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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 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Thermodynamic Phase Transition in Magnetic Reconnection

By examining the entropy production in fully kinetic simulations of collisional plasmas, it is shown that the transition from collisional Sweet-Parker reconnection to collisionless Hall reconnection may be viewed as a thermodynamic phase transition. The phase transition occurs when the reconnection electric field satisfies E = $E_{D}\sqrt{m{e}/{m}_i}$ , where ${m{e}/{m}_i}$ is the electron-to-ion mass ratio and E D is the Dreicer electric field. This condition applies for all ${m{e}/{m}_i}$, including ${m{e}/{m}_i}$ = 1 , where the Hall regime vanishes and a direct phase transition from the collisional to the kinetic regime occurs. In the limit ${m{e}/{m}_i}$ → 0, this condition is equivalent to there being a critical electron temperature $Te ≈ m_iΩ^{2}_{i}δ^{2}$, where $Ω_i$ is the ion cyclotron frequency and δ is the current sheet half-thickness. The heat capacity of the current sheet changes discontinuously across the phase transition, and a critical power law is identified in an effective heat capacity. A model for the time-dependent evolution of an isolated current sheet in the collisional regime is derived.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

A Study on Particle Trajectory Error in Finite-Element Particle-in-Cell Algorithms

Particle-in-cell (PIC) algorithms are widely used for the simulation of kinetic plasmas. PIC algorithms account for the interaction between charged particles in a plasma and the electromagnetic field in ambient space, including self-field interactions. The objective of this article is to study the error in charged particle trajectories present in finite-element (FE)-based PIC algorithms on unstructured meshes. We study how the trajectory error behaves according to the FE mesh resolution and the matrix solver employed in the FE algorithm. The study is performed by considering a trajectory established by a parabolic electric potential and an axial magnetic force acting on the charged particle. Under a proper choice combination of electric and magnetic field parameters, the 2-D particle trajectories comprise closed orbits. Numerical errors cause small perturbations on the trajectories, with cumulative effects. As a result, the resulting orbital trajectories exhibit distortions including spurious apsidal precession. These distortions provide a clear imprint of the numerical error. Here, we also study the numerical error in a quantitative fashion by computing the distance norm between the trajectories obtained by the exact fields and numerical fields.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Quantum-Accurate Molecular Dynamics Potential for Tungsten

The purpose of this short contribution is to report on the development of a Spectral Neighbor Analysis Potential (SNAP) for tungsten. We have focused on the characterization of elastic and defect properties of the pure material in order to support molecular dynamics simulations of plasma-facing materials in fusion reactors. A parallel genetic algorithm approach was used to efficiently search for fitting parameters optimized against a large number of objective functions. In addition, we have shown that this many-body tungsten potential can be used in conjunction with a simple helium pair potential1 to produce accurate defect formation energies for the W-He binary system.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Calculation of the First Moment of Energy Using D-T Reactivity Formalisms Under the Maxwell-Boltzmann Distribution (Pt. 1)

Nuclear fusion science is an example of a scientific field with a rich history of expert involvement and scientific publications, which together, form an expert-knowledge base. One example of this history is the utilization of published reaction rates from a variety of authors. Investigators for Deuterium-Tritium (D-T) ion fusion can choose from using frequently cited methods: the Bosch and Hale reactivity, thermonuclear reaction rates from Caughlan and Fowler, and the reactivity evaluation from Miley, Towner & Ivich which forms the basis of the Naval Research Lab (NRL) formulary. There are other choices available. Each of the reactivity formulations considered here, are based upon the Maxwell- Boltzmann velocity distribution for D-T fusion ion reactants. Numerical methods for computer codes simulating hot, energetic plasmas, include tabulations of the reactivity, and the first moment of energy. The purpose of this study is to answer the question: what is the first moment of energy, and how has it been formulated? This report is part of a series of reports by the authors on D-T fusion-reaction formalism. The present focus is on defining the mathematical relationship of the first moment of D-T fusion ion kinetic energy, $\langle$E$\rangle$, with the fusion crosssection, fusion reactivity and its derivative with respect to ion-temperature. Three variants of the first moment $\langle$E$\rangle$ are analytically developed and explored: 1) constant cross-section, 2) a normalized first moment, and 3) a particular function of the first moment. Much of the mathematical development is relegated to the Appendices, for a concise presentation of topics and results. A research component of this discussion is our comparison of some of the reactivity and its derivative results between evaluations (1) versus (2) and (3), which the authors have not found in any other publication to date. This investigation is useful for validation, verification (V&V) and uncertainty quantification (UQ) as it compares the work of several authors.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Calculation Of The First Moment Of Energy Using D-T Reactivity Formalisms Under The Maxwell-Boltzmann Distribution--Part II

Nuclear fusion science is an example of a scientific field with a rich history of expert involvement and scientific publications, which together, form an expert-knowledge base. One example of a nuclear fusion formalism is the utilization of published reaction rates from a variety of authors. Investigators for Deuterium- Tritium (D-T) ion fusion can choose from using frequently cited methods: the Bosch and Hal reactivity, thermonuclear reaction rates from Caughlan and Fowler, and the reactivity evaluation from Miley, Towner & Ivich which forms the basis of the Naval Research Lab (NRL) formulary. There are other choices available. Each of the reactivity formulations considered here, are based upon the Maxwell-Boltzmann velocity distribution for D-T fusion ion reactants. Numerical methods for computer codes simulating hot, energetic plasmas, include tabulations of the reactivity, and the first moment of energy. This report continues the step toward building understanding of nuclear fusion reactivity formalisms. It is part of a series of reports with the same goal, [5-10] and is the continuation of the Part I paper for defining the mathematical relationship of the first moment of D-T fusion ion kinetic energy, <$E$>, with the fusion cross-section, fusion reactivity and its derivative with ion-temperature. In Part I, three variants of the first moment <$E$> were analytically developed and explored: 1) constant cross-section, 2) a normalized first moment, and 3) a particular function of the first moment from Brysk. In Part II, attention is given to the definition of <$K$>, originally described as a ratio of moments from Brysk, and its relationship to the first moment definitions from Part I. One measure of the progress made in these documents is the identification that Brysk’s ratio of the second moment to the first moment ratio, <$K$>, does not correspond to his provided solution of the first moment of energy. Another measure of (our) progress from this work is the comparison of first moment variants. That comparison includes confirming the importance of cross sections defined in terms of energy. The analytical relationships we have developed among important physics quantities are useful tools in validation and verification (V&V). For example, we can calculate the kinetic energy as a mean or as a first moment, or as a function of the first moment. These analytically-determined values can be compared directly with numerically-determined values, supplied to the authors, representing <$E$>.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Relations between Shot Noise, Gain Bandwidth, and Saturation of Instabilities

There are numerous instabilities present in charged particle beams that undergo exponential growth and reach saturation. In various applications, such as free-electron lasers or micro-bunching light sources, achieving saturation is desirable. Conversely, there are applications where these instabilities are utilized as linear broad-band amplifiers for signals embedded in the charged beam. In the latter scenario, the saturation of an instability induces non-linear distortions in the imprinted signal, thereby limiting the useful range of such amplifiers. Accurate evaluation of these instabilities necessitates a complete and comprehensive modeling approach that includes shot noise within the beam. Unfortunately, such modeling is not always feasible or practical. In this paper, we introduce a methodology utilizing the frequency and bandwidth of the instability as key parameters. Through this, we derive an estimation for the range of linear instability growth. Our derivation is conducted in a model-independent manner, making it applicable to a broad spectrum of instabilities. To validate our approach, we employ established and thoroughly benchmarked simulations with a free electron laser (FEL) code as well as self-consistent 3-dimensional simulation of plasma-cascade instability using code SPACE.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Stochastic Ion Acceleration by the Ion-cyclotron Instability in a Growing Magnetic Field

Using 1D and 2D particle-in-cell simulations of a plasma with a growing magnetic field ${\boldsymbol{B}}$, we show herein that ions can be stochastically accelerated by the ion-cyclotron (IC) instability. As ${\boldsymbol{B}}$ grows, an ion pressure anisotropy ${p}_{\perp ,i}\gt {p}_{| | ,i}$ arises due to the adiabatic invariance of the ion magnetic moment (${p}_{| | ,i}$ and $p_{⊥,i}$ are the ion pressures parallel and perpendicular to ${\boldsymbol{B}}$). When initially $β_ i$ = 0.5 (${\beta }_{i}\equiv 8\pi {p}_{i}/| {\boldsymbol{B}}{| }^{2}$, where $p_i$ is the ion isotropic pressure), the pressure anisotropy is limited mainly by inelastic pitch-angle scattering provided by the IC instability, which in turn produces a nonthermal tail in the ion energy spectrum. After ${\boldsymbol{B}}$ is amplified by a factor of ~2.7, this tail can be approximated as a power law of index ~3.4 plus two nonthermal bumps and accounts for 2%–3% of the ions and ~18% of their kinetic energy. On the contrary, when initially $β_i$ = 2, the ion scattering is dominated by the mirror instability, and the acceleration is suppressed. This implies that efficient ion acceleration requires that initially, $β_{i} \lesssim$ 1. Although we focus on cases where ${\boldsymbol{B}}$ is amplified by plasma shear, we check that the acceleration occurs similarly if ${\boldsymbol{B}}$ grows due to plasma compression. Our results are valid in a subrelativistic regime where the ion thermal energy is ~10% of the ion rest-mass energy. This acceleration process can thus be relevant in the inner region of low-luminosity accretion flows around black holes.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1969

Dispersion of ion-acoustic waves

Dispersion of ion-acoustic waves in quiescent rare gas discharge plasmas, discussing model simulating ion waves generated by finite sine wave bursts

Alexeff, I.↗
NASA NTRS1977

Effect of simulated Earth reentry exposure on mechanical properties of several oxide dispersion strengthened and superalloy sheet materials

The effects of simulated multiple reentry into the earth's atmosphere on the mechanical properties of several high temperature metallic sheet materials were evaluated. The materials included five tin-gage (nominally 0.025- or 0.037-cm) oxide dispersion strengthened (ODS) alloys and two thin-gage (nominally 0.037-cm) superalloys. Multiple reentry conditions were simulated through cyclic Plasma Arc Tunnel (PAT) exposure. PAT exposure generally consisted of 100 cycles of 600 second duration at 1255, 1366, or 1477 K in a Mach 4.6 airstream with an impact pressure of nominally 800 N/m2. PAT exposure generally produced a uniform oxide scale, oxide pits or intergranular oxidation, Kirkendall porosity, and alloy depletion zones except for the aluminum-containing ODS alloys. Only a uniform oxide scale was formed on the aluminum-containing ODS alloys. PAT exposure did not significantly affect the mechanical properties of the thin-gage (nominally 0.025- or 0.037-cm) alloys evaluated. Thus it appears that the microstructural changes produced by Plasma Arc Tunnel exposure has little influence on mechanical properties.

Whittenberger, J. D.↗
NASA NTRS1977

Materials and techniques for spacecraft static charge control

An overview of the design, development, fabrication, and testing of transparent conductive coatings and conductive lattices deposited or formed on high resistivity spacecraft dielectric materials to obtain control static charge buildup on spacecraft external surfaces is presented. Fabrication techniques for the deposition of indium/tin oxide coatings and copper grid networks on Kapton and FEP Teflon films and special frit coatings for OSR and solar cell cover glasses are discussed. The techniques include sputtering, photoetching, silkscreening, and mechanical processes. A facility designed and built to simulate the electron plasma at geosynchronous altitudes is described along with test procedures. The results of material characterizations as well as electron irradiation aging effects in this facility for spacecraft polymers treated to control static charge are presented. The data presents results for electron beam energies up to 30 kV and electron current densities of 30 nA/cm squared. Parameters measured include secondary emission, surface leakage, and through the sample currents as a function of primary beam energy and voltage.

Amore, L. J.↗
NASA NTRS1979

Nuclear-Pumped Lasers

The state of the art in nuclear pumped lasers is reviewed. Nuclear pumped laser modeling, nuclear volume and foil excitation of laser plasmas, proton beam simulations, nuclear flashlamp excitation, and reactor laser systems studies are covered.

Source record↗
NASA NTRS1985

Ion-acoustic-like waves excited by the reflected ions at the earth's bow shock

Some model distributions based on recent observations and simulations of the plasma at the earth's bow shock are found to be unstable to obliquely propagating electrostatic instabilities. The model distributions consist of either an ion beam or an ion velocity ring accompanied by a bi-Maxwellian background ion distribution and a flattop electron distribution. Ion anisotropies and nonthermal electrons are capable of significantly lowering the threshold of the ion beam instability. The generated waves share many properties in common with the ion acoustic waves that have been observed at the earth's bow shock. The results also indicate the importance of an anisotropy in the background ion velocity distribution in identifying sources of the ion-acoustic-like waves observed in the ion foreshock and the solar wind.

Akimoto, K.↗
NASA NTRS1987

Double layers in plasmas; Proceedings of the Conference, Huntsville, AL, Mar. 1986

Papers are presented on such topics as double layers (DLs) and plasma-wave resistivity in extragalactic jets; the formation of a DL leading to the critical velocity phenomenon; formation mechanisms of laboratory DLs in triple plasma devices; and linear Vlasov stability in one-dimensional DLs. Consideration is also given to weak DLs in the auroral ionosphere; the dynamical properties of very strong DLs in a triple plasma device; particle simulation of auroral DLs; a muonic X-ray laser assisted by the catalyzed fusion of deuterium and tritium; and the feasbility of measuring the nuclear reaction cross sections at energies of several keV in a target under laser compression.

Williams, Alton C.↗
NASA NTRS1987

The theory of ionospheric focused heating

Ionospheric modification by high power radio waves and by chemical releases are combined in a theoretical study of ionospheric focused heating. The release of materials which promote electron-ion recombination creates a hole in the bottomside ionosphere. The ionospheric hole focuses high power radio waves from a ground-based transmitter to give a 20 dB or greater enhancement in power density. The intense radio beam excites atomic oxygen by collisions with accelerated electrons. Airglow from the excited oxygen provides a visible trace of the focused beam. The large increase in the intensity of the radio beam stimulates new wave-plasma interactions. Numerical simulations show that the threshold for the two-plasmon decay instability is exceeded. The interaction of the pump electromagnetic wave with the backward plasmon produces a scattered electromagnetic wave at 3/2 the pump frequency. The scattered wave provides a unique signature of the two-plasmon decay process for ground-based detection.

Bernhardt, P. A.↗
NASA NTRS1988

Multistream hydrodynamic modeling of interhemispheric plasma flow

Interhemispheric plasma flow was simulated using one-stream and two-stream hydrodymic models in order to test the suggestion of Banks et al. (1971) and others that the collision of high-speed flows originating from the conjugate hemispheres will cause the formation of a pair of shocks. The single-fluid hydrodynamic equations were modified to include multiple ion streams, allowing for the possibility of counterstreaming flow. It was found that a counterstreaming of ion streams from conjugate hemispheres does occur during the early stages of the refilling of plamaspheric flux tubes, and that a pair of reverse shocks does form. These shocks form away from the equator, and their subsequent motion creates conditions similar to those predicted by the single-stream hydrodynamic models. The findings support the conclusion of earlier studies that the refilling of the plasmasphere occurs from the equatorial region downward.

Rasmussen, C. E.↗