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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 1,747 records · Page 97

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NASA NTRS1992

Chemistry in circumstellar disks - CS toward HL Tauri

High spatial and spectral resolution dust continuum and CS line-emission maps of the material immediately surrounding HL Tauri are presented. The 3.06-thermal dust map gives an upper limit to the source size of roughly 200 AU. When combined with previous millimeter continuum measurements, a beta value of 1.2 +/-0.3 is derived along with a disk mass of 0.1 solar mass, in agreement with previous disk radiative transfer models of the IR and submillimeter flux from HL Tau. The low dust emissivity index as compared to particles in the diffuse ISM is best explained by grain growth or composition evolution. The present observations of the CS and CO emission lines forming the molecular cloud surrounding HL Tauri are consistent with the 'canonical' temperatures, densities, and abundances derived in other Taurus cloud cores. In contrast, the CS emission in aperture synthesis maps at 650-AU spatial resolution is most consistent with CS/CO ratios at least 25-50 times lower in the gas immediately surrounding HL Tauri if the CS emission is optically thin. The continuum and spectral line results obtained are strong indicators of conditions thought to be similar to those in the presolar nebula some 4.5 AE ago.

Blake, Geoffrey A.↗

NASA NTRS1994

The resonance lines of MG2 as diagnostics of the upper solar chromosphere

The resonance lines of singly ionized magnesium, the MgII h&k lines at about 280 nm, are two of the small number of lines in the solar spectrum that are optically thick in the chromospheric part of the solar atmosphere. Potentially these lines contain information on the initial temperature rise that occurs at the top of the photosphere. Unfortunately, few good observations of the lines exist due to their wavelength near 280 nm the ultraviolet. However, a fair number of observations (on the order of 200) are available from the data base of the UltraViolet Polarimeter and Spectrometer (UVSP) instrument that flew on board of NASA's Solar Maximum Mission (SMM) satellite. In addition, this data base contains a number of spectra that include the Mg I resonance line at (lambda)285.2nm, just longward of the h&k lines. The neutral magnesium line is not as strong as its ionic counterparts and samples slightly lower parts of the atmosphere. Its width is a sensitive diagnostic of the ionization balance between neutral and singly ionized magnesium, which determines the opacity scale (and formation height) of other diagnostically important MgI lines like the 457.1 nm intercombination line, the magnesium b lines and the infrared MgI emission lines near 12 microns. Analysis of the observed line profiles shows that it is necessary to include the effects of partial frequency redistribution (PRD) in the formation of the line as in the case of the h&k lines. This implies that the core of the line is very sensitive to the way scattering is treated in the modeling of the line, and in turn this allows us to separate the uncertain effects in the atomic data (viz. the Van der Waals broadening) from the uncertainties in the underlying atmospheric model. The main objective of this research was to compare observed spectra of the magnesium resonance lines against theoretical line profiles calculated from recent models of the solar atmosphere by Fontenla et al., hereafter called FAL. These models extend earlier solar models by Avrett et al. and provide yet a better match between observed and calculated spectra, in particular of the hydrogen Lyman line, by including the effects of ambipolar diffusion of hydrogen and helium in the mass and energy transport equations for the chromosphere-corona transition region. Although the transition region models can be built self-consistently (without additional observational input) once the proper boundary conditions are given at the top of the chromosphere, there are uncertainties in the models precisely because these boundary conditions are not well known. With the analysis of UVSP magnesium observations we strive to constrain these uncertainties.

Avrett, Eugene H.↗

NASA NTRS1993

Velocity space diffusion and nongyrotropy of pickup water group ions at comet Grigg-Skjellerup

The diffusion of water group cometary ions in velocity space at comet Grigg-Skjellerup was measured during the Giotto spacecraft encounter. The evolution of the collapsed pitch angle and energy distributions during the inbound and outbound passes shows that the timescale for energy diffusion may be similar to that for pitch angle diffusion. Fully isotropic pitch angle distributions were never seen. Also the bulk parameters of the three-dimensional distributions are examined. Transformation of these parameters into a field-aligned solar wind frame allows us to test the gyrotropy of the distributions. These observations imply that there were deviations from gyrotropy throughout the encounter becoming most important near to closest approach.

Coates, A. J.↗

NASA NTRS2003

Formation of Primitive Bodies in the Protoplanetary Nebula

We have developed a simple model of global transport of solids in the protoplanetary nebula, including radial drift of large particles and diffusion of small ones. The model has been applied to the formation and redistribution of the Ca-A1 rich refractory mineral inclusions (CAIs) found in primitive chondrites. These objects form at much higher temperatures, and appear to be 1-3 million years older than, the dominant (chondrule) components found in the same parent bodies. A widespread concern has been the retention of CAIs for this long against gas-drag-induced radial drift into the sun. We show that outward radial diffusion in a weakly turbulent nebula can overwhelm inward drift, and prevent significant numbers of CAI-size particles from being lost into the sun for tines on the order of several Myr. An element of this model is rapid inward radial drift of boulder-sized primitive (carbon-rich) silicate material, more like Halley-dust than CI chondrites in the early days of the nebula. Thls process can enrich the abundance of silicate and carbon material in the inner nebula, and may provide possible explanations for both chemical and isotopic properties of CAIs. The predicted enhancement of CO relative to water might be of relevance to recent IR astronomical observations of CO in the inner disks of several actively accreting T Tauri stars. This process has applications to the transport and redistribution of volatiles in general. Depending on the rubble particle size distribution, rapid radial drift of boulder-sized solids can bring more material inwards across a condensation front, to evaporate, than can subsequently be removed by nebula advection or diffusion, until a strong local enhancement is produced which allows diffusive loss to balance the drifting source. Application of this process to enhancement of the abundance of water near the "ice line" will be discussed. Supported by the Origins of Solar Systems program.

Cuzzi, Jeffrey N.↗

NASA NTRS2018

Determining the Mode, Frequency, and Azimuthal Wave Number of ULF Waves During a HSS and Moderate Geomagnetic Storm

Ultralow frequency (ULF) waves play a fundamental role in the dynamics of the inner magnetosphere and outer radiation belt during geomagnetic storms. Broadband ULF wave power can transport energetic electrons via radial diffusion, and discrete ULF wave power can energize electrons through a resonant interaction. Using observations from the Magnetospheric Multiscale mission, we characterize the evolution of ULF waves during a highspeed solar wind stream (HSS) and moderate geomagnetic storm while there is an enhancement of the outer radiation belt. The Automated Flare Inference of Oscillations code is used to distinguish discrete ULF wave power from broadband wave power during the HSS. During periods of discrete wave power and utilizing the close separation of the Magnetospheric Multiscale spacecraft, we estimate the toroidal mode ULF azimuthal wave number throughout the geomagnetic storm. We concentrate on the toroidal mode as the HSS compresses the dayside magnetosphere resulting in an asymmetric magnetic field topology where toroidal mode waves can interact with energetic electrons. Analysis of the mode structure and wave numbers demonstrates that the generation of the observed ULF waves is a combination of externally driven waves, via the KelvinHelmholtz instability, and internally driven waves, via unstable ion distributions. Further analysis of the periods and toroidal azimuthal wave numbers suggests that these waves can couple with the core electron radiation belt population via the drift resonance during the storm. The azimuthal wave number and structure of ULF wave power (broadband or discrete) have important implications for the inner magnetospheric and radiation belt dynamics.

Murphy, Kyle R.↗

DOE OSTI2019

Removing Biases from Rotating Shadowband Radiometers: Preprint

Three types of biases are examined for a rotating shadowband radiometer (RSR): temperature bias, spectral bias, and deviation from a Lambertian cosine response. A step-by-step method is presented to illustrate how to use this information to develop a model for adjustment algorithms for a RSR. Comparisons are made with a RSR adjusted using the model and measure direct normal, diffuse, and global irradiance.

14 SOLAR ENERGY↗

NASA NTRS2015

Magnetospheric Multiscale Overview and Science Objectives

Magnetospheric Multiscale (MMS), a NASA four-spacecraft constellation mission launched on March 12, 2015, will investigate magnetic reconnection in the boundary regions of the Earth's magnetosphere, particularly along its dayside boundary with the solar wind and the neutral sheet in the magnetic tail. The most important goal of MMS is to conduct a definitive experiment to determine what causes magnetic field lines to reconnect in a collisionless plasma. The significance of the MMS results will extend far beyond the Earth's magnetosphere because reconnection is known to occur in interplanetary space and in the solar corona where it is responsible for solar flares and the disconnection events known as coronal mass ejections. Active research is also being conducted on reconnection in the laboratory and specifically in magnetic-confinement fusion devices in which it is a limiting factor in achieving and maintaining electron temperatures high enough to initiate fusion. Finally, reconnection is proposed as the cause of numerous phenomena throughout the universe such as comet-tail disconnection events, magnetar flares, supernova ejections, and dynamics of neutron-star accretion disks. The MMS mission design is focused on answering specific questions about reconnection at the Earth's magnetosphere. The prime focus of the mission is on determining the kinetic processes occurring in the electron diffusion region that are responsible for reconnection and that determine how it is initiated; but the mission will also place that physics into the context of the broad spectrum of physical processes associated with reconnection. Connections to other disciplines such as solar physics, astrophysics, and laboratory plasma physics are expected to be made through theory and modeling as informed by the MMS results.

Space plasma physics↗

NASA NTRS1977

Development of a high efficiency thin silicon solar cell

A key to the success of this program was the breakthrough development of a technology for producing ultra-thin silicon slices which are very flexible, resilient, and tolerant of moderate handling abuse. Experimental topics investigated were thinning technology, gaseous junction diffusion, aluminum back alloying, internal reflectance, tantalum oxide anti-reflective coating optimization, slice flexibility, handling techniques, production rate limiting steps, low temperature behavior, and radiation tolerance.

Lindmayer, J.↗

DOE OSTI2020

Methods of forming interdigitated back contact solar cells

Methods for forming interdigitated back contact solar cells from III-V materials are provided. According to an aspect of the invention, a method includes depositing a patterned Zn layer to cover first areas of an n-type emitter region, wherein the emitter region comprises a III-V material, and forming a passivated back contact region by counter-doping the first areas of the emitter region by diffusing Zn from the patterned Zn layer into the first areas of the emitter region, such that the first areas of the emitter region become p-type.

14 SOLAR ENERGY↗

NASA NTRS2010

The Search for Interstellar Sulfide Grains

The lifecycle of sulfur in the galaxy is poorly understood. Fe-sulfide grains are abundant in early solar system materials (e.g. meteorites and comets) and S is highly depleted from the gas phase in cold, dense molecular cloud environments. In stark contrast, sulfur is essentially undepleted from the gas phase in the diffuse interstellar medium, indicating that little sulfur is incorporated into solid grains in this environment. It is widely believed that sulfur is not a component of interstellar dust grains. This is a rather puzzling observation unless Fe-sulfides are not produced in significant quantities in stellar outflows, or their lifetime in the ISM is very short due to rapid destruction. Fe sulfide grains are ubiquitous in cometary samples where they are the dominant host of sulfur. The Fe-sulfides (primarily pyrrhotite; Fe(1-x)S) are common, both as discrete 0.5-10 micron-sized grains and as fine (5-10 nm) nanophase inclusions within amorphous silicate grains. Cometary dust particles contain high abundances of well-preserved presolar silicates and organic matter and we have suggested that they should contain presolar sulfides as well. This hypothesis is supported by the observation of abundant Fe-sulfides grains in dust around pre- and post-main sequence stars inferred from astronomical spectra showing a broad 23 micron IR feature due to FeS. Fe-sulfide grains also occur as inclusions in bona fide circumstellar amorphous silicate grains and as inclusions within deuterium-rich organic matter in cometary dust samples. Our irradiation experiments show that FeS is far more resistant to radiation damage than silicates. Consequently, we expect that Fe sulfide stardust should be as abundant as silicate stardust in solar system materials.

Keller, Lindsay P.↗

DOE OSTI2024

Exploring the Performance and Reliability of Screen-Printable Fire-Through Copper Paste on PERC Solar Cells

For 40 TW of PV required to transition our planet to 100% renewables, the silver (Ag) should disappear from PV production. Advantages of copper (Cu) over silver (Ag) include 1) bulk Cu has a similar conductivity to Ag (1.7 mu O-cm for Cu, 1.6 mu O-cm for Ag) and 2) Cu is approximately 100 times cheaper than Ag, making it an excellent potential replacement. Problems associated with copper (Cu) contacts include 1) easy oxidation and 2) diffusion into the Si cell and recombination activity.

copper paste↗

DOE OSTI2018

Growth and characterization of Cu3SbSe4 thin films through thermally diffusing Sb2Se3 – CuSe by chemical bath deposition (CBD)

Highlights: • Cu{sub 3}SbSe{sub 4} films were formed by chemical bath deposition followed by a heat treatment. • Prepared Cu{sub 3}SbSe{sub 4} thin films have promising properties to absorbing layer in a solar cell or thermoelectric material. • Electrical conductivity values of Cu{sub 3}SbSe{sub 4} are high, considering its manufacturing method and the previous reports in the field. - Abstract: In the present work, Cu{sub 3}SbSe{sub 4} thin films have been successfully synthesized by chemical bath deposition (CBD) involving a sequential deposition of antimony selenide (Sb{sub 2}Se{sub 3}) and copper selenide (CuSe) films and then annealing in a vacuum atmosphere. The influence of CuSe deposition time on the previously deposited Sb{sub 2}Se{sub 3} films was investigated to obtain the ternary phase. A study of the structural, morphological, optical and electrical properties of these films was carried out using appropriate characterization techniques. X-ray diffraction analysis revealed that the films show a tetragonal crystalline crystalline structure corresponding to the Permingeatite phase (Cu{sub 3}SbSe{sub 4}). The crystal size increases with the CuSe deposition time. It is identified by Raman spectroscopy that at low CuSe deposition times a low concentration of Sb{sub 2}Se{sub 3} coexists in the thin film. The optical band gap energy of these films was evaluated in the range of 0.67–1.18 eV, decreasing by increasing CuSe deposition time. By field-emission scanning electron microscopy (FESEM) a morphological study was carried out, observing that by increasing the deposition time of CuSe there is an increase of agglomerates and decrease the porosity in the samples. An elemental analysis was carried out by energy dispersive X-ray spectroscopy to observe the composition and elemental distribution in the ternary compound. The films showed a p-type electrical conductivity with values between 0.417 and 55.55 (Ω cm{sup −1}). The mobility and carrier density were performed by Hall Effect and Thermoelectric measurements observing a slight increase in the values by increasing the time of CuSe deposition. All results obtained for thin films of Cu{sub 3}SbSe{sub 4} suggest that it could be used as an absorber material in a solar cell or thermoelectric material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS2009

Integration of the Radiation Belt Environment Model Into the Space Weather Modeling Framework

We have integrated the Fok radiation belt environment (RBE) model into the space weather modeling framework (SWMF). RBE is coupled to the global magnetohydrodynamics component (represented by the Block-Adaptive-Tree Solar-wind Roe-type Upwind Scheme, BATS-R-US, code) and the Ionosphere Electrodynamics component of the SWMF, following initial results using the Weimer empirical model for the ionospheric potential. The radiation belt (RB) model solves the convection-diffusion equation of the plasma in the energy range of 10 keV to a few MeV. In stand-alone mode RBE uses Tsyganenko's empirical models for the magnetic field, and Weimer's empirical model for the ionospheric potential. In the SWMF the BATS-R-US model provides the time dependent magnetic field by efficiently tracing the closed magnetic field-lines and passing the geometrical and field strength information to RBE at a regular cadence. The ionosphere electrodynamics component uses a two-dimensional vertical potential solver to provide new potential maps to the RBE model at regular intervals. We discuss the coupling algorithm and show some preliminary results with the coupled code. We run our newly coupled model for periods of steady solar wind conditions and compare our results to the RB model using an empirical magnetic field and potential model. We also simulate the RB for an active time period and find that there are substantial differences in the RB model results when changing either the magnetic field or the electric field, including the creation of an outer belt enhancement via rapid inward transport on the time scale of tens of minutes.

Glocer, A.↗

NASA NTRS1993

The abundances of hydrogen, helium, oxygen, and iron accelerated in large solar particle events

Energy spectra measured in 10 large flares with the University of Maryland/Max-Planck-Institut sensors on ISEE I and Goddard Space Flight Center sensors on IMP 8 allowed us to determine the average H, He, O, and Fe abundances as functions of energy in the range of about 0.3-80 MeV/nucleon. Model fits to the spectra of individual events using the predictions of a steady state stochastic acceleration model with rigidity-dependent diffusion provided a means of interpolating small portions of the energy spectra not measured with the instrumentation. Particles with larger mass-to-charge ratios were relatively less abundant at higher energies in the flare-averaged composition. The Fe/O enhancement at low SEP energies was less than the Fe/O ratios observed in He-3-rich flares. Unlike the SEP composition averaged above 5 MeV/nucleon, the average SEP abundances above 0.3 MeV/nucleon were similar to the average solar wind.

Mazur, J. E.↗

DOE OSTI2020

The Role of Demixing and Crystallization Kinetics on the Stability of Non‐Fullerene Organic Solar Cells

Abstract With power conversion efficiency now over 17%, a long operational lifetime is essential for the successful application of organic solar cells. However, most non‐fullerene acceptors can crystallize and destroy devices, yet the fundamental underlying thermodynamic and kinetic aspects of acceptor crystallization have received limited attention. Here, room‐temperature (RT) diffusion coefficients of 3.4 × 10 −23 and 2.0 × 10 −22 are measured for ITIC‐2Cl and ITIC‐2F, two state‐of‐the‐art non‐fullerene acceptors. The low coefficients are enough to provide for kinetic stabilization of the morphology against demixing at RT. Additionally profound differences in crystallization characteristics are discovered between ITIC‐2F and ITIC‐2Cl. The differences as observed by secondary‐ion mass spectrometry, differential scanning calorimetry (DSC), grazing‐incidence wide‐angle X‐ray scattering, and microscopy can be related directly to device degradation and are attributed to the significantly different nucleation and growth rates, with a difference in the growth rate of a factor of 12 at RT. ITIC‐4F and ITIC‐4Cl exhibit similar characteristics. The results reveal the importance of diffusion coefficients and melting enthalpies in controlling the growth rates, and that differences in halogenation can drastically change crystallization kinetics and device stability. It is furthermore delineated how low nucleation density and large growth rates can be inferred from DSC and microscopy experiments which could be used to guide molecular design for stability.

Hu, Huawei↗

DOE OSTI2021

Toward predictive permeabilities: Experimental measurements and multiscale simulation of methanol transport in Nafion

A polymer membrane's permeability to solutes determines its suitability for various applications: a permeability value is essential for predicting performance in diverse contexts. Using aqueous methanol permeation through Nafion as an example, we describe a methodology for determining membrane permeability that accounts for boundary layer effects and the possibility of swelling. For the materials and apparatus used herein, analysis of a permeance measurement and computational fluid dynamics simulations show that the mass transfer boundary layer is on the order of ones to tens of microns. Additionally, the data are used to develop and validate a multiscale model describing solute permeation through a hydrated membrane as a series of physical mechanistic steps: reversible adsorption from solution at the membrane interface, diffusion driven by a concentration gradient within the membrane, and reversible desorption into solution at the opposite membrane interface. The validated model is used to predict methanol transport across a solar-driven CO 2 reduction device and to assess the impact of polymer changes on the measured value. The approach of combining experimental data, computational fluid dynamics, and the mechanistic multiscale model is expected to provide more accurate analysis of membrane permeation data in cases with polymer swelling or unusual device geometries, among others.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1974

Solar particles /observations, relationship to the sun acceleration, interplanetary medium/

The major features of the propagation of flare particles in the interplanetary medium are discussed in terms of the classic well-behaved flare having unique impulsive injection and a smooth time profile. Topics include flare events, their frequency of occurrence, development of a typical event, energy spectra, proton and electron types, charge and isotopic composition, solar flares and particle accelerations, radio and X-ray observations, the Fermi mechanism, the betatron mechanism, acceleration models, plasma instabilities, two-stage acceleration, propagation mechanisms, the anisotropic stage, the diffusive stage, and the convection and energy loss stage.

Mcdonald, F. B.↗

NASA NTRS1977

Heat exchanger-ingot casting/slicing process, phase 1: Silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

A controlled growth, heat-flow and cool-down process is described that yielded silicon with a high degree of single crystallinity. Even when the seed melted out, very large grains formed. Solar cell samples made from cast material yielded conversion efficiency of over 9%. Representative characterizations of grown silicon demonstrated a dislocation density of less than 100/sq cm and a minority carrier diffusion length of 31 micron. The source of silicon carbide in silicon ingots was identified to be from graphite retainers in contact with silica crucibles. Higher growth rates were achieved with the use of a graphite plug at the bottom of the silica crucible.

Schmid, F.↗