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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 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Atmosphere expansion and mass loss of close-orbit giant exoplanets heated by stellar XUV. II. Effects of planetary magnetic field; structuring of inner magnetosphere

This is the second paper in a series where we build a self-consistent model to simulate the mass-loss process of a close-orbit magnetized giant exoplanet, so-called hot Jupiter (HJ). In this paper we generalize the hydrodynamic (HD) model of an HJ's expanding hydrogen atmosphere, proposed in the first paper, to include the effects of intrinsic planetary magnetic field. The proposed self-consistent axisymmetric 2D magnetohydrodynamics model incorporates radiative heating and ionization of the atmospheric gas, basic hydrogen chemistry for the appropriate account of major species composing HJ's upper atmosphere and related radiative energy deposition, and H{sub 3}{sup +} and Lyα cooling processes. The model also takes into account a realistic solar-type X-ray/EUV spectrum for calculation of intensity and column density distribution of the radiative energy input, as well as gravitational and rotational forces acting in a tidally locked planet–star system. An interaction between the expanding atmospheric plasma and an intrinsic planetary magnetic dipole field leads to the formation of a current-carrying magnetodisk that plays an important role for topology and scaling of the planetary magnetosphere. A cyclic character of the magnetodisk behavior, composed of consequent phases of the disk formation followed by the magnetic reconnection with the ejection of a ring-type plasmoid, has been discovered and investigated. We found that the mass-loss rate of an HD 209458b analog planet is weakly affected by the equatorial surface field <0.3 G, but is suppressed by an order of magnitude at the field of 1 G.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Modeling of intense pulsed ion beam heated masked targets for extreme materials characterization

Intense, pulsed ion beams locally heat materials and deliver dense electronic excitations that can induce material modifications and phase transitions. Material properties can potentially be stabilized by rapid quenching. Pulsed ion beams with pulse lengths of order ns have recently become available for materials processing. Here, we optimize mask geometries for local modification of materials by intense ion pulses. The goal is to rapidly excite targets volumetrically to the point where a phase transition or local lattice reconstruction is induced followed by rapid cooling that stabilizes desired material's properties fast enough before the target is altered or damaged by, e.g., hydrodynamic expansion. By using a mask, the longitudinal dimension can be large compared to the transverse dimension, allowing the possibility of rapid transverse cooling. We performed HYDRA simulations that calculate peak temperatures for a series of excitation conditions and cooling rates of silicon targets with micro-structured masks and compare these to a simple analytical model. In conclusion, the model gives scaling laws that can guide the design of targets over a wide range of pulsed ion beam parameters.

36 MATERIALS SCIENCE↗
DOE OSTI2024

On the computation of moments in the Super-Transition-Arrays model for radiative opacity calculations

In the Super-Transition-Array statistical method for the computation of radiative opacity of hot dense matter, the moments of the absorption or emission features involve partition functions with reduced degeneracies, occurring through the calculation of averages of products of subshell populations. Here, in the present work, we discuss several aspects of the computation of such peculiar partition functions, insisting on the precautions that must be taken in order to avoid numerical difficulties. In a previous work, we derived a formula for supershell partition functions, which takes the form of a functional of the distribution of energies within the supershell and allows for fast and accurate computations, truncating the number of terms in the expansion. The latter involves coefficients for which we obtained a recursion relation and an explicit formula. We show that such an expansion can be combined with the recurrence relation for shifted partition functions. We also propose, neglecting the effect of fine structure as a first step, a positive-definite formula for the Super-Transition-Array moments of any order, providing an insight into the asymmetry and sharpness of the latter. The corresponding formulas are free of alternating sums. Several ways to speed up the calculations are also presented.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Automated Fitting of a Semi-empirical Multiphase Equation of State for Carbon

The equation of state (EOS) of carbon is important in high explosive, geophysical, and inertial confinement fusion applications. Within the semi-empirical Sesame framework, the EOS of each phase is represented by a sum of cold, vibrational, and thermal electronic Helmholtz free energy contributions. Each phase has ~5-10 independent parameters that are adjusted to reproduce single-phase data (e.g., thermal expansion, isothermal compression) as well as experimentally- and computationally- derived phase boundaries. Manual calibration of the full multiphase EOS is arduous. We present our progress in development of automated EOS parameterization based on minimization of an objective function. Here, this function encodes deviation of model EOS results from experimental/computational benchmarks. Optimization is implemented as a combination of global (particle swarm) and local optimization techniques.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Formulation And Implementation of A 1.75D Streamer Model

Streamers are a type of ionization wave occurring during the early time phase of a gas discharge. They are typically launched when the evolving space charge of an electron avalanche reaches a certain critical level, beyond which the field of the space charge itself is sufficient to drive further evolution of the ionization process. One of the most common ways to model streamers is known as a 1.5D model where the field of a uniformly charged set of discs of chosen radius is evaluated along the cylinder axis. This field drives a one-dimensional kinetic ionization process, which results in the nonlinear evolution of the streamer. This model is efficient, but has the drawback of fixing the radius and requiring it as an input parameter. Previously, we tried to extend the 1.5D model to include evolution of its radius by developing a two-step process of axial and radial expansion but we encountered stability issues with the model that we thought could have been due to decoupling the two steps. In this report we introduce a new formulation of a streamer model that includes radial expansion. The goal is to take radial moments of the starting axisymmetric fluid equations and thereby include the radial evolution of the streamer naturally and self-consistently from the beginning. We first develop the fluid model moments without electron attachment. We review the calculation of the electric fields required for the model and investigate approximations to improve computational efficiency. We discuss the code implementation of the model and finally, we add attachment to allow the treatment of electronegative gases.

42 ENGINEERING↗
NASA NTRS1986

An updated theory of the polar wind

The 'classical' polar wind is an ambipolar outflow of thermal plasma from the terrestrial ionosphere at high latitudes. As the plasma escapes along diverging geomagnetic flux tubes, it undergoes four major transitions, including a transition from chemical to diffusion dominance, a transition from subsonic to supersonic flow, a transition from collision-dominated to collisionless regimes, and a transition from a heavy to a light ion. A further complication arises because of horizontal convection of the flux tubes owing to magnetospheric electric fields. Recent modelling predictions indicate that the polar wind has the following characteristics: (1) the ion and electron distributions are anisotropic and asymmetric in the collisionless regime; (2) elevated electron temperatures act to produce significant escape fluxes of suprathermal O(+) ions; (3) the interaction of the hot magnetospheric and cold ionospheric electron population leads to a localized (double layer) electric field which accelerates the polar wind ions; (4) a time-dependent expansion produces suprathermal ions; and (5) large perturbations lead to the formation of forward and reverse shocks. These and other results are reviewed.

Schunk, R. W.↗
DOE OSTI2015

Thermal enhancement cartridge heater modified tritium hydride bed development, Part 2 - Experimental validation of key conceptual design features

The Thermal Enhancement Cartridge Heater Modified (TECH Mod) tritium hydride bed is an interim replacement for the first generation (Gen1) process hydride beds currently in service in the Savannah River Site (SRS) Tritium Facilities. 3 new features are implemented in the TECH Mod hydride bed prototype: internal electric cartridge heaters, porous divider plates, and copper foam discs. These modifications will enhance bed performance and reduce costs by improving bed activation and installation processes, in-bed accountability measurements, end-of-life bed removal, and He-3 recovery. A full-scale hydride bed test station was constructed at the Savannah River National Laboratory (SRNL) in order to evaluate the performance of the prototype TECH Mod hydride bed. Controlled hydrogen (H{sub 2}) absorption/ desorption experiments were conducted to validate that the conceptual design changes have no adverse effects on the gas transfer kinetics or H{sub 2} storage/release properties compared to those of the Gen1 bed. Inert gas expansions before, during, and after H{sub 2} flow tests were used to monitor changes in gas transfer rates with repeated hydriding/de-hydriding of the hydride material. The gas flow rates significantly decreased after initial hydriding of the material; however, minimal changes were observed after repeated cycling. The data presented herein confirm that the TECH Mod hydride bed would be a suitable replacement for the Gen1 bed with the added enhancements expected from the advanced design features. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2015

Harmonic growth of spherical Rayleigh-Taylor instability in weakly nonlinear regime

Harmonic growth in classical Rayleigh-Taylor instability (RTI) on a spherical interface is analytically investigated using the method of the parameter expansion up to the third order. Our results show that the amplitudes of the first four harmonics will recover those in planar RTI as the interface radius tends to infinity compared against the initial perturbation wavelength. The initial radius dramatically influences the harmonic development. The appearance of the second-order feedback to the initial unperturbed interface (i.e., the zeroth harmonic) makes the interface move towards the spherical center. For these four harmonics, the smaller the initial radius is, the faster they grow.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1993

Structure of the dayside reconnection layer in resistive MHD and hybrid models

Numerical simulations were performed to investigate the structure of the reconnection layer at the dayside magnetopause. Two typical cases are examined in detail; both are asymmetric in magnetic field and plasma density. In case 1, the guide fields in the magnetosheath and in the magnetosphere are set at zero and thus the tangential magnetic fields on the two sides of the initial current sheet are exactly antiparallel. In case 2, the angle between the tangential magnetic fields on the two sides of the initial current sheet is 145 deg. The results obtained from a resistive MHD model and from a hybrid model are found to be different. In the MHD simulation of case 1, a 2-4 intermediate shock is found to bound the reconnection layer on the magnetosheath side, while an Alfven wave pulse bounds the reconnection layer on the magnetospheric side. In case 2, it is found that a time-dependent intermediate shock (TDIS) bounds the reconnection layer on the magnetosheath side, with a slow expansion wave propagating behind. With the MHD simulations, in the general case in which the tangential magnetic fields on the two sides of the initial current sheet are not exactly antiparallel, a rotational discontinuity across which the tangential magnetic field rotates, a large angle is found to bound the reconnection layer on the magnetosheath side.

Lin, Y.↗
DOE OSTI2018

Heavy-ion collisions - hot QCD in a lab

High-energy heavy-ion collisions provide a unique opportunity to study the properties of the hot and dense strongly-interacting system composed of deconfined quarks and gluons -- the quark-gluon plasma (QGP) -- in laboratory conditions. The formation of a QGP is predicted by lattice QCD calculations as a crossover transition from hadronic matter (at zero baryochemical potential) and is expected to take place once the system temperature reaches values above 155 MeV and/or the energy density above $0.5~\mathrm{GeV}/\mathrm{fm}^{3}$. The nature of such a strongly coupled QGP has been linked to the early Universe at some microseconds after the Big Bang. To characterize the physical properties of the short-lived matter (lifetime of about $10~\mathrm{fm}/c$) experimental studies at Relativistic Heavy-Ion Collider and the Large Hadron collider use auto-generated probes, such as high-energy partons created early in the hadronic collisions, thermally emitted photons, and a set of particle correlations that are sensitive to the collective expansion and the dynamics of the system. The lectures briefly introduced some of the experimental techniques and provided a glimpse at some of the results.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Influence of lateral target size on hot electron production and electromagnetic pulse emission from laser-irradiated metallic targets

The influences of lateral target size on hot electron production and electromagnetic pulse emission from laser interaction with metallic targets have been investigated. Particle-in-cell simulations at high laser intensities show that the yield of hot electrons tends to increase with lateral target size, because the larger surface area reduces the electrostatic field on the target, owing to its expansion along the target surface. At lower laser intensities and longer time scales, experimental data characterizing electromagnetic pulse emission as a function of lateral target size also show target-size effects. Charge separation and a larger target tending to have a lower target potential have both been observed. The increase in radiation strength and downshift in radiation frequency with increasing lateral target size can be interpreted using a simple model of the electrical capacity of the target.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1991

Electric propulsion system technology

The work performed on the Ion Propulsion System Technology Task in FY90 is described. The objectives of this work fall under two broad categories. The first of these deals with issues associated with the application of xenon ion thrusters for primary propulsion of planetary spacecraft, and the second with the investigation of technologies which will facilitate the development of larger, higher power ion thrusters to support more advanced mission applications. Most of the effort was devoted to investigation of the critical issues associated with the use of ion thrusters for planetary spacecraft. These issues may be succinctly referred to as life time, system integration, and throttling. Chief among these is the engine life time. If the engines do not have sufficient life to perform the missions of interest, then the other issues become unimportant. Ion engine life time was investigated through two experimental programs: an investigation into the reduction of ion engine internal sputter erosion through the addition of small quantities of nitrogen, and a long duration cathode life test. In addition, a literature review and analysis of accelerator grid erosion were performed. The nitrogen addition tests indicated that the addition of between 0.5 and 1.0 percent of nitrogen by mass to the xenon propellant results in a reduction in the sputter erosion of discharge chamber components by a factor of between 20 and 50, with negligible reduction in thruster performance. The long duration test of a 6.35-mm dia. xenon hollow cathode is still in progress, and has accumulated more than 4,000 hours of operation at an emission current of 25 A at the time of this writing. One of the major system integration issues concerns possible interactions of the ion thruster produced charge exchange plasma with the spacecraft. A computer model originally developed to describe the behavior of mercury ion thruster charge exchange plasmas was resurrected and modified for xenon propellant. This model enables one to calculate the flow direction and local density of the charge exchange plasma, and indicates the degree to which this plasma can flow upstream of the thruster exhaust plane. A continuing effort to investigate the most desirable throttling technique for noble gas ion thrusters concentrated this year on experimentally determining the fixed flow rate throttling range of a 30-cm dia. thruster with a two-grid accelerator system. These experiments demonstrated a throttling capability which covers a 2.8 to 1 variation in input power. This throttling range is 55 percent greater than expected, and is due to better accelerator system performance at low net-to-total voltage ratios than indicated in the literature. To facilitate the development of large, higher power ion thrusters several brief studies were performed. These include the development of a technique which simulates ion thruster operation without beam extraction, the development of an optical technique to measure ion thruster grid distortion due to thermal expansion, tests of a capacitance measurement technique to quantify the accelerator system grid separation, and the development of a segmented thruster geometry which enables near term development of ion thrusters at power levels greater than 100 kW. Finally, a paper detailing the benefits of electric propulsion for the Space Exploration Initiative was written.

Brophy, John R.↗
DOE OSTI2016

Time-resolved x-ray imaging of a laser-induced nanoplasma and its neutral residuals

The evolution of individual, large gas-phase xenon clusters, turned into a nanoplasma by a high power infrared laser pulse, is tracked from femtoseconds up to nanoseconds after laser excitation via coherent diffractive imaging, using ultra-short soft x-ray free electron laser pulses. A decline of scattering signal at high detection angles with increasing time delay indicates a softening of the cluster surface. Here we demonstrate, for the first time a representative speckle pattern of a new stage of cluster expansion for xenon clusters after a nanosecond irradiation. The analysis of the measured average speckle size and the envelope of the intensity distribution reveals a mean cluster size and length scale of internal density fluctuations. Furthermore, the measured diffraction patterns were reproduced by scattering simulations which assumed that the cluster expands with pronounced internal density fluctuations hundreds of picoseconds after excitation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Stabilization of orthorhombic phase in single-crystal ZnSnN{sub 2} films

We report on the crystal structure of epitaxial ZnSnN{sub 2} films synthesized via plasma-assisted vapor deposition on (111) yttria stabilized zirconia (YSZ) and (001) lithium gallate (LiGaO{sub 2}) substrates. X-ray diffraction measurements performed on ZnSnN{sub 2} films deposited on LiGaO{sub 2} substrates show evidence of single-crystal, phase-pure orthorhombic structure in the Pn2{sub 1}a symmetry [space group (33)], with lattice parameters in good agreement with theoretically predicted values. This Pn2{sub 1}a symmetry is imposed on the ZnSnN{sub 2} films by the LiGaO{sub 2} substrate, which also has orthorhombic symmetry. A structural change from the wurtzite phase to the orthorhombic phase in films grown at high substrate temperatures ∼550°C and low values of nitrogen flux ∼10{sup −5} Torr is observed in ZnSnN{sub 2} films deposited on YSZ characterized by lattice contraction in the basal plane and a 5.7% expansion of the out-of-plane lattice parameter.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Toward Understanding the QGP with the STAR Experiment at RHIC

By accelerating heavy atomic nuclei (ions) to very large energies and then colliding these heavy ions at points where large particle detectors are positioned, the Relativistic Heavy Ion Collider (RHIC) provides the laboratory for studying nuclear matter under extreme conditions. It is under these extreme conditions that the matter is expected to undergo a phase transition, “melting” the protons and neutrons into their more fundamental constituents (quarks and gluons). The resulting state of matter is the so-called Quark Gluon Plasma (QGP) phase and is believed to have existed in the early universe, briefly after the Big Bang, before it cooled and formed into the matter that we know today. RHIC, at Brookhaven National Laboratory, has been providing high-energy heavy-ion collisions since the year 2000. One of the particle detectors at RHIC is called the Solenoidal Tracker at RHIC (STAR). New sub-detectors within the STAR experiment are capitalizing on the high collision rates currently provided by RHIC, allowing the experiment to select and record certain rare physics observables. The production of rare particles requires a large amount of energy and thus occurs early in a heavy-ion collision, allowing those rare particles to experience the full evolution of the collision, including the medium creation under extreme (hot and dense) conditions and subsequently the cooling and expansion of the matter. The rare particles therefore serve as probes of the medium created. Two rare-probe measurements will be investigated in this project: 1) particles resulting from scatterings of quarks and gluons with a large energy transfer in the early stage of a heavy-ion collision, and 2) particles that are made up of heavy-quark pairs. The study of such rare probes can provide information about the density and temperature of the medium created at RHIC.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Nondestructive Evaluation of Alkali-Silica Reaction in High-Strength Concrete for Aging Structures Sustainability

Concrete is a multiphase geo-material, which is utilized extensively in passive supporting and shielding structures at nuclear facilities. Chemo-mechanical degradation of concrete in old structures is a challenge to sustainability of aging commercial light water reactors. Alkali-silica reaction (ASR) is a common slowly evolving chemo-mechanical damage mechanism of concrete, which could take tens of years to reach the threshold stage when visible cracks appear in a concrete structure. In ASR, concrete constituents react with each other, namely the alkalis in the pore solution of hydrated cement paste (mostly K{sup +}OH{sup -} and Na{sup +}OH{sup -}) react with non-crystalline silica (SiO{sub 2}) of the aggregates to form highly hydrophilic gel. At sufficient levels of ambient relative humidity (typically above 85%), imbibition of water causes expansion of the ASR gel, which results in cracking of constrained reinforced concrete and ultimate structural weakening below safety margin levels. Stability and functional performance of concrete structures potentially suffering from chemo-mechanical deterioration due to ASR is evaluated in a multi-stage process involving material evaluation and structural engineering analysis. Existing methods used by industry for concrete material evaluation are based on extrusion of cores from multiple locations in a structure, and destructive laboratory tests on cores. Because each destructive test requires separate core extrusion, the total number of cores taken from the structure at once could be numbering in hundreds. Laboratory tests include petrography (high resolution optical microscopy of core sections) to develop damage rating index (DRI) score of concrete cores. Another test may involve chemical pore solution extraction from cores, and solution speciation analysis using inductively coupled plasma and mass spectroscopy (ICP/MS). Other tests may consist of mechanical evaluation of cores strength and fracture toughness. The DRI score of concrete material as well as other information obtained from the laboratory tests is subsequently used in structural engineering calculations, where stresses in the entire structure are modeled to evaluate its safety and mechanical stability. Extrusion of a large number of cores is highly undesirable for evaluation of nuclear facility concrete structures. The amount of destructive material testing could be minimized by developing methods for in-situ NDE of ASR to quantify the amount of deterioration that is occurring in the structure, and to identify areas in the structure where more deterioration may be occurring.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Low-shear three-dimensional equilibria and vacuum magnetic fields with flux surfaces

Stellarators are generically small current and low plasma beta devices. Often the construction of vacuum magnetic fields with good magnetic surfaces is the starting point for an equilibrium calculation. Although in cases with some continuous spatial symmetry, flux functions can always be found for vacuum magnetic fields, an analogous function does not, in general, exist in three dimensions. This work examines several simple equilibria and vacuum magnetic field problems with the intent of demonstrating the possibilities and limitations in the construction of such states. Starting with a simple vacuum magnetic field with closed field lines in a topological torus (toroidal shell with a flat metric), we obtain a self-consistent formal perturbation series using the amplitude of the non-symmetric vacuum fields as a small parameter. We show that systems possessing stellarator symmetry allow the construction order by order. We further indicate the significance of stellarator symmetry in the amplitude expansion of the full ideal magnetohydrodynamics (MHD) problem as well. We then investigate the conditions that guarantee neighbouring flux surfaces given the data on one surface, by expanding in the distance from that surface. We show that it is much more difficult to find low shear vacuum fields with surfaces than force-free fields or ideal MHD equilibrium. Finally, we demonstrate the existence of a class of vacuum magnetic fields, analogous to ‘snakes’ observed in tokamaks, which can be expanded to all orders.

Physics↗
DOE OSTI2025

The Three Hundred Project: Modeling baryon and hot-gas fraction evolution in simulated clusters

The baryon fraction of galaxy clusters, expressed as the ratio between the mass in baryons (including both stars and cold or hot gas) and the total mass, is a powerful tool to provide information on the cosmological parameters, while the hot-gas fraction provides indications on the physics of the intracluster plasma and its interplay with the processes that drive galaxy formation. Using cosmological hydrodynamical simulations of about 300 simulated massive galaxy clusters with a median mass M 500 ≈ 7 × 10 14 M ⊙ at z = 0, we model the relations between total mass and either baryon fraction or the hot gas fractions at overdensities Δ = 2500, 500, and 200 with respect to the cosmic critical density, and their evolution from z ∼ 0 to z ∼ 1.3. We utilized the simulated galaxy clusters from the Three Hundred project, which include star formation and feedback from both supernovae and active galactic nuclei. We fit the simulation results for such scaling relations against three analytic forms (linear, quadratic, and logarithmic in a logarithmic plane) and three forms for the redshift dependence, and we considered as a variable both the inverse of the cosmic scale factor, (1 + z), and the Hubble expansion rate, E(z). We show that power-law dependencies on cluster mass poorly describe the investigated relations. A power law fails to simultaneously capture the flattening of the total baryon and gas fractions at high masses, their drop at low masses, and the transition between these two regimes. The other two functional forms provide a more accurate description of the curvature in mass scaling. The fractions measured within smaller radii exhibit a stronger evolution than those measured within larger radii. From the analysis of these simulations, we evince that as long as we include systems in the mass range herein investigated, the baryon or gas fraction can be accurately related to the total mass through either a parabola or a logarithm in the logarithmic plane. The trends are common to all modern hydro simulations, although the amplitude of the drop at low masses might differ. Being able to observationally determine the gas fraction in groups will thus provide constraints on the baryonic physics.

galaxy clusters↗