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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 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
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↗
DOE OSTI2011

Acceleration Mechanism Of Pulsed Laser-Electromagnetic Hybrid Thruster

A fundamental study of a newly developed rectangular pulsed laser-electromagnetic hybrid thruster was conducted. Laser-ablation plasma in the thruster was induced through laser beam irradiation onto a solid target and accelerated by electrical means instead of direct acceleration only by using a laser beam. The performance of the thrusters was evaluated by measuring the ablated mass per pulse and impulse bit. As results, significantly high specific impulses up to 7,200 s were obtained at charge energies of 8.6 J. Moreover, from the Faraday cup measurement, it was confirmed that the speed of ions was accelerated with addition of electric energy.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Relativistic electromagnetic flat top solitons and their stability

The inclusion of ion response in the study of relativistically intense electromagnetic laser pulse propagation in plasma yields certain distinct varieties of single peak solitonic structures. A flat top slow moving structure (for which the various fields have a flat profile over a wide spatial range) is one such solution. A detailed characterization of these solutions along with the eigen spectrum of their formation in the parameter space has been presented. The evolution of this particular solution is studied in detail with the help of a coupled fluid Maxwell set of equations. The study shows that the flat top solution is unstable. The instability is characterized as the backward Brillouin instability for which the electron quiver velocity plays the role of the effective temperature.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

The dispersion relation and excitation of transverse magnetic mode electromagnetic waves in rippled-wall waveguide with a plasma rod and an annular dielectric

By using the linear field theory, the dispersion relation of electromagnetic waves in a rippled-wall waveguide with a plasma rod and an annular dielectric is obtained. In addition, by injecting a finite thick annular intense relativistic electron beam in this waveguide, the excitation of these waves is investigated. Furthermore, the effects of the radius of the plasma rod, the radius of the dielectric, the corrugation amplitude, and period on the frequency spectrum are investigated. Besides, the time growth rate of excitation of these waves by an annular relativistic electron beam is studied. Finally, to demonstrate the advantages of this rippled-wall waveguide, the dispersion relation and the growth rate of three simplified cases are investigated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Observation of electron plasma waves inside large amplitude electromagnetic pulses in a temporally growing plasma

Observation of electron plasma waves excited inside high power ({approx}10 kW) short pulse ({approx}20 {mu}s) electromagnetic (em) waves interacting with a gaseous medium (argon) in the pressure range 0.2-2.5 mTorr is reported. The waves have long wavelength ({approx}13 cm) and get damped at time scales slower ({approx}3 {mu}s) than the plasma period (0.1-0.3 {mu}s), the energy conveyed to the medium lead to intense ionization (ion density n{sub i} {approx} 10{sup 11} cm{sup -3} and electron temperature T{sub e} {approx} 6-8 eV) and rapid growth of the plasma ({approx}10{sup 5} s{sup -1}) beyond the waves. Time frequency analysis of the generated oscillations indicate the presence of two principal frequencies centered around 3.8 MHz and 13.0 MHz with a spread {Delta}f {approx} 4 MHz, representing primarily two population of electrons in the plasma wave. The experimental results are in reasonable agreement with a model that considers spatiotemporal forces of the em wave on the medium, space charges and diffusion.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Weakly dissipative dust-ion-acoustic solitons in complex plasmas and the effect of electromagnetic radiation

Possibility for dust ion-acoustic solitons to exist in complex (dusty) plasmas in the presence of electromagnetic radiation, which results in positive dust particle charges, is investigated. Dissipative processes occurring during the propagation of dust ion-acoustic perturbations, among which are the charging of dust grains, the absorption of ions by grains, the transfer of the ion momentum to the grains, and ion-neutral collisions, are taken into account. Temporal evolution of the soliton-like perturbation and interaction of two soliton-like perturbations are studied. Compressive soliton-like perturbations are shown to possess the main properties of the soltons, in particular, the interacting perturbations conserve their form.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Nucleon electromagnetic form factors and electroexcitation of low lying nucleon resonances up to Q^2 = 12 GeV^2 in a light-front relativistic quark model

We utilize a light-front relativistic quark model to predict the 3q core contribution to the electroexcitation amplitudes for the {Delta}(1232)P{sub 33}, N(1440)P{sub 11}, N(1520)D{sub 13}, and N(1535)S{sub 11} up to Q{sup 2} = 12 GeV{sup 2}. The parameters of the model have been specified via description of the nucleon electromagnetic form factors in the approach that combines 3{sub q} and pion-cloud contributions in the light-front dynamics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Comment on ''Electron acceleration by a short laser beam in the presence of a long-wavelength electromagnetic wave'' [J. Appl. Phys. 102, 056106 (2007)]

Gupta et al.[J. Appl. Phys. 102, 056106 (2007)] investigated vacuum electron acceleration by a short laser beam in the presence of a long-wavelength electromagnetic wave. However, we consider that their simulation results to be questionable. We have investigated their simulation in detail and present our own simulation results, which do not match the good acceleration as theirs given in the original paper.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Effect of electron density profile on power absorption of high frequency electromagnetic waves in plasma

Considering different typical electron density profiles, a multi slab approximation model is built up to study the power absorption of broadband (0.75-30 GHz) electromagnetic waves in a partially ionized nonuniform magnetized plasma layer. Based on the model, the power absorption spectra for six cases are numerically calculated and analyzed. It is shown that the absorption strongly depends on the electron density fluctuant profile, the background electron number density, and the collision frequency. A potential optimum profile is also analyzed and studied with some particular parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗