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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

The Mu2e experiment — Searching for charged lepton flavor violation

The Mu2e experiment will search for a Standard Model violating rate of neutrinoless conversion of a muon into an electron in the presence of an aluminum nucleus. Observation of this charged lepton flavor violating process would be an unambiguous sign of new physics. Mu2e will improve upon previous searches for this process by four orders of magnitude. This requires the world’s highest-intensity muon beam, a detector system capable of efficiently reconstructing the 105 MeV/c conversion electron signal, and minimizing sensitivity to background events. A pulsed 8 GeV proton beam strikes a target, producing pions that decay into muons. Beam outside the pulse must be suppressed to < 1 0 – 10 to reduce beam-related backgrounds. The muon beam is guided from the production target along the transport system and onto the aluminum stopping target. Conversion electrons leave the stopping target and propagate inside a solenoidal magnetic field to the tracker and electromagnetic calorimeter. The tracker is a system of straw tube panels filled with Ar/CO 2 at 1 atm that tracks particles inside of a solenoidal B-field and measures their momenta with ~ 100 keV/c resolution to resolve signal events from decay-in-orbit backgrounds. The CsI calorimeter provides E / p and is used to seed the track reconstruction algorithm with σ E / E ~ 10 % and σ t < 500 ps . Additionally, a novel cosmic ray veto with greater than 99.99% efficiency brings the expected number of background events to fewer than one over three years of running. Finally, to normalize the experiment, the stopping target monitor measures the rate of capture photons from muons incident on the stopping target by using a system of high-purity germanium and lanthanum bromide scintillators.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1991

Instantaneous planar visualization of reacting supersonic flows using silane seeding

A new visualization technique for reacting flows has been developed. This technique, which is suitable for supersonic combustion flows, has been demonstrated on a scramjet combustor model. In this application, gaseous silane (SiH4) was added to the primary hydrogen fuel. When the fuel reacted, so did the (SiH4), producing silica (SiO2) particles in situ. The particles were illuminated with a laser sheet formed from a frequency-doubled Nd:YAG laser (532 nm) beam and the Mie scattering signal was imaged. These planar images of the silica Mie scattering provided instantaneous 'maps' of combustion progress within the turbulent reacting flowfield.

Smith, Michael W.↗
DOE OSTI2020

Kinetic beaming in radiative relativistic magnetic reconnection: a mechanism for rapid gamma-ray flares in jets

ABSTRACT Rapid gamma-ray flares pose an astrophysical puzzle, requiring mechanisms both to accelerate energetic particles and to produce fast observed variability. These dual requirements may be satisfied by collisionless relativistic magnetic reconnection. On the one hand, relativistic reconnection can energize gamma-ray emitting electrons. On the other hand, as previous kinetic simulations have shown, the reconnection acceleration mechanism preferentially focuses high energy particles – and their emitted photons – into beams, which may create rapid blips in flux as they cross a telescope’s line of sight. Using a series of 2D pair-plasma particle-in-cell simulations, we explicitly demonstrate the critical role played by radiative (specifically inverse Compton) cooling in mediating the observable signatures of this ‘kinetic beaming’ effect. Only in our efficiently cooled simulations do we measure kinetic beaming beyond one light crossing time of the reconnection layer. We find a correlation between the cooling strength and the photon energy range across which persistent kinetic beaming occurs: stronger cooling coincides with a wider range of beamed photon energies. We also apply our results to rapid gamma-ray flares in flat-spectrum radio quasars, suggesting that a paradigm of radiatively efficient kinetic beaming constrains relevant emission models. In particular, beaming-produced variability may be more easily realized in two-zone (e.g. spine-sheath) set-ups, with Compton seed photons originating in the jet itself, rather than in one-zone external Compton scenarios.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Critical magnetic Reynolds number of the turbulent dynamo in collisionless plasmas

The intracluster medium of galaxy clusters is an extremely hot and diffuse, nearly collisionless plasma, which hosts dynamically important magnetic fields of ~μG strength. Seed magnetic fields of much weaker strength of astrophysical or primordial origin can be present in the intracluster medium. In collisional plasmas, which can be approximated in the magnetohydrodynamical (MHD) limit, the turbulent dynamo mechanism can amplify weak seed fields to strong dynamical levels efficiently by converting turbulent kinetic energy into magnetic energy. However, the viability of this mechanism in weakly collisional or completely collisionless plasma is much less understood. In this study, we explore the properties of the collisionless turbulent dynamo using three-dimensional hybrid-kinetic particle-in-cell simulations. We explore the properties of the collisionless turbulent dynamo in the kinematic regime for different values of the magnetic Reynolds number, Rm, initial magnetic-to-kinetic energy ratio, (E mag /E kin ) i , and initial Larmor ratio, (r Larmor /L box ) i , i.e. the ratio of the Larmor radius to the size of the turbulent system. We find that in the ‘un-magnetized’ regime, (r Larmor /L box ) i > 1, the critical magnetic Reynolds number for the dynamo action Rm crit ≈ 107 ± 3. In the ‘magnetized’ regime, (r Larmor /L box ) i ≲ 1, we find a marginally higher Rm crit = 124 ± 8. We find that the growth rate of the magnetic energy does not depend on the strength of the seed magnetic field when the initial magnetization is fixed. We also study the distribution and evolution of the pressure anisotropy in the collisionless plasma and compare our results with the MHD turbulent dynamo.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Conversion of Syngas and CO2 to Light Olefins using Multi-Functional Catalysts

This report describes our effort in developing a novel zeolite encapsulated metal nanoparticle catalyst for the conversion of syngas to light olefins. We have adopted a ligand assisted synthesis protocol in which first metal-amine was prepared using metal salts and suitable amine ligands. The stable metal-amine complex thus prepared was then used as the seed for the growth of zeolite in alkaline solution. We have optimized the synthesis condition as well as different amine ligand to identify the condition to obtain stable metal-amine complex. Upon synthesis of zeolite, metal particles are encapsulated inside the zeolite in a confined space. We have synthesized both Fe and Co catalyst inside silicalite and chabazite zeolite. Catalytic activity of these catalysts were evaluated for syngas conversion reaction and compared with a baseline catalyst. The activity trend of zeolite encapsulated catalyst show very different activity trend compared to the baseline catalyst. While a distribution of products with different carbon number was obtained with baseline catalyst, zeolite encapsulated catalyst show ethylene as the major product. While ~73% selectivity to C 2 -C 6 products were obtained with cahabazite encapsulated Fe catalyst, only 53% selectivity was obtained for the corresponding products with silica-alumina supported Fe catalyst. Not only higher selectivity, Fe-chabazite also produces only C 2 products (ethylene/ethane) while a distribution of products was obtained with Fe-SiAl catalyst. The significantly different reactivity associated with the chabazite encapsulated Fe catalyst was attributed to the confinement effect. We hypothesized that due to the small size of the pore, only ethylene was obtained as the product.

10 SYNTHETIC FUELS↗
DOE OSTI2024

Advanced Functional Membranes for Noble Gas Management: Fabrication and Testing of Membranes on Porous Support

We selected several porous materials including PNW-24, CC3, SAPO-34, SAPO-56 and PNW-6, as the basis for fabricating membranes for Kr/Xe separation. Initially, we synthesized powder samples of the candidates and confirmed their crystallinity and morphology with X-ray diffraction and microscopy. In the case of PNW-24 and PNW-6, we further confirmed its Xe selectivity through Xe and Kr adsorption experiments, while we relied on literature reports for CC3, SAPO-34 and SAPO-56. We subsequently proceeded to fabricate membranes on porous alumina supports using techniques such as seeded-assisted secondary growth, in-situ growth and solution-processed method. PXRD on the membranes verified that the structures were well-grown on the surface of alumina support, while SEM provided visual confirmation of particle morphology. Importantly, defects were not visually observed in the fabricated membranes, which was further verified with pressure retention tests. We analyzed the separation performance of the synthesized membranes using a dilute gas mixture comprising of xenon, krypton and argon. We focused on PNW-6 to optimize the synthesis reaction time and study the effects of time on gas separation. While more research is necessary to reach a comprehensive conclusion, in alignment with our milestones, we have successfully achieved our goals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2024

Double Power-law Formation by Sequential Particle Acceleration

Spectral double power laws are common in solar high-energy phenomena such as flares and interplanetary energetic-electron events. However, the physical mechanism that produces the changes in power-law index within a single spectrum is unclear. We developed a fully analytical method of forming single power-law spectra from sequential acceleration of particles orbiting inside and hopping between simulated large-scale magnetic islands formed by flare reconnection. Here, we extend the analytical method to the formation of double power-law spectra by assuming sequential acceleration in two successive regions with different acceleration and particle-transport rates. The resulting spectral distribution is continuous and smooth, with a flattening at low energies, two power-law regions at mid-energies, and a steep rollover at high energies. The model provides analytical expressions for the spectral indices, all energy breaks, and normalization constants as functions of just three physical parameters of each acceleration region: (1) the energy gain in each accelerator, (2) the percentage of particles transferred between accelerators, and (3) the number of accelerators visited. One of the most salient predictions of our work is that the spectral index at high (low) energies is determined by the parameters of the first "seed" (second) acceleration region. By constructing the spectral distribution through an iterative analytical process, the evolution toward a double power law is easily characterized and explained. Our analytical model provides tools to interpret space- and ground-based observations from RHESSI, FOXSI, NuSTAR, Solar Orbiter/STIX, EOVSA, and future high-energy missions.

Solar flares↗
DOE OSTI2020

The cosmological bootstrap: weight-shifting operators and scalar seeds

A key insight of the bootstrap approach to cosmological correlations is the fact that all correlators of slow-roll inflation can be reduced to a unique building block - the four-point function of conformally coupled scalars, arising from the exchange of a massive scalar. Correlators corresponding to the exchange of particles with spin are then obtained by applying a spin-raising operator to the scalar-exchange solution. Similarly, the correlators of massless external fields can be derived by acting with a suitable weight-raising operator. In this paper, we present a systematic and highly streamlined derivation of these operators (and their generalizations) using tools of conformal field theory. Our results greatly simplify the theoretical foundations of the cosmological bootstrap program.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The Cosmological Bootstrap: Spinning correlators from symmetries and factorization

We extend the cosmological bootstrap to correlators involving massless spinning particles, focusing on spin-1 and spin-2. In de Sitter space, these correlators are constrained both by symmetries and by locality. In particular, the de Sitter isometries become conformal symmetries on the future boundary of the spacetime, which are reflected in a set of Ward identities that the boundary correlators must satisfy. We solve these Ward identities by acting with weight-shifting operators on scalar seed solutions. Using this weight-shifting approach, we derive three- and four-point correlators of massless spin-1 and spin-2 fields with conformally coupled scalars. Four-point functions arising from tree-level exchange are singular in particular kinematic configurations, and the coefficients of these singularities satisfy certain factorization properties. We show that in many cases these factorization limits fix the structure of the correlators uniquely, without having to solve the conformal Ward identities. The additional constraint of locality for massless spinning particles manifests itself as current conservation on the boundary. We find that the four-point functions only satisfy current conservation if the s, t, and u-channels are related to each other, leading to nontrivial constraints on the couplings between the conserved currents and other operators in the theory. For spin-1 currents this implies charge conservation, while for spin-2 currents we recover the equivalence principle from a purely boundary perspective. For multiple spin-1 fields, we recover the structure of Yang--Mills theory. Finally, we apply our methods to slow-roll inflation and derive a few phenomenologically relevant scalar-tensor three-point functions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

EDGE2D-EIRENE and ERO2.0 predictions of nitrogen molecular break-up and transport in the divertor of JET low-confinement mode plasmas

EDGE2D-EIRENE simulations of nitrogen-seeded partially detached JET L-mode plasmas show that the divertor N I to N V radiation distributions are highly sensitive to the upstream electron density, and less sensitive to changes in the assumed cross-field particle diffusivity for nitrogen ions. The EDGE2D-EIRENE simulations reproduce the peak intensities of N I to N V as measured by vertically viewing divertor filterscopes to within 50 % for a narrow range of the upstream electron density within the experimental uncertainties, while the predicted profiles are narrower than the measured ones. Including nitrogen atoms only in the ERO2.0 simulations implies lower N III and N IV peak intensities by one and two thirds, respectively, compared to EDGE2D-EIRENE. If nitrogen is assumed to recycle exclusively as molecules instead of atoms, ERO2.0 predicts that the N III and N IV intensities in the divertor increase by up to a factor of two and that the time-averaged, volume-integrated number of N 5+ to N 7+ ions in the plasma also increases by approximately a factor of 2.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1972

Project Fog Drops. Part 2: Laboratory investigations

Measurements of the total nucleus concentration and cloud condensation nuclei (CCN) were acquired for several conditions representing both high normal and severe pollution levels for the Los Angeles Basin as well as clean filtered air. The data show that in filtered air there is a large photochemically induced increase in the total particle content within a few minutes after starting the lamp. The concentration of CCN remains near zero, until sufficient coagulation and condensation occurs on the smaller Aitken particles. The addition of gaseous pollutants to filtered air results in large increases in the photochemical production of both the cloud and Aitken nucleus concentration. Fogs were also generated under controlled, reproducible conditions in the cloud chamber and seeded with aerosols of various compounds which form monomolecular surface films at air-water interfaces. Visibility characteristics and droplet data were obtained. The data suggest that droplet growth on treated nuclei can be retarded but fog formation was not significantly altered by the chemical seeding.

Kocmond, W. C.↗
NASA NTRS1985

Research in computer science

Synopses are given for NASA supported work in computer science at the University of Virginia. Some areas of research include: error seeding as a testing method; knowledge representation for engineering design; analysis of faults in a multi-version software experiment; implementation of a parallel programming environment; two computer graphics systems for visualization of pressure distribution and convective density particles; task decomposition for multiple robot arms; vectorized incomplete conjugate gradient; and iterative methods for solving linear equations on the Flex/32.

Ortega, J. M.↗
DOE OSTI2020

Simultaneous Observations of Localized and Global Drift Resonance

In this study, we present Van Allen Probe observations showing that seed (hundreds of keV) and core ( ≳ 1 MeV) electrons can resonate with ultra-low-frequency (ULF) wave modes with distinctive m values simultaneously. An unusual electron energy spectrogram with double-banded resonant structure was recorded by energetic particle, composition, and thermal plasma (ECT)-magnetic electron ion spectrometer (MagEIS) and, meanwhile, boomerang stripes in pitch angle spectrogram appeared at the lower energy band. A localized drift resonance with m = 10 wave component was responsible for the resonant band peaked at ~200 keV while a global drift resonance with m = 3 component gave rise to the upper band resonance peaked at ~1 MeV. Time-Of-Flight on boomerang stripes suggested that the localized drift resonance with ~200 keV electrons was confined within the plasmaspheric plume. Electron flux modulations were reproduced by numerical simulations in good consistency with the observations, supporting the scenario that localized and global drift resonance could coexist in the outer belt electron dynamics simultaneously.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Observations on Microbunching of Electrons in Laser-Driven Plasma Accelerators and Free-Electron Lasers

The periodic longitudinal density modulation of relativistic electrons at the resonant wavelength (microbunching) is a fundamental aspect of free-electron lasers (FELs). In one case, microbunching fractions reached 20% at saturation of a self-amplified spontaneous emission (SASE) FEL resulting in gains of 1 million at 530 nm. In that experiment the $\textit{z}$-dependent gain of coherent optical transition radiation (COTR) was also measured. In laser-driven plasma accelerators (LPAs), microbunching at visible wavelengths has also been recently reported as evidenced by significant COTR enhancements measured in near-field and far-field images on a single shot for the first time. An analytical model for COTR interferometry (COTRI) addresses both cases. The broadband microbunching observed in the LPA case could act as a seed for a SASE FEL experiment with tunability in principle over the visible regime.

43 PARTICLE ACCELERATORS↗
NASA NTRS2002

Ceramic Inclusions In Powder Metallurgy Disk Alloys: Characterization and Modeling

Powder metallurgy alloys are increasingly used in gas turbine engines, especially as the material chosen for turbine disks. Although powder metallurgy materials have many advantages over conventionally cast and wrought alloys (higher strength, higher temperature capability, etc.), they suffer from the rare occurrence of ceramic defects (inclusions) that arise from the powder atomization process. These inclusions can have potentially large detrimental effect on the durability of individual components. An inclusion in a high stress location can act as a site for premature crack initiation and thereby considerably reduce the fatigue life. Because these inclusions are exceedingly rare, they usually don't reveal themselves in the process of characterizing the material for a particular application (the cumulative volume of the test bars in a fatigue life characterization is typically on the order of a single actual component). Ceramic inclusions have, however, been found to be the root cause of a number of catastrophic engine failures. To investigate the effect of these inclusions in detail, we have undertaken a study where a known population of ceramic particles, whose composition and morphology are designed to mimic the 'natural' inclusions, are added to the precursor powder. Surface connected inclusions have been found to have a particularly large detrimental effect on fatigue life, therefore the volume of ceramic 'seeds' added is calculated to ensure that a minimum number will occur on the surface of the fatigue test bars. Because the ceramic inclusions are irregularly shaped and have a tendency to break up in the process of extrusion and forging, a method of calculating the probability of occurrence and expected intercepted surface and embedded cross-sectional areas were needed. We have developed a Monte Carlo simulation to determine the distributions of these parameters and have verified the simulated results with observations of ceramic inclusions found in macro slices from extrusions and forgings. The ultimate goal of this study will be to use probabilistic methods to determine the reliability detriment that can be attributed to these ceramic inclusions.

Bonacuse, Pete↗
NASA NTRS2020

Characterization of Cosmic Grain Analogs Formed at Low Temperature from Small Hydrocarbon Precursors in the NASA Ames COSmIC Facility

Here, we present the results of the first solid-phase ex situ analysis of cosmic grain analogs produced at low temperature (<200 K) in the NASA Ames COsmic SImulation Chamber (COSmIC) from small hydrocarbon precursors, methane (CH4) and acetylene (C2H2), seeded in an argon supersonic jet expansion and submitted to a plasma discharge. The plasma-induced chemical reactions, initiated between the precursor molecules and their atomic and molecular fragments, radicals and ions, produce larger molecules and eventually solid particles that are collected in situ under controlled conditions. Scanning electron microscopy (SEM) imaging was used to provide insight on the morphology and growth structure of the grains produced in COSmIC, and to investigate how the precursors used to produce the grains affect these parameters. This SEM study has shown that under identical experimental conditions with fixed physical and chemical parameters (precursor density, temperature, energy, and reaction time), heavier precursors in the initial mixture produce larger grains and in larger quantity, most likely as a result of a more complex chemistry: most of the grains produced in the Ar/CH4 (95:5) gas mixture ranged from 15 to 385 nm in diameter with an average density of 2.1 grains per sq.μm, while the grains produced in the Ar/C2H2 (95:5) gas mixture ranged from 40 to 650 nm with a density of 3.5 grains per sq.μm. Changes in the morphology were also observed, with grains produced from acetylene (C2H2) precursors tending to be more spherical than grains produced from methane (CH4) precursors. This change in morphology could be associated with different stages of growth formation at low temperature from a more "planar" growth at first, followed by coagulation into more spherical particles. This study demonstrates that the COSmIC experimental setup can be used to investigate carbon grain formation from small gas-phase molecular precursors at low temperature (<200 K), i.e., under a temperature regime that is representative of the dust condensation zone and outer region of circumstellar envelopes.

Ella Sciamma-O'Brien↗
DOE OSTI2023

Los Alamos National Laboratory Double Shell Program Target Development

The Double Shell Program at Los Alamos National Laboratory is studying an alternative platform for achieving robust alpha-particle heating at the National Ignition Facility. Double shells benefit from having a low convergence ratio and lower predicted temperature for achieving volume ignition. The joint required to assemble a double shell has an imperfection in the outer shell that seeds instabilities that can greatly impact the inner capsule’s implosion at bang time. Furthermore, different variations of the shape and placement of the joint were implemented with improvements in the quality of the machining leading to measurable improvements in yield. High-Z coatings on the outer joint mitigated the impact of the 1- to 2-μm gap sometimes found in double shell assemblies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗