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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

O–X mode conversion in a non-symmetric torus at electron cyclotron frequencies

Previous work on this topic, [Weitzner, Phys. Plasmas 11, 866 (2004)], applicable in a system with toroidal symmetry, is here extended to the case of a non-symmetric background equilibrium state. Maxwell's equations with the cold plasma dielectric tensor are used to represent the plasma-electromagnetic wave interaction. Away from the mode conversion region, geometrical optics adequately characterizes the wave propagation. A new, simpler derivation of the wave equations in the mode conversion region is given. Aside from one very special case in which a general plasma equilibrium behaves like a stratified medium, the previous results apply and highly effective mode conversion is found. The matching of the mode conversion solution to the geometrical optics solution, not previously examined, is discussed. A relatively weak condition on the perpendicular wave number near the resonance layer is found. Provided that the perpendicular wave number is small, it tends to zero at the mode conversion layer and the solutions match effectively.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Three-dimensional core-collapse supernova models with phenomenological treatment of neutrino flavor conversions

Abstract We perform three-dimensional supernova simulations with a phenomenological treatment of neutrino flavor conversions. We show that the explosion energy can increase to as high as $\sim 10^{51}$ erg depending on the critical density for the onset of flavor conversions, due to a significant enhancement of the mean energy of electron antineutrinos. Our results confirm previous studies showing such energetic explosions, but for the first time in three-dimensional configurations. In addition, we predict neutrino and gravitational wave (GW) signals from a nearby supernova explosion aided by flavor conversions. We find that the neutrino event number decreases because of the reduced flux of heavy-lepton neutrinos. In order to detect GWs, next-generation GW telescopes such as Cosmic Explorer and the Einstein Telescope are needed even if the supernova event is located at the Galactic Center. These findings show that the neutrino flavor conversions can significantly change supernova dynamics and highlight the importance of further studies on the quantum kinetic equations to determine the conditions of the conversions and their asymptotic states.

Mori, Kanji↗
DOE OSTI2024

Photon Frequency Conversion in High-Q Superconducting Resonators: Axion Electrodynamics, QED, and Nonlinear Meissner Radiation

High-Q superconducting resonators have been proposed and developed as detectors of light-by-light scattering mediated by the hypothesized axion or virtual electron–positron pairs in quantum electrodynamics: the Euler–Heisenberg (EH) interaction. Photon frequency and mode conversion is central to the scheme for detecting such rare events. Superconducting resonators are nonlinear devices. The Meissner screening currents that confine the electromagnetic fields to the vacuum region of a superconducting RF cavity are nonlinear functions of the EM field at the vacuum–superconducting interface, and as a result can generate source currents and frequency conversion of microwave photons in the cavity. In this report we consider photon frequency and mode conversion in superconducting resonators with high quality factors from Meissner currents in single- and dual-cavity setups proposed for axion and QED searches based on light-by-light scattering. In a single cavity with two pump modes, photon frequency conversion by the Meissner screening current dominates photon generation by the EH interaction for cavities with Q≲1012⁠. The Meissner currents also generate background photons that limit the operation of the resonator for axion detection in three-mode, single-cavity setups. We also consider the leakage of photons from pump modes into the signal mode for both axion- and EH-mediated light-by-light scattering. Photon frequency conversion by the EH interaction can compete with Meissner and leakage radiation in ultra-high-Q cavities that are beyond the current state of the art. Meissner radiation and leakage backgrounds can be suppressed in dual-cavity setups with appropriate choices for pump and spectator modes, as well as the single-cavity setup proposed for heterodyne detection of galactic axion dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Raman Wavelength Conversion in Ionic Liquids

Here, we explore the use of room-temperature ionic liquids (ILs) as Raman wavelength converters. ILs provide an engineerable framework to design suitable liquids for wavelength conversion over a broad spectral range, through careful selection of the molecular structures of the IL anions and cations so that specific characteristics can be obtained, such as a desirable Raman shift, low Brillouin scattering, and good optical transmission in the pump and Stokes wavelengths. Applying such criteria, we demonstrate that 1-ethyl-3-methylimidazolium dicyanamide (EMIM DCA) is an effective medium for conversion of 532-nm pulses from a Q-switched Nd :YAG laser to 603 nm. This corresponds to an approximate 2200 cm –1 shift, which can be used to generate mid-infrared radiation through subsequent difference frequency generation for optical pumping of CO 2 lasers. Threefold-higher Raman conversion efficiency is obtained in EMIM DCA compared with water under identical conditions in a proof-of-principle single-pass conversion setup, resulting in an efficient generation of multimillijoule, <6 ns duration, high-quality orange laser pulses in a wavelength region that is difficult to access at high energies. Consequently, we examine ILs representing two other classes of Raman-active functional groups and obtain conversion up to the fifth-order Stokes shift and first anti-Stokes shift. Through the tunable selection of their components and their useful dynamical properties, ILs provide a platform for efficient, simple, and alignment-tolerant high-energy Raman shifting with numerous industrial and technological applications.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Two first-order phase transitions in hybrid compact stars: Higher-order multiplet stars, reaction modes, and intermediate conversion speeds

We study compact stars with hybrid equations of state consisting of a nuclear outer region and two nested quark phases, each separated from the lower density phase by a strong first-order phase transition. The stability of these models is determined by calculating their radial oscillation modes with different conversion rates between adjacent phases and hence junction conditions for the modes at the phase separation interface between them. In the case when the timescale of transition is faster than the period of oscillations, we recover the traditional stability criterion implying that ∂M/∂ρ c > 0 on the stable branch(es), where M is the mass and ρ c is the central density. In the opposite limit of slow conversion, we find stable stellar multiplets beyond triplets consisting of stars that are stable by the usual criterion plus slow-conversion (denoted by s) hybrid stars with ∂M/∂ρ c < 0 that are stabilized due to an alternative junction condition on the fluid displacement field at the interface reflecting the slow rate of conversion. We also study the properties of the reaction mode, the radial mode that only exists for stars with rapid (abbreviated by r) phase transitions, in stars with either two rapid phase transitions or alternating rapid and slow phase transitions for the first time. Here, the implications of alternative junction conditions are also examined, with these conditions generally being found to provide stability properties similar to those for a slow conversion rate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Distinguishing Charged Lepton Flavor Violation Scenarios with Inelastic 𝜇 → 𝑒 Conversion

The Mu2e and COMET experiments are expected to improve existing limits on charged lepton flavor violation (CLFV) by roughly 4 orders of magnitude. 𝜇 → 𝑒 conversion experiments are typically optimized for electrons produced without nuclear excitation, as this maximizes the electron energy and minimizes backgrounds from the free decay of the muon. Here we argue that Mu2e and COMET will be able to extract additional constraints on CLFV from inelastic 𝜇 → 𝑒 conversion, given the 27 Al target they have chosen and backgrounds they anticipate. We describe CLFV scenarios in which inelastic CLFV can induce measurable distortions in the near-endpoint spectrum of conversion electrons, including cases where certain contributing operators cannot be probed in elastic 𝜇 → 𝑒 conversion. We extend the nonrelativistic EFT treatment of elastic 𝜇 → 𝑒 conversion to include the new nuclear operators needed for the inelastic process, evaluate the associated nuclear response functions, and describe several new-physics scenarios where the inelastic process can provide additional information on CLFV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

TU-EF-304-06: A Comparison of CT Number to Relative Linear Stopping Power Conversion Curves Used by Proton Therapy Centers

Purpose: To compare the CT Number (CTN) to Relative Linear Stopping Power (RLSP) conversion curves used by 14 proton institutions in their dose calculations. Methods: The proton institution’s CTN to RLSP conversion curves were collected by the Imaging and Radiation Oncology Core (IROC) Houston QA Center during its on-site dosimetry review audits. The CTN values were converted to scaled CT Numbers. The scaling assigns a CTN of 0 to air and 1000 to water to allow intercomparison. The conversion curves were compared and the mean curve was calculated based on institutions’ predicted RLSP values for air (CTN 0), lung (CTN 250), fat (CTN 950), water (1000), liver (CTN 1050), and bone (CTN 2000) points. Results: One institution’s curve was found to have a unique curve shape between the scaled CTN of 1025 to 1225. This institution modified its curve based on the findings. Another institution had higher RLSP values than expected for both low and high CTNs. This institution recalibrated their two CT scanners and the new data placed their curve closer to the mean of all institutions. After corrections were made to several conversion curves, four institutions still fall outside 2 standard deviations at very low CTNs (100–200), and two institutions fall outside between CTN 850–900. The largest percent difference in RLSP values between institutions for the specific tissues reviewed was 22% for the lung point. Conclusion: The review and comparison of CTN to RLSP conversion curves allows IROC Houston to identify any outliers and make recommendations for improvement. Several institutions improved their clinical dose calculation accuracy as a Result of this review. There is still area for improvement, particularly in the lung area of the curve. The IROC Houston QA Center is supported by NCI grant CA180803.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Highly Efficient Non-Oxidative Methane Conversion with Continuous Hydrogen Removal

A non-oxidative methane conversion catalytic system has been successfully developed. Ball-milling and annealing above 1973 K are necessary in order to synthesize the unique methane activation catalyst. Characterization and evaluation of catalysts shows that the surface area should be carefully controlled to minimize coke deposition. The influence of temperature, pressure, space velocity and hydrogen concentration on catalytic process was systematically studied. The reaction conditions were optimized to a combination of 1323 K, ambient pressure and a space velocity of 4900 ml/g·h. A process, using 0.5% Fe/SiO 2 catalyst under these conditions, yield a methane conversion of 15.62%, with product distribution of 40.05% C 2 , 26.48% BTX and 10.7% naphthalene and demonstrated stable operation of at least 50 hours. This result meets the milestone in the phase I proposal. A non-oxidative methane catalyst-integrated SOFC reactor was accomplished, using nickel-free cells of both ScSZ oxygen-ion conductor and BZY proton conductor. With in-situ hydrogen removal enabled by SOFC, hydrogen concentration in the reactor was effectively reduced, shifting reaction equilibrium and boosting methane conversion. However, due to the high temperature requirement of this reaction, most available proton-conducting SOFCs become oxygen-ion conducting, leading to side reactions and counteracting the benefits from hydrogen removal. To take advantage of the enhanced oxygen-ion conductance of SOFC at high temperatures, we have also paired the nickel-free SOFCs with high-performance oxidative coupling of methane (OCM) catalysts. The SOFC-OCM tubular membrane reactor, employing a Mn-Ce-Na 2 WO 4 /SiO 2 -based catalyst, demonstrates a remarkable performance of 60.7% methane conversion with 41.6% C 2 + selectivity, 5.8 ethylene-to-ethane ratio and 19.4% ethylene yield. The use of integrated SOFC-OCM reactor enables better hydrocarbon selectivity and higher ethylene-to-ethane ratio, eliminating the need of an expensive air separation unit and preventing the direct co-feed of explosive methane-oxygen mixture. We believe this presents a great promise towards commercialization as an advanced methane conversion technology.

02 PETROLEUM↗
DOE OSTI2023

Strategies for Achieving the DOE Hydrogen Shot Goal: Thermal Conversion Approaches

In July 2021 the United States (U.S.) Department of Energy (DOE) launched the first of a series of Department-wide Energy Earthshot goals designed to accelerate breakthroughs of more abundant, affordable, and reliable clean energy solutions within the decade. The Hydrogen Shot goal seeks to reduce the cost of clean hydrogen to $\$$1 per 1 kilogram in 1 decade ("1 1 1"). Today, thermal conversion of fossil fuels represents the predominant, lowest cost method of hydrogen production. In 2020 approximately 75 percent of global, dedicated hydrogen production was produced via fossil fuels using thermal conversion approaches such as steam reforming and gasification. However, carbon management techniques such as CO 2 capture and sequestration (CCS) and pyrolysis are not widely represented in the current fossil-based hydrogen production fleet. Lowering the cost of clean hydrogen production from commercial and advanced thermal conversion-based technologies is critical for successfully achieving the Hydrogen Shot goal. This report presents the findings from an initial screening analysis of several scenarios that explore cost drivers related to clean hydrogen production. The screening encompasses commercially available and developing thermal conversion technology alternatives as well as factors exogenous to the plant such as feedstock/byproduct pricing, CO 2 pipeline and storage infrastructure costs, and scale to assess potential pathways towards meeting the Hydrogen Shot goal. Additionally, this report presents initial Research and Development (R&D) strategies to advance thermal conversion technology towards meeting the Hydrogen Shot goal.

08 HYDROGEN↗
DOE OSTI2023

Hydrogen Shot Technology Assessment: Thermal Conversion Approaches

In July 2021 the United States (U.S.) Department of Energy (DOE) launched the first of a series of Department-wide Energy Earthshot™ goals designed to accelerate breakthroughs of more abundant, affordable, and reliable clean energy solutions within the decade. The Hydrogen Shot goal seeks to reduce the cost of clean hydrogen to $\$$1 per 1 kilogram in 1 decade ("1 1 1"). Today, thermal conversion of fossil fuels represents the predominant, lowest cost method of hydrogen production. In 2020 approximately 75 percent of global, dedicated hydrogen production was produced via fossil fuels using thermal conversion approaches such as steam reforming and gasification. However, carbon management techniques such as CO 2 capture and sequestration (CCS) and pyrolysis are not widely represented in the current fossil-based hydrogen production fleet. Lowering the cost of clean hydrogen production from commercial and advanced thermal conversion-based technologies is critical for successfully achieving the Hydrogen Shot goal. This report presents the findings from an initial screening analysis of several scenarios that explore cost drivers related to clean hydrogen production. The screening encompasses commercially available and developing thermal conversion technology alternatives as well as factors exogenous to the plant such as feedstock/byproduct pricing, CO 2 pipeline and storage infrastructure costs, and scale to assess potential pathways towards meeting the Hydrogen Shot goal. Additionally, this report presents initial Research and Development (R&D) strategies to advance thermal conversion technology towards meeting the Hydrogen Shot™ goal.

08 HYDROGEN↗
DOE OSTI2024

Microwave-Assisted Conversion of 1,6-Hexanediol into Polycarbonate

The conversion of carbon dioxide into higher value chemicals is a viable way to support sustainability and net-zero economy goals. Of the different CO2 conversion routes, direct conversion offers a simplified process, lower reaction temperatures, and thus low energy input. Alcohols can be directly combined with CO2 to produce polycarbonates, e.g., DMC (dimethyl carbonate) formation from methanol and CO2. Recently CO2 and 1,6-hexanediol were shown to convert into poly(hexamethylene carbonate)diol using an atmospheric flow based process in single step. For these conversions, CeO2-based catalysts are widely used due to the abundance of oxygen vacancies that are believed to be the active sites for this reaction. Microwave (MW) heating is a unique approach that can provide selective volume-based heating and enhanced reaction rates and/or selectivities. For the current work, CO2 and diol conversion into polymers were investigated on different CeO2 catalysts under microwave heating and the performance was compared against conventional heating. The reaction products were analyzed using infrared spectroscopy (IR) and nuclear magnetic resonance (NMR) spectroscopy. Preliminary results showed microwaves irradiation produced faster rates of polycarbonate production as evidenced by IR data.

Kanitkar, Swarom↗
DOE OSTI2026

Kinetics Modeling and Reactor Design Study of Glucose-to-Terpenes Cell-Free Conversion

Cell-free systems offer many advantages over traditional biological conversion by eliminating biological growth constraints. It also offers easy manipulation and finetuning of the reaction conditions for each individual enzyme. The conversion of cellulosic glucose to Limonene, a terpene, is a promising pathway for producing fuels and chemicals. Recent advances in developing cell-free systems focuses on bench scale optimization of terpene yield and to demonstrate its feasibility towards commercialization [1,2]. There is significant knowledge gap regarding reaction kinetics of these cell-free systems to further study how it will perform at larger scale. We present here, our studies on reaction kinetics and reactor design implications of cell-free glucose to Limonene conversion to facilitate the further development and commercialization of this process. We developed a novel kinetic model based on the metabolic-network structure of the cell-free system with multi-substrate reversible Michaelis-Menten rate law. To estimate kinetic parameters for this system of rate equations, we employed Bayesian optimization to perform global search with the assistance of gaussian processes to balance exploration and exploitation. The model parameters estimated showed good results compared with experimental data. The estimated parameters were used to perform sensitivity analysis. We found that Hexokinase is one of the most critical enzymes that affect the conversion of the glucose. We also observed that abundance of co-factors is also critical to the conversion of glucose to limonene. We investigated packed bed reactors with enzymes immobilized on the surface of particles to convert glucose stream into Limonene for larger scale production. The reactor design such as particle size, enzyme loading, and flow rate are found to be critical for improving yields. [1] Dudley, Q.M., Nash, C.J. and Jewett, M.C., 2019. Synthetic Biology, 4(1), p.ysz003. [2] Korman, T.P., Opgenorth, P.H. and Bowie, J.U., 2017. Nature communications, 8(1), p.15526.

09 BIOMASS FUELS↗
NASA NTRS1983

Limits to solar power conversion efficiency with applications to quantum and thermal systems

An analytical framework is presented that permits examination of the limit to the efficiency of various solar power conversion devices. Thermodynamic limits to solar power efficiency are determined for both quantum and thermal systems, and the results are applied to a variety of devices currently considered for use in space systems. The power conversion efficiency for single-threshold energy quantum systems receiving unconcentrated air mass zero solar radiation is limited to 31 percent. This limit applies to photovoltaic cells directly converting solar radiation, or indirectly, as in the case of a thermophotovoltaic system. Photoelectrochemical cells rely on an additional chemical reaction at the semiconductor-electrolyte interface, which introduces additional second-law demands and a reduction of the solar conversion efficiency. Photochemical systems exhibit even lower possible efficiencies because of their relatively narrow absorption bands. Solar-powered thermal engines in contact with an ambient reservoir at 300 K and operating at maximum power have a peak conversion efficiency of 64 percent, and this occurs for a thermal reservoir at a temperature of 2900 K. The power conversion efficiency of a solar-powered liquid metal magnetohydrodydnamic generator, a solar-powered steam turbine electric generator, and an alkali metal thermoelectric converter is discussed.

Byvik, C. E.↗
NASA NTRS1985

Static conversion systems

Historically, all space power systems that have actually flown in space have relied on static energy conversion technology. Thus, static conversion is being considered for space nuclear power systems as well. There are four potential static conversion technologies which should be considered. These include: the alkali metal thermoelectric converter (AMTEC), the thermionic converter, the thermoelectric converter, and the thermophotovoltaic converter (TPV). These four conversion technologies will be described in brief detail along with their current status and development needs. In addition, the systems implications of using each of these conversion technologies with a space nuclear reactor power system will be evaluated and some comparisons made.

Ewell, R.↗
NASA NTRS1989

Performance impacts of look-ahead execution in the conversation scheme

The look-ahead execution approach, which allows participant processes that exist early to exit from a conversation before other participants finish their conversation activities, is presented here as a fundamental approach to reducing the synchronization overhead. Queuing network models are developed for systems operating under the basic conversation execution scheme and systems operating under the look-ahead execution scheme. Based on the models, various performance indicators such as the system throughput, the average number of processors idling inside a conversation due to the synchronization required, and the average time spent in conversation are evaluated numerically for different application environments. The results provide insights into the extent of benefits provided by the look-ahead execution approach.

Kim, K. H.↗
NASA NTRS1989

Laser energy conversion

The conversion of laser energy to other, more useful, forms is an important element of any space power transmission system employing lasers. In general the user, at the receiving sight, will require the energy in a form other than laser radiation. In particular, conversion to rocket power and electricity are considered to be two major areas where one must consider various conversion techniques. Three systems (photovoltaic cells, MHD generators, and gas turbines) have been identified as the laser-to-electricity conversion systems that appear to meet most of the criteria for a space-based system. The laser thruster also shows considerable promise as a space propulsion system. At this time one cannot predict which of the three laser-to-electric converters will be best suited to particular mission needs. All three systems have some particular advantages, as well as disadvantages. It would be prudent to continue research on all three systems, as well as the laser rocket thruster. Research on novel energy conversion systems, such as the optical rectenna and the reverse free-electron laser, should continue due to their potential for high payoff.

Jalufka, N. W.↗
NASA NTRS1994

High efficiency GaP power conversion for Betavoltaic applications

AstroPower is developing a gallium phosphide (GaP) based energy converter optimized for radio luminescent light-based power supplies. A 'two-step' or 'indirect' process is used where a phosphor is excited by radioactive decay products to produce light that is then converted to electricity by a photovoltaic energy converter. This indirect conversion of beta-radiation to electrical energy can be realized by applying recent developments in tritium based radio luminescent (RL) light sources in combination with the high conversion efficiencies that can be achieved under low illumination with low leakage, gallium phosphide based devices. This tritium to light approach is inherently safer than battery designs that incorporate high activity radionuclides because the beta particles emitted by tritium are of low average energy and are easily stopped by a thin layer of glass. GaP layers were grown by liquid phase epitaxy and p/n junction devices were fabricated and characterized for low light intensity power conversion. AstroPower has demonstrated the feasibility of the GaP based energy converter with the following key results: 23.54 percent conversion efficiency under 968 muW/sq cm 440 nm blue light, 14.59 percent conversion efficiency for 2.85 muW/sq cm 440 nm blue light, and fabrication of working 5 V array. We have also determined that at least 20 muW/sq cm optical power is available for betavoltaic power systems. Successful developments of this device is an enabling technology for low volume, safe, high voltage, milliwatt power supplies with service lifetimes in excess of 12 years.

Sims, Paul E.↗
NASA NTRS2000

Characterization of Molybdate Conversion Coatings for Aluminum Alloys by Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy (EIS) was used to investigate the corrosion inhibiting properties of newly developed proprietary molybdate conversion coatings on aluminum alloy 2024-T3 under immersion in aerated 5% (w/w) NaCl. Corrosion potential and EIS measurements were gathered for six formulations of the coating at several immersion times for two weeks. Nyquist as well as Bode plots of the data were obtained. The conversion-coated alloy panels showed an increase in the corrosion potential during the first 24 hours of immersion that later subsided and approached a steady value. Corrosion potential measurements indicated that formulations A, D, and F exhibit a protective effect on aluminum 2024-T3. The EIS spectra of the conversion-coated alloy were characterized by an impedance that is higher than the impedance of the bare alloy at all the immersion times. The low frequency impedance, Z(sub lf) (determined from the value at 0.05 Hz) for the conversion-coated alloy was higher at all the immersion times than that of the bare panel. This indicates improvement of corrosion resistance with addition of the molybdate conversion coating. Scanning electron microscopy (SEM) revealed the presence of cracks in the coating and the presence of cubic crystals believed to be calcium carbonate. Energy dispersive spectroscopy (EDS) of the test panels revealed the presence of high levels of aluminum, oxygen, and calcium but did not detect the presence of molybdenum on the test panels. X-ray photoelectron spectroscopy (XPS) indicated the presence of less than 0.01 atomic percent molybdenum on the surface of the coating.

Calle, Luz Marina↗