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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Numerical modeling of radiation-dominated and quantum-electrodynamically strong regimes of laser-plasma interaction

Ultra-strong laser pulses can be so intense that an electron in the focused beam loses significant energy due to {gamma}-photon emission while its motion deviates via the radiation back-reaction. Numerical methods and tools designed to simulate radiation-dominated and quantum-electrodynamically strong laser-plasma interactions are summarized here.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

The two modes extension to the Berk-Breizman equation: Delayed differential equations and asymptotic solutions

The integro-differential Berk-Breizman (BB) equation, describing the evolution of particle-driven wave mode is transformed into a simple delayed differential equation form {nu}{partial_derivative}a({tau})/{partial_derivative}{tau}=a({tau}) -a{sup 2}({tau}- 1) a({tau}- 2). This transformation is also applied to the two modes extension of the BB theory. The obtained solutions are presented together with the derived asymptotic analytical solutions and the numerical results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Time-fractional KdV equation for plasma of two different temperature electrons and stationary ion

Using the time-fractional KdV equation, the nonlinear properties of small but finite amplitude electron-acoustic solitary waves are studied in a homogeneous system of unmagnetized collisionless plasma. This plasma consists of cold electrons fluid, non-thermal hot electrons, and stationary ions. Employing the reductive perturbation technique and the Euler-Lagrange equation, the time-fractional KdV equation is derived and it is solved using variational method. It is found that the time-fractional parameter significantly changes the soliton amplitude of the electron-acoustic solitary waves. The results are compared with the structures of the broadband electrostatic noise observed in the dayside auroral zone.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Stochastic heating of dust particles in complex plasmas as an energetic instability of a harmonic oscillator with random frequency

The paper describes the occurrence of stochastic heating of dust particles in dusty plasmas as an energy instability due to the correlations between dust grain charge and electric field fluctuations. The possibility that the mean energy (''temperature'') of dust particles can grow in time has been found both from the self-consistent kinetic description of dusty plasmas taking into account charge fluctuations [U. de Angelis, A. V. Ivlev, V. N. Tsytovich, and G. E. Morfill, Phys. Plasmas 12(5), 052301 (2005)] and from a Fokker-Planck approach to systems with variable charge [A. V. Ivlev, S. K. Zhdanov, B. A. Klumov, and G. E. Morfill, Phys. Plasmas 12(9), 092104 (2005)]. Here, a different derivation is given by using the mathematical techniques of the so called multiplicative stochastic differential equations. Both cases of ''fast'' and ''slow'' fluctuations are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Megavolt range voltage measurement in vacuum through a short-circuited line

Method of voltage measurement at a vacuum load by means of homogeneous short-circuited vacuum-isolated line was considered. Prior to appearance of a measured high-voltage pulse, a magnetic field is formed in the line due to the bias current. Biasing provides fulfillment of magnetic electron isolation conditions and strong pressing of an electron layer down to the cathode already at the voltage wave front. As a result, a weak change of the ''hot'' line wave impedance is achieved during a pulse. Theoretical consideration and numerical simulation of the measuring line operation in the presence of bias current basing the applicability of the method was carried out. The method was used to determine the plasma-filled diode voltage at a megavolt voltage level. The absence of electron leakages at the voltage wave propagation of the amplitude {approx_equal}1 MV along the measuring line of the length 2.3 m with the wave impedance of 136 {Omega} and initial bias current of {approx_equal}6 kA was realized.

42 ENGINEERING↗
DOE OSTI2011

Measurement of the sheath capacitance of a planar probe

The sheath capacitance was measured on a planar probe dc-biased with respect to the plasma potential using the phase sensitive detection method in the region separated from the rf discharge plasmas by an immersed grid. It was observed that the sheath capacitance was negative when the collecting electrode of the probe was positioned downward toward the grid and biased near the plasma potential. This indicates that a double sheath had built up near the probe electrode. This tendency can be explained by the sheath capacitance, which is calculated using Poisson's equation with a non-zero electrical field and an ion velocity condition at the sheath edge.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Decay kinetics of the excited S{sub 1} state of the cyanine dye Cy{sup +}I{sup -} (thiacarbocyanine iodide): The computation of quantum yields for different pathways

This work explains the unordinary solvent effect which was observed in the photochemical decay kinetics for the cyanine dye thiacarbocyanine iodide (Cy{sup +}I{sup -}) in binary solvent mixtures toluene/dimethylsulfoxide. The interpretation is formulated in terms of the probability density F(R) describing the distribution of interionic distances R in the ion pair Cy{sup +}I{sup -} and depending on the solvent composition. The proper normalization of this distribution is expressed via the degree of association {alpha} for the ion pair in a given solvent mixture. The {alpha} values are, in turn, extracted by means of the mass action law from the ionic association constants computed in a separate publication. The detailed kinetic scheme includes the empirical parametrization of the R-dependent kinetic constants for different decay channels. The multiparameter fitting procedure represents, with the reasonable parameter values, the dependence of the observed quantum yields on the solvent composition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Waves in a bounded quantum plasma with electron exchange-correlation effects

Within a quantum hydrodynamic model, the collective excitations of the quantum plasma with electron exchange-correlation effects in a nano-cylindrical wave guide are studied both analytically and numerically. The influences of the electron exchange-correlation potential, the radius of the wave guide, and the quantum effect on the dispersion properties of the bounded quantum plasma are discussed. Significant frequency-shift induced by the electron exchange-correlation effect, the radius of the wave guide and the quantum correction are observed. It is found that the influence of the electron exchange-correlation, the radius of the wave guide and the quantum correction on the wave modes in a bounded nano-waveguide are strongly coupled.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Charge distribution over dust particles in a flowing plasma

This paper presents an analytical model for the physical understanding of the charge distribution on dust particles in meso-thermal flow of plasmas where the flow speed of plasma relative to the dust particle is larger than the ion thermal speed but much less than the thermal speed of electrons. The formulation is based on the master difference equation for population balance and the number and energy balance considerations, allowing the charge to be only an integral multiple (positive or negative) of the electronic charge. The kinetics for (i) dark complex plasmas where accretion of electrons/ionic species are the dominant charging mechanisms and (ii) illuminated complex plasmas where photoemission significantly contributes to dust charging has been developed. The expression for the mean energy associated with the accretion of ionic species over dust gains in meso-thermal flow of complex plasmas has been derived and employed to obtain the charge distribution and other relevant plasma parameters. The high speed of meso-thermal flow of the plasma influences the dust charging towards more positive character and leads to significant reduction in electron and ion densities, even in the presence of photoemission from dust grains.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Nonlinear waves and coherent structures in the quantum single-wave model

Starting from the von Neumann-Maxwell equations for the Wigner quasi-probability distribution and for the self-consistent electric field, the quantum analog of the classical single-wave model has been derived. The linear stability of the quantum single-wave model has been studied, and periodic in time patterns have been found both analytically and numerically. In addition, some features of quantum chaos have been detected in the unstable region in parameter space. Further, a class of standing-wave solutions of the quantum single-wave model has also been found, which have been observed to behave as stable solitary-wave structures. The analytical results have been finally compared to the exact system dynamics obtained by solving the corresponding equations in Schrodinger representation numerically.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Dispersion relations for circular single and double dusty plasma chains

We derive dispersion relations for a system of identical particles confined in a two-dimensional annular harmonic well and which interact through a Yukawa potential, e.g., a dusty plasma ring. When the particles are in a single chain (i.e., a one-dimensional ring), we find a longitudinal acoustic mode and a transverse optical mode which show approximate agreement with the dispersion relation for a straight configuration for large radii of the ring. When the radius decreases, the dispersion relations modify: there appears an anticrossing of the modes near the crossing point resulting in a frequency gap between the lower and upper branches of the modified dispersion relations. For the double chain (i.e., a two-dimensional zigzag configuration), the dispersion relation has four branches: longitudinal acoustic and optical and transverse acoustic and optical.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

The influence of finite Larmor radius effects on the radial interchange motions of plasma filaments

The influence of finite Larmor radius (FLR) effects on the perpendicular convection of isolated particle density filaments driven by interchange motions in magnetized plasmas is investigated using a two-moment gyrofluid model. By means of numerical simulations on a two-dimensional, bi-periodic domain perpendicular to the magnetic field, it is demonstrated that the radial velocities of the blob-like filaments are roughly described by the inertial scaling, which prescribes a velocity proportional to the square root of the summed electron and ion pressures times the square root of the blob width. Due to FLR effects, the poloidal up-down symmetry in the particle density field observed in the zero Larmor radius limit is broken. The symmetry breaking implies a poloidal motion of the blobs in the Bx{nabla}B direction. At later times, the direction of the poloidal motion is reversed when the blob is decelerated. It is shown that the spatial structure of the blobs depends on the ratio of the ion gyroradius to the initial filament size {rho}{sub i}/{sigma}. Blobs with {rho}{sub i}/{sigma} > or approx. 0.2 remain coherent as they move through the scrape-off layer, whereas blobs with {rho}{sub i}/{sigma} < or approx. 0.1 form plume-like structures that loose their coherence and eventually become fragmented. After having traveled approximately five times their initial widths, coherent blobs carry {approx}2-3 times the particle density of fragmented blobs. It is shown that FLR effects reduce mixing, stretching, and generation of small spatial scales in the particle density field by setting up a sheared flow surrounding the blob.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

On kinetic description of electromagnetic processes in a quantum plasma

A nonlinear kinetic equation for nonrelativistic quantum plasma with electromagnetic interaction of particles is obtained in the Hartree's mean-field approximation. It is cast in a convenient form of Vlasov-Boltzmann-type equation with ''quantum interference integral'', which allows for relatively straightforward modification of existing classical Vlasov codes to incorporate quantum effects (quantum statistics and quantum interference of overlapping particles wave functions), without changing the bulk of the codes. Such modification (upgrade) of existing Vlasov codes may provide a direct and effective path to numerical simulations of nonlinear electrostatic and electromagnetic phenomena in quantum plasmas, especially of processes where kinetic effects are important (e.g., modulational interactions and stimulated scattering phenomena involving plasma modes at short wavelengths or high-order kinetic modes, dynamical screening and interaction of charges in quantum plasma, etc.) Moreover, numerical approaches involving such modified Vlasov codes would provide a useful basis for theoretical analyses of quantum plasmas, as quantum and classical effects can be easily separated there.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Nonlinear wake potential and stopping power for charged particles interacting with a one-dimensional electron gas

We examine the interaction of particles with a one-dimensional electron gas by employing the quantum hydrodynamic (QHD) theory, where the nonlinear wake potential and stopping power have been numerically calculated by solving the nonlinear QHD equations with flux corrected transport (FCT) numerical method. In our calculation, the nonlinear effects on the wake potential and stopping power are clearly observed and presented. In the moving coordinate, comparisons are made between the nonlinear and linear wake potentials, in which the maximum values are larger and more oscillations appear behind the projectile in a nonlinear case in contrast to that in a linear case. The nonlinear wake potentials show a clear dependence on time, that is, the FCT algorithm solves the nonlinear QHD equations by time integration starting from the initial time. It is shown that the nonlinear effects can enhance the wake potential and stopping power for particle velocities greater than a few Bohr velocities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Oscillatory quantum screening effects on the positronium (Ps) formation in quantum plasmas

The oscillatory quantum screening effects on the positronium formation by the positron are investigated in quantum plasmas. It is found that the oscillatory screening effects suppress the positronium formation radius as well as the positronium formation cross section. It is also found that the positronium formation radius decreases with increasing quantum wave number. It is found that the peak position of the differential cross section is receded from the projectile with decreasing quantum wave number. In addition, the oscillatory screening effects on the positronium formation cross section are found to be decreased with an increase of the collision energy.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Automatic generation of IGUN{sup (C)} input files for enhanced mesh resolution at the plasma meniscus

The plasma-beam interface (meniscus) is highly nonlinear and its correct simulation needs a mesh resolution of the order of the Debye length. In high intensity ion sources, the plasma density is usually too high and the Debye length is too small for a sufficient mesh resolution. A well established method to overcome this dilemma is the use of a field line and an equipotential line to be created in a first run, in order to dissect the simulation problem into a plasma part with much higher mesh resolution and a transport part with usual resolution. In the past many users of IGUN have found it difficult to perform this dissection. Therefore, a new feature has been added to IGUN to automatically write new input files for the dissected areas. For this a field line starting point needs to be defined as well as the potential of a pseudo electrode. The field line then is used for the plasma part as a slanted and curved Neumann boundary, while the pseudo electrode will act as the extraction electrode. The trajectory end data then are used in the automatically generated concatenating run as ion starting input without any need for the user to adjust for positions or different mesh resolutions. Here we show as an example the simulation of the well-known CHORDIS ion source, the calculated field line, the pseudo equipotential line, and the resulting simulations for the automatically generated input files for the plasma and the transport parts.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

A new mode and its interaction through ponderomotive force in electron-positron-ion plasmas

A new mode is found in e-p-i plasma in the presence of density and temperature difference of lighter particles. The electron beam induced Cherenkov instability condition for the excitation of positron sound wave is obtained for the system under consideration. Zakharov's equation with sign modification due to negative Ponderomotive pressure is obtained. Nonlinear Schroedinger wave equation for the envelope type solitary waves is derived. Both stationary and nonstationary solutions are found and the subsonic and supersonic limits are also discussed. In the stationary case, rarefactive type solitary solution is obtained, whereas the nonstationary case yields the ion acoustic shock like structure solution which is very interesting. The importance of the study with relevance to both laboratory and astrophysical plasmas is pointed out.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Statistical analysis of high power microwave surface flashover delay times in nitrogen with metallic field enhancements

The physical mechanisms that contribute to atmospheric breakdown induced by high power microwaves (HPMs) are of particular interest for the further development of high power microwave systems and related technologies. For a system in which HPM is produced in a vacuum environment for the purpose of radiating into atmosphere, it is necessary to separate the atmospheric environment from the vacuum environment with a dielectric interface. Breakdown across this interface on the atmospheric side and plasma development to densities prohibiting further microwave propagation are of special interest. In this paper, the delay time between microwave application and plasma emergence is investigated. Various external parameters, such as UV illumination or the presence of small metallic points on the surface, provide sources for electron field emission and influence the delay time which yields crucial information on the breakdown mechanisms involved. Due to the inherent statistical appearance of initial electrons and the statistics of the charge carrier amplification mechanisms, the flashover delay times deviate by as much as {+-}50% from the average, for the investigated case of discharges in N{sub 2} at pressures of 60-140 Torr and a microwave frequency of 2.85 GHz with 3 {mu}s pulse duration, 50 ns pulse risetime, and MW/cm{sup 2} power densities. The statistical model described in this paper demonstrates how delay times for HPM surface flashover events can be effectively predicted for various conditions given sufficient knowledge about ionization rate coefficients as well as the production rate for breakdown initiating electrons.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗