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Results for “ELECTROMAGNETIC RADIATION”

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
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DOE OSTI2013

The wave energy flux of high frequency diffracting beams in complex geometrical optics

We consider the construction of asymptotic solutions of Maxwell's equations for a diffracting wave beam in the high frequency limit and address the description of the wave energy flux transported by the beam. With this aim, the complex eikonal method is applied. That is a generalization of the standard geometrical optics method in which the phase function is assumed to be complex valued, with the non-negative imaginary part accounting for the finite width of the beam cross section. In this framework, we propose an argument which simplifies significantly the analysis of the transport equation for the wave field amplitude and allows us to derive the wave energy flux. The theoretical analysis is illustrated numerically for the case of electron cyclotron beams in tokamak plasmas by using the GRAY code [D. Farina, Fusion Sci. Technol. 52, 154 (2007)], which is based upon the complex eikonal theory. The results are compared to those of the paraxial beam tracing code TORBEAM [E. Poli et al., Comput. Phys. Commun. 136, 90 (2001)], which provides an independent calculation of the energy flow.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Frequency shift of the propagating ultraintense field in a plasma with a fraction of electron-positron pairs under the conditions of response saturation

A model is derived from the Maxwell and fluid dynamics equations to describe the interactions between a relativistically intense electromagnetic wave and a cold unmagnetized plasma composed of an electron-ion background and a fraction of electron-positron pairs. Combining the envelope approximation for the propagating field and the quasistatic treatment of the plasma dynamics, the model sustains fully nonlinear plane-wave solutions and shows that saturation of the plasma response occurs at ultrarelativistic intensities of the incident field even for pair concentrations far below those of the electron-ion background. Stability of the electromagnetic wave under the saturation conditions is demonstrated and an expression is derived to link its interaction-induced frequency shift to the concentration of the electron-positron pairs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Spontaneous electromagnetic fluctuations in unmagnetized plasmas. II. Relativistic form factors of aperiodic thermal modes

General expressions for the electromagnetic fluctuation spectra in unmagnetized plasmas are derived using fully relativistic dispersion functions and form factors for the important class of isotropic plasma particle distribution functions including in particular relativistic Maxwellian distributions. In order to obtain fluctuation spectra valid in the entire complex frequency plane, the proper analytical continuations of the unmagnetized form factors and dispersion functions are presented. The results are illustrated for the important special case of isotropic Maxwellian particle distribution functions providing in particular the thermal fluctuations of aperiodic modes. No restriction to the plasma temperature value is made, and the electromagnetic fluctuation spectra of ultrarelativistic thermal plasmas are calculated. The fully relativistic calculations also provide more general results in the limit of nonrelativistic plasma temperatures being valid in the entire complex frequency plane. They complement our earlier results in paper I and III of this series for negative values of the imaginary part of the frequency. A new collective, transverse, damped aperiodic mode with the damping rate γ∝−k{sup −5/3} is discovered in an isotropic thermal electron-proton plasma with nonrelativistic temperatures.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

On nonlinear physics of shear Alfvén waves

Shear Alfvén waves (SAW) are electromagnetic oscillations prevalent in laboratory and nature magnetized plasmas. Due to their anisotropic nature, it is well known that the linear wave propagation and dispersiveness of SAW are fundamentally affected by plasma nonuniformities and magnetic field geometries, such as the existence of continuous spectrum, spectral gaps, and discrete eigenmodes in toroidal plasmas. This work discusses the pure Alfvénic state and demonstrates the crucial roles that finite ion compressibility, non-ideal kinetic effects, and geometry play in breaking it and, thereby, the nonlinear physics of SAW wave-wave interactions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Simulations of drift resistive ballooning L-mode turbulence in the edge plasma of the DIII-D tokamak

Results from simulations of electromagnetic drift-resistive ballooning turbulence for tokamak edge turbulence in realistic single-null geometry are reported. The calculations are undertaken with the BOUT three-dimensional fluid code that solves Braginskii-based fluid equations [X. Q. Xu and R. H. Cohen, Contrib. Plasma Phys. 36, 158 (1998)]. The simulation setup models L-mode edge plasma parameters in the actual magnetic geometry of the DIII-D tokamak [J. L. Luxon et al., Fusion Sci. Technol. 48, 807 (2002)]. The computations track the development of drift-resistive ballooning turbulence in the edge region to saturation. Fluctuation amplitudes, fluctuation spectra, and particle and thermal fluxes are compared to experimental data near the outer midplane from Langmuir probe and beam-emission-spectroscopy for a few well-characterized L-mode discharges in DIII-D. The simulations are comprised of a suite of runs in which the physics model is varied to include more fluid fields and physics terms. The simulations yield results for fluctuation amplitudes, correlation lengths, particle and energy fluxes, and diffusivities that agree with measurements within an order of magnitude and within factors of 2 or better for some of the data. The agreement of the simulations with the experimental measurements varies with respect to including more physics in the model equations within the suite of models investigated. The simulations show stabilizing effects of sheared E × B poloidal rotation (imposed zonal flow) and of lower edge electron temperature and density.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Enhanced nonlinear interaction of powerful electromagnetic waves with ionospheric plasma near the second electron gyroharmonic

Plasma experiments in which a powerful electromagnetic pump wave is transmitted into the ionosphere from the ground give access to a rich range of phenomena, including gyroharmonic effects when the pump frequency is near an harmonic of the ionospheric electron gyrofrequency. For pump frequencies close to the second gyroharmonic, experiments show a strong enhancement, as observed in radar scatter from pump-induced geomagnetic field-aligned density striations and optical emissions. This is in contrast to the case at the third harmonic and higher at which most of the effects are instead suppressed. We show theoretically that electrostatic oscillations can be localized in density inhomogeneities associated with small scale striations. The localized field is a mixture of the electron Bernstein and upper hybrid modes when the pump frequency is near the second gyroharmonic. The coupling of the modes is enabled by a symmetry feature of the linear electron Bernstein and upper hybrid dispersion properties that occur only near the second gyroharmonic. Electron acceleration inside the density inhomogeneities by localized azimuthal electrostatic oscillations is more efficient near the second gyroharmonic than at higher frequencies, consistent with the observed enhancements.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Stimulated Raman back scattering of extraordinary electromagnetic waves from periodically magnetized nanoparticle lattice

Stimulated Raman back scattering of extraordinary electromagnetic waves from the nanoparticle lattice is investigated in the presence of the static magnetic field. In the context of macroscopic theory, dispersion relation and growth rate of extraordinary mode for different values of static magnetic field and lattice parameters are derived and analyzed. It is found that when the static magnetic field is off, dispersion relation has two branches. These branches are related to the plasmonic and body wave branches of the plane polarized wave. Low frequency branch of the pump wave is not involved in the instability while the other branch is not stable, and the growth rate of Raman back scattered wave has one peak. If the electrons have cyclotron frequency by static magnetic field, dispersion has three branches. These branches are related to the plasmonic and body wave branches of left and right hand circularly polarized waves. In this situation, it is found that low frequency lower branch of the pump wave is stable while other branches are not stable, and the growth rate of Raman back scattered wave has three peaks. Numerical study of growth rate in various cyclotron frequencies shows that the growth rate increases and the instability band width decreases with increasing static magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Excitation and propagation of electromagnetic fluctuations with ion-cyclotron range of frequency in magnetic reconnection laboratory experiment

Large-amplitude electromagnetic fluctuations of ion-cyclotron-frequency range are detected in a laboratory experiment inside the diffusion region of a magnetic reconnection with a guide field. The fluctuations have properties similar to kinetic Alfvén waves propagating obliquely to the guide field. Temporary enhancement of the reconnection rate is observed during the occurrence of the fluctuations, suggesting a relationship between the modification in the local magnetic structure given by these fluctuations and the intermittent fast magnetic reconnection.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Electron-exchange and quantum screening effects on the Thomson scattering process in quantum Fermi plasmas

The influence of the electron-exchange and quantum screening on the Thomson scattering process is investigated in degenerate quantum Fermi plasmas. The Thomson scattering cross section in quantum plasmas is obtained by the plasma dielectric function and fluctuation-dissipation theorem as a function of the electron-exchange parameter, Fermi energy, plasmon energy, and wave number. It is shown that the electron-exchange effect enhances the Thomson scattering cross section in quantum plasmas. It is also shown that the differential Thomson scattering cross section has a minimum at the scattering angle Θ=π/2. It is also found that the Thomson scattering cross section increases with an increase of the Fermi energy. In addition, the Thomson scattering cross section is found to be decreased with increasing plasmon energy.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Temperature dependence of mode conversion in warm, unmagnetized plasmas with a linear density profile

We study theoretically the linear mode conversion between electromagnetic waves and Langmuir waves in warm, stratified, and unmagnetized plasmas, using a numerically precise calculation based on the invariant imbedding method. We verify that the principle of reciprocity for the forward and backward mode conversion coefficients holds precisely regardless of temperature. We also find that the temperature dependence of the mode conversion coefficient is substantially stronger than that previously reported. Depending on the wave frequency and the incident angle, the mode conversion coefficient is found to increase or decrease with the increase of temperature.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Functional composites of plasmas and metamaterials: Flexible waveguides, and variable attenuators with controllable phase shift

Numerical predictions and experimental results in this study verify that plasmas with negative permittivity work as functional media for electromagnetic waves and that their composites with metallic metamaterials show further extraordinary properties. Chain structures of individual plasmas with negative permittivity, forming a straight line and a L-shaped bent line, serve flexible waveguides via coupling structures of localized surface waves standing around each plasma. Further progresses as wave controllers are achievable in an array of the composites of plasmas and micro metallic resonators; functions of phase shifters and attenuators are individually controlled, with rotation of working points on the complex refractive index plane by varying gas conditions and permeability modulation. Such proposed sets of flexible combination will lead to advanced scientific products with novel functions.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Heating of ions by high frequency electromagnetic waves in magnetized plasmas

The heating of ions by high frequency electrostatic waves in magnetically confined plasmas has been a paradigm for studying nonlinear wave-particle interactions. The frequency of the waves is assumed to be much higher than the ion cyclotron frequency and the waves are taken to propagate across the magnetic field. In fusion type plasmas, electrostatic waves, like the lower hybrid wave, cannot access the core of the plasma. That is a domain for high harmonic fast waves or electron cyclotron waves—these are primarily electromagnetic waves. Previous studies on heating of ions by two or more electrostatic waves are extended to two electromagnetic waves that propagate directly across the confining magnetic field. While the ratio of the frequency of each wave to the ion cyclotron frequency is large, the frequency difference is assumed to be near the ion cyclotron frequency. The nonlinear wave-particle interaction is studied analytically using a two time-scale canonical perturbation theory. The theory elucidates the effects of various parameters on the gain in energy by the ions—parameters such as the amplitudes and polarizations of the waves, the ratio of the wave frequencies to the cyclotron frequency, the difference in the frequency of the two waves, and the wave numbers associated with the waves. For example, the ratio of the phase velocity of the envelope formed by the two waves to the phase velocity of the carrier wave is important for energization of ions. For a positive ratio, the energy range is much larger than for a negative ratio. So waves like the lower hybrid waves will impart very little energy to ions. The theoretical results are found to be in good agreement with numerical simulations of the exact dynamical equations. The analytical results are used to construct mapping equations, simplifying the derivation of the motion of ions, which are, subsequently, used to follow the evolution of an ion distribution function. The heating of ions can then be properly quantified in terms of the wave parameters and can be conveniently used to find ideal conditions needed to heat ions by high frequency electromagnetic waves.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Finite beta effects on low- and high-frequency magnetosonic waves in a two-ion-species plasma

A magnetosonic wave propagating perpendicular to a magnetic field in a two-ion-species plasma has two branches, high-frequency and low-frequency modes. The finite beta effects on these modes are analyzed theoretically on the basis of the three-fluid model with finite ion and electron pressures. First, it is shown that the Korteweg-de Vries (KdV) equation for the low-frequency mode is valid for amplitudes ε<ε{sub max}, where the upper limit of the amplitude ε{sub max} is given as a function of β (β is the ratio of the kinetic and magnetic energy densities), the density ratio, and the cyclotron frequency ratio of two ion species. Next, the linear dispersion relation and KdV equation for the high-frequency mode are derived, including β as a factor. In addition, the theory for heavy ion acceleration by the high-frequency mode pulse and the pulse damping due to this energy transfer in a finite beta plasma are presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

On the fully nonlinear acoustic waves in a plasma with positrons beam impact and superthermal electrons

Arbitrary amplitude ion-acoustic waves in an unmagnetized plasma consisting of cold positive ions, superthermal electrons, and positrons beam are reported. The basic set of fluid equations is reduced to an energy-balance like equation. The latter is numerically analyzed to examine the existence regions for solitary and shock waves. It is found that only solitary waves can propagate, however, the model cannot support shocks. The effects of superthermality and beam parameters (via, positrons concentration and streaming velocity) on the existence region, as well as solitary wave profile have been discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Nonlinear interaction of intense electromagnetic waves with a magnetoactive electron-positron-ion plasma

The nonlinear coupling between circularly polarized electromagnetic (CPEM) waves and acoustic-like waves in a magnetoactive electron-positron-ion (e-p-i) plasma is studied, taking into account the relativistic motion of electrons and positrons. The possibility of modulational instability and its growth rate as well as the envelope soliton formation and its characteristics in such plasmas are investigated. It is found that the growth rate of modulation instability increases in the case that ω{sub c}/ω<1 (ω{sub c} and ω are the electron gyrofrequency and the CPEM wave frequency, respectively) and decreases in the case that ω{sub c}/ω>1. It is also shown that in a magnetoactive e-p-i plasma, the width of bright soliton increases/decreases in case of (ω{sub c}/ω)<1/(ω{sub c}/ω)>1 by increasing the magnetic field strength.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

A 1-D dusty plasma photonic crystal

It is demonstrated numerically that a 1-D plasma crystal made of micron size cylindrical dust particles can, in principle, work as a photonic crystal for terahertz waves. The dust rods are parallel to each other and arranged in a linear string forming a periodic structure of dielectric-plasma regions. The dispersion equation is found by solving the waves equation with the boundary conditions at the dust-plasma interface and taking into account the dielectric permittivity of the dust material and plasma. The wavelength of the electromagnetic waves is in the range of a few hundred microns, close to the interparticle separation distance. The band gaps of the 1-D plasma crystal are numerically found for different types of dust materials, separation distances between the dust rods and rod diameters. The distance between levitated dust rods forming a string in rf plasma is shown experimentally to vary over a relatively wide range, from 650 μm to about 1350 μm, depending on the rf power fed into the discharge.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Chirality-induced negative refraction in magnetized plasma

Characteristic equations in magnetized plasma with chirality are derived in simple formulations and the dispersion relations for propagation parallel and perpendicular to the external magnetic field are studied in detail. With the help of the dispersion relations of each eigenwave, the author explores chirality-induced negative refraction in magnetized plasma and investigates the effects of parameters (i.e., chirality degree, external magnetic field, etc.) on the negative refraction. The results show that the chirality is the necessary and only one factor which leads to negative refraction without manipulating electrical permittivity and magnetic permeability. Both increasing the degree of chirality and reducing the external magnetic field can result in greater range negative refraction. Parameter dependence of the effects is calculated and discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Electron cyclotron harmonic resonances in high-frequency heating of the ionosphere

Electron acceleration by upper hybrid waves under cyclotron harmonic resonance interaction is studied. Theory is formulated; the analytical solutions in the second and fourth harmonic cyclotron resonance cases are obtained, and in the third harmonic case, a first order differential equation governing the evolution of the electron energy is derived. The theory is applied for explaining the generation of artificial ionization layers observed in high-frequency (HF) ionospheric heating experiments. The upper hybrid waves are assumed to be excited parametrically by the O-mode HF heating wave. As the decay mode is the lower hybrid wave, the excited upper hybrid waves have wavelengths ranging from 0.25 to 0.5 m, which are short enough to effectively incorporate the finite Larmour radius effect for the harmonic cyclotron resonance interactions as well as have a frequency bandwidth of about 20 kHz, which provides an altitude region of about 10 km for continuous harmonic cyclotron resonance interaction between electrons and descending waves in the slightly inhomogeneous geomagnetic field. The numerical results on electron acceleration show that electron fluxes with energies larger than 14 eV are generated in the three harmonic cases. These energetic electrons cause impact ionizations, which are descending to form artificial ionization layers at the bottom of the ionospheric F region.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗