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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Experimental 4D Tracking of a Single Electron in IOTA

We present the results of the first experiments on 4-dimensional phase-space tracking of a single electron in a storage ring, using a linear multi-anode photomultiplier tube for simultaneously measuring transverse coordinates and arrival times of synchrotron-radiation pulses. During the next few months, full 6D tracking will be implemented. This technology makes it possible to characterize the motion of a single particle, i.e. simultaneously tracking of amplitudes and phases for slow synchrotron oscillations and fast betatron oscillations. Complete tracking of a single particle enables the first direct measurements of dynamical properties, including invariants, amplitude-dependent tunes, and chaotic behavior.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Nanosecond Repetitively Pulsed (NRP) Plasmas: Relationship Between Induced Flow and Plasma Characteristics at Atmospheric Pressure (Final Technical Report)

The local flow fields induced by plasma discharges at atmospheric pressure can play a critical role in aerodynamic flow and combustion control and have significant implications for plasma-based technologies in medicine and environmental engineering. However, the coupling between the plasma characteristics, the geometry and the induced flow field is not well understood. The primary goal of this work is to determine the relationship between the plasma characteristics and the induced flow field for nanosecond pulsed discharges at atmospheric pressure. A comprehensive experimental investigation of plasmas produced by nanosecond high-voltage pulses in a pin-to-pin electrode configuration was conducted, employing several measurement techniques including microwave and laser Rayleigh scattering, optical emission spectroscopy, and high-speed imaging. The flow field induced by the nanosecond plasma was measured and characterized using measurements of the velocity (particle image velocimetry) and density (background oriented schlieren) with unprecedented spatiotemporal resolution. The experimental measurements were complemented by development of a one-dimensional model of the plasma discharge and a high-fidelity computational fluid dynamics (CFD) simulation of the subsequent plasma-induced flow field.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Synthesis and Characterization of Mesoporous Silica Nanoparticles Loaded with Pt Catalysts

Coating the catalyst with a nanoporous layer has been demonstrated to be an effective approach to improve catalyst stability. Herein, we systematically investigate two types of core-shell mesoporous silica nanoparticles with a platinum nanocatalyst using a variety of characterization methods. One of the mesoporous particles has a unique amine ring structure in the middle of a shell (Ring-mSiO 2 /Pt-5.0/SiO 2 ), and the other one has no ring structure (mSiO 2 /Pt-5.0/SiO 2 ). Brunauer–Emmett–Teller/Barrett–Joyner–Halenda (BET/BJH) presented a similar surface area for both particles, and the pore size was 2.4 nm. Ultra-Small-Angle X-ray Scattering (USAXS)/ Small-Angle X-ray Scattering (SAXS) showed the size of mSiO 2 /Pt-5.0/SiO 2 and Ring-mSiO 2 /Pt-5.0/SiO 2 were 420 nm and 272 nm, respectively. It also showed that the ring structure was 30 nm above the silica core. Using high-resolution Transmission Electron Microscopy (TEM), it was found that the platinum nanoparticles are loaded evenly on the surface of the silica. In situ SAXS heating experiments and Thermogravimetric Analysis (TGA) indicated that the mSiO 2 /Pt-5.0/SiO 2 were more stable during the high temperature, while the Ring-mSiO 2 /Pt-5.0/SiO 2 had more change in the particle.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Structure of Active Sites of Fe-N-C Nano-Catalysts for Alkaline Exchange Membrane Fuel Cells

Platinum group metal-free (PGM-free) catalysts based on transition metal-nitrogen-carbon nanomaterials have been studied by a combination of ex situ and in situ synchrotron X-ray spectroscopy techniques; high-resolution Transmission Electron Microscope (TEM); Mößbauer spectroscopy combined with electrochemical methods and Density Functional Theory (DFT) modeling/theoretical approaches. The main objective of this study was to correlate the HO2− generation with the chemical nature and surface availability of active sites in iron-nitrogen-carbon (Fe-N-C) catalysts derived by sacrificial support method (SSM). These nanomaterials present a carbonaceous matrix with nitrogen-doped sites and atomically dispersed and; in some cases; iron and nanoparticles embedded in the carbonaceous matrix. Fe-N-C oxygen reduction reaction electrocatalysts were synthesized by varying several synthetic parameters to obtain nanomaterials with different composition and morphology. Combining spectroscopy, microscopy and electrochemical reactivity allowed the building of structure-to-properties correlations which demonstrate the contributions of these moieties to the catalyst activity, and mechanistically assign the active sites to individual reaction steps. Associated with Fe-Nx motive and the presence of Fe metallic particles in the electrocatalysts showed the clear differences in the variation of composition; processing and treatment conditions of SSM. From the results of material characterization; catalytic activity and theoretical studies; Fe metallic particles (coated with carbon) are main contributors into the HO2− generation.

Kishi, Hirofumi↗
DOE OSTI2021

On Stochastic Heating and Its Phase-space Signatures in Low-beta Kinetic Turbulence

We revisit the theory of stochastic heating of ions and investigate its phase-space signatures in kinetic turbulence of relevance to low- β portions of the solar wind. In particular, we retain a full scale-dependent approach in our treatment, and we explicitly consider the case in which electric-field fluctuations can be described by a generalized Ohm's law that includes Hall and thermoelectric effects. These two electric-field terms provide the dominant contributions to stochastic ion heating when the ion-Larmor scale is much smaller than the ion skin depth, ρ i << d i , which is the case at β << 1. Employing well-known spectral scaling laws for Alfvén-wave and kinetic-Alfvén-wave turbulent fluctuations, we obtain scaling relations characterizing the field-perpendicular particle-energization rate and energy diffusion coefficient associated with stochastic heating in these two regimes. Phase-space signatures of ion heating are then investigated using three-dimensional hybrid-kinetic simulations of continuously driven Alfvénic turbulence at low β (namely, β i = β e = 0.3 and β i = β e = 1/9). In these simulations, energization of ions parallel to the magnetic field is subdominant compared to its perpendicular counterpart ( Q ∥,i << Q ⊥,i ), and the fraction of turbulent energy that goes into ion heating is ≈75% at β i = 0.3 and ≈40% at β i ≃ 0.1. The phase-space signatures of ion energization are consistent with Landau-resonant collisionless damping and a ( β -dependent) combination of ion-cyclotron and stochastic heating. We demonstrate good agreement between our scale-dependent theory and various signatures associated with the stochastic portion of the heating. We discuss briefly the effect of intermittency on stochastic heating and the implications of our work for the interpretation of stochastic heating in solar-wind spacecraft data.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1977

Characteristics of first order shock induced magnetic transitions in iron and discrimination from TRM

Reflected light microscopy provides information on first-order shock transitions in iron and iron-nickel and permits discrimination of microstructures due to shock transitions from those imparted by thermal transitions. In addition, thin-foil electron microscopy is used to characterize magnetic transitions in fine-particle iron. First-order magnetic phase changes, such as that from the antiferromagnetic face centered cubic state to the ferromagnetic body centered cubic state, are studied with the aim of calibrating the shock and thermal mechanisms of magnetization in iron with a particle size range between 250 and 1200 A. The efficiency of remanence due to shock transition is also estimated.

Wasilewski, P.↗
NASA NTRS1977

Apollo 17 ropy glasses

Ropy glasses are a major soil component in the Apollo 17 gray soils 74240 and 74260. These particles form a distinct morphological type characterized by a wide range of dynamic shapes with a diagnostic sorted and welded fine-grained debris coating. Apollo 17 ropy glasses show abundant evidence for shock. Shocked lithic and mineral inclusions, lack of any igneous textures, and lechatelierite, all indicate an impact origin. A striking similarity is observed between the lunar ropy glasses and the glass impact bombs (Flaedle) of the Ries Crater in Germany. A highland basaltic composition was observed for the Apollo 17 ropy glasses in contrast to the KREEP composition of ropy glasses from the Apollo 12 and Apollo 14 landing sites. Other workers have presented convincing evidence that ejecta from Tycho reached the Taurus-Littrow Valley, and these ropy glasses may represent Tycho ejecta. However, the close stratigraphic association of the ropy glasses with the greater than 3.5 b.y. old orange glass suggests the ropy glasses may be too old to be Tycho ejecta, which should be only about 100 m.y. old. If this is the case, the ropy glasses represent impact glasses from a very old impact in an unknown highlands source area.

Fruland, R. M.↗
NASA NTRS1979

Quantitative Analysis of Defects in Silicon

The evaluation and prediction of the conversion efficiency for a variety of silicon samples with differences in structural defects, such as grain boundaries, twin boundaries, precipitate particles, dislocations, etc. are discussed. Quantitative characterization of these structural defects, which were revealed by etching the surface of silicon samples, is performed by using an image analyzer. Due to different crystal growth and fabrication techniques the various types of silicon contain a variety of trace impurity elements and structural defects. The two most important criteria in evaluating the various silicon types for solar cell applications are cost and conversion efficiency.

Natesh, R.↗
NASA NTRS1979

Latitudinal variations of stratospheric aerosols

We have obtained stratospheric aerosols from tropical to northern latitudes using special collectors on U-2 aircraft during 1976 and 1977. Aerosols characterized by large numbers of small particles are found in the tropical zone suggesting this is a region of particle growth; whereas aerosols containing mostly larger particles are distributed throughout the Northern Hemisphere indicating a well-mixed, mature population. We find the aerosol layer extends from higher altitudes near the equator to lower ones toward the pole. Although this gradient suggests mature aerosols may leave the stratosphere at high latitudes, the data are, as yet, inconclusive. Comparisons of our data with those of other investigators using different instruments are generally encouraging, suggesting that if similar populations were sampled, the results would be similar. When our calculated sulfate mass mixing ratios are compared with those measured directly by others, we find better agreement is achieved if we assume more dilute sulfate and water mixtures than previously proposed.

Farlow, N. H.↗
NASA NTRS1982

Suprathermal electrons produced by beam-plasma-discharge

Experiments conducted with a low energy plasma lens, HARP, in the electron beam of the large vacuum chamber at Johnson Space Center indicate that an enhanced population of 50 to 300 volt electrons appear when the beam goes into the Beam-Plasma Discharge (BPD) mode. Below the BPD instability the electron distribution appears to be characterized as non-energized single particle scattering and energy loss. At 100 cm from the beam core in the BPD mode the fluxes parallel to the beam are reduced by a factor of 20 with respect to the fluxes at 25 cm. Some evidence for isotropy near the beam core is presented.

Sharp, W. E.↗
NASA NTRS1983

A source of the backstreaming ion beams in the foreshock region

The proposed source mechanism for the 'reflected' ion beams observed in the bow shock region's foreshock places the origin of the beams in the magnetosheath, downstream of the quasi-perpendicular shock portion whose transition is characterized by the downstream ion populations. Particle simulations indicate that highly anisotropic downstream ion distributions can excite electromagnetic ion cyclotron waves which, in turn, pitch angle-scatter the gyrating ions in a few ion gyroperiods. As a result, some ions acquire large parallel velocities and move fast enough along the convecting downstream magnetic field to escape back across the bow shock into the upstream region. The results presented are in general agreement with ISEE reflected ion observations.

Tanaka, M.↗
NASA NTRS1987

Particle and flow field holography: A critical survey

A brief background is provided for the fields of particle and flow visualization holography. A summary of methods currently in use is given, followed by a discussion of more recent and unique applications. The problem of data reduction is discussed. A state of the art summary is then provided with a prognosis of the future of the field. Particle and flow visualization holography are characterized as powerful tools currently in wide use and with significant untapped potential.

Trolinger, James D.↗
NASA NTRS1986

Velocity distributions of ion beams in the plasma sheet boundary layer

The value of measured ion-beam velocity distributions as diagnostic tools to characterize the propagation and acceleration of particle beams in the plasma-sheet boundary layer is assessed. Models based on adiabatic deformation of a flowing Maxwellian, acceleration by field-aligned potentials, and current-sheet acceleration are fitted to observational data, and the results are presented in extensive diagrams and graphs. The data are found to be consistent with models involving field-aligned or cross-tail potential drops, but not with models based solely on the adiabatic deformation of initially isotropic distributions.

Eastman, T. E.↗
NASA NTRS1989

Thermal infrared (2.5-13.5-micron) spectroscopic remote sensing of igneous rock types on particulate planetary surfaces

The compositional significance of outstanding spectral features in the reflectance spectra of particulate igneous rocks was investigated by analyzing directional reflectance spectra, obtained with an FTIR spectrophotometer at 2.17-13.5 microns, of a suite of well-characterized igneous rocks ground to fine particle size. It was found that, using spectral features associated with the principal Christiansen frequency and with a region of relative transparency between the Si-O stretching and bending bands, it is possible to identify general rock type using the Walter and Salisbury (1989) SCFM chemical index, SCFM, defined as SCFM = SiO2/(SiO2 + CaO + FeO + MgO). It is emphasized, however, that the appearance and the wavelength of these features may be affected by environmental factors.

Salisbury, John W.↗
NASA NTRS1990

Stochastic Fermi acceleration in solar flares

Proton spectra, valid from non- to ultra-relativistic energies, resulting from stochastic Fermi acceleration in solar flares are calculated. These spectra were obtained by numerically solving the Fokker-Planck equation, in which the escape of the particles from the acceleration region is characterized by an energy-independent escape time. In addition to equilibrium spectra, time-dependent energy spectra showing the approach to equilibrium are also presented. These numerical equilibrium spectra are compared with previous results which were obtained either by Monte Carlo simulations or approximate analytical treatments. There are no analytic solutions valid in the transrelativistic regime, which is very important for the production of pions and neutrons in solar flares. The acceleration efficiency is related to physical parameters, in particular the energy density in either magnetosonic or Alfven waves, and a lower limit is placed on either of these energy densities from acceleration times implied by gamma-ray observations. Also discussed is the physical interpretation of the escape time.

Miller, James A.↗
NASA NTRS1991

Numerical exploration of planetary arc dynamics

After analytically characterizing the response of a test particle to the combined effects of corotation and Lindblad resonances, due to the satellites of Neptune, as two coupled dynamical systems whose coupling depends on the collective effects in the arc, a formula is obtained for the energy imparted by the Lindblad resonance. This energy confines the arc material around the corotation resonance radius. The fact that the gradient of the torque density around the arc must be negative confirms the constraints defined by Lin et al. (1987) on the relative positions of the corotation and the Lindblad resonances if the arc is to be stable. These results are tested with a direct numerical simulation for two different arc configurations.

Sicardy, Bruno↗
NASA NTRS1993

The growth of small corrosion fatigue cracks in alloy 2024

The corrosion fatigue crack growth characteristics of small surface and corner cracks in aluminum alloy 2024 is established. The damaging effect of salt water on the early stages of small crack growth is characterized by crack initiation at constituent particle pits, intergranular microcracking for a less than 100 micrometers, and transgranular small crack growth for a micrometer. In aqueous 1 percent NaCl and at a constant anodic potential of -700 mV(sub SCE), small cracks exhibit a factor of three increase in fatigue crack growth rates compared to laboratory air. Small cracks exhibit accelerated corrosion fatigue crack growth rates at low levels of delta-K (less than 1 MPa square root of m) below long crack delta-K (sub th). When exposed to Paris regime levels of crack tip stress intensity, small corrosion fatigue cracks exhibit growth rates similar to that observed for long cracks. Results suggest that crack closure effects influence the corrosion fatigue crack growth rates of small cracks (a less than or equal to 100 micrometers). This is evidenced by similar small and long crack growth behavior at various levels of R. Contrary to the corrosion fatigue characteristics of small cracks in high strength steels, no pronounced chemical crack length effect is observed for Al by 2024 exposed to salt water.

Piascik, Robert S.↗
NASA NTRS1993

Evaluation of lunar rocks and soils for resource utilization: Detailed image analysis of raw materials and beneficiated products

The rocks and soils of the Moon will be the raw materials for fuels and construction needs at a lunar base. This includes sources of materials for the generation of hydrogen, oxygen, metals, and other potential construction materials. For most of the bulk material needs, the regolith, and its less than 1 cm fraction, the soil, will suffice. But for specific mineral resources, it may be necessary to concentrate minerals from rocks or soils, and it is not always obvious which is the more appropriate feedstock. Besides an appreciation of site geology, the mineralogy and petrography of local rocks and soils is important for consideration of the resources which can provide feedstocks of ilmenite, glass, agglutinates, anorthite, etc. In such studies, it is very time-consuming and practically impossible to correlate particle counts (the traditional method of characterizing lunar soil petrography) with accurate modal analyses and with mineral associations in multi-mineralic grains. But x ray digital imaging, using x rays characteristic of each element, makes all this possible and much more (e.g., size and shape analysis). An application of beneficiation image analysis, in use in our lab (Oxford Instr. EDS and Cameca SX-50 EMP), was demonstrated to study mineral liberation from lunar rocks and soils. Results of x ray image analysis are presented.

Taylor, Lawrence A.↗