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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Effects of cluster correlations on fragment emission in 12 C+ 12 C at 50 MeV/nucleon

The effects of cluster correlations have been studied in the 12 C + 12 C reaction at 50 MeV/nucleon, using three AMD models, the AMD (AMD/D) without any additional cluster correlations, AMD/D-COALS with nucleon correlations based on a coalescence prescription for light cluster formations with A ≤ 4 and AMD-Cluster with an extended cluster correlation in two-nucleon collision processes and a special treatment for intermediate fragment formation with A ≤ 9. The angular distributions and energy spectra of fragments have been simulated and compared with the available experimental data. It is found that the cluster correlations take a crucial role to describe the productions of light charged particles (LCPs) and intermediate mass fragments (IMFs), and the AMD-cluster studied here provides a consistent overall reproduction of the experimental data. It is also shown that the significant effects of the secondary decay processes are involved for the fragment production besides the dynamical productions in the AMD stage. Detailed LCP and IMF production mechanisms involved in the intermediate energy heavy ion collisions are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1995

Vibrational and Electronic Energy Transfer and Dissociation of Diatomic Molecules by Electron Collisions

At high altitudes and velocities equal to or greater than the geosynchronous return velocity (10 kilometers per second), the shock layer of a hypersonic flight will be in thermochemical nonequilibrium and partially ionized. The amount of ionization is determined by the velocity. For a trans atmospheric flight of 10 kilometers per second and at an altitude of 80 kilometers, a maximum of 1% ionization is expected. At a velocity of 12 - 17 kilometer per second, such as a Mars return mission, up to 30% of the atoms and molecules in the flow field will be ionized. Under those circumstances, electrons play an important role in determining the internal states of atoms and molecules in the flow field and hence the amount of radiative heat load and the distance it takes for the flow field to re-establish equilibrium. Electron collisions provide an effective means of transferring energy even when the electron number density is as low as 1%. Because the mass of an electron is 12,760 times smaller than the reduced mass of N2, its average speed, and hence its average collision frequency, is more than 100 times larger. Even in the slightly ionized regime with only 1% electrons, the frequency of electron-molecule collisions is equal to or larger than that of molecule-molecule collisions, an important consideration in the low density part of the atmosphere. Three electron-molecule collision processes relevant to hypersonic flows will be considered: (1) vibrational excitation/de-excitation of a diatomic molecule by electron impact, (2) electronic excitation/de-excitation, and (3) dissociative recombination in electron-diatomic ion collisions. A review of available data, both theory and experiment, will be given. Particular attention will be paid to tailoring the molecular physics to the condition of hypersonic flows. For example, the high rotational temperatures in a hypersonic flow field means that most experimental data carried out under room temperatures are not applicable. Also, the average electron temperature is expected to be between 10,000 and 20,000 K. Thus only data for low energy electrons are relevant to the model.

Huo, Winifred M.↗
NASA NTRS1974

Collisional coupling in counterstreaming laser-produced plasmas

The collisional processes which transfer momentum between counterstreaming plasmas are reviewed and applied to the example of a laser-produced plasma expanding into a partially ionized background. Experimental measurements of the dependence of the ion flow field on collisional momentum transfer demonstrate the validity of the simplified treatment of collision processes which have been adopted. A numerical model which simulates the laser-plasma interaction with the background confirms the importance of collisions in previous experimental studies of momentum coupling, and provides some insight into the distinction between collisional and collisionless flow regimes.

Koopman, D. W.↗
DOE OSTI2024

Inelastic Triatom-Atom Quantum Close-Coupling Dynamics in Full Dimensionality: All Rovibrational Mode Quenching of Water Due to the H Impact on a Six-Dimensional Potential Energy Surface

The rovibrational level populations, and subsequent emission in various astrophysical environments, are driven by inelastic collision processes. The available rovibrational rate coefficients for water have been calculated using a number of approximations. We present a numerically exact calculation for the rovibrational quenching for all water vibrational modes due to collisions with atomic hydrogen. The scattering theory implements a quantum close-coupling (CC) method on a high level ab initio six-dimensional (6D) potential energy surface (PES). Total rovibrational quenching cross sections for excited bending levels were compared with earlier results on a 4D PES with the rigid-bender closecoupling (RBCC) approximation. General agreement between 6D-CC and 4DRBCC calculations are found, but differences are evident including the energy and amplitude of low-energy orbiting resonances. Quenching cross sections from the symmetric and asymmetric stretch modes are provided for the first time. The current 6D-CC calculation provides accurate inelastic data needed for astrophysical modeling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1984

Molecular processes in a high temperature shock layer

Models of the shock layer encountered by an Aeroassisted Orbital Transfer Vehicle require as input accurate cross sections and rate constants for the atomic and molecular processes that characterize the shock radiation. From the estimated atomic and molecular densities in the shock layer and the expected residence time of 1 m/s, it can be expected that electron-ion collision processes will be important in the shock model. Electron capture by molecular ions followed by dissociation, e.g., O2(+) + e(-) yields 0 + 0, can be expected to be of major importance since these processes are known to have high rates (e.g., 10 to the -7th power cu/cm/sec) at room temperature. However, there have been no experimental measurements of dissociative recombination (DR) at temperatures ( 12000K) that are expected to characterize the shock layer. Indeed, even at room temperature, it is often difficult to perform experiments that determine the dependence of the translational energy and quantum yields of the product atoms on the electronic and vibrational state of the reactant molecular ions. Presented are ab initio quantum chemical studies of DR for molecular ions that are likely to be important in the atmospheric shock layer.

Guberman, S. L.↗
NASA NTRS1991

Collisional effects in laser detection of tropospheric OH

The use of laser-induced fluorescence to measure OH in the troposphere is discussed. It is noted that quantitative laser detection of OH requires knowledge of collisional processes affecting the measurements and interference effects due to OH generated by laser photolytic processes. Collisions induce quenching of the excited A-state, as well as vibrational and rotational energy transfer in the excited and ground states. It is noted that the state-specific nature of these processes is important, especially the rotational level dependence of quenching and vibrational transfer in excited OH. Also important is the temperature dependence according to which quenching cross sections sharply increase with decreasing temperature. Laboratory experiments studying these collisional processes are described, and their implications for laser detection of tropospheric OH are examined.

Crosley, David R.↗
NASA NTRS1991

Ionosphere-exosphere coupling through charge exchange and momentum transfer in hydrogen-proton collisions

The implications of a traditional assumption of exospheric physics, that collisions of hydrogen atoms and protons preferentially result in charge exchange with negligible momentum transfer are examined. Initially adopted as a necessary convenience to accommodate limited computer resources in exosphere model calculations, this approximation results in a direct transformation of the proton velocity distribution into a hot component of neutral hydrogen. With expanding computational facilities, the need for the approximation has passed. As the first step toward its replacement with a realistic, quantum mechanical model of the H - H(+) collision process, differential and cumulative cross sections were calculated for quantum elastic scattering of indistinguishable nuclei for a fine grid of encounter energies and scattering angles. These data are used to study the nature of ionosphere-exosphere coupling through H - H(+) collisions, and to demonstrate that the distribution of velocities of scattered H produced in the traditional exospheric charge exchange approximation, as well as that arising from an alternative, fluid dynamic approach, leads to unacceptable abundances of coronal atoms in long-term, highly elliptic trajectories.

Hodges, R. R., Jr.↗
DOE OSTI2023

Semirelativistic antisymmetrized molecular dynamics for the production of energetic neutrons in intermediate-energy heavy-ion reactions

Relativistic corrections have been made in the nonrelativistic antisymmetrized molecular dynamics (amd) simulations to apply to the high-energy neutron production in the 12 C + 12 C and 16 O + 12 C collisions at incident energies of 290 and 400 MeV/nucleon. The corrections are made in kinematics alone and neither nucleon-nucleon inelastic scatterings nor meson productions are taken into account, and amd with the relativistic corrections is called semirelativistic amd. The three-nucleon collision (3NC) and Fermi boost in the collision processes are taken into account in the nonrelativistic AMD. Since the relativistic corrections tend to compensate in each other, the difference between the semirelativistic and nonrelativistic results become small. High-energy tails of the available experimental neutron double-differential cross sections, especially at larger angles, are well reproduced by amd with the 3NC term both with nonrelativistic and semirelativistic simulations. Furthermore, these results indicate that the high-energy neutrons are dominantly produced by the 3NC process in this incident energy range.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1993

Collision cross sections and diffusion parameters for H and D in atomic oxygen

Modeling the behavior of H and D in planetary exospheres requires detailed knowledge of the differential scattering cross sections for all of the important neutral-neutral and ion-neutral collision processes affecting these species over their entire ranges of interaction energies. In the upper atmospheres of Earth, Venus, and other planets as well, the interactions of H and D with atomic oxygen determine the rates of diffusion of escaping hydrogen isotopes through the thermosphere, the velocity distributions of exospheric atoms that encounter the upper thermosphere, the lifetimes of exospheric orbiters with periapsides near the exobase, and the transfer of momentum in collisions with hot O. The nature of H-O and D-O collisions and the derivation of a data base consisting of phase shifts and the differential, total, and momentum transfer cross sections for these interactions in the energy range 0.001 - 10 eV are discussed. Coefficients of mutual diffusion and thermal diffusion factors are calculated for temperatures of planetary interest.

Hodges, R. R., Jr.↗
DOE OSTI2025

Competing ionization and dissociation: Extension of the energy-dependent frame transformation to the gerade symmetry of H 2

This article solves two major tasks that frequently arise in the theory of electron collisions with a target molecular cation. First, it extends the energy-dependent frame transformation (EDFT) treatment, which is needed to map fixed-nuclei electron-molecule scattering matrices into an energy-dependent laboratory-frame scattering matrix with vibrational channel indices. The EDFT mapping can now be carried out even when the target molecule possesses multiple low-energy potential curves, significantly transcending previous applications. Second, it implements a method to extract the rest of the full laboratory-frame scattering matrix, i.e., the columns and rows describing input and/or output dissociation channels. The treatment is benchmarked in this article against the essentially exact solution of a refined two-dimensional model of the singlet gerade Σ symmetry of H 2 . Our tests demonstrate that the theory accurately maps fixed-nuclei scattering information, of the type provided by existing electron-molecule computer codes, into a laboratory-frame scattering matrix that includes both ionization and dissociation. Furthermore, this treatment can provide a general framework applicable to a broad class of electron collision processes involving diatomic target ions, suitable for an accurate description of challenging processes such as dissociative recombination.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1984

Collision-induced transport processes in planetary rings

The physics of collision-dominated particle disks around planets is analyzed from both the analytical and numerical point of view. The existence of Saturn's ringlet structure is analyzed in terms of a radial instability induced by viscous diffusion. The detailed model described is based on the assumption of uniform particle size. Modifications caused by finite particle size, gravitational effects, and a distribution of particle sizes are discussed.

Stewart, G. R.↗
NASA NTRS1974

Immiscible materials and alloys

Only immiscible materials which involve a fluid phase have a potential advantage when considered for space processing. Processing of such systems at low gravity can lead to a material which is very homogeneous and contains a finely dispersed mixture of phases. Materials with such structures may exhibit potentially useful properties for such applications as superconductors, dispersion-strengthened materials, superplastic materials, permanent magnets, etc. These conclusions have resulted from review of past efforts in the field of low-g processing of materials containing a liquid phase miscibility gap and from present efforts dealing with such systems. These studies have concentrated on precipitation of liquid droplets in a host liquid during cooling through the miscibility gap. This effort has been to study the agglomeration of the droplets both experimentally and through computer simulation in order to understand the mechansism involved and to deduce the effect of gravity on the droplet distribution and resulting structure of the solidified material. The agglomeration mechanisms treated in detail are those due to diffusional growth and collision processes caused by Stokes on convection current-induced droplet migration.

Markworth, A. J.↗
DOE OSTI2025

Scalable quantum simulations of scattering in scalar field theory on 120 qubits

Simulations of collisions of fundamental particles on a quantum computer are expected to have an exponential advantage over classical methods and promise to enhance searches for new physics. Furthermore, scattering in scalar field theory has been shown to be bounded-error quantum polynomial time (BQP) complete, making it a representative problem for which quantum computation is efficient. As a step toward large-scale quantum simulations of collision processes, scattering of wave packets in one-dimensional scalar field theory is simulated using 120 qubits of IBM’s Heron superconducting quantum computer ibm_fez. Variational circuits compressing vacuum preparation, wave packet initialization, and time evolution are determined using classical resources. By leveraging physical properties of states in the theory, such as symmetries and locality, the variational quantum algorithm constructs scalable circuits that can be used to simulate arbitrarily large system sizes. A new strategy is introduced to mitigate errors in quantum simulations, which enables the extraction of meaningful results from circuits with up to 4924 two-qubit gates and two-qubit gate depths of 103. The effect of interactions is clearly seen, and is found to be in agreement with classical matrix product state simulations. Finally, the developments that will be necessary to simulate high-energy inelastic collisions on a quantum computer are discussed.

quantum circuits↗
NASA NTRS2003

Laboratory Studies in UV and EUV Solar Physics

The Ion Beam Experiment at the Center for Astrophysics is dedicated to the study of ion-electron collision processes of importance in solar physics. A paper describing our most recent measurement 'Absolute cross section for Si(2+)(3s3p(sup 3)Rho (sup 0) yields 3s3p(sup 1)Rho(sup 0)) electron-impact excitation' was published during the past year. Dr. Paul Janzen received his PhD. from the Harvard Physics Department on the basis of this and other work, such as the new electron cyclotron resonance (ECR) ion source. The ion source is producing stable beams with large currents for our present work on C(2+), and it also produces stable beams with large currents of more highly charged systems, for future work on systems such as O(4+). The past year has been focussed on our current program to measure absolute cross sections for Electron Impact Excitation (EIE) in C(2+), one of the primary ions used for probing the solar transition region. C(2+) beams produced by the ion source have been transported to the interaction region of the experiment, where the collisions are studied, and Visiting Scientist Dr. Adrian Daw is currently collecting data to measure the C(2+)(2s2p(sup 3)Rho(sup 0) yields 2p(sup 2)(sup 3)Rho) EIE cross section as a function of collision energy, under the guidance of Drs. John Kohl, Larry Gardner and Bill Parkinson. Also this year, modifications were made to the ECR ion source in order to produce greater currents of highly charged ions. Testing of the ion source was completed. Modifications were designed to extend the photon detection capabilities of the apparatus to shorter UV wavelengths, or EUV. Following the work on C(2+)(2s2p(sup 3)Pho(sup 0) yields 2p(sup 2)(sup 3)Rho), the extended UV detection capabilities will be used to measure the C(2+)(2s(sup 2)(sup 1)S yields 2s2p(sup 1)Rho(sup 0)) EIE cross section. The EUV modifications complement those of the new ion source, by enabling detection of EUV light generated by high charge state ions and putting us in a position to measure the excitation cross sections for more highly charged ions as well.

Parkinson, William↗
DOE OSTI2024

Dynamic mode decomposition of nonequilibrium electron-phonon dynamics: accelerating the first-principles real-time Boltzmann equation

Abstract Nonequilibrium dynamics governed by electron–phonon ( e -ph) interactions plays a key role in electronic devices and spectroscopies and is central to understanding electronic excitations in materials. The real-time Boltzmann transport equation (rt-BTE) with collision processes computed from first principles can describe the coupled dynamics of electrons and atomic vibrations (phonons). Yet, a bottleneck of these simulations is the calculation of e –ph scattering integrals on dense momentum grids at each time step. Here we show a data-driven approach based on dynamic mode decomposition (DMD) that can accelerate the time propagation of the rt-BTE and identify dominant electronic processes. We apply this approach to two case studies, high-field charge transport and ultrafast excited electron relaxation. In both cases, simulating only a short time window of ~10% of the dynamics suffices to predict the dynamics from initial excitation to steady state using DMD extrapolation. Analysis of the momentum-space modes extracted from DMD sheds light on the microscopic mechanisms governing electron relaxation to a steady state or equilibrium. The combination of accuracy and efficiency makes our DMD-based method a valuable tool for investigating ultrafast dynamics in a wide range of materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Insights from multinucleon transfer reactions in 206 Pb+ 118 Sn

Multinucleon transfer reactions for the 206 Pb + 118 Sn system were measured at E lab = 1200 MeV using the PRISMA large solid-angle magnetic spectrometer. The experiment was conducted at laboratory angles around the grazing angle, covering an angular range of approximately 20°. The resulting differential and total cross sections, along with Q-value distributions for various neutron and proton pick-up and stripping channels, are presented. The Q-value distributions suggest a transition from quasi-elastic to deep inelastic collision processes, particularly in channels involving nucleon transfers. The experimental results have been compared with GRAZING code calculations, showing good agreement for few-nucleon transfer channels, while channels with large nucleon transfers are underestimated, indicating the involvement of more complex processes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Two-photon polymerization printed lattices as support structures in multi-shell ICF targets: Platform development and initial assessment

Recent interest in fielding direct drive multi-shell targets on the NIF [K. Molvig et al., Phys. Rev. Lett. 116, 255003 (2016) and S. X. Hu et al., Phys. Rev. E 100, 063204 (2019)] has highlighted the need for a low density structure to support the inner shell(s) and to avoid energy loss in the acceleration and collision process. We have developed a two-shell platform to evaluate the use of low density two-photon polymerization (2PP) printed lattices as a support structure between the shells. Here, 2PP structures are an attractive option because they can be produced at densities as low as 5 mg/cc, which is ideal for multi-shell targets, and their 3D structure can be tailored to the user's needs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

1D modeling of plasma streamers at ammonia-air flame conditions

Abstract Self-consistent 1D modeling of streamers in ammonia-oxygen-nitrogen-water mixtures has been performed in this work. A fluid model that includes species transport, electrostatic potential, and detailed chemistry was developed and verified. This model is then used to simulate the avalanche, streamer formation and propagation phases, driven by a nanosecond voltage pulse, at different thermochemical conditions derived from a 1D laminar premixed ammonia-air flame. The applicability of the Meek’s criterion in predicting the streamer inception location was successfully confirmed. Streamer formation and propagation duration were found to vary significantly with different thermochemical conditions, due to the difference in ionization rates. The thermochemical state also affected the breakdown characteristics which was tested by maintaining the background reduced electric field constant. Detailed kinetic analyses revealed the importance of O ( 1 D ) in the production of key radicals, such as O, OH, and NH 2 . Furthermore, the contributions of the dissociative electronic excitation of NH 3 towards the production of H and NH 2 radicals have also been reported. Spatial and temporal evolution of the electron energy loss fractions for various inelastic collision processes at different thermochemical states uncovered the input plasma energy spent of fuel dissociation and the large variability in the dominant processes during the avalanche and streamer propagation phases. The methodology and analyses reported in this work are key towards developing effective strategies for controlled nanosecond-pulsed non-equilibrium plasma sources used for ammonia ignition and flame stabilization.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗