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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Increased light-use efficiency in northern terrestrial ecosystems indicated by CO 2 and greening observations: INCREASE IN NH LIGHT USE EFFICIENCY

Observations show an increasing amplitude in the seasonal cycle of CO2 (ASC) north of 45°N of 56 ± 9.8% over the last 50 years and an increase in vegetation greenness of 7.5–15% in high northern latitudes since the 1980s. However, the causes of these changes remain uncertain. Historical simulations from terrestrial biosphere models in the Multiscale Synthesis and Terrestrial Model Intercomparison Project are compared to the ASC and greenness observations, using the TM3 atmospheric transport model to translate surface fluxes into CO2 concentrations. We find that the modeled change in ASC is too small but the mean greening trend is generally captured. Modeled increases in greenness are primarily driven by warming, whereas ASC changes are primarily driven by increasing CO2. We suggest that increases in ecosystem-scale light use efficiency (LUE) have contributed to the observed ASC increase but are underestimated by current models. We highlight potential mechanisms that could increase modeled LUE.

Thomas, Rebecca T.↗
DOE OSTI2018

Xenon Gas Separation and Storage using Metal-Organic Frameworks

The global demand for Xe, a noble gas with applications in electronics, lighting, and the medical industry, is expected to rise significantly over the coming decades. However, the low abundance of Xe in the earth’s atmosphere and the costly cryogenic distillation process that is used to obtain Xe commercially via air separation have limited the scale of applications of Xe. A physisorption-based separation using porous materials may be a viable and cost-effective alternative to cryogenic distillation. In particular, metal-organic frameworks (MOFs) have shown promise as highly Xe-selective, porous solids. In this review, we detail the recent advances of MOFs as adsorbents for noble gas adsorption/separation and the role of computer simulation in finding optimal materials for Xe adsorption.

MOFs, Xenon, Krypton↗
DOE OSTI2015

Use of external magnetic fields in hohlraum plasmas to improve laser-coupling

Efficient coupling of laser energy into hohlraum targets is important for indirect drive ignition. Laser-plasma instabilities can reduce coupling, reduce symmetry, and cause preheat. We consider the effects of an external magnetic field on laser-energy coupling in hohlraum targets. Experiments were performed at the Omega Laser Facility using low-Z gas-filled hohlraum targets which were placed in a magnetic coil with B{sub z} ≤ 7.5-T. We found that an external field B{sub z} = 7.5-T aligned along the hohlraum axis results in up to a 50% increase in plasma temperature as measured by Thomson scattering. The experiments were modeled using the 2-D magnetohydrodynamics package in HYDRA and were found to be in good agreement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Experimental and numerical investigations of beryllium strength models using the Rayleigh-Taylor instability

We present a set of high explosive driven Rayleigh-Taylor strength experiments for beryllium to produce data to distinguish predictions by various strength models. Design simulations using existing strength model parameterizations from Steinberg-Lund and Preston-Tonks-Wallace (PTW) suggested an optimal design that would delineate between not just different strength models, but different parameters sets of the PTW model. Application of the models to the post-shot results, however, suggests growth consistent with little material strength. We focus mostly on efforts to simulate the data using published strength models as well as the more recent RING relaxation model developed at VNIIEF. The results of the strength experiments indicate weak influence of strength in mitigating the growth with the RING model coming closest to predicting the material behavior. Finally, we present shock and ramp-loading recovery experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Study of cosmic ray events with high muon multiplicity using the ALICE detector at the CERN Large Hadron Collider

ALICE is one of four large experiments at the CERN Large Hadron Collider near Geneva, specially designed to study particle production in ultra-relativistic heavy-ion collisions. Located 52 meters underground with 28 meters of overburden rock, it has also been used to detect muons produced by cosmic ray interactions in the upper atmosphere. Here, we present the multiplicity distribution of these atmospheric muons and its comparison with Monte Carlo simulations. Our analysis exploits the large size and excellent tracking capability of the ALICE Time Projection Chamber. A special emphasis is given to the study of high multiplicity events containing more than 100 reconstructed muons and corresponding to a muon areal density rho(mu) > 5.9 m(-2). Similar events have been studied in previous underground experiments such as ALEPH and DELPHI at LEP. While these experiments were able to reproduce the measured muon multiplicity distribution with Monte Carlo simulations at low and intermediate multiplicities, their simulations failed to describe the frequency of the highest multiplicity events. In this work we show that the high multiplicity events observed in ALICE stem from primary cosmic rays with energies above 10(16) eV and that the frequency of these events can be successfully described by assuming a heavy mass composition of primary cosmic rays in this energy range. Furthermore, the development of the resulting air showers was simulated using the latest version of QGSJET to model hadronic interactions. This observation places significant constraints on alternative, more exotic, production mechanisms for these events.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Measurement of carbon condensates using small-angle x-ray scattering during detonation of the high explosive hexanitrostilbene

The dynamics of carbon condensation in detonating high explosives remains controversial. Detonation model validation requires data for processes occurring at nanometer length scales on time scales ranging from nanoseconds to microseconds. A new detonation endstation has been commissioned to acquire and provide time-resolved small-angle x-ray scattering (SAXS) from detonating explosives. Hexanitrostilbene (HNS) was selected as the first to investigate due to its ease of initiation using exploding foils and flyers, vacuum compatibility, high thermal stability, and stoichiometric carbon abundance that produces high carbon condensate yields. The SAXS data during detonation, collected with 300 ns time resolution, provide unprecedented signal fidelity over a broad q-range. This fidelity permits the first analysis of both the Guinier and Porod/power-law regions of the scattering profile during detonation, which contains information about the size and morphology of the resultant carbon condensate nanoparticles. To bolster confidence in these data, the scattering angle and intensity were additionally cross-referenced with a separate, highly calibrated SAXS beamline. The data show that HNS produces carbon particles with a radius of gyration of 2.7 nm in less than 400 ns after the detonation front has passed, and this size and morphology are constant over the next several microseconds. These data directly contradict previous pioneering work on RDX/TNT mixtures and TATB, where observations indicate significant particle growth (50% or more) continues over several microseconds. The power-law slope is about −3, which is consistent with a complex disordered, irregular, or folded sp{sup 2} sub-arrangement within a relatively monodisperse structure possessing radius of gyration of 2.7 nm after the detonation of HNS.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Generating femtosecond X-ray pulses using an emittance-spoiling foil in free-electron lasers

Generation of femtosecond to sub-femtosecond pulses is attracting much attention in X-ray free-electron laser user community. One method is to use a slotted, emittance-spoiling foil which was proposed before (P. Emma et al., Phys. Rev. Lett. 92, 074801 (2004)) and has been widely used at the Linac Coherent Light Source. Direct experimental characterization of the slotted-foil performance was previously unfeasible due to a lack of appropriate diagnostics. With a recently installed X-band radio-frequency transverse deflector, we are able to characterize the electron bunch spoiling effect and X-ray pulse when using the slotted foil. We show that few-femtosecond X-ray pulses are generated with flexible control of the single-pulse duration or double-pulse separation with comparison to the theoretical model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

The structure of liquid water up to 360 MPa from x-ray diffraction measurements using a high Q-range and from molecular simulation

X-ray diffraction measurements of liquid water are reported at pressures up to 360 MPa corresponding to a density of 0.0373 molecules per Å{sup 3}. The measurements were conducted at a spatial resolution corresponding to Q{sub max} = 16 Å{sup −1}. The method of data analysis and measurement in this study follows the earlier benchmark results reported for water under ambient conditions having a density of 0.0333 molecules per Å{sup 3} and Q{sub max} = 20 Å{sup −1} [J. Chem. Phys. 138, 074506 (2013)] and at 70 °C having a density of 0.0327 molecules per Å{sup 3} and Q{sub max} = 20 Å{sup −1} [J. Chem. Phys. 141, 214507 (2014)]. The structure of water is very different at these three different T and P state points and thus they provide the basis for evaluating the fidelity of molecular simulation. Measurements show that at 360 MPa, the 4 waters residing in the region between 2.3 and 3 Å are nearly unchanged: the peak position, shape, and coordination number are nearly identical to their values under ambient conditions. However, in the region above 3 Å, large structural changes occur with the collapse of the well-defined 2nd shell and shifting of higher shells to shorter distances. The measured structure is compared to simulated structure using intermolecular potentials described by both first-principles methods (revPBE-D3) and classical potentials (TIP4P/2005, MB-pol, and mW). The DFT-based, revPBE-D3, method and the many-body empirical potential model, MB-pol, provide the best overall representation of the ambient, high-temperature, and high-pressure data. The revPBE-D3, MB-pol, and the TIP4P/2005 models capture the densification mechanism, whereby the non-bonded 5th nearest neighbor molecule, which partially encroaches the 1st shell at ambient pressure, is pushed further into the local tetrahedral arrangement at higher pressures by the more distant molecules filling the void space in the network between the 1st and 2nd shells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Machine Learning Based Network Parameter Estimation Using AMI Data

The expansion of distribution power system and the growing penetration of distributed energy resources present new challenges for situational awareness. Calibrating the extended system model with sensor measurements and maintaining the usability is critical for utilities. This paper presents a distribution network parameter estimation (DNPE) approach using machine learning (ML) and metering data that improve the quality of extended distribution power system modeling. The reliability model can improve the ability of endpoint data to be translated into network-level situational awareness in real time and help distribution system operators (DSOs) solve branch flow and voltage problems. In addition, a data analytic and automate processing scheme is proposed to improve the sensor data quality and prevent misleading information. The effectiveness of the proposed method is verified with actual advanced metering infrastructure (AMI) data on a real utility feeder model, while considering the higher penetration of photovoltaic power generation. The test of DNPE and study results are demonstrated in this paper.

Parameter estimation, machine learning, power dist↗
DOE OSTI2016

Repair of a mirror coating on a large optic for high laser damage applications using ion milling and over-coating methods

Here, when an optical coating is damaged, deposited incorrectly, or is otherwise unsuitable, the conventional method to restore the optic often entails repolishing the optic surface, which can incur a large cost and long lead time. We propose three alternative options to repolishing, including (i) burying the unsuitable coating under another optical coating, (ii) using ion milling to etch the unsuitable coating completely from the optic surface and then recoating the optic, and (iii) using ion milling to etch through a number of unsuitable layers, leaving the rest of the coating intact, and then recoating the layers that were etched. Repairs were made on test optics with dielectric mirror coatings according to the above three options. The mirror coatings to be repaired were quarter wave stacks of HfO 2 and SiO 2 layers for high reflection at 1054 nm at 45 deg incidence in P-polarization. One of the coating layers was purposely deposited incorrectly as Hf metal instead of HfO2 to evaluate the ability of each repair method to restore the coating’s high laser-induced damage threshold (LIDT) of 64.0 J/cm 2 . The repaired coating with the highest resistance to laser-induced damage was achieved using repair method (ii) with an LIDT of 49.0 to 61.0 J/cm 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2015

Achieving Hard X-ray Nanofocusing Using a Wedged Multilayer Laue Lens

Here, we report on the fabrication and the characterization of a wedged multilayer Laue lens for x-ray nanofocusing. The lens was fabricated using a sputtering deposition technique, in which a specially designed mask was employed to introduce a thickness gradient in the lateral direction of the multilayer. X-ray characterization shows an efficiency of 27% and a focus size of 26 nm at 14.6 keV, in a good agreement with theoretical calculations. Our results indicate that the desired wedging is achieved in the fabricated structure. Furthermore, we anticipate that continuous development on wedged MLLs will advance x-ray nanofocusing optics to new frontiers and enrich capabilities and opportunities for hard X-ray microscopy.

42 ENGINEERING↗
DOE OSTI2026

Co-sputter deposition of Nb₃Sn layer into SRF cavity using Nb-Sn composite target

Nb₃Sn, with its superior superconducting critical temperature (Tc ~18.3 K) and superheating field (Hsh ~400 mT), is considered a promising material for superconducting radiofrequency (SRF) cavities, offering enhanced cryogenic performance compared to bulk niobium cavities. A Nb₃Sn coating technique has been developed for Nb SRF cavities using co-sputtering of Nb-Sn composite target in a DC cylindrical magnetron sputtering system. The composite target configuration and discharge conditions for co-sputtering were optimized to deposit Nb-Sn films on flat Nb substrates, followed by annealing to form Nb₃Sn. Multiple strategies have been explored to improve the surface homogeneity of the Nb₃Sn coating, including optimizing a two-step annealing process, annealing in Sn vapor, and a light Sn recoating process. A 1.5 µm Nb-Sn co-sputtered film was deposited on the interior of a 2.6 GHz Nb SRF cavity and annealed at 600 °C for 6 h, followed by 950 °C for 1 h. Cryogenic RF testing of the annealed cavity demonstrated a Tc of 17.8 K, confirming the formation of Nb₃Sn. Then, the annealed cavity underwent a light recoating treatment and attained a quality factor (Q0) of 8.5E+08 at 2.0 K.

Accelerator Physics↗