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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Multichannel Deconvolution of Vibrational Shock Signals: An Inverse Filtering Approach

When transporting critical systems of national security interest, out-of-the ordinary, impulsive events that can potentially be undetected and affect overall system performance are of great concern. Impulsive events that can occur are essentially pulse-like, transient signals of short duration that evolve from various phenomena. Here the event can be created by either the dropping of a test object, the system, subjecting it to a compact high-energy blow or being struck unintentionally during transit resulting in potential damage. The intensity and location of the strike can cause an inoperability condition that is unacceptable in a national security environment. Therefore, it is essential to detect, classify and localize damage of any test object subjected to an impulsive-event. This effort was targeted to evaluate the vibrational response of test objects that are subjected to “transport” shocks and roadway vibrations during shipping and handling. Any potential damage that could be inflicted during transportation must not only be detected, but also be evaluated to determine the operational readiness of a test object before and after transport. This event is a critical task that must be addressed as part of the Lawrence Livermore National Laboratory (LLNL) national security mission. The estimation of excitation signals from noisy data is termed the deconvolution problem in the signal processing literature. The deconvolution problem is based on recovering the input excitation signal from a system characterized by its impulse response sequence. Using this model of the system, an “inverse” representation or filter is developed to remove the system from the measured data and recover the input. Deconvolution techniques have existed for a long-time; however, transient deconvolution presents a few uncommon problems, since the signal has a finite-length time duration resulting in a limited amount of data containing information about the excitation process. The transient is wideband in the frequency domain relative to any measurement sensor implying that the smaller bandwidth sensor system “filters” the excitation eliminating some of its essential information for recovery. This fact, coupled with the filtering effect of the test object itself makes this excitation recovery (deconvolution) problem a challenge for signal processing.

42 ENGINEERING↗
DOE OSTI2021

Evaluating the state-of-the-art in remote volcanic eruption characterization Part I: Raikoke volcano, Kuril Islands

Raikoke, a small, unmonitored volcano in the Kuril Islands, erupted in June 2019. We integrate data from satellites (including Sentinel-2, TROPOMI, MODIS, Himawari-8), the International Monitoring System (IMS) infrasound network, and global lightning detection network (GLD360) with information from local authorities and social media to retrospectively characterize the eruptive sequence and improve understanding of the pre-, syn- and post- eruptive behavior. In this work, we observe six infrasound pulses beginning on 21 June at 17:49:55 UTC as well as the main Plinian phase on 21 June at 22:29 UTC. Each pulse is tracked in space and time using lightning and satellite imagery as the plumes drift eastward. Post-eruption visible satellite imagery shows expansion of the island's surface area, an increase in crater size, and a possibly-linked algal bloom south of the island. We use thermal satellite imagery and plume modeling to estimate plume height at 10–12 km asl and 1.5–2 × 10 6 kg/s mass eruption rate. Remote infrasound data provide insight into syn-eruptive changes in eruption intensity. Our analysis illustrates the value of interdisciplinary analyses of remote data to illuminate eruptive processes. However, our inability to identify deformation, pre-eruptive outgassing, and thermal signals, which may reflect the relatively short duration (~12 h) of the eruption and minimal land area around the volcano and/or the character of closed-system eruptions, highlights current limitations in the application of remote sensing for eruption detection and characterization.

58 GEOSCIENCES↗
DOE OSTI2021

Influence of Agricultural Managed Aquifer Recharge (AgMAR) and Stratigraphic Heterogeneities on Nitrate Reduction in the Deep Subsurface

This data package contains input files for TOUGHREACT for a modeling study examining the effects of managed aquifer recharge on agricultural lands on nitrate cycling and transport in the Central Valley of CA near Modesto. The files contain all the geochemical species, reactions, and hydrological parameters for the model. The files are text files used for the TOUGH family of code created by LBNL. To use the files a license is required. https://tough.lbl.gov/licensing-download/toughreact-licensing-download/Accompanying Paper Abstract: Agricultural managed aquifer recharge (AgMAR) is a proposed management strategy whereby surface water flows are used to intentionally flood croplands with the purpose of recharging underlying aquifers. However, legacy nitrate (NO3-) contamination in agriculturally-intensive regions poses a threat to groundwater resources under AgMAR. To address these concerns, we use a reactive transport modeling framework to better understand the effects of AgMAR management strategies (i.e., by varying the frequency, duration between flooding events, and amount of water) on N leaching to groundwater under different stratigraphic configurations and antecedent moisture conditions. In particular, we examine the potential of denitrification and nitrogen retention in deep vadose zone sediments (~15 m) using variable AgMAR application rates on two-dimensional representations of differently textured soils, soils with discontinuous bands/channels, and soils with preferential flow paths characteristic of typical agricultural field sites. Our results indicate that finer textured sediments, such as silt loams, alone or embedded within high flow regions, are important reducing zones providing conditions needed for denitrification. Simulation results further suggest that applying water all-at-once rather than in increments for a fixed volume of recharge transports higher concentrations of NO3- deeper into the profile, which has the potential to exacerbate groundwater quality. This transport into deeper depths can be aggravated by wetter antecedent soil moisture conditions. However, applying water all-at-once also increases denitrification within the vadose zone by promoting anoxic conditions. We conclude that AgMAR management strategies can be designed to enhance denitrification in the subsurface and reduce N leaching to groundwater, while specifically accounting for lithologic heterogeneity, antecedent soil moisture conditions, and depth to the water table. Our findings are potentially relevant to other systems that experience flooding inundation such as riparian corridors, floodplains, wetlands, and other managed landscapes like dedicated recharge basins.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Thermomechanical response of thickly tamped targets and diamond anvil cells under pulsed hard x-ray irradiation

In the laboratory study of extreme conditions of temperature and density, the exposure of matter to high intensity radiation sources has been of central importance. Here, we interrogate the performance of multi-layered targets in experiments involving high intensity, hard x-ray irradiation, motivated by the advent of extremely high brightness hard x-ray sources, such as free electron lasers and 4th-generation synchrotron facilities. Intense hard x-ray beams can deliver significant energy in targets having thick x-ray transparent layers (tampers) around samples of interest for the study of novel states of matter and materials’ dynamics. Heated-state lifetimes in such targets can approach the microsecond level, regardless of radiation pulse duration, enabling the exploration of conditions of local thermal and thermodynamic equilibrium at extreme temperature in solid density matter. The thermal and mechanical responses of such thick layered targets following x-ray heating, including hydrodynamic relaxation and heat flow on picosecond to millisecond timescales, are modeled using radiation hydrocode simulation, finite element analysis, and thermodynamic calculations. Assessing the potential for target survival over one or more exposures and resistance to damage arising from heating and resulting mechanical stresses, this study doubles as an investigation into the performance of diamond anvil high pressure cells under high x-ray fluences. Long used in conjunction with synchrotron x-ray radiation and high power optical lasers, the strong confinement afforded by such cells suggests novel applications at emerging high intensity x-ray facilities and new routes to studying thermodynamic equilibrium states of warm, very dense matter.

Meza-Galvez, J. (ORCID:000000032699849X)↗
DOE OSTI2021

Broadband X-ray burst spectroscopy of the fast-radio-burst-emitting Galactic magnetar

Magnetars are young, magnetically powered neutron stars that possess the strongest magnetic fields in the Universe. Fast radio bursts (FRBs) are extremely intense millisecond-long radio pulses of primarily extragalactic origin, and a leading attribution for their genesis focuses on magnetars. A hallmark signature of magnetars is their emission of bright, hard X-ray bursts of sub-second duration. On 27 April 2020, the Galactic magnetar SGR J1935+2154 emitted hundreds of X-ray bursts within a few hours. One of these temporally coincided with an FRB, the first known detection of an FRB from the Milky Way. Here, we present spectral and temporal analyses of 24 X-ray bursts emitted 13 hours prior to the FRB and seen simultaneously with the Neutron Star Interior Composition Explorer (NICER) mission of the National Aeronautics and Space Administration and with the Fermi Gamma-ray Burst Monitor (GBM) mission in their combined energy range of 0.2 keV to 30 MeV. These broadband spectra permit direct comparison with the spectrum of the FRB-associated X-ray burst (FRB-X). We demonstrate that all 24 NICER and GBM bursts are very similar temporally to the FRB-X, but strikingly different spectrally. The singularity of the FRB-X burst is perhaps indicative of an uncommon locale for its origin. We suggest that this event originated in quasi-polar open or closed magnetic field lines that extend to high altitudes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

An extended moments model of quantum efficiency for metals and semiconductors

The complexity of photocathode designs and detector materials, and the need to model their performance for short pulse durations, response to high frequency photons, presence of coatings and/or thinness of the absorptive layer, necessitates modifications to three-step and moments models of photoemission that are used in simulation codes. Here, methods to include input from computationally intensive approaches, such as density functional theory to model optical properties and transfer matrix approaches to treat emission from the surface or transport past coatings, by means of parametric models are demonstrated. First, a technique to accurately represent optical behavior so as to model reflectivity and penetration depth is given. Second, modifications to bulk models arising from the usage of thin film architectures, and a means to rapidly calculate them, is provided. Third, a parameterization to model the impact of wells associated with coatings and surface layers on the transmission probably is given. In all cases, the methods are computationally efficient and designed to allow for including input from numerically intensive approaches that would otherwise be unavailable for simulations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Seedless nonresonant gas-flow velocimetry with single-shot coherent Rayleigh-Brillouin scattering

We demonstrate neutral gas-flow velocimetry by exploiting the optical dipole forces exerted by precisely tailored high-intensity laser fields on polarizable particles, in the form of single-shot coherent Rayleigh-Brillouin scattering (CRBS). This enables mapping of the velocity distribution function of the particles in a single laser shot of approximately 200 ns duration, allowing us to perform spectroscopic measurements in the time, rather than the frequency, domain. Importantly, CRBS results in a coherent signal beam, which renders the technique ideal for measurements in optically noisy environments. By correlating the time shift of the resulting spectrum to the Doppler shift caused by the bulk motion of particles, we perform neutral gas-flow velocimetry without the need to seed the flow, nondestructively, for a variety of gases, atomic or molecular. We demonstrate gas-flow velocimetry at flow velocities as low as 1 m ⁢s −1 , with similar velocity resolution, while temperature and gas density can also be estimated from the same single-shot spectra. To prove the effectiveness of the measurement technique, we benchmark it against Pitot tube measurements, which show excellent agreement.

Gerakis, Alexandros [Luxembourg Institute of Scien↗
DOE OSTI2021

Deep learning reconstruction of attosecond X-ray pulses from an angularly streaked 2D photoelectron momentum distribution

The Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory produces intense X-ray pulses using a beam of accelerated electrons. The X-ray laser enhanced attosecond pulse generation (XLEAP) project at SLAC has enabled LCLS to produce much shorter X-ray pulses than previously possible, with durations of a few hundred attoseconds. To measure the time-profile of these extremely short pulses a velocity map imaging spectrometer (VMI) was developed. The pulse duration is measured with using an angular streaking method.

Franz, Paris↗
DOE OSTI2021

Generation of straight and curved hollow plasma channels by laser-generated nonlinear wakefields and studies of ultra-intense laser pulse guiding

We report on a study of highly controllable, quasi-static hollow plasma channels generated by ion motion following a laser–plasma interaction via numerical simulations. These channels are generated by ion motion in a nonlinear wakefield, which has an asymmetry between focusing and defocusing periods. Such plasma channels, driven by a fs duration, 100 TW level laser pulse, have the capability to guide more powerful laser pulses. Moreover, we show that curved plasma channels can be generated in a transverse density gradient plasma and alloptical guiding of a second, significantly more powerful laser pulse in such a curved plasma channel. This mechanism may be useful for creating plasma optics for multi-stage TeV laser plasma accelerators and compact synchrotron radiation sources.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

On the control of electron heating for optimal laser radiation pressure ion acceleration

We study the onset of electron heating in intense laser–solid interactions and its impact on the spectral quality of radiation pressure accelerated ions in both hole boring and light sail regimes. Two- and three-dimensional particle-in-cell (PIC) simulations are performed over a wide range of laser and target parameters and reveal how the pulse duration, profile, polarization and target surface stability control the electron heating, the dominant ion acceleration mechanisms and the ion spectra. We find that the onset of strong electron heating is associated with the growth of the Rayleigh–Taylor-like instability at the front surface and must be controlled to produce high-quality ion beams, even when circularly polarized lasers are employed. We define a threshold condition for the maximum duration of the laser pulse that allows mitigation of electron heating and radiation pressure acceleration of narrow energy spread ion beams. The model is validated by three-dimensional PIC simulations, and the few experimental studies that reported low energy spread radiation pressure accelerated ion beams appear to meet the derived criteria. The understanding provided by our work will be important in guiding future experimental developments, for example for the ultrashort laser pulses becoming available at state-of-the-art laser facilities, for which we predict that proton beams with $\sim$ 150–250 MeV, $\sim$ 30% energy spread, and a total laser-to-proton conversion efficiency of $\sim$ 20% can be produced.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Observed Warm-Season Characteristics of MCS and Non-MCS Rainfall and Their Recent Changes in the Central United States

Warm-season rainfall characteristics in the central US are investigated as they play important roles in ecohydrology and agricultural productivity. Using rainfall observations, we compare the April-August mesoscale convective systems (MCS) and non-MCS rainfall characteristics and examine their linear trends between 1997 and 2018. We found that MCS rainfall is ~7 times more intense than non-MCS rainfall but it occurs less frequently in time and space. MCS rainfall peaks in nocturnal hours, with synchronized timing of rainfall intensity, area and occurrence, while non-MCS rainfall peaks in late-afternoon hours, mostly attributed to the timing of peak rainfall area. MCS rainfall has increased in the last 22 years due to an increase in frequency and a longer duration per MCS. In contrast, non-MCS rainfall has decreased mainly due to a reduction in rainfall area, leading to fewer total wet days and increased dry intervals between storms

Hu, Huancui↗
DOE OSTI2020

Planar multifrequency mid-IR microwave-pumped lasers

The characteristics of planar repetitively pulsed diffusion-cooled HF, DF, HF – DF, Xe, and HF – DF – Xe(Kr) lasers pumped by a microwave discharge (2.45 GHz) are studied depending on the pump pulse duration (10 – 40 μs) and repletion rate (50 – 400 Hz), as well as on the composition and pressure of the working gas mixture (30 – 200 Torr) at low (to 0.6 L s{sup −1}) gas flow rates. It is demonstrated for the first time that a HF – DF – Xe gas-discharge laser may simultaneously operate as a HF – DF chemical molecular laser and a recombination laser based on xenon atom transitions and generate broadband (octave) radiation in the range 2.0 – 4.2 μm with an average output power of 43 mW and an efficiency of 0.9 %. With substitution of xenon for krypton, lasing in a HF – DF – Kr laser is obtained at wavelengths of 2.52 – 4.15 μm. Lasing in a HF – DF laser was achieved simultaneously in two spectral regions (2.7 – 2.9 and 3.6 – 4.2 μm) with an output power of ∼50 mW. It is found that a decrease in the pump pulse duration with a simultaneous increase in the pulse repletion rate for retaining the average energy deposition leads to an increase in the average output power and efficiency of the laser. At low pulse repetition rates (50 – 100 Hz) and a low gas mixture flow rate, helium buffer gas can be effectively substituted for neon. Operation of the Xe laser was achieved in the spectral range 2.03 – 3.65 μm with an average output power of 580 Mw at a pump pulse duration of 20 μs, a pulse repetition rate to 10 kHz, and a maximum efficiency of 55 %. The obtained experimental results demonstrate the possibility of creating broadband HF – DF – Xe lasers emitting in the frequency range 2 – 4 μm with a desired ratio of intensities in different spectral ranges. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Magnetic field generation in a laser-irradiated thin collisionless plasma target by return current electrons carrying orbital angular momentum

Abstract Magnetized high energy density physics offers new opportunities for observing magnetic field-related physics for the first time in the laser–plasma context. We focus on one such phenomenon, which is the ability of a laser-irradiated magnetized plasma to amplify a seed magnetic field. We performed a series of fully kinetic 3D simulations of magnetic field amplification by a picosecond-scale relativistic laser pulse of intensity 4.2 × 10 18 W cm −2 incident on a thin overdense target. We observe axial magnetic field amplification from an initial 0.1 kT seed to 1.5 kT over a volume of several cubic microns, persisting hundreds of femtoseconds longer than the laser pulse duration. The magnetic field amplification is driven by electrons in the return current gaining favorable orbital angular momentum from the seed magnetic field. This mechanism is robust to laser polarization and delivers order-of-magnitude amplification over a range of simulation parameters.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Nonlinear Thomson scattering of a tightly focused relativistically intense laser pulse by an ensemble of particles

We report a study of the process of nonlinear Thomson scattering (NTS) of a tightly focused relativistically intense laser pulse by an ensemble of electrons simulating the result of ionisation of an ultrathin nanofoil. The description of all six components of a laser pulse is based on the Stratton – Chu integrals describing radiation focused by an off-axis parabolic mirror into a spot down to the diffraction limit, which is of practical interest for modern experiments with extreme-intensity lasers, including diagnostics of their parameters. The interaction of a laser pulse with electrons is simulated by the test-particle method, and the resulting trajectories are used to calculate the characteristics of secondary electromagnetic radiation. The effect of the laser-pulse focal spot diameter in the range λ – 6λ on the angular distributions of the radiated energy and NTS spectra, as well as of a laser-beam peak intensity of 10{sup 21} – 10{sup 22} W cm{sup −2} on the spectral width of the secondary radiation is studied in relation to the experimentally implemented focusing scheme using the example of a laser pulse with an initial homogeneous spatial distribution and a duration of ∼25 fs. (interaction of laser radiation with matter. laser plasma)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Performance and durability of electrically conductive tape for shingled Si heterojunction technology cells

We report electrically conductive tape (ECT) was characterized and used to assemble shingled cell strings at low temperature to achieve high reliability Pb- and Ag-free interconnections. The volume resistivity for two considered ECTs are 0.13 ± 0.06 mΩ·cm and 0.47 ± 0.20 mΩ·cm and specific contact resistances, 6.85± 2.00 mΩ·cm 2 and 6.30 ± 0.37 mΩ·cm 2 using the emerging IEC 62788-8-1 Technical Specification for assessment of electrically conductive adhesives (ECA). Durability and performance of the technology in glass–glass mini modules were evaluated with temperature cycling, damp heat testing, and combined-accelerated stress testing (CAST). Through temperature cycling (-40°C to 85°C) applying five times the mini module short-circuit current in forward bias and in the multi climate CAST protocol, there was negligible degradation of fill factor after replacing connectors at the modules' cable leads; however, CAST resulted in short circuit current loss attributed to degradation in light collection by the cells, not the ECT. The IEC 61215-2 85°C, 85% relative humidity damp heat testing showed susceptibility of the HJT cells to effects of humidity in the electroluminescence intensity around the module perimeter that degraded power performance by 4% (relative). Contrasting the IEC 61215-2 qualification testing-based damp heat testing with CAST, factors such as the optical stress of CAST may precipitate the degradation of the modules whereas the humidity levels and duration of IEC 61215-2 damp heat testing may lead to excessive levels of humidity diffused into the modules, potentially resulting in degradation that is unrepresentative of the field.

14 SOLAR ENERGY↗
DOE OSTI2021

Preferred orientation of calcium aluminosilicate hydrate compacts: Implications for creep and indentation

Nano/micro-indentation has been extensively used to examine elastic properties and creep of cement-based materials. However, there have been inconsistencies in the measured elastic moduli and debate on the creep mechanism of calcium (alumino) silicate hydrates (C-(A-)S-H). To bring new insights, we examined the deviatoric stress-induced preferred orientation of calcium aluminosilicate hydrate (C-A-S-H), portlandite, and ettringite compacts, using synchrotron-based X-ray diffraction. Intense preferred orientations were observed in C-A-S-H compacts, and the c-axis of unit cells is highly aligned with the compression direction; weaker c-axis related fiber-type texture formed in portlandite and ettringite. Higher humidity, greater compacting pressure, and/or increased duration of the pressure intensified the C-A-S-H preferred orientation, which is facilitated by gel-pore water lubrication. This pressure-induced time-dependent preferential re-orientation of crystallites can contribute to the creep of cement-based materials, and it may cause overrepresentation of the soft c-axis of C-(A-)S-H unit-cell in nanoindentation experiments and underestimation of Young's modulus.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Peak Rain Rate Sensitivity to Observed Cloud Condensation Nuclei and Turbulence in Continental Warm Shallow Clouds During CACTI

Abstract Warm clouds strongly affect Earth's energy budget but remain imperfectly represented in climate models, partly due to the complexity and covariability of relevant processes influencing warm rain. This work presents a detailed analysis of different factors affecting rain rate peak intensity (RR) in continental warm clouds. Clouds were identified with vertically pointing radar and lidar observations and categorized via a temperature‐based cloud type classification algorithm from which warm clouds were isolated. Observations and retrievals of liquid water path (LWP), cloud condensation nuclei concentration (N CCN ), cloud depth, and cloud duration of more than 3,000 separate warm clouds sampled during the Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign are analyzed in this work. Multiple linear regression (MLR) and random forest (RF) models are applied to assess the relative impact of these variables on RR. Overall, RR tends to increase as cloud depth, LWP, and cloud duration increase, or N CCN decreases. Cloud depth affects RR the most while N CCN impacts it the least. When considering over 170 warm clouds observed at least 1 hr in which in‐cloud turbulence is retrieved, the effect of N CCN on RR remains most likely suppressive, but it is not significant at a 75% level for MLR and is highly uncertain for RF. The impact of in‐cloud turbulence depends on the moment and location it is sampled. Cloud base turbulence around the time of RR suppresses RR, while cloud top turbulence effects are inconclusive. Possible difficulties in isolating robust CCN and turbulence effects on RR are discussed.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Direct density modulation of photo-assisted field emission from an RF cold cathode

This paper explores direct density modulation of high-current electron beam emission from an RF cold cathode using optical excitation. We theoretically study the photo-assisted field emission of periodically bunched electron beams of various pulse shapes under the combined excitation of an RF field and an optical field, using an exact quantum model. Both continuous-wave (CW) and pulsed optical fields are considered. The emission current pulse amplitude, pulse width, electron number density per pulse, as well as pulse shape and its harmonic contents are investigated in detail. For CW photon sources in the UV to NIR range (i.e., 200–1200 nm), increasing the optical intensity under an RF bias tends to change the current pulse from a Gaussian to sinusoidal-like shape, thus offering strong flexibility to control the frequency components in beam current emission. Pulsed photon sources combined with an RF field can produce sharp, high-current electron bunches with pulse duration comparable with or even less than that of the optical pulse. A contour map of the density modulation depth is constructed for different combinations of RF and laser fields. The results provide insight into unlocking new opportunities to achieve direct density modulation during electron current emission by optical means.

Physics↗