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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 235 records · Page 13

All sources NASA NTRS DOE OSTI

NASA NTRS2013

Computational Studies of Magnetic Nozzle Performance

An extensive literature review of magnetic nozzle research has been performed, examining previous work, as well as a review of fundamental principles. This has allow us to catalog all basic physical mechanisms which we believe underlie the thrust generation process. Energy conversion mechanisms include the approximate conservation of the magnetic moment adiabatic invariant, generalized hall and thermoelectric acceleration, swirl acceleration, thermal energy transformation into directed kinetic energy, and Joule heating. Momentum transfer results from the interaction of the applied magnetic field with currents induced in the plasma plume., while plasma detachment mechanisms include resistive diffusion, recombination and charge exchange collisions, magnetic reconnection, loss of adiabaticity, inertial forces, current closure, and self-field detachment. We have performed a preliminary study of Hall effects on magnetic nozzle jets with weak guiding magnetic fields and weak expansions (p(sub jet) approx. = P(sub background)). The conclusion from this study is that the Hall effect creates an azimuthal rotation of the plasma jet and, more generally, creates helical structures in the induced current, velocity field, and magnetic fields. We have studied plasma jet expansion to near vacuum without a guiding magnetic field, and are presently including a guiding magnetic field using a resistive MHD solver. This research is progressing toward the implementation of a full generalized Ohm's law solver. In our paper, we will summarize the basic principle, as well as the literature survey and briefly review our previous results. Our most recent results at the time of submittal will also be included. Efforts are currently underway to construct an experiment at the University of Michigan Plasmadynamics and Electric Propulsion Laboratory (PEPL) to study magnetic nozzle physics for a RF-thruster. Our computational study will work directly with this experiment to validate the numerical model, in order to study magnetic nozzle physics and optimize magnetic nozzle design. Preliminary results from the PEPL experiment will also be presented.

Ebersohn, Frans H.↗

NASA NTRSDate not supplied

Exploring Cryogenic Propellant Behavior in Low-Gravity Environments, Insights from the Saturn AS-203 Vent Experiments and CFD Analysis

In the 1960s, NASA embarked on a series of groundbreaking flight tests on the Saturn AS-203, aiming to understand the complex dynamics of propellants in the distinctive low-gravity lunar environment. These tests centered on venting experiments, subjecting cryogenic liquid hydrogen to conditions beneath its saturation pressure while accelerating the vehicle to manage the propellant's positioning. During these experiments, NASA meticulously scrutinized the propellant tank using a suite of instruments, including temperature and pressure sensors, as well as a camera placed internal to the liquid hydrogen tank. The outcomes provided anecdotal evidence revealing the phenomenon of boiling along the tank's walls and the intriguing formation of liquid globules and droplets in the ullage during the venting process. Notably, the substantial drop in liquid temperature during these tests suggests adiabatic cooling as liquid hydrogen evaporates. This evaporation leads to a cooling of the remaining hydrogen due to the heat it releases. This paper presents the outcomes of our initial analysis, wherein CFD models were used to simulate the observed boiling phenomena and the bulk movement of the liquid hydrogen propellant, both qualitatively and quantitatively. The implications of these findings may extend to mission and vehicle designers, providing invaluable insights for crafting more efficient and effective in-space propulsion systems utilizing cryogenic propellant including impacts to vehicle control systems. Understanding propellant behavior under these conditions may better inform GNC teams, ensuring more stable vehicle operations when utilizing cryogenic propellants. This includes essential considerations for cryogenic propellant transfer and storage systems, integral to NASA's forthcoming Artemis missions. While we recognize the challenges tied to CFD models, this study represents a step forward, highlighting current progress and signaling the potential for refining our predictive understanding in the future.

Computational Fluid Dynamics↗

NASA NTRSDate not supplied

Exploring Cryogenic Propellant Behavior in Low-Gravity Environments, Insights from the Saturn AS-203 Vent Experiments and CFD Analysis

Computational Fluid Dynamics↗

DOE OSTI2014

Electronic and optical properties of pure and modified diamondoids studied by many-body perturbation theory and time-dependent density functional theory

Diamondoids are small diamond nanoparticles (NPs) that are built up from diamond cages. Unlike usual semiconductor NPs, their atomic structure is exactly known, thus they are ideal test-beds for benchmarking quantum chemical calculations. Their usage in spintronics and bioimaging applications requires a detailed knowledge of their electronic structure and optical properties. In this paper, we apply density functional theory (DFT) based methods to understand the electronic and optical properties of a few selected pure and modified diamondoids for which accurate experimental data exist. In particular, we use many-body perturbation theory methods, in the G{sub 0}W{sub 0} and G{sub 0}W{sub 0}+BSE approximations, and time-dependent DFT in the adiabatic local density approximation. We find large quasiparticle gap corrections that can exceed thrice the DFT gap. The electron-hole binding energy can be as large as 4 eV but it is considerably smaller than the GW corrections and thus G{sub 0}W{sub 0}+BSE optical gaps are about 50% larger than the Kohn-Sham (KS) DFT gaps. We find significant differences between KS time-dependent DFT and GW+BSE optical spectra on the selected diamondoids. The calculated G{sub 0}W{sub 0} quasiparticle levels agree well with the corresponding experimental vertical ionization energies. We show that nuclei dynamics in the ionization process can be significant and its contribution may reach about 0.5 eV in the adiabatic ionization energies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Disentangling conical intersection and coherent molecular dynamics in methyl bromide with attosecond transient absorption spectroscopy

Attosecond probing of core-level electronic transitions provides a sensitive tool for studying valence molecular dynamics with atomic, state, and charge specificity. In this report, we employ attosecond transient absorption spectroscopy to follow the valence dynamics of strong-field initiated processes in methyl bromide. By probing the 3d core-to-valence transition, we resolve the strong field excitation and ensuing fragmentation of the neutral σ* excited states of methyl bromide. The results provide a clear signature of the non-adiabatic passage of the excited state wavepacket through a conical intersection. We additionally observe competing, strong field initiated processes arising in both the ground state and ionized molecule corresponding to vibrational and spin-orbit motion, respectively. The demonstrated ability to resolve simultaneous dynamics with few-femtosecond resolution presents a clear path forward in the implementation of attosecond XUV spectroscopy as a general tool for probing competing and complex molecular phenomena with unmatched temporal resolution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

An ATLAS distributed computing architecture for HL-LHC

The ATLAS collaboration started a process to understand the computing needs for the High Luminosity LHC era. Based on our best understanding of the computing model input parameters for the HL-LHC data taking conditions, results indicate the need for a larger amount of computational and storage resources with respect to the projection of constant yearly budget for computing in 2026. Filling the gap between the projection and the needs will be one of the challenges in preparation for HL-LHC. While the gains from improvements in offline software will play a crucial role in this process, a different model for data processing, management, access and bookkeeping should also be envisaged to optimise resource usage. In this contribution we will describe a straw man of this model, founded on basic principles such as single event level granularity for data processing and virtual data. We will explain how the current architecture will evolve adiabatically into the future distributed computing system, through the prototyping of building blocks that would be integrated in the production infrastructure as early as possible, so that specific use cases can be covered much earlier with respect to the HL-LHC time scale. We will also discuss how such system would adapt to and drive the evolution of the WLCG infrastructure in terms of facilities and services.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1974

Magnetic storm dynamics of the thermosphere

A theoretical study of the Dst component of magnetic storms is presented. The dynamic characteristics are found significantly different for Joule dissipation and electron precipitation, leading to the conclusion that the former is probably the predominant heat source for the upper thermosphere. Composition measurements on OGO-6, which reveal markedly different characteristics in N2, O and He, can be explained on the basis of energy advection and diffusive mass transport by thermospheric winds. Essential features in the F2-region response are explicable in terms of these dynamic processes. Electric field induced motions are estimated and it is concluded that resultant adiabatic heating could be significant.

Mayr, H. G.↗

NASA NTRS1977

Role of condensed phase details in the oscillatory combustion of composite propellants

The response functions of composite propellants are theoretically derived, including explicitly the pressure-dependent degradation term in the condensed phase, hypothesizing that the overall rate-limiting reactions are in the relatively low temperature condensed phase. The method of 'inner' and 'outer' expansions with the reduced activation energy as the singular perturbation parameter has been employed. The results cover subsurface reactions with and without surface reactions, adiabatic and uniform-combustion models for the quasi-steady gas phase processes. The response functions display several experimentally observed features like dependence on mean pressure and the instability behavior of some 'zero-n' propellants.

Kumar, R. N.↗

NASA NTRS1985

Near-conjugate observations of inverted-V electron precipitation using DE 1 and DE 2

A major focus of auroral research has been related to the inverted-V electron precipitation event, distinguished by the 'inverted-V' variation of peak energy flux in an energy-time spectrogram. Thieman and Hoffman (1984), in an examination of plasma data from near-conjugate DE 1/2 passes in the southern hemisphere, have found that some inverted-V events remain reasonably stable over a time span of up to 18 min, while other events change over shorter time periods. The present investigation has the objective to study quantitatively the energization of inverted-V electron fluxes and to compare the results with predictions from adiabatic acceleration by an electrostatic field. The obtained results suggest that the turbulent processes might contirbute minimally to the energy flux of secondary electrons for some events, but significantly for others.

Lin, C. S.↗

NASA NTRS1989

The role of diabatic heating in maintaining the upper-tropospheric baroclinic zone in the South Pacific

The four-dimensional structure of a region that encompasses the South Pacific Convergence Zone (SPCZ) is presently examined using a modified set of FGGE level III-b analyses, during the January 10-18, 1979 period when two cyclones formed in the tropics and propagated southeastward along the SPCZ to middle latitudes. An effort is made to ascertain the significance of kinematic and thermodynamic processes in maintaining the the upper baroclinic region coincident with the subtropical jet. A partitioned form of the frontogenetical function, used to diagnose the adiabatic and diabatic contributions to the maintenance of baroclinicity in the SPCZ's vicinity, indicates a major balance between the frontogenetical contribution by differential diabatic heating and the opposing diabatic tilting processes.

Robertson, Franklin R.↗

NASA NTRS1995

Observational and numerical studies of extreme frontal scale contraction

The general objective of this effort is to increase understanding of how frontal scale contraction processes may create and sustain intense mesoscale precipitation along intensifying cold fronts. The five-part project (an expansion of the originally proposed two-part project) employed conventional meteorological data, special mesoscale data, remote sensing measurements, and various numerical models. First an idealized hydrostatic modeling study of the scale contraction effects of differential cloud cover on low-level frontal structure and dynamics was completed and published in a peer-reviewed journal. The second objective was to complete and publish the results from a three dimensional numerical model simulation of a cold front in which differential sensible heating related to cloud coverage patterns was apparently crucial in the formation of a severe frontal squall line. The third objective was to use a nonhydrostatic model to examine the nonlinear interactions between the transverse circulation arising from inhomogeneous cloud cover, the adiabatic frontal circulation related to semi-geostrophic forcing, and diabatic effects related to precipitation processes, in the development of a density current-like microstructure at the leading edge of cold fronts. Although the development of a frontal model that could be used to initialize such a primitive equation model was begun, we decided to focus our efforts instead on a project that could be successfully completed in this short time, due to the lack of prospects for continued NASA funding beyond this first year (our proposal was not accepted for future funding). Thus, a fourth task was added, which was to use the nonhydrostatic model to test tentative hypotheses developed from the most detailed observations ever obtained on a density current (primarily sodar and wind profiler data). These simulations were successfully completed, the findings were reported at a scientific conference, and the results have recently been submitted to a peer-reviewed journal. The fifth objective was to complete the analysis of data collected during the Cooperative Oklahoma Profiler Studies (COPS-91) field project, which was supported by NASA. The analysis of the mesoscale surface and sounding data, Doppler radar imagery, and other remote sensing data from multi frequency wind profiler, microwave radiometer, and the Radio Acoustic Sounding System has been completed. This study is a unique investigation of processes that caused the contraction of a cold front to a microscale zone exhibiting an undular bore-like structure. Results were reported at a scientific conference and are being prepared for publication. In summary, considerable progress has been achieved under NASA funding in furthering our understanding of frontal scale contraction and density current - gravity wave interaction processes, and in utilizing models and remotely sensed data in such studies.

Koch, Steven E.↗

NASA NTRS1990

Near-infrared absorption spectra of (O-16)3 and (O-18)3 - Adiabatic energy of the 1A2 state?

The band positions and isotope shifts for the weak vibronic bands of O3 near 1 micron are determined experimentally using a low-resolution dual-beam absorption spectrometer with a 0.2-m holographic-grating monochromator and identical absorption chambers of volume about 600 cu cm and optical path length 46 cm. The experimental setup and procedures and the signal-processing methods applied are described, and the results are presented in tables and graphs. It is found that the adiabatic energy of the 1A2 state lies 9990 + or - 70/cm (1.24 + or - 0.01 eV) above the electronic ground state, close to the O + O2 dissociation limit. The applicability of the present results to studies of O3 in the upper atmosphere is indicated.

Anderson, S. M.↗

DOE OSTI2016

Coupled wave-packets for non-adiabatic molecular dynamics: a generalization of Gaussian wave-packet dynamics to multiple potential energy surfaces

Accurate simulation of the non-adiabatic dynamics of molecules in excited electronic states is key to understanding molecular photo-physical processes. Here we present a novel method, based on a semiclassical approximation, that is as efficient as the commonly used mean field Ehrenfest or ad hoc surface hopping methods and properly accounts for interference and decoherence effects. This novel method is an extension of Heller's thawed Gaussian wave-packet dynamics that includes coupling between potential energy surfaces. By studying several standard test problems we demonstrate that the accuracy of the method can be systematically improved while maintaining high efficiency. The method is suitable for investigating the role of quantum coherence in the non-adiabatic dynamics of many-atom molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

The Role of Excited State Proton Relays on the Photochemical Dynamics of Water Nanodroplets

In this work, we applied non-adiabatic excited state molecular dynamics in tandem with ab initio electronic structure theory to illustrate a complete mechanistic landscape underpinning the UV absorption initiated photochemical dynamics in water nanodroplets. The goal is to understand the nonequilibrium excited state molecular dynamics initiated by the relaxation of solvated photoelectron, and consequential photochemical processes. The lowest-lying excited state shows the proton dissociation for a single water molecule forming intermediate hydronium complexes through a proton relay. At approximately 100 femtoseconds, the proton relay process gives rise to the relaxation of the excited state accompanied with a rapid increase in the non-adiabatic coupling strength with the ground state, and the nanodroplet non-radiatively decays. The non-adiabatic transition to the ground state produces excited vibrational states that facilitate the recombination of the dissociated proton and hydroxyl group, eventually leading to the desorption of water molecules from the nanodroplet. Additionally, lifetimes of transient photochemical events are also resolved for the relaxation of solvated electron, excited state proton relay, and non-radiative transition.

Stetina, Torin F.↗

DOE OSTI2024

Emittance preservation for the electron arm in a single PWFA-LC stage using quasi-adiabatic plasma density ramp matching sections

Plasma-based acceleration (PBA) is being considered for a next generation linear collider (LC). In some PBA-LC designs for the electron arm, the extreme beam parameters are expected to trigger background ion motion within the witness beam, which can lead to longitudinally varying nonlinear focusing forces and result in an unacceptable emittance growth of the beam. To mitigate this, we propose to use quasi-adiabatic plasma density ramps as matching sections at the entrance and exit of each stage. We match the witness electron beam to the low density plasma entrance, where the beam initially has a large matched spot size so the ion motion effects are relatively small. As the beam propagates in the plasma density upramp, it is quasi-adiabatically focused, and its distribution maintains a non-Gaussian equilibrium distribution in each longitudinal slice throughout the process, even when severe ion collapse has occurred. This only causes small amounts of slice emittance growth. The phase mixing between slices with different betatron frequencies leads to additional projected emittance growth within the acceleration stage. A density downramp at the exit of an acceleration section can eliminate much of the slice and projected emittance growth as the beam and ion motion adiabatically defocuses and decreases, respectively. Simulation results from QuickPIC with Azimuthal Decomposition show that within a single acceleration stage with a 25 GeV energy gain, this concept can limit the projected emittance growth to only ∼2% for a 25 GeV, 100 nm emittance witness beam and ∼20% for a 100 GeV, 100 nm normalized emittance witness beam. The trade-off between the adiabaticity of the plasma density ramp and the initial ion motion at the entrance for a given length of the plasma density ramp is also discussed.

Physics↗

DOE OSTI2024

Si/SiGe QuBus for single electron information-processing devices with memory and micron-scale connectivity function

The connectivity within single carrier information-processing devices requires transport and storage of single charge quanta. Single electrons have been adiabatically transported while confined to a moving quantum dot in short, all-electrical Si/SiGe shuttle device, called quantum bus (QuBus). Here we show a QuBus spanning a length of 10 μm and operated by only six simply-tunable voltage pulses. We introduce a characterization method, called shuttle-tomography, to benchmark the potential imperfections and local shuttle-fidelity of the QuBus. The fidelity of the single-electron shuttle across the full device and back (a total distance of 19 μm) is (99.7 ± 0.3) %. Using the QuBus, we position and detect up to 34 electrons and initialize a register of 34 quantum dots with arbitrarily chosen patterns of zero and single-electrons. The simple operation signals, compatibility with industry fabrication and low spin-environment-interaction in 28 Si/SiGe, promises long-range spin-conserving transport of spin qubits for quantum connectivity in quantum computing architectures.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2014

Design and fabrication of a CMOS-compatible MHP gas sensor

A novel micro-hotplate (MHP) gas sensor is designed and fabricated with a standard CMOS technology followed by post-CMOS processes. The tungsten plugging between the first and the second metal layer in the CMOS processes is designed as zigzag resistor heaters embedded in the membrane. In the post-CMOS processes, the membrane is released by front-side bulk silicon etching, and excellent adiabatic performance of the sensor is obtained. Pt/Ti electrode films are prepared on the MHP before the coating of the SnO{sub 2} film, which are promising to present better contact stability compared with Al electrodes. Measurements show that at room temperature in atmosphere, the device has a low power consumption of ∼19 mW and a rapid thermal response of 8 ms for heating up to 300 °C. The tungsten heater exhibits good high temperature stability with a slight fluctuation (<0.3%) in the resistance at an operation temperature of 300 °C under constant heating mode for 336 h, and a satisfactory temperature coefficient of resistance of about 1.9‰/°C.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Analytical derivatives of the individual state energies in ensemble density functional theory. II. Implementation on graphical processing units (GPUs)

Conical intersections control excited state reactivity, and thus, elucidating and predicting their geometric and energetic characteristics are crucial for understanding photochemistry. Locating these intersections requires accurate and efficient electronic structure methods. Unfortunately, the most accurate methods (e.g., multireference perturbation theories such as XMS-CASPT2) are computationally challenging for large molecules. The state-interaction state-averaged restricted ensemble referenced Kohn–Sham (SI-SA-REKS) method is a computationally efficient alternative. The application of SI-SA-REKS to photochemistry was previously hampered by a lack of analytical nuclear gradients and nonadiabatic coupling matrix elements. We have recently derived analytical energy derivatives for the SI-SA-REKS method and implemented the method effectively on graphical processing units. We demonstrate that our implementation gives the correct conical intersection topography and energetics for several examples. Furthermore, our implementation of SI-SA-REKS is computationally efficient, with observed sub-quadratic scaling as a function of molecular size. This demonstrates the promise of SI-SA-REKS for excited state dynamics of large molecular systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗