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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

The geometrical-optics law of reflection for electromagnetic waves in magnetically confined plasmas: Specular reflection of rays at the last closed flux surface

Within the geometrical-optics approximation, it is shown that the reflection of rays describing the propagation of electromagnetic waves in fusion-grade, magnetically confined plasmas and impinging on the last closed flux surface, or plasma surface, is necessarily specular or mirror-like. More precisely, the component of the wave vector tangential to that surface does not change, whereas the component normal to it reverses its sign while keeping its magnitude. The well-known law of reflection, stating that the angle of incidence equals that of reflection, is thus generalized to anisotropic media.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Electromagnetic bound states in the radiation continuum for periodic double arrays of subwavelength dielectric cylinders

Electromagnetic bound states in the radiation continuum are studied for periodic double arrays of subwavelength dielectric cylinders in TM polarization. They are similar to localized waveguide mode solutions of Maxwell's equations for metal cavities or defects of photonic crystals, but, in contrast to the latter, their spectrum lies in the radiation continuum. The phenomenon is identical to the existence of bound states in the radiation continuum in quantum mechanics, discovered by von Neumann and Wigner. In the formal scattering theory, these states appear as resonances with the vanishing width. For the system studied, the bound states are shown to exist at specific distances between the arrays in the spectral region where one or two diffraction channels are open. Analytic solutions are obtained for all bound states (below the radiation continuum and in it) in the limit of thin cylinders (the cylinder radius is much smaller than the wavelength). The existence of bound states is also established in the spectral region where three and more diffraction channels are open, provided the dielectric constant and radius of the cylinders are fine-tuned. The near field and scattering resonances of the structure are investigated when the distance between the arrays varies in a neighborhood of its critical values at which the bound states are formed. In particular, it is shown that the near field in the scattering process becomes significantly amplified in specific regions of the array as the distance approaches its critical values. The effect may be used to control optical nonlinear effects by varying the distance between the arrays near its critical values.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Dark-state polariton in magnetized plasma under electromagnetically induced transparency

This paper derives a wave equation in magnetized plasma under electromagnetically induced transparency (EIT) regime for probe electron cyclotron wave. The equation has a solution indicating a state analogous to 'dark-state polaritons' [M. Fleischhauer and M. D. Lukin, Phys. Rev. Lett. 84, 5094 (2000)] in quantum atomic system. The state analogous to dark-state polaritons is a propagating coupled state of the probe-wave electric field and longitudinal plasma oscillation. The propagation of the coupled state can be stopped as its waveform is maintained if injection of pump wave is properly controlled in time domain. The 'stop-light' is achieved by adiabatic transition from a state in which the probe-wave field is dominant to a state in which the longitudinal plasma oscillation is dominant. This study also recaptures a phenomenon analogous to 'coherent population trap' in conventional EIT of quantum atomic system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Rectangular Pulsed Laser-Electromagnetic Hybrid Accelerator

Experimental investigation of impulse-bit and propellant consumption rate, or mass shot, per single pulse discharge was conducted to characterize the thrust performance of the rectangular laser-electromagnetic hybrid acceleration thruster with various propellant materials. From the result, alumina propellant showed significantly superior performance. The largest values of the measured impulse-bit, specific impulse and thrust efficiency were 49 {mu}Nsec, 6,200 sec and 22%, respectively.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Adiabatic description of capture into resonance and surfatron acceleration of charged particles by electromagnetic waves

We present an analytical and numerical study of the surfatron acceleration of nonrelativistic charged particles by electromagnetic waves. The acceleration is caused by capture of particles into resonance with one of the waves. We investigate capture for systems with one or two waves and provide conditions under which the obtained results can be applied to systems with more than two waves. In the case of a single wave, the once captured particles never leave the resonance and their velocity grows linearly with time. However, if there are two waves in the system, the upper bound of the energy gain may exist and we find the analytical value of that bound. We discuss several generalizations including the relativistic limit, different wave amplitudes, and a wide range of the waves' wavenumbers. The obtained results are used for qualitative description of some phenomena observed in the Earth's magnetosphere.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Covariance for electromagnetic current for two bosons at higher order in the light front

We show that the electromagnetic current for a system composed by two charged bosons has a structure of many bodies even in the impulse approximation, when described in the time x{sup +}. In terms of the two body component for the bound state, the current contains two body operators. We discuss the process of pair creation by the photon and interpret it as a zero mode contribution to the current and its consequences for the components of currents in the light front.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Chiral symmetry breaking and electromagnetic structure of the nucleon

The electromagnetic form factors are the most fundamental quantities to describe the internal structure of the nucleon and are related to the charge radii of the baryons. We have calculated the charge radii of octet baryons in the framework of chiral constituent quark model with the inclusion of the spin-spin generated configuration mixing. This model is quite successful in predicting the low energy hadron matrix elements. The results obtained in the case of charge radii are also comparable to the latest experimental studies and show improvement over some theoretical interpretations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

The interaction of electromagnetic wave and plasma wave in an electron beam-ion channel system

The features of the waves and the instability induced by the interaction of electromagnetic (EM) wave with plasma wave in the electron beam-ion channel system are studied. Characteristics of waves in the system are displayed through the dispersion relation and two kinds of EM instabilities are found. The first one is excited by the interaction of the fast plasma wave and the forward EM wave, and the other one is induced by the coupling of the fast plasma wave and the backward EM wave, the numerical results show that this is caused by the virtual cathode oscillation. The conditions of these EM instabilities are given and the related physical mechanisms have been discussed in detail.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Nonlinear evolution of electromagnetic ion cyclotron waves

Hybrid Vlasov-Fourier modeling is used to investigate the nonlinear evolution of electromagnetic ion cyclotron (EMIC) waves driven by proton temperature anisotropy in plasmas with a population of He{sup +} ions and a cold proton background. In the pure proton-electron plasma, most of the free energy is converted into high-amplitude waves and currents. In the nonlinear stage, within a few hundred proton gyroperiods after the saturation, the wave spectrum shifts toward lower wave numbers and frequencies, from {omega}{approx}0.6{Omega}{sub p} to below {omega}{approx}0.25{Omega}{sub p}. In the presence of even a small population of He{sup +} ions almost all of the free energy is used in He{sup +} heating. The wave activity in the saturated state moves from the linearly unstable upper branch to the linearly stable lower one. In the presence of a background of cold protons, the waves can propagate in the frequency stop-band. Our results demonstrate that linear stability theory cannot be used to estimate the characteristics of the expected saturated wave spectra in the terrestrial magnetosphere. Significantly, our nonlinear simulations produce wave spectra which are in close agreement with the EMIC waves observed in situ by satellites as well as by ground-based magnetometers positioned at the ends of the magnetic field lines.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Controlling chaotic behavior of the equilibrium electrons by simultaneous using of two guiding fields in a free-electron laser with an electromagnetic-wave wiggler

In the present paper the effects of the combination of the axial-guide magnetic field and the ion-channel guiding on the chaotic trajectories in a free-electron laser with electromagnetic-wave wiggler have been considered. It is shown that the simultaneous using of the two guiding fields in the certain conditions causes chaotic behavior in the electron motion. It is also illustrated that the chaotic trajectories decrease as the ion-channel density or the strength of the axial magnetic field increases. The transition from the chaotic trajectories to regular trajectories, occurs at a special ion-channel density, {omega}{sub it}, or a particular amount of the strength of the axial magnetic field, a{sub t}. Furthermore numerically calculation shows that the normalized ion-channel frequency of the transition, {omega}{sub it}, reduces by increasing the axial magnetic field. Also {omega}{sub i} increase causes the trajectories to be regular at the weaker a{sub t}. The electron motion has been altered significantly by the self-fields effects. It is demonstrated that, the self-fields cause a decrement in the chaotic trajectories. This is in contrast to the idealized helical wiggler FEL with the axial magnetic field guiding.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Inclusive electromagnetic decay ratios of heavy quarkonium from QCD

We consider a different power counting in potential NRQCD by incorporating the static potential exactly in the leading order Hamiltonian. We compute the leading relativistic corrections to the inclusive electromagnetic decay ratios in this new scheme. The effect of this new power counting is found to be large (even for top). We produce an updated value for the {eta}{sub b} decay to two photons. This scheme also brings consistency between the weak coupling computation and the experimental value of the charmonium decay ratio.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Self-focusing of a Gaussian electromagnetic beam in a complex plasma

This paper analyzes the propagation of a Gaussian electromagnetic beam in a complex plasma; the paraxial approach has been invoked for the study of the propagation characteristics. The analytical model emphasizes the open nature of complex plasmas and incorporates the charge, number density, and energy balance of the plasma constituents along with the plasma neutrality. Diffusion due to the density and temperature gradients, thermal conduction, Ohmic heating, and energy exchange in collisions/accretion have also been taken into account. For a numerical appreciation of the results, the critical curves for the propagation of the beam in dark plasmas have been discussed. The dependence of the beam width parameter on distance of propagation has been evaluated for three typical cases viz., of steady divergence, oscillatory divergence, and self-focusing. The equality of electron and ion density, an assumption inherent in the earlier analysis, has been discarded on account of the presence of charged dust particles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Heating of solar chromosphere by electromagnetic wave absorption in a plasma slab model

The heating of solar chromospheric internetwork regions by means of the absorption of electromagnetic (EM) waves that originate from the photospheric blackbody radiation is studied in the framework of a plasma slab model. The absorption is provided by the electron-neutral collisions in which electrons oscillate in the EM wave field and electron-neutral collisions damp the EM wave. Given the uncertain nature of the collision cross-section due to the plasma microturbulence, it is shown that for plausible physical parameters, the heating flux produced by the absorption of EM waves in the chromosphere is between 20% and 45% of the chromospheric radiative loss flux requirement. It is also established that there is an optimal value for the collision cross-section, 5x10{sup -18} m{sup 2}, which produces the maximal heating flux of 1990 W m{sup -2}.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Dynamical Invariants and Robertson-Schroedinger Correlated States of Electromagnetic Field in Nonstationary Linear Media

Dynamical invariants and statistical properties of the quantized electromagnetic field in nonstationary linear media (dielectric and/or conductive) are considered in the framework of Choi-Yeon quantization scheme. It is shown that in the eigenstates of linear dynamical invariant the Robertson-Schroedinger uncertainty relation is minimized, both for the photon annihilation operator quadratures and for the electric and magnetic field components. The time evolution of initial Glauber coherent states and Fock (photon number) states is considered. On an initial coherent state the medium conductivity and the time-dependent electric permeability both are shown to act as squeezing and correlating factors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Comment on ''Chaotic electron trajectories in an electromagnetic wiggler free-electron laser with ion-channel guiding'' [Phys. Plasmas 17, 093103 (2010)]

The chaotic electron dynamics in a free-electron laser with electromagnetic-wave wiggler and ion-channel has been recently reported by A. Taghavi et al.[Phys. Plasmas 17, 093103 (2010)]. We comment on the authors use of a set of initial condition that is not correct based on the dispersion relation and steady-state orbits.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Response to ''Comment on 'Chaotic electron trajectories in an electromagnetic wiggler free-electron laser with ion-channel guiding''' [Phys. Plasmas 17, 093103 (2010)]

Nasr and Hasanbeigi in their comment [Phys. Plasmas 17, 093103 (2010)] have claimed that, in our recent paper [Phys. Plasmas 17, 093103 (2010)], incorrect initial conditions have been used based on dispersion relation (or normalized electromagnetic wave frequency {omega}{sub w}) and mean axial velocity {beta}{sub b}. We use a self-consistent method to calculate more accurate values of {omega}{sub w} and {beta}{sub b} and show that all results presented in our recent paper are correct.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Evolution of polarization of an electromagnetic wave propagating in magnetized plasma: Comparison between two alternative formalisms

Two alternative formalisms for the analysis of the evolution of electromagnetic wave polarization in a magnetized plasma are considered: the coupled wave formalism and the Stokes vector formalism. The first formalism is developed and extended to more general magnetic field configurations than considered hitherto, thus obtaining a new polarization evolution equation. The two formalisms are compared and their relative merits and limitations are described. In particular, it is shown that the equations for polarization evolution are valid for arbitrarily strong anisotropy induced by the magnetic field and that these equations treat implicitly the effect of coupling between the characteristic waves.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗