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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Effects of supercooling in the initial solidification of PbTe-SnTe solid solutions

Deviations from compositions anticipated by the thermal equilibrium phase diagram have been observed in Bridgman-grown crystals of Pb(1-x)Sn(x)Te, in the first to freeze region of the boule. A set of experiments were conducted to determine the extent of thermal supercooling of Pb(1-x)Sn(x)Te in a Bridgman-like configuration. The results of the compositional profiles and the supercooling measurements are consistent with a diffusionless transformation occurring at the onset of solidification, and the length of uncontrolled growth is inversely related to the temperature gradient of the furnace.

Fripp, A. L.↗
NASA NTRS1994

High Velocity Clouds

We calculate the thermal equilibrium gas temperature of high velocity clouds (HVCs) in the Galactic Halo. Our method accounts for the photoelectric heating from small grains and PAHs, and includes a detailed treatment of the ionization rates and heating due to the soft X-ray background and due to cosmic rays. Phase diagrams (thermal pressure P versus gas density n) are presented for gas with a range of dust/gas ratios (D/G) and a range of metallicities (Z). Variations in D/G affect mainly the photoelectric heating rate, while variations in Z affect both the photoelectric heating and gas cooling. Curves are shown for D/G = 1 (local value) to D/G less than approx. equal to 0.005 and for Z=1 (local value) to Z= 0.005. We find that a two phase medium (CNM + WNM) can be in pressure equilibrium with a hot (T approximately 1-2 x 10(exp 6) K) halo within a range of permitted pressures, P(sup min) to P(sup max). We take halo parameters consistent with observed properties of the soft X-ray background. In general, both P(sup min) and P(sup max) decrease with lower D/G due to a drop in photoelectric heating from grains, while. P(sup min) and P(sup max) increase with lower Z due to a drop in gas coolants. We demonstrate that successful two phase models can be constructed with pressure in the range 10(exp 3) less than approximately equal to P/k less than approximately equal to 10(exp 4) K cm(exp -3) consistent with the thermal pressure in the Galactic disk. In addition, using the observed relation between CNM density and distance in HVCs, (n = 75/fDkpc cm(exp -3); Wakker & Schwarz 1991, AA, 250, 484) we show that our pressure curves constrain the allowed range of HVC heights to be between 0.3 - 16 kpc.

Wolfire, M. G.↗
DOE OSTI2022

Quantum simulation of nonequilibrium dynamics and thermalization in the Schwinger model

In this work, we present simulations of nonequilibrium dynamics of quantum field theories on digital quantum computers. As a representative example, we consider the Schwinger model, a (1+1)-dimensional U(1) gauge theory, coupled through a Yukawa-type interaction to a thermal environment described by a scalar field theory. We use the Hamiltonian formulation of the Schwinger model discretized on a spatial lattice. With the thermal scalar fields traced out, the Schwinger model can be treated as an open quantum system and its real-time dynamics are governed by a Lindblad equation in the Markovian limit. The interaction with the environment ultimately drives the system to thermal equilibrium. In the quantum Brownian motion limit, the Lindblad equation is related to a field theoretical Caldeira-Leggett equation. By using the Stinespring dilation theorem with ancillary qubits, we perform studies of both the nonequilibrium dynamics and the preparation of a thermal state in the Schwinger model using IBM's simulator and quantum devices. The real-time dynamics of field theories as open quantum systems and the thermal state preparation studied here are relevant for a variety of applications in nuclear and particle physics, quantum information and cosmology.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1993

Aerothermodynamics of a MESUR Martian entry

Computational fluid dynamics models for the thermodynamics and transport properties used in an equilibrium version of the Langley Aerothermodynamics Upwind Relaxation Algorithm (LAURA) for Martian Atmospheric entries are described. In addition, the physical models used in a nonequilibrium version of LAURA for Martian-entry flows are described. Uncertainties exist in defining constants used in the transport properties for the equilibrium model and in many of the physical models for the nonequilibrium version. Solutions from the two codes using the best available constants are examined at the Martian-entry conditions characteristic of the Mars Environmental Survey (MESUR) mission. While the flowfields are near thermal equilibrium, chemical nonequilibrium effects are present in the entry cases examined. Convective heating at the stagnation point for these flows (assuming fully catalytic wall boundary conditions) is approximately 100 W/sq cm. Radiative heating is negligible.

Mitcheltree, R. A.↗
DOE OSTI2020

Unification of nonequilibrium molecular dynamics and the mode-resolved phonon Boltzmann equation for thermal transport simulations

Nano-size confinement induces many intriguing non-Fourier heat conduction phenomena, such as nonlinear temperature gradients, temperature jumps near the contacts, and size-dependent thermal conductivity. Over the past decades, these effects have been studied and interpreted by nonequilibrium molecular dynamics (NEMD) and phonon Boltzmann transport equation (BTE) simulations separately, but no theory that unifies these two methods has ever been established. In this work, we unify these methods using a quantitative mode-level comparison and demonstrate that they are equivalent for various thermostats. We show that different thermostats result in different non-Fourier thermal transport characteristics due to the different mode-level phonon excitations inside the thermostats, which explains the different size-dependent thermal conductivities calculated using different reservoirs, even though they give the same bulk thermal conductivity. Specifically, the Langevin thermostat behaves like a thermalizing boundary in phonon BTE and provides mode-level thermal-equilibrium phonon outlets, while the Nose-Hoover chain thermostat and velocity rescaling method behave like biased reservoirs, which provide a spatially uniform heat generation and mode-level nonequilibrium phonon outlets. These findings explain why different experimental measurement methods can yield different size-dependent thermal conductivity. They also indicate that the thermal conductivity of materials can be tuned for various applications by specifically designing thermostats. Finally, the unification of NEMD and phonon BTE will largely facilitate the study of thermal transport in complex systems in the future by, e.g., replacing computationally unaffordable first-principles NEMD simulations with computationally less expensive spectral BTE simulations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Sensitivity of Neutron-Rich Nuclear Isomer Behavior to Uncertainties in Direct Transitions

Nuclear isomers are populated in the rapid neutron capture process (r process) of nucleosynthesis. The r process may cover a wide range of temperatures, potentially starting from several tens of GK (several MeV) and then cooling as material is ejected from the event. As the r-process environment cools, isomers can freeze out of thermal equilibrium or be directly populated as astrophysically metastable isomers (astromers). Astromers can undergo reactions and decays at rates very different from the ground state, so they may need to be treated independently in nucleosythesis simulations. Two key behaviors of astromers—ground state ↔ isomer transition rates and thermalization temperatures—are determined by direct transition rates between pairs of nuclear states. We perform a sensitivity study to constrain the effects of unknown transitions on astromer behavior. Detailed balance ensures that ground → isomer and isomer → ground transitions are symmetric, so unknown transitions are equally impactful in both directions. We also introduce a categorization of astromers that describes their potential effects in hot environments. We provide a table of neutron-rich isomers that includes the astromer type, thermalization temperature, and key unmeasured transition rates.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1982

The atmospheres of Io and other satellites

Voyager measurements of gaseous SO2 in a hot spot region and of ions of sulfur, oxygen, and SO2(+) in the plasma torus, combined with the groundbased measurements of SO2 frost on the surface, indicate that SO2 is perhaps the dominant constituent of Io's atmosphere. Indeed the ionosphere of Io can be sustained by a pure SO2 atmosphere in thermal equilibrium with the surface. Upper limits on common volatiles H2O, CO2, NH3, and CH4 and exceedingly small, although S2 and Ar may still be present. Photochemistry of SO2 could lead to O2 as the major gas on the night side. Reasonable processes for loss to the torus include thermal escape, sputtering, and sweep-up of ions. The symmetry of the sodium cloud between eastern and western elongation is difficult to reconcile with any substantial, diurnally varying atmosphere. Europa, Ganymede, and Callisto may have oxygen atmospheres resulting from photolysis of water vapor. A pressure of approximately 10 to the -6th microbar is predicted, consistent with the Voyager upper limit for Ganymede. A much higher pressure might be present if the water vapor pressure is increased by a low albedo (Callisto) or sputtering (Europa).

Kumar, S.↗
NASA NTRS1975

Thermal coupling apparatus for electroexplosive devices

This paper describes the equipment for nondestructive testing of electroexplosive devices using a thermal coupling technique. The technique utilizes a self-balancing bridge to apply a nominal amount of power to the bridge wire of the device. The bridge wire behaving as a thermal sensor detects heat flow into the device when heat is preferentially directed down the center of the explosive column toward the bridge wire. Thermal equilibrium is upset and the change in power from the self-balancing bridge is measured directly in watts. Faults such as omissions, incorrect materials, contamination, and so on, can be detected by observing the rate of heat flow to the bridge wire. The response is indicative of the thermal resistance and diffusivity of the system. The paper also presents data on electroexplosive devices loaded with inert and explosive materials.

Menichelli, V. J.↗
DOE OSTI2022

Holographic Kolmogorov-Sinai entropy and the quantum Lyapunov spectrum

In classical chaotic systems the entropy, averaged over initial phase space distributions, follows a universal behavior. While approaching thermal equilibrium it passes through a stage where it grows linearly, while the growth rate, the Kolmogorov-Sinai entropy (rate), is given by the sum over all positive Lyapunov exponents. A natural question is whether a similar relation is valid for quantum systems. We argue that the Maldacena-Shenker-Stanford bound on quantum Lyapunov exponents implies that the upper bound on the growth rate of the entropy, averaged over states in Hilbert space that evolve towards a thermal state with temperature T, should be given by πT times the thermal state’s von Neumann entropy. Strongly coupled, large N theories with black hole duals should saturate the bound. To test this we study a large number of isotropization processes of random, spatially homogeneous, far from equilibrium initial states in large N, $\mathcal{N}$ = 4 Super Yang Mills theory at strong coupling and compute the ensemble averaged growth rate of the dual black hole’s apparent horizon area. We find both an analogous behavior as in classical chaotic systems and numerical evidence that the conjectured bound on averaged entropy growth is saturated granted that the Lyapunov exponents are degenerate and given by λ i = ±2πT. This fits to the behavior of classical systems with plus/minus symmetric Lyapunov spectra, a symmetry which implies the validity of Liouville’s theorem.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Pseudogauge dependence of the spin polarization and of the axial vortical effect

The mean spin polarization vector of spin 1/2 particles in a relativistic fluid at local thermal equilibrium (LTE) in different pseudogauges (PGs), i.e., with different choices for the decomposition of orbital and spin angular momentum, is obtained. The spin polarization obtained in the canonical PG differs from the one obtained in the Belinfante PG. It is found that this difference can not be written by replacing the thermal vorticity with the spin potential in the usual polarization formula. Other PG choices affect the contribution of thermal shear to the spin polarization. So, the choice of a PG affects the predictions for the polarization measured in heavy-ion collisions. In general, it is shown that the Wigner function of a noninteracting Dirac field at LTE is affected by the PG transformations. Explicit expressions of the mean axial current are also calculated and it is found that even the axial vortical effect conductivity depends on the PG.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1999

Relaxation from Steady States Far from Equilibrium and the Persistence of Anomalous Shock Behavior in Weakly Ionized Gases

The decay of anomalous effects on shock waves in weakly ionized gases following plasma generator extinction has been measured in the anticipation that the decay time must correlate well with the relaxation time of the mechanism responsible for the anomalous effects. When the relaxation times cannot be measured directly, they are inferred theoretically, usually assuming that the initial state is nearly in thermal equilibrium. In this paper, it is demonstrated that relaxation from any steady state far from equilibrium, including the state of a weakly ionized gas, can proceed much more slowly than arguments based on relaxation from near equilibrium states might suggest. This result justifies a more careful analysis of the relaxation times in weakly ionized gases and suggests that although the experimental measurements of relaxation times did not lead to an unambiguous conclusion, this approach to understanding the anomalous effects may warrant further investigation.

Rubinstein, Robert↗
NASA NTRS1992

Thermonuclear flash model for long X-ray tails from Aquila X-1

Attention is given to a thermonuclear flash model for long X-ray tails from the recurrent transient Aql X-1, in which the extended phase of nuclear burning is due to the fact that the envelope is out of thermal equilibrium. Only the first X-ray burst emitted by Aql X-1 during its transient outburst exhibits a long X-ray tail. The properties of subsequent bursts are distinguished by a lack of an X-ray tail reflecting the much smaller accumulated masses which result from the effects of thermal inertia in the neutron star envelope. The characteristics of the latter bursts are similar to those of typical X-ray bursters. For a neutron star characterized by a mass and radius of 1.4 solar mass and 9.1 km, respectively, the occurrence of the long X-ray tail requires that the mass of the accumulated layer be less than 10 exp 23 g and that the envelope temperatures of the neutron star be less than 1.5 x 10 exp 7. This interpretation is found to be consistent with the thermal relaxation of the neutron star envelope during the quiescent state of Aql X-1 and with the mass accretion rates inferred for the transient outburst itself.

Fushiki, Ikko↗
NASA NTRSDate not supplied

The Third Flight of the Marshall Grazing Incidence X-Ray Spectrometer (MaGIXS-3)

The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is the first X-ray slitless imaging spectrograph sounding rocket instrument designed to observe spectrally dispersed soft X-ray images of the solar corona over a wide field-of-view. During the first flight of MaGIXS (MaGIXS-1), occurred on 30 July 2021, several emission lines from coronal structures including X-ray bright points were observed. Further, MaGIXS-1 analysis also demonstrated the successful inversion of overlappograms using robust unfolding algorithms. Given the demonstrated success of MaGIXS-1, the second flight of the instrument with a simplified optical design, MaGIXS-2, is scheduled for 2024 to observe high temperature diagnostic emission lines. Results from MaGIXS-1 discovered dominant missing emission lines near 15A, arising from relatively cool plasma that peaks around 2 MK. This wavelength region hosts several closely spaced satellite lines of Fe XVII, Fe XVI and Fe XV ions, which are expected to be enhanced at lower temperatures and are currently unmodeled in the CHIANTI atomic database. This wavelength region offers one of the most unique diagnostics to measure electron temperature, as well as signatures of equilibrium state of the plasma in active regions, which has not been studied so far. The goal of MaGIXS-3 mission is the to determine coronal heating parameters, such as the spatial and temporal properties of coronal heating events, by measuring discriminating observations, such as electron temperature, effective temperature, density, abundance, and departures from thermal equilibrium of the plasma, by observing the Sun in the SXR wavelength range. To meet this goal, the MaGIXS instrument will be upgraded with a new X-ray telescope mirror that will provide higher spatial and spectral resolution and throughput, allowing for spectral lines to be observed at the relevant spatial and temporal scales. In addition, MaGIXS-3 will also carry The Resolving Inversion Context X-ray Spectrometer (TRICXS), a high dispersion Bragg crystal spectrometer to spectrally resolve the lines near 14.9 to 15.9A, critical to unlock the full diagnostic potential of this wavelength range. Here we will present the preliminary concept design of MaGIXS-3 and discuss the potential observations.

X-ray Imaging↗
DOE OSTI2021

Effects of non-thermal termolecular chemistry on detonation development in hydrogen (H2) / methane (CH4) - air mixtures

In combustion simulations, it is usually assumed that highly-energized collision complexes (either radical or stable species) formed in exothermic reactions are always under thermal equilibrium as they evolve through competing networks of reactions. However, in practical flames, non-trivial amounts of reactive radicals such as H, O and OH are present apart from O2. As a result, collisions of these reactive species with the energized collision complexes have been shown in recent studies to induce non-thermal reactivity. These studies have also demonstrated that such non-thermal reactions can be suitably represented in macroscopic kinetics models as chemically termolecular reactions. The present work was focused on identifying and quantifying the effects of including such reactions on the evolution of an initial deflagration front to a developing detonation in H2/CH4-air mixtures under boosted internal combustion (IC) engine conditions. Specifically, fully resolved simulations, with and without non-thermal reactivity, were performed for a constant volume reactor containing stoichiometric H2/CH4-air mixture. It was found that inclusion of termolecular chemistry resulted in a delayed onset of end-gas auto-ignition. Concurrently, the developing detonation intensity was observed to be significantly higher. Chemical explosive mode analysis (CEMA) was performed to identify the dominant species/reactions responsible for the observed variation in the results.

Detonation↗
DOE OSTI2025

Disentangling the impact of quasiparticles and two-level systems on the statistics of superconducting-qubit lifetime

Temporal fluctuations in the superconducting qubit lifetime, T 1 , present additional challenges in the pursuit of fault-tolerant quantum computing. Although the exact mechanisms remain unclear, T 1 fluctuations are generally attributed to strong coupling between the qubit and a few near-resonant two-level systems (TLSs), which can exchange energy with an ensemble of thermally fluctuating two-level fluctuators (TLFs) at low frequencies. Here, we report T 1 measurements of qubits with varying geometrical footprints and surface dielectrics as a function of temperature. By analyzing the noise spectrum of the qubit depolarization rate, Γ 1 = 1 / T 1 , we disentangle the contributions of TLSs, nonequilibrium quasiparticles (QPs), and equilibrium (thermally excited) QPs to the variance in Γ 1 . We find that the Γ 1 variance in qubits with smaller footprints is more susceptible to QP and TLS fluctuations than that in larger-footprint qubits. Furthermore, the QP-induced variances in all qubits align with the theoretical framework of QP diffusion and fluctuation. These findings offer valuable insights for future qubit design and engineering optimization.

Zhu, Shaojiang [Fermilab] (ORCID:0000000293180092)↗
NASA NTRS1985

Earth Radiation Budget Satellite

The Earth Radiation Budget Experiment (ERBE) waqs designed to examine the thermal equilibrium between the sun, the earth, and space. The major space-based component of the experiment is the Earth Radiation Budget Satellite (ERBS) which was launched from Shuttle (Mission 41-G) on October 5, 1984. The ERBS is a three-axis momentum-biased spacecraft containing its own subsystems for attitude control, power generation, thermal control, and data handling. The satellite transmits data via the NASA Spacecraft Tracking and Data Network (STDN) and the Tracking and Data Relay Satellite System (TDRSS). The ERBS instrument package includes eight channels in two sensor packages: a nonscanning radiometer and a scanning radiometer. The combined spectral range of the two instruments is 0.2-5.0 microns and the scale of the radiometer measurements can be changed to collect regional, zonal, or global data. A series of schematic diagrams of the ERBS spacecraft and its instrument package is provided.

Dezio, J. A.↗
DOE OSTI2024

Impacts of Irradiation Structural Behavior on Thermal Hydraulics Safety Analysis to Support MURR LEU Conversion

The University of Missouri Research Reactor (MURR) located in Columbia, Missouri is one of six U.S. High Performance Research Reactors (USHPRR), including one critical facility, that is actively collaborating with U. S. Department of Energy (DOE) National Nuclear Security Administration (NNSA) Material Management and Minimization (M3) Office of Reactor Conversion and Uranium Supply to convert from the use of highly enriched uranium (HEU; ≥20 wt% U-235) to low-enriched uranium (LEU; <20 wt% U-235) fuel. A new type of very high-density LEU fuel based on an alloy of uranium and 10 wt% molybdenum (U-10Mo) is expected to allow the conversion to LEU of MURR, as well as four other USHPRR. MURR has been working with the Reactor Conversion Pillar at Argonne to perform fuel element design and fuel cycle performance analyses, steady-state thermal hydraulics safety analysis, and accident safety analyses in preparation for the conversion of MURR and to support a preliminary safety analysis report for conversion to LEU fuels. Subsequent analyses have also been performed, including transition cycles where all-fresh LEU fuel elements are introduced upon conversion and progressing through reactor operations the core is brought to equilibrium. Thermal hydraulics safety analyses performed as part of the above have employed an assumption on channel gap reduction due to burnup-related phenomena including fuel swelling, irradiation creep, and oxide layer buildup. Recently, a series of structural analyses have been performed on the MURR LEU fuel plates and an element due to significant differences between the plate and element designs of the MURR HEU and LEU fuels. In addition, NUREG-1537 indicates that structural phenomena are to be evaluated. Two separate types of structural analyses were performed for the MURR LEU fuel element: fluid-structure interaction (FSI) and irradiation thermo-mechanical. The FSI analysis evaluated the effects of hydraulic forces on the MURR LEU fuel element to quantify the flow-induced plate deflection, and a minimal impact to the channel gap thickness was predicted under prototypic and bounding conditions. The irradiation thermo-mechanical analysis evaluated the effects of fuel swelling, irradiation creep, and thermal expansion for the MURR LEU plates and the element for prototypic thermal and irradiation conditions based on a high-fidelity approach multiphysics approach. Overall, this thermo-mechanical analysis predicts smaller gap thickness changes in previously limiting regions. Larger changes are predicted in the middle of channels, and for end channels where power density is not typically a maximum. An additional thermo-mechanical analysis was performed for the outermost HEU fuel plate, which showed a similar magnitude of deflection as the outermost LEU plate. Due to substantial differences between the channel gap reductions assumed for the previous safety analyses and those predicted by the irradiation thermo-mechanical analysis, a need to evaluate their impact on the thermal hydraulics safety analyses arose. This report presents the results from the steady-state safety analyses for normal operation as well as the accident analyses for the two most limiting accident scenarios.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRSDate not supplied

The Next Generation Marshall Grazing Incidence X-Ray Spectrometer (MaGIXS) Sounding Rocket Experiments

The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket experiment that carries an X-ray slitless imaging spectrograph to observe spectrally dispersed soft X-ray (SXR) images of the solar corona over a wide field-of-view. The first flight of MaGIXS occurred on 30 July 2021, during which several emission lines from coronal structures including X-ray bright points were observed. Analysis of MaGIXS-1 data demonstrated the application of new inversion techniques and opened a new arena of inverting complex spectroheliogram data, which has spatial-spectral information overlapped. The second flight of MaGIXS, with a simplified optical design, is scheduled for 2024. The goal of MaGIXS-2 is to observe high temperature diagnostic emission lines within an active region core. MaGIXS-1 discovered dominant missing emission lines near 15Å wavelength region, which hosts several closely spaced satellite lines of Fe XVII, Fe XVI, and Fe XV ions, arising from relatively cool plasma that peaks near 2MK. These lines are expected to be enhanced at lower temperatures and offers one of the most unique diagnostics to measure electron temperature, as well as signatures of equilibrium state of the plasma in active regions, which has not been studied so far. The science goal of the third sounding rocket flight of MaGIXS is to determine coronal heating parameters, such as the spatial and temporal properties of coronal heating events, by measuring discriminating observations, such as electron temperature, effective temperature, density, abundance, and departures from thermal equilibrium of the plasma, by observing the Sun in the SXR wavelength range. For this, the MaGIXS instrument will be upgraded with a new X-ray telescope mirror that will provide higher spatial and spectral resolution and throughput, allowing for spectral lines to be observed at the relevant spatial and temporal scales. In addition, MaGIXS-3 will also carry The Resolving Inversion Context X-ray Spectrometer (TRICXS), a high dispersion Bragg crystal spectrometer to spectrally resolve the lines near 15Å, critical to unlock the full diagnostic potential of this wavelength range. Here we will present the preliminary concept design of MaGIXS-3 and discuss the potential observations.

X-ray Imaging↗