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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 OSTI2016

Modeling of reduced effective secondary electron emission yield from a velvet surface

Complex structures on a material surface can significantly reduce total secondary electron emission from that surface. A velvet is a surface that consists of an array of vertically standing whiskers. The reduction occurs due to the capture of low-energy, true secondary electrons emitted at the bottom of the structure and on the sides of the velvet whiskers. We performed numerical simulations and developed an approximate analytical model that calculates the net secondary electron emission yield from a velvet surface as a function of the velvet whisker length and packing density, and the angle of incidence of primary electrons. We found that to suppress secondary electrons, the following condition on dimensionless parameters must be met: (π/2) DΑ tan θ >> 1, where theta is the angle of incidence of the primary electron from the normal, D is the fraction of surface area taken up by the velvet whisker bases, and A is the aspect ratio, A = h/r, the ratio of height to radius of the velvet whiskers. We find that velvets available today can reduce the secondary electron yield by 90% from the value of a flat surface. As a result, the values of optimal velvet whisker packing density that maximally suppresses the secondary electron emission yield are determined as a function of velvet aspect ratio and the electron angle of incidence.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Secondary electron emission yield from high aspect ratio carbon velvet surfaces

The plasma electrons bombarding a plasma-facing wall surface can induce secondary electron emission (SEE) from the wall. A strong SEE can enhance the power losses by reducing the wall sheath potential and thereby increasing the electron flux from the plasma to the wall. The use of the materials with surface roughness and the engineered materials with surface architecture is known to reduce the effective SEE by trapping the secondary electrons. In this work, we demonstrate a 65% reduction of SEE yield using a velvet material consisting of high aspect ratio carbon fibers. The measurements of SEE yield for different velvet samples using the electron beam in vacuum demonstrate the dependence of the SEE yield on the fiber length and the packing density, which is strongly affected by the alignment of long velvet fibers with respect to the electron beam impinging on the velvet sample. Furthermore, the results of SEE measurements support the previous observations of the reduced SEE measured in Hall thrusters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Measurement of sputtered beryllium yield and angular distribution during nanostructure growth in a helium plasma

Here, the angular distribution and sputtering yield of beryllium exposed to helium plasma are estimated from analysis of line-integrated 2D imaging of Be-I line emission in a steady-state linear plasma device. As the surface nanostructure forms during plasma exposure on a ~100 s timescale (corresponding to a fluence of order 10 20 /cm 2 ) from nearly mono-energetic ion bombardment, a narrowing of the beryllium sputtering angle and a significant (~5×) drop in sputtering yield are observed. Lastly, these trends are found to be qualitatively consistent with modeling taking into account the effect of the surface morphology on sputtering yield and angular distribution.

36 MATERIALS SCIENCE↗
DOE OSTI2018

High quantum yield of the Egyptian blue family of infrared phosphors (MCuSi 4 O 10 , M = Ca, Sr, Ba)

The alkaline earth copper tetra-silicates, blue pigments, are interesting infrared phosphors. The Ca, Sr, and Ba variants fluoresce in the near-infrared (NIR) at 909, 914, and 948 nm, respectively, with spectral widths on the order of 120 nm. The highest quantum yield Φ reported thus far is ca. 10%. We use temperature measurements in sunlight to determine this parameter. The yield depends on the pigment loading (mass per unit area) ω with values approaching 100% as ω → 0 for the Ca and Sr variants. Although maximum quantum yield occurs near ω = 0, maximum fluorescence occurs near ω = 70 g m -2 , at which Φ = 0.7. The better samples show fluorescence decay times in the range of 130 to 160 μs. The absorbing impurity CuO is often present. Good phosphor performance requires long fluorescence decay times and very low levels of parasitic absorption. In conclusion, the strong fluorescence enhances prospects for energy applications such as cooling of sunlit surfaces (to reduce air conditioning requirements) and luminescent solar concentrators.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Cloud and microjet mix: A possible source of yield limitation of the National Ignition Facility targets

The National Ignition Facility (NIF) megajoule laser at the Lawrence Livermore National Laboratory (LLNL) has produced a significant amount of useful physics results related to inertial confinement fusion since it began operating in 2010. However, the achievement of its primary goal of generating ignition in a thermonuclear plasma has proven elusive, and measured yields were far below those expected under ideal illumination and target structure conditions. The reason for the limited yields has not been explained in detail. Here, this work proposes and shows support for the possibility that the low yields may be, at least partly, the result of ejecta from the interior of the target containment and driving shell.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Carbon nanotube substrates enhance SARS-CoV-2 spike protein ion yields in matrix-assisted laser desorption–ionization mass spectrometry

Nanostructured surfaces enhance ion yields in matrix-assisted laser desorption–ionization mass spectrometry (MALDI-MS). The spike protein complex, S1, is one fingerprint signature of Sars-CoV-2 with a mass of 75 kDa. Here, we show that MALDI-MS yields of Sars-CoV-2 spike protein ions in the 100 kDa range are enhanced 50-fold when the matrix–analyte solution is placed on substrates that are coated with a dense forest of multi-walled carbon nanotubes, compared to yields from uncoated substrates. Nanostructured substrates can support the development of mass spectrometry techniques for sensitive pathogen detection and environmental monitoring.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

First demonstration of improved yield with reduced adiabat in inertial confinement fusion implosions on the National Ignition Facility

Laser-driven, indirect-drive inertial confinement fusion (ICF) experiments at the National Ignition Facility (NIF) recently achieved a target gain greater than one, where fusion energy output exceeds input laser energy [Abu-Shawareb et al., Phys. Rev. Lett. 132, 065102 (2024)]. Despite this milestone, gain levels remain insufficient for practical applications such as inertial fusion energy, making performance improvement critical. One promising approach is increasing fuel compression by lowering the implosion adiabat. To explore reduced adiabat, experiments were conducted modifying the laser pulse shape and shock timing of an existing 1.9-MJ-drive implosion design performing near the ignition cliff [Abu-Shawareb et al., Phys. Rev. Lett. 129, 075001 (2022)]. These experiments demonstrated increased compression and fusion yield in ICF implosions at the NIF by using a lower fuel adiabat, and increased compression with a reduced adiabat in high-density carbon ablators. The updated design achieved up to 80% higher fusion yield and 14% greater fuel compression compared to the previous best-performing 1.9-MJ experiment, with repeatable performance, and is the only implosion design to achieve a target gain exceeding one with < 2.04 MJ laser energy. Notably, this work was made possible because of recent advances in target quality and pulse shape control allowing experimental access to the ignition regime, and thereby increased sensitivity to adiabat. This work addresses a long-standing question in ICF research and lays the foundation for higher target gains through optimized implosion strategies. It underscores the potential of reduced adiabat designs to enhance compression and fusion yields for future ICF applications.

Hohenberger, M. [Lawrence Livermore National Labor↗
DOE OSTI2016

Ellipticity dependence of high harmonic yield in intense laser field: case of s-valence electron

Having solved numerically the time-dependent Schrödinger equation, we have analysed the dependence of the high harmonic generation yield on the ellipticity of an intense laser field. For the case of a zero angular momentum of an initial state, it has been shown that the ellipticity dependence of the HHG yield is affected by the harmonic number. The numerical results are interpreted in the framework of our recently developed quasi-classical analytical model for HHG. In the quasi-classical approximation, the difference in the ellipticity dependence of the HHG yield for different harmonics is shown to be caused by the interference effects of quantum orbits. (extreme laser radiation: physics and fundamental applications)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

High-yield hydrogen production from biomass by in vitro metabolic engineering: Mixed sugars coutilization and kinetic modeling

The use of hydrogen (H 2 ) as a fuel offers enhanced energy conversion efficiency and tremendous potential to decrease greenhouse gas emissions, but producing it in a distributed, carbon-neutral, low-cost manner requires new technologies. Herein we demonstrate the complete conversion of glucose and xylose from plant biomass to H 2 and CO 2 based on an in vitro synthetic enzymatic pathway. Glucose and xylose were simultaneously converted to H 2 with a yield of two H 2 per carbon, the maximum possible yield. Parameters of a nonlinear kinetic model were fitted with experimental data using a genetic algorithm, and a global sensitivity analysis was used to identify the enzymes that have the greatest impact on reaction rate and yield. After optimizing enzyme loadings using this model, volumetric H 2 productivity was increased 3-fold to 32 mmol H 2 ∙L ₋1 ∙h ₋1 . The productivity was further enhanced to 54 mmol H 2 ∙L ₋1 ∙h ₋1 by increasing reaction temperature, substrate, and enzyme concentrations—an increase of 67-fold compared with the initial studies using this method. The production of hydrogen from locally produced biomass is a promising means to achieve global green energy production.

08 HYDROGEN↗
DOE OSTI2019

Using excitation-energy dependent fission yields to identify key fissioning nuclei in r -process nucleosynthesis

The possibility that nucleosynthesis in neutron star mergers may reach fissioning nuclei introduces significant uncertainties in predicting the relative abundances of $r$-process material from such events. We evaluate the impact of using sets of fission yields given by the 2016 GEF code for spontaneous (sf), neutron-induced $((n, f))$, and $β$-delayed (βdf) fission processes which take into account the approximate initial excitation energy of the fissioning compound nucleus. We further explore energy-dependent fission dynamics in the $r$ process by considering the sensitivity of our results to the treatment of the energy sharing and de-excitation of the fission fragments using the FREYA code. We show that the asymmetric-to-symmetric yield trends predicted by GEF 2016 can reproduce the high-mass edge of the second $r$-process peak seen in solar data and examine the sensitivity of this result to the mass model and astrophysical conditions applied. We consider the effect of fission yields and barrier heights on the nuclear heating rates used to predict kilonova light curves. We find that fission barriers influence the contribution of 254 Cf spontaneous fission to the heating at ~100 d, such that a light curve observation consistent with such late-time heating would both confirm that actinides were produced in the event and imply the fission barriers are relatively high along the 254 Cf β-feeding path. We lastly determine the key nuclei responsible for setting the r-process abundance pattern by averaging over thirty trajectories from a 1.2–1.4 M ⊙ neutron star merger simulation. Finally, we show it is largely the odd-N nuclei undergoing $(Z, N)(n, f)$ and $(Z, N)β$df that control the relative abundances near the second peak. We find the 'hot spots' for β-delayed and neutron-induced fission given all mass models considered and show most of these nuclei lie between the predicted $N$ = 184 shell closure and the location of currently available experimental decay data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Yield ratio of hypertriton to light nuclei in heavy-ion collisions from = 4.9 GeV to 2.76 TeV *

Abstract We argue that the difference in the yield ratio measured in Au+Au collisions at = 200 GeV and in Pb-Pb collisions at = 2.76 TeV is mainly owing to the different treatment of the weak decay contribution to the proton yield in the Au+Au collisions at = 200 GeV. We then use the coalescence model to extract from measured the information about the and nucleon density fluctuations at the kinetic freeze-out of heavy-ion collisions. We also show, using available experimental data, that the yield ratio is a more promising observable than for probing the local baryon-strangeness correlation in the produced medium.

Physics↗
DOE OSTI2017

Effect of low electric fields on alpha scintillation light yield in liquid argon

Measurements were made of scintillation light yield of alpha particles from the $^{222}$Rn decay chain within the DarkSide-50 liquid argon time projection chamber. Furthermore, the light yield was found to increase as the applied electric field increased, with alphas in a 200 V/cm electric field exhibiting a 2% increase in light yield compared to alphas in no field.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Multiphenomenology explosion monitoring (MultiPEM): a general framework for data interpretation and yield estimation

SUMMARY An underground nuclear explosion (UNE) couples mechanical energy into crustal rock, which propagates as seismic and acoustic waves. These different physical phenomena transport, by different pathways, to standoff detectors at varying distances. The transport pathways attenuate the original signal but in different ways. Enabled by correct statistical weighting, signal attenuation models can be used to combine these disparate sensor data to estimate the yield of an UNE. Contemporaneous statistical models, used in yield estimation, can be improved with an advanced partition of error for these physical signal propagation models. We present an advanced multivariate approach to error modelling of multiphenomenology physical signatures. In addition to measurement error, our error model represents physical model biases as random with a physics-based covariance structure. To illustrate this proposed framework, we demonstrate the estimation of explosion yield using openly available seismic and acoustic data from chemical single-point explosions.

Williams, Brian J.↗
DOE OSTI2016

Expression of cyanobacterial FBP/SBPase in soybean prevents yield depression under future climate conditions

Predictions suggest that current crop production needs to double by 2050 to meet global food and energy demands. Based on theory and experimental studies, overexpression of the photosynthetic enzyme sedoheptulose-1,7-bisphosphatase (SBPase) is expected to enhance C3 crop photosynthesis and yields. Here we test how expression of the cyanobacterial, bifunctional fructose-1,6/sedoheptulose-1,7-bisphosphatase (FBP/SBPase) affects carbon assimilation and seed yield (SY) in a major crop (soybean, Glycine max). For three growing seasons, wild-type (WT) and FBP/SBPase-expressing (FS) plants were grown in the field under ambient (400 μmol mol-1) and elevated (600 μmol mol-1) CO2 concentrations [CO2] and under ambient and elevated temperatures (+2.7 °C during daytime, +3.4 °C at night) at the SoyFACE research site. Across treatments, FS plants had significantly higher carbon assimilation (4–14%), Vc,max (5–8%), and Jmax (4–8%). Under ambient [CO2], elevated temperature led to significant reductions of SY of both genotypes by 19–31%. However, under elevated [CO2] and elevated temperature, FS plants maintained SY levels, while the WT showed significant reductions between 11% and 22% compared with plants under elevated [CO2] alone. These results show that the manipulation of the photosynthetic carbon reduction cycle can mitigate the effects of future high CO2 and high temperature environments on soybean yield.

Plant Sciences↗
DOE OSTI2019

Nucleosynthetic yields from neutron stars accreting in binary common envelopes

Massive-star binaries can undergo a phase where one of the two stars expands during its advanced evolutionary stage as a giant and envelops its companion, ejecting the hydrogen envelope and tightening its orbit. Such a common envelope phase is required to tighten the binary orbit in the formation of many of the observed X-ray binaries and merging compact binary systems. In the formation scenario for neutron star binaries, the system might pass through a phase where a neutron star spirals into the envelope of its giant star companion. These phases lead to mass accretion on to the neutron star. Accretion on to these common-envelope-phase neutron stars can eject matter that has undergone burning near to the neutron star surface. This paper presents nucleosynthetic yields of this ejected matter, using population synthesis models to study the importance of these nucleosynthetic yields in a galactic chemical evolution context. Depending on the extreme conditions in temperature and density found in the accreted material, both proton-rich and neutron-rich nucleosynthesis can be obtained, with efficient production of neutron-rich isotopes of low Z material at the most extreme conditions, and proton-rich isotopes, again at low Z, in lower density models. Final yields are found to be extremely sensitive to the physical modelling of the accretion phase. Finally, we show that neutron stars accreting in binary common envelopes might be a new relevant site for galactic chemical evolution, and therefore more comprehensive studies are needed to better constrain nucleosynthesis in these objects.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Bremsstrahlung Dose Yield for High-Intensity Short-Pulse Laser–Solid Experiments

A bremsstrahlung source term has been developed by the Radiation Protection (RP) group at SLAC National Accelerator Laboratory for high-intensity short-pulse laser–solid experiments between 10 17 and 10 22 W cm –2 . This source term couples the particle-in-cell plasma code EPOCH and the radiation transport code FLUKA to estimate the bremsstrahlung dose yield from laser–solid interactions. EPOCH characterizes the energy distribution, angular distribution, and laser-to-electron conversion efficiency of the hot electrons from laser–solid interactions, and FLUKA utilizes this hot electron source term to calculate a bremsstrahlung dose yield (mSv per J of laser energy on target). The goal of this paper is to provide RP guidelines and hazard analysis for high-intensity laser facilities. In conclusion, a comparison of the calculated bremsstrahlung dose yields to radiation measurement data is also made.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2025

First Demonstration of Improved Fusion Yield with Increased Compression through Reduced Adiabat in Inertial Confinement Fusion Experiments at the National Ignition Facility

Recent advancements in indirect-drive inertial confinement fusion (ICF) experiments at the National Ignition Facility (NIF) have achieved a significant milestone by demonstrating target gains greater than one, yet future applications necessitate much higher target gains. One approach to achieving improved implosion performance is to pursue increased fuel compression via a lowered implosion adiabat. Experiments have been performed testing a reduced adiabat by introducing small changes to the drive laser pulse shape and the resulting shock timing for an existing implosion design at 1.9 MJ laser drive with near-ignition performance (experiment N210808). Experiments using the updated design demonstrate, for the very first time, increased compression and fusion yield in ICF implosions on the NIF by using a lower fuel adiabat, and increased compression with a reduced adiabat in high-density carbon ablators. Compared to the previously best-performing experiment with a laser energy of 1.9 MJ, these experiments exhibit increases of up to 80% and 14% in nuclear fusion yield and fuel compression, respectively, and with repeatable performance. Further, it is the only implosion design to have achieved a target gain exceeding one with a laser energy of less than 2 MJ. These findings highlight the efficacy of reduced adiabat designs in achieving higher compression and fusion yields, offering a promising pathway for future ICF applications. In conclusion, this Letter not only addresses a long-standing question in ICF but also paves the way for achieving higher target gains with optimized implosion strategies.

Hohenberger, M. [Lawrence Livermore National Labor↗
DOE OSTI2011

Absolute frequencies of the {sup 6,7}Li 2S {sup 2}S{sub 1/2}{yields}3S {sup 2}S{sub 1/2} transitions

The measurement of the absolute frequencies of the 2S{yields}3S of atomic lithium is reported. To reduce systematic effects, we employed a frequency-comb-stabilized excitation laser, a weakly collimated atomic beam, and the cascading 2P{yields}2S 670 nm fluorescence as the signal. The transition frequencies, including two isotopes ({sup 6,7}Li), were measured to an accuracy of < 330 kHz. In comparison with the previous GSI Group experiment, the frequency of the 2S{sub 1/2}{yields}3S{sub 1/2} transition of {sup 7}Li is 815 618 181.45(9) MHz, which is improved by a factor of 2. The resultant hyperfine constants of the 3S state and the deduced difference of the nuclear charge radii {delta} from the isotope shift are in good agreement with previous results. Since a more straightforward methodology is adopted, our measurement is less model dependent and serves as an independent investigation of the reported transitions.

74 ATOMIC AND MOLECULAR PHYSICS↗