Cataclysmic Variables

Current understanding of the winds from Cataclysmic Variables is discussed, with particular emphasis on the understanding and modeling of the line profiles. Recent efforts at constructing such models are summarized, and a dynamical model is constructed which may serve to illustrate some of the physical principles acting in CV winds.

Kallman, T.↗
NASA NTRS1989

Spectroscopic study of combustion diagnostics on hydroxyl radicals

Experimental observations of propane/air flames have been carried out. Measurements of hydroxyl (OH) radical concentration have been made using resonance line absorption techniques. A microwave-pumped low pressure discharge in argon and water vapor is employed to produce strong OH radical band radiation in the 308 nm region. This radiation is transmitted through the plume and absorption data is taken at various radial positions using an optical multichannel analyzer. This absorption data is used to compute OH number density using a model for the absorption band characteristics as a function of temperature based on an atlas of line strengths. A numerical computation of flow fields, temperature profile, OH number density and water vapor mass fraction profiles was carried out by using a technique of computational fluid dynamics (CFD). The results of CFD computation are compared with experimental observation with a good agreement.

Eskridge, Richard↗
NASA NTRS1931

The use of slots for increasing the lift of airplane wings

This report discusses in detail the results obtained with devices for preventing the separation of the boundary layer. In order to give an idea of the order of magnitude of the positive and negative pressures involved, we made a diagram of them, as measured at 15 degrees angle of attack on the Gottigen profile 387. The pressure scale is graduated in terms of the dynamic pressure q, which enables the evaluation of the positive and negative pressures at all velocities.

Haus, FR↗
NASA NTRS1993

Autonomous rendezvous and docking for Space Station Freedom

Viewgraphs on autonomous rendezvous and docking (AR&D) for Space Station Freedom are presented. Topics covered include: requirements for AR&D experience; Comet spacecraft performance; AR&D mission profile; analytical models for approach trajectory, loosely coupled configuration, and contact dynamics; and application to space infrastructure.

Garrison, James L., Jr.↗
NASA NTRS1995

Thermal Characterization of the Universal Multizone Crystallizator

The Universal Multizone Crystallizator (UMC) is a special apparatus for crystal growth under terrestrial and microgravity conditions. The use of twenty-five zones allows the, UMC to be used for several normal freezing growth techniques. The thermal profile is electronically translated along the stationary sample by systematically reducing the power to the control zones. Elimination of mechanical translation devices increases the systems reliability while simultaneously reducing the size and weight. This paper addresses the UMC furnace design, sample cartridge, typical thermal profiles and corresponding power requirements necessary for two normal freezing techniques: dynamic gradient freeze and zone melting crystal growth.

Watring, D. A.↗