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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 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Resonant excitation of coupled Rayleigh waves in a short and narrow fluid channel clad between two identical metal plates

Transmission of ultrasonic waves through a slit between two water immersed brass plates is studied for sub-wavelength plate thicknesses and slit apertures. Extraordinary high absorption is observed at discrete frequencies corresponding to resonant excitation of Rayleigh waves on the both sides of the channel. The coupling of the Rayleigh waves occurs through the fluid and the corresponding contribution to the dispersion has been theoretically derived and also experimentally confirmed. Symmetric and anti-symmetric modes are predicted but only the symmetric mode resonances have been observed. It follows from the dispersion equation that the coupled Rayleigh waves cannot be excited in a channel with apertures less than the critical one. The calculated critical aperture is in a good agreement with the measured acoustic spectra. These findings could be applied to design a broadband absorptive metamaterial.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

The dispersive behavior of collective excitations in fluids: An experimental test for the generalized collective modes theory

The predictions of the generalized collective modes (GCM) theory on the non-hydrodynamic dispersion of collective excitations of liquids and supercritical fluids have been tested against previous inelastic x-ray scattering measurements on samples of increasing complexity. We observed a good agreement between experimental results and theoretical predictions within the hypothesis that sound propagation is adiabatic. Overall, the performed comparison provides an experimental validation of GCM predictions and shows that, even in the transition region between the hydrodynamic and the mesoscopic regimes, thermal fluctuations have a minor influence on the dispersion, whose non-hydrodynamic effects are mostly driven by viscoelastic phenomena.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Design of a continuous-flow reactor for in situ x-ray absorption spectroscopy of solids in supercritical fluids

This paper presents the design and performance of a novel high-temperature and high-pressure continuous-flow reactor, which allows for x-ray absorption spectroscopy or diffraction in supercritical water and other fluids under high pressure and temperature. The in situ cell consists of a tube of sintered, polycrystalline aluminum nitride, which is tolerant to corrosive chemical media, and was designed to be stable at temperatures up to 500 deg. C and pressures up to 30 MPa. The performance of the reactor is demonstrated by the measurement of extended x-ray absorption fine structure spectra of a carbon-supported ruthenium catalyst during the continuous hydrothermal gasification of ethanol in supercritical water at 400 deg. C and 24 MPa.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Solitons in two-fluid plasma

We examine ion-acoustic solitons in two-fluid plasmas without the usual simplification of setting electron mass to zero. Assuming one-dimensional, electrostatic and cold protons, the system is treated analytically, resulting in an integral form solution. We present numerical calculations which resolve the ion-acoustic solitary wave signatures. Also, we consider the conditions for which ion-acoustic solitons may exist. The existence conditions set up a Mach number threshold. Our result shows that the Mach number threshold depends on the electron-to-proton mass ratio and the electron adiabatic index; for a special adiabatic index {gamma}= 2, the condition reduces to a cubic equation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Long wavelength gradient drift instability in Hall plasma devices. I. Fluid theory

The problem of long wavelength instabilities in Hall thruster plasmas is revisited. A fluid model of the instabilities driven by the E{sub 0} Multiplication-Sign B drift in plasmas with gradients of density, electron temperature, and magnetic field is proposed. It is shown that full account of compressibility of the electron flow in inhomogeneous magnetic field leads to quantitative modifications of earlier obtained instability criteria and characteristics of unstable modes. Modification of the stability criteria due to finite temperature fluctuations is investigated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Revisited global drift fluid model for linear devices

The problem of energy conserving global drift fluid simulations is revisited. It is found that for the case of cylindrical plasmas in a homogenous magnetic field, a straightforward reformulation is possible avoiding simplifications leading to energetic inconsistencies. The particular new feature is the rigorous treatment of the polarisation drift by a generalization of the vorticity equation. The resulting set of model equations contains previous formulations as limiting cases and is suitable for efficient numerical techniques. Examples of applications on studies of plasma blobs and its impact on plasma target interaction are presented. The numerical studies focus on the appearance of plasma blobs and intermittent transport and its consequences on the release of sputtered target materials in the plasma. Intermittent expulsion of particles in radial direction can be observed and it is found that although the neutrals released from the target show strong fluctuations in their propagation into the plasma column, the overall effect on time averaged profiles is negligible for the conditions considered. In addition, the numerical simulations are utilised to perform an a-posteriori assessment of the magnitude of energetic inconsistencies in previously used simplified models. It is found that certain popular approximations, in particular by the use of simplified vorticity equations, do not significantly affect energetics. However, popular model simplifications with respect to parallel advection are found to provide significant deterioration of the model consistency.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Derivation of nonlinear Schroedinger equation for electrostatic and electromagnetic waves in fully relativistic two-fluid plasmas by the reductive perturbation method

The reductive perturbation method is used to derive a generic form of nonlinear Schroedinger equation (NLSE) that describes the nonlinear evolution of electrostatic (ES)/electromagnetic (EM) waves in fully relativistic two-fluid plasmas. The matrix eigenvector analysis shows that there are two mutually exclusive modes of waves, each mode involving only either one of two electric potentials, A and {phi}. The general result is applied to the electromagnetic mode in electron-ion plasmas with relativistically high electron temperature (T{sub e} Much-Greater-Than m{sub e}c{sup 2}). In the limit of high frequency (ck Much-Greater-Than {omega}{sub e}), the NLSE predicts bump type electromagnetic soliton structures having width scaling as {approx}kT{sub e}{sup 5/2}. It is shown that, in electron-positron pair plasmas with high temperature, dip type electromagnetic solitons can exist. The NLSE is also applied to electrostatic (Langmuir) wave and it is shown that dip type solitons can exist if k{lambda}{sub D} Much-Less-Than 1, where {lambda}{sub D} is the electron's Debye length. For the k{lambda}{sub D} Much-Greater-Than 1, however, the solution is of bump type soliton with width scaling as {approx}1/(k{sup 5}T{sub e}). It is also shown that dip type solitons can exist in cold plasmas having relativistically high streaming speed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

The drag force on a subsonic projectile in a fluid complex plasma

The incompressible Navier-Stokes equation is employed to describe a subsonic particle flow induced in complex plasmas by a moving projectile. Drag forces acting on the projectile in different flow regimes are calculated. It is shown that, along with the regular neutral gas drag, there is an additional force exerted on the projectile due to dissipation in the surrounding particle fluid. This additional force provides significant contribution to the total drag.

42 ENGINEERING↗
DOE OSTI2012

Collisionless kinetic-fluid simulation of zonal flows in non-circular tokamaks

Fluid simulation of linear zonal flow damping is done with a closure model based on the collisionless gyrokinetics [Sugama et al., Phys. Plasmas 14, 022502 (2007)]. Simulation results of residual zonal flow for low radial wavenumbers are compared with theoretical formulas for circular and non-circular tokamaks. The effects of the elongation and the triangularity are shown to be properly treated in the closure model. Effects of initial parallel flows on zonal flow evolution are also clarified. An appropriate choice of the initial parallel flow gives a much higher residual level than the conventional result with no initial parallel flow. Besides, the zonal flow simulations are done with the E Multiplication-Sign B nonlinearity as initial sources, which is evaluated from linear gyrokinetic microinstabilities such as ion temperature gradient modes, trapped electron modes, and electron temperature gradient modes, in order to estimate efficiency of zonal flow generation by the source instabilities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Fluid equations in the presence of electron cyclotron current drive

Two-fluid equations, which include the physics imparted by an externally applied radiofrequency source near electron cyclotron resonance, are derived in their extended magnetohydrodynamic forms using the formalism of Hegna and Callen [Phys. Plasmas 16, 112501 (2009)]. The equations are compatible with the closed fluid/drift-kinetic model developed by Ramos [Phys. Plasmas 17, 082502 (2010); 18, 102506 (2011)] for fusion-relevant regimes with low collisionality and slow dynamics, and they facilitate the development of advanced computational models for electron cyclotron current drive-induced suppression of neoclassical tearing modes.

42 ENGINEERING↗
DOE OSTI2013

Fluid modeling of radio frequency and direct currents in a biased magnetized plasma

This model aims at simulating a magnetized plasma column connected on one side to a probe and on the other side to an ICRH (Ion Cyclotron Resonant Heating) antenna. This is a double probe modeling of a plasma flux tube exchanging perpendicular currents: rf polarization current and dc currents (inertia, viscous, and friction) perpendicular to the magnetic field. A self consistent solution for the rectified potential and the density is obtained under the assumptions of flute hypothesis, inertialess electrons, and no collision in parallel direction. The main effect of rf biasing on the antenna side is to shift the IV characteristic so that the floating potential can be increased up to ln(I{sub 0}(eV{sub rf}/(k{sub B}T{sub e}))), with I{sub 0} the modified Bessel function of the first kind. On the contrary, the effect of dc currents is to decrease the plasma potential and the sheath potential which can be lower than 3k{sub B}T{sub e}/e or even be negative. Experimental characteristics are well matched by the 1D fluid code and exhibit very high negative currents (more than 30 j{sub i} the ion saturation current) for high positive biasing of the probe and for long flux tube (10 m). The non-saturation of the electron current is here due to high transverse transport enhanced by convective fluxes and dc currents able to bring an amount of density around the biased flux tube. During comparisons with experiments, the floating potential measured by a reciprocating probe is recovered by the code revealing that for a 120 V measured peak potential on the probe, the rf potential on the ICRH antenna is twice this value. Finally, the density profile can be flattened or steepened as a function of the transverse dc current direction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Global two-fluid simulations of geodesic acoustic modes in strongly shaped tight aspect ratio tokamak plasmas

Following recent observations suggesting the presence of the geodesic acoustic mode (GAM) in ohmically heated discharges in the Mega Amp Spherical Tokamak (MAST) [J. R. Robinson et al., Plasma Phys. Controlled Fusion 54, 105007 (2012)], the behaviour of the GAM is studied numerically using the two fluid, global code CENTORI [P. J. Knight et al. Comput. Phys. Commun. 183, 2346 (2012)]. We examine mode localisation and effects of magnetic geometry, given by aspect ratio, elongation, and safety factor, on the observed frequency of the mode. An excellent agreement between simulations and experimental data is found for simulation plasma parameters matched to those of MAST. Increasing aspect ratio yields good agreement between the GAM frequency found in the simulations and an analytical result obtained for elongated large aspect ratio plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Improved fluid simulations of radio-frequency plasmas using energy dependent ion mobilities

Symmetric and asymmetric capacitively coupled radio-frequency plasmas in oxygen at 40 Pa, 300 V voltage amplitude and a discharge gap of 40 mm are investigated by means of one-dimensional numerical semi-kinetic fluid modeling on the basis of a simplified reaction scheme including the dominant positive and negative ions, background gas, and electrons. An improved treatment, by accounting for the dependence of ion mobilities on E/N, is compared to the standard approach, based on using zero-field mobility values only. The charged particle dynamics as a result of direct electron impact ionization of oxygen, secondary electron release from the electrodes, the spatial distribution of all involved particles as well as impact of geometry and model modification on ion energies is analyzed and compared to independent simulations and experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Second-order radio frequency kinetic theory revisited: Resolving inconsistency with conventional fluid theory

The second-order velocity distribution function was calculated from the second-order rf kinetic theory [Jaeger et al., Phys. Plasmas 7, 641 (2000)]. However, the nonresonant ponderomotive force in the radial direction derived from the theory is inconsistent with that from the fluid theory. The inconsistency arises from that the multiple-timescale-separation assumption fails when the second-order Vlasov equation is directly integrated along unperturbed particle orbits. A slowly ramped wave field including an adiabatic turn-on process is applied in the modified kinetic theory in this paper. Since this modification leads only to additional reactive/nonresonant response relevant with the secular resonant response from the previous kinetic theory, the correct nonresonant ponderomotive force can be obtained while all the resonant moments remain unchanged.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Effect of confinement on the solid-liquid coexistence of Lennard-Jones Fluid

The solid-liquid coexistence of a Lennard-Jones fluid confined in slit pores of variable pore size, H, is studied using molecular dynamics simulations. Three-stage pseudo-supercritical transformation path of Grochola [J. Chem. Phys. 120(5), 2122 (2004)] and multiple histogram reweighting are employed for the confined system, for various pore sizes ranging from 20 to 5 molecular diameters, to compute the solid-liquid coexistence. The Gibbs free energy difference is evaluated using thermodynamic integration method by connecting solid-liquid phases under confinement via one or more intermediate states without any first order phase transition among them. Thermodynamic melting temperature is found to oscillate with wall separation, which is in agreement with the behavior seen for kinetic melting temperature evaluated in an earlier study. However, thermodynamic melting temperature for almost all wall separations is higher than the bulk case, which is contrary to the behavior seen for the kinetic melting temperature. The oscillation founds to decay at around H = 12, and beyond that pore size dependency of the shift in melting point is well represented by the Gibbs-Thompson equation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

A two-fluid model for relativistic heat conduction

Three years ago it was presented in these proceedings the relativistic dynamics of a multi-fluid system together with various applications to a set of topical problems [1]. In this talk, I will start from such dynamics and present a covariant formulation of relativistic thermodynamics which provides us with a causal constitutive equation for the propagation of heat in a relativistic setting.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Elastically Cooperative Activated Barrier Hopping Theory of Relaxation in Viscous Fluids. II. Thermal Liquids

Building on the elastically collective nonlinear Langevin equation theory developed for hard spheresin Paper I, we propose and implement a quasi-universal theory for the alpha relaxation of thermalliquids based on mapping them to an effective hard sphere fluid via the dimensionless compressibility.The result is a zero adjustable parameter theory that can quantitatively address in a unifiedmanner the alpha relaxation time over 14 or more decades. The theory has no singularities abovezero Kelvin, and relaxation in the equilibrium low temperature limit is predicted to be of a roughlyArrhenius form. The two-barrier (local cage and long range collective elastic) description results ina rich dynamic behavior including apparent Arrhenius, narrow crossover, and deeply supercooledregimes, and multiple characteristic or crossover times and temperatures of clear physical meaning.Application of the theory to nonpolar molecules, alcohols, rare gases, and liquids metals is carriedout. Overall, the agreement with experiment is quite good for the temperature dependence of thealpha time, plateau shear modulus, and Boson-like peak frequency for van der Waals liquids, thoughless so for hydrogen-bonding molecules. The theory predicts multiple growing length scales uponcooling, which reflect distinct aspects of the coupled local hopping and cooperative elastic physics.Calculations of the growth with cooling of an activation volume, which is strongly correlated with ameasure of dynamic cooperativity, agree quantitatively with experiment. Comparisons with elastic,entropy crisis, dynamic facilitation, and other approaches are performed, and a fundamental basisfor empirically extracted crossover temperatures is established. The present work sets the stage foraddressing distinctive glassy phenomena in polymer melts, and diverse liquids under strong confinement.

Mirigian, Stephen↗
DOE OSTI2014

Melting transition of Lennard-Jones fluid in cylindrical pores

Three-stage pseudo-supercritical transformation path and multiple-histogram reweighting technique are employed for the determination of solid-liquid coexistence of the Lennard-Jones (12-6) fluid, in a structureless cylindrical pore of radius, R, ranging from 4 to 20 molecular diameters. The Gibbs free energy difference is evaluated using thermodynamic integration method by connecting solid and liquid phases under confinement via one or more intermediate states without any first order phase transition among them. The thermodynamic melting temperature, T{sub m}, is found to oscillate for pore size, R < 8, which is in agreement with the behavior observed for the melting temperature in slit pores. However, T{sub m} for almost all pore sizes is less than the bulk case, which is contrary to the behavior seen for the slit pore. The oscillation in T{sub m} decays at around pore radius R = 8, and beyond that shift in the melting temperature with respect to the bulk case is in line with the prediction of the Gibbs-Thomson equation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

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