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Results for “ELECTROMAGNETIC PROPAGATION”

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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

The Potential for Ambient Plasma Wave Propulsion

A truly robust space exploration program will need to make use of in-situ resources as much as possible to make the endeavor affordable. Most space propulsion concepts are saddled with one fundamental burden; the propellant needed to produce momentum. The most advanced propulsion systems currently in use utilize electric and/or magnetic fields to accelerate ionized propellant. However, significant planetary exploration missions in the coming decades, such as the now canceled Jupiter Icy Moons Orbiter, are restricted by propellant mass and propulsion system lifetimes, using even the most optimistic projections of performance. These electric propulsion vehicles are inherently limited in flexibility at their final destination, due to propulsion system wear, propellant requirements, and the relatively low acceleration of the vehicle. A few concepts are able to utilize the environment around them to produce thrust: Solar or magnetic sails and, with certain restrictions, electrodynamic tethers. These concepts focus primarily on using the solar wind or ambient magnetic fields to generate thrust. Technically immature, quasi-propellantless alternatives lack either the sensitivity or the power to provide significant maneuvering. An additional resource to be considered is the ambient plasma and magnetic fields in solar and planetary magnetospheres. These environments, such as those around the Sun or Jupiter, have been shown to host a variety of plasma waves. Plasma wave propulsion takes advantage of an observed astrophysical and terrestrial phenomenon: Alfven waves. These are waves that propagate in the plasma and magnetic fields around and between planets and stars. The generation of Alfven waves in ambient magnetic and plasma fields to generate thrust is proposed as a truly propellantless propulsion system which may enable an entirely new matrix of exploration missions. Alfven waves are well known, transverse electromagnetic waves that propagate in magnetized plasmas at frequencies below the ion cyclotron frequency. They have been observed in both laboratory and astrophysical settings. On Earth, they are being investigated as a possible means for plasma heating, current drive, and momentum addition in magnetic confinement fusion systems. In addition, Alfven waves have been proposed as a mechanism for acceleration of the solar wind away from the sun.

THE POTENTIAL FOR AMBIENT PLASMA WAVE PROPULSION↗
NASA NTRS1992

Frequency up-conversion of a high-power microwave pulse propagating in a self-generated plasma

In the study of the propagation of a high-power microwave pulse, one of the main concerns is how to minimize the energy loss of the pulse before reaching the destination. A frequency autoconversion process that can lead to reflectionless propagation of powerful electromagnetic pulses in self-generated plasmas is studied. The theory shows that, under the proper condition, the carrier frequency omega of the pulse shifts upward during the growth of local plasma frequency omega(pe). Thus, the self-generated plasma remains underdense to the pulse. A chamber experiment to demonstrate the frequency autoconversion during the pulse propagation through the self-generated plasma is conducted. The detected frequency shift is compared with the theoretical result calculated by using the measured electron density distribution along the propagation path of the pulse. Good agreement is obtained.

Kuo, S. P.↗
NASA NTRS1982

Sferics in the stratosphere

Experimental and theoretical work on describing the propagation of sferics (electromagnetic waves) in the stratosphere is reviewed. Measurements are made with a double Langmuir probe that measures the potential difference between two identical, separated conductors, thereby permitting calculation of the electric field. The probe is usually mounted on a balloon floated up to the stratosphere. Data are presented that were taken over a thunderstorm and a theory of sferic propagation is developed, including defined relationships among the source, the propagation medium, and the detected signal. It is demonstrated that the signals recorded by the balloon instrumentation can be used to define the upper limit of the current density and total current in the stratosphere when a sferic is propagating.

Holzworth, R. H.↗
DOE OSTI2015

Near-field radiative thermal transport: From theory to experiment

Radiative thermal transport via the fluctuating electromagnetic near-field has recently attracted increasing attention due to its fundamental importance and its impact on a range of applications from data storage to thermal management and energy conversion. After a brief historical account of radiative thermal transport, we summarize the basics of fluctuational electrodynamics, a theoretical framework for the study of radiative heat transfer in terms of thermally excited propagating and evanescent electromagnetic waves. Various approaches to modeling near-field thermal transport are briefly discussed, together with key results and proposals for manipulation and utilization of radiative heat flow. Subsequently, we review the experimental advances in the characterization of both near-field heat flow and energy density. We conclude with remarks on the opportunities and challenges for future explorations of radiative heat transfer at the nanoscale.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Finite difference time domain analysis of chirped dielectric gratings

The finite difference time domain (FDTD) method for solving Maxwell's time-dependent curl equations is accurate, computationally efficient, and straight-forward to implement. Since both time and space derivatives are employed, the propagation of an electromagnetic wave can be treated as an initial-value problem. Second-order central-difference approximations are applied to the space and time derivatives of the electric and magnetic fields providing a discretization of the fields in a volume of space, for a period of time. The solution to this system of equations is stepped through time, thus, simulating the propagation of the incident wave. If the simulation is continued until a steady-state is reached, an appropriate far-field transformation can be applied to the time-domain scattered fields to obtain reflected and transmitted powers. From this information diffraction efficiencies can also be determined. In analyzing the chirped structure, a mesh is applied only to the area immediately around the grating. The size of the mesh is then proportional to the electric size of the grating. Doing this, however, imposes an artificial boundary around the area of interest. An absorbing boundary condition must be applied along the artificial boundary so that the outgoing waves are absorbed as if the boundary were absent. Many such boundary conditions have been developed that give near-perfect absorption. In this analysis, the Mur absorbing boundary conditions are employed. Several grating structures were analyzed using the FDTD method.

Hochmuth, Diane H.↗
NASA NTRS1986

Electromagnetic instabilities and gyrophase-bunched particles

The linear theory of electromagnetic instabilities at propagation parallel or antiparallel to a uniform magnetic field B(0) is used to calculate the relative phase angle between the fluctuating velocity vector of the jth component and the fluctuating magnetic field. A criterion that determines when this phase relationship leads to observable gyrophase bunching during the linear growth phase of an instability is also derived. The theory is applied to bunching of ion components by ion beam instabilities. Among the electromagnetic cool ion beam instabilities, it is found that the right-hand resonant mode is most likely to cause observable gyrophase bunching of an ion beam during linear growth.

Gary, S. P.↗
DOE OSTI2014

Interaction of a two-dimensional electromagnetic breather with an electron inhomogeneity in an array of carbon nanotubes

Propagation of ultrashort laser pulses through various nano-objects has recently became an attractive topic for both theoretical and experimental studies due to its promising perspectives in a variety of problems of modern nanoelectronics. Here, we study the propagation of extremely short two-dimensional bipolar electromagnetic pulses in a heterogeneous array of semiconductor carbon nanotubes. Heterogeneity is defined as a region of enhanced electron density. The electromagnetic field in an array of nanotubes is described by Maxwell's equations, reduced to a multidimensional wave equation. Our numerical analysis shows the possibility of stable propagation of an electromagnetic pulse in a heterogeneous array of nanotubes. Furthermore, we establish that, depending on its speed of propagation, the pulse can pass through the area of increased electron concentration or be reflected therefrom.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Spin-based detection of terahertz and sub-terahertz electromagnetic radiation

Systems and methods for spin-based detection of electromagnetic radiation at terahertz and sub-terahertz frequencies is provided. The detector can include a heterostructure, a magnetic field generator, and an electrical circuit. The heterostructure can include a first layer formed of an antiferromagnetic material (AFM) in contact with a second layer of a heavy metal (HM) or a topological insulator. The magnetic field generator can generate a magnetic field oriented approximately parallel to an easy axis of the first layer and approximately parallel to a propagation direction of electromagnetic radiation. The circuit can be in electrical communication with the second layer. The first layer can inject a spin current into the second layer in response to receipt of electromagnetic radiation having a sub-terahertz or terahertz frequency. The second layer can convert the injected spin current into a potential difference. The circuit can be configured to output a signal corresponding to the potential difference.

Shi, Jing↗
DOE OSTI2020

Low-frequency Electromagnetic Detection Limits of Underground Nuclear Explosions

Underground nuclear explosions produce a broadband electromagnetic signal that can propagate to the surface at some distance. We perform a logistic regression on historical electromagnetic detections to calculate a probabilistic detection curve for prediction of the propagation distance for any given underground nuclear explosion. The curve predicts positive detections at scaled ranges of 2414.6, 2025.7, 1908.3, and 1672.4 m/ktonne 1/3 at probabilities of 50, 90, 95 and 99%, respectively. For a theoretical 100 ktonne underground nuclear explosion these scaled ranges translate to absolute ranges of 11.2, 9.4, 8.9, and 7.8 km at probabilities of 50, 90, 95 and 99%, respectively. We also motivate a need for improved electromagnetic sensor design and deployment by extending the detection analysis using the quoted signal-to-noise ratio of two and noise amplitude of 10 pT along with attenuation relationships that go as 1/r to 1/r 3 . We find that reducing the noise floor by a factor often could extend the detection limit to approximately 5 to 25 km/ktonne 1/3 , which translates to 24 to 112 km for a theoretical 100 ktonne underground nuclear explosion.

58 GEOSCIENCES↗
DOE OSTI2021

Electromagnetic waveguide based thermal energy extraction with emissive materials and modifications

The method presented uses thermally emissive materials for the extraction of heat through the use of electromagnetic waveguides, wherein the emissive material comprises materials which emit electromagnetic radiation due to thermal excitation, wherein the electromagnetic radiation is coupled to electromagnetic waveguides; a receiver adapted to receive the electromagnetic radiation for utilization, wherein the extracted electromagnetic radiation may propagate arbitrary distances inside the waveguides before the need for processing, for example, to maximize the temperature differential between the emissive material and that of the receiver; and the exchange of the chemical composition of some portion of the environment the apparatus is housed in. The thermal energy extraction apparatus described herein has the purpose of removing heat from a source for conversion to other forms of energy such as electricity and for thermal management applications. Wherein for heat management, the benefit of waveguides would constitute reduced interference with electronics through electromagnetic coupling.

Poole, Zsolt↗
DOE OSTI2015

Kinetic theory of weak turbulence in magnetized plasmas: Perpendicular propagation

The present paper formulates a weak turbulence theory in which electromagnetic perturbations are assumed to propagate in directions perpendicular to the ambient magnetic field. By assuming that all wave vectors lie in one direction transverse to the ambient magnetic field, the linear solution and second-order nonlinear solutions to the equation for the perturbed distribution function are obtained. Nonlinear perturbed current from the second-order nonlinearity is derived in general form, but the limiting situation of cold plasma temperature is taken in order to derive an explicit nonlinear wave kinetic equation that describes three-wave decay/coalescence interactions among X and Z modes. A potential application of the present formalism is also discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Theoretical Plasma Physics

Lattice Boltzmann algorithms are a mesoscopic method to solve problems in nonlinear physics which are highly parallelized – unlike the direction solution of the original problem. These methods are applied to both fluid and magnetohydrodynamic turbulence. By introducing entropic constraints one can enforce the positive definiteness of the distribution functions and so be able to simulate fluids at high Reynolds numbers without numerical instabilities. By introducing a vector distribution function for the magnetic field one can enforce the divergence free condition on the magnetic field automatically, without the need of divergence cleaning as needed in most direct numerical solutions of the resistive magnetohydrodynamic equations. The principal reason for the high parallelization of lattice Boltzmann codes is that they consist of a kinetic collisional relaxation step (which is purely local) followed by a simple shift of the relaxed data to neighboring lattice sites. In large eddy simulations, the closure schemes are highly nonlocal – the most famous of these schemes is that due to Smagorinsky. Under a lattice Boltzmann representation the Smagorinsky closure is purely local – being simply a particular moment on the perturbed distribution fucntions. After nonlocal fluid moment models were discovered to represent Landau damping, it was found possible to model these fluid models using an appropriate lattice Boltzmann algorithm. The close to ideal parallelization of the lattice Boltzmann codes permitted us to be Gordon Bell finalists on using the Earth Simulation in Japan. We have also been involved in the radio frequency propagation of waves into a tokamak and into a spherical overdense tokamak plasma. Initially we investigated the use of a quasi-optical grill for the launching of lower hybrid waves into a tokamak. It was found that the conducting walls do not prevent the rods from being properly irradiated, the overloading of the quasi-optical grill is not severe with the electric field only being about three times higher than in the ideal case. Moreover, the quasi-optical grill was significantly fewer structural elements that the multijunction grill. Nevertheless there has not been much interest from experimental fusion groups to implementing these structures. Hence we have returned to optimizing the multijunction grill so that the large number of coupling matrix elements can be efficiently evaluated using symmetry arguments. In overdense plasmas, the standard electromagnetic waves cannot propagate into the plasma center, but are reflected at the plasma edge. By optimizing mode conversion processes (in particular, the O-X-B wave propagation of Ordinary Mode converting to an Extraordinary mode which then converts into an electrostatic Bernstein wave) one can excite within the plasma an electrostatic Bernstein wave that does not suffer density cutoffs and is absorbed on the electron cyclotron harmonics. Finally we have started looking at other mesoscopic lattice algorithms that involve unitary collision and streaming steps. Because these algorithms are unitary they can be run on quantum computers when they become available – unlike their computational cousin of lattice Boltzmann which is a purely classical code. These quantum lattice gas algorithms have been tested successfully on exact analytic soliton collision solution. These calculations are hoped to be able to study Bose Einstein condensed atomic gases and their ground states in an optical lattice.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Cyclotron resonance in plasma flow

This paper is devoted to the mechanism of particle acceleration via resonant interaction with the electromagnetic circular wave propagating along the inhomogeneous background magnetic field in the presence of a plasma flow. We consider the system where the plasma flow velocity is large enough to change the direction of wave propagation in the rest frame. This system mimics a magnetic field configuration typical for inner structure of a quasi-parallel shock wave. We consider conditions of gyroresonant interaction when the force corresponding to an inhomogeneity of the background magnetic field is compensated by the Lorentz force of the wave-magnetic field. The wave-amplitude is assumed to be about 10% of the background magnetic field. We show that particles can gain energy if kv{sub sw}>ω>kv{sub sw}−Ω{sub c} where k is the wave number, v{sub sw} is a plasma flow velocity, and ω and Ω{sub c} are the wave frequency and the particle gyrofrequency, respectively. This mechanism of acceleration resembles the gyrosurfing mechanism, but the effect of the electrostatic field is replaced by the effect of the magnetic field inhomogeneity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Mie-Resonant Membrane Huygens' Metasurfaces

All-dielectric metasurfaces have become a new paradigm for flat optics as they allow flexible engineering of the electromagnetic space of propagating waves. Such metasurfaces are usually composed of individual subwavelength elements embedded into a host medium or placed on a substrate, which often diminishes the quality of the resonances. The substrate imposes limitations on the metasurface functionalities, especially for infrared and terahertz frequencies. Here a novel concept of membrane Huygens' metasurfaces is introduced. The metasurfaces feature an inverted design, and they consist of arrays of holes made in a thin membrane of high-index dielectric material, with the response governed by the electric and magnetic Mie resonances excited within dielectric domains of the membrane. Highly efficient transmission combined with the 2π phase coverage in the freestanding membranes is demonstrated. Several functional metadevices for wavefront control are designed, including beam deflector, a lens, and an axicon. Lastly, such membrane metasurfaces provide novel opportunities for efficient large-area metadevices, whose advanced functionality is defined by structuring rather than by chemical composition.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Multi-moment advection scheme in three dimension for Vlasov simulations of magnetized plasma

We present an extension of the multi-moment advection scheme [T. Minoshima, Y. Matsumoto, T. Amano, Multi-moment advection scheme for Vlasov simulations, Journal of Computational Physics 230 (2011) 6800–6823] to the three-dimensional case, for full electromagnetic Vlasov simulations of magnetized plasma. The scheme treats not only point values of a profile but also its zeroth to second order piecewise moments as dependent variables, and advances them on the basis of their governing equations. Similar to the two-dimensional scheme, the three-dimensional scheme can accurately solve the solid body rotation problem of a gaussian profile with little numerical dispersion or diffusion. This is a very important property for Vlasov simulations of magnetized plasma. We apply the scheme to electromagnetic Vlasov simulations. Propagation of linear waves and nonlinear evolution of the electron temperature anisotropy instability are successfully simulated with a good accuracy of the energy conservation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

An In-situ and Direct Confirmation of Super-Planckian Thermal Radiation Emitted From a Metallic Photonic-Crystal at Optical Wavelengths

Planck’s law predicts the distribution of radiation energy, color and intensity, emitted from a hot object at thermal equilibrium. The Law also sets the upper limit of radiation intensity, the blackbody limit. Recent experiments reveal that micro-structured tungsten can exhibit significant deviation from the blackbody spectrum. However, whether thermal radiation with weak non-equilibrium pumping can exceed the blackbody limit in the far field remains un-answered experimentally. Here, we compare thermal radiation from a micro-cavity/tungsten photonic crystal (W-PC) and a blackbody, which are both measured from the same sample and also in-situ. We show that thermal radiation can exceed the blackbody limit by >8 times at λ=1.7 μm resonant wavelength in the far-field. Our observation is consistent with a recent calculation by Wang and John performed for a 2D W-PC filament. This finding is attributed to non-equilibrium excitation of localized surface plasmon resonances coupled to nonlinear oscillators and the propagation of the electromagnetic waves through non-linear Bloch waves of the W-PC structure. This discovery could help create super-intense narrow band thermal light sources and even an infrared emitter with a laser-like input-output characteristic.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

A new low-frequency backward mode in inhomogeneous plasmas

When an electromagnetic transverse wave propagates through an inhomogeneous plasma so that its electric field has a component in the direction of the background density gradient, there appears a disbalance of charge in every plasma layer, caused by the density gradient. Due to this, some additional longitudinal electric field component appears in the direction of the wave vector. This longitudinal field may couple with the usual electrostatic longitudinal perturbations like the ion acoustic, electron Langmuir, and ion plasma waves. As a result, these standard electrostatic waves are modified and in addition to this a completely new low-frequency mode appears. Some basic features of the coupling and modification of the ion acoustic wave, and properties of the new mode are discussed here, in ordinary electron-ion and in pair plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Quantitative resonant soft x-ray reflectivity of ultrathin anisotropic organic layers: Simulation and experiment of PTCDA on Au

Resonant soft X-ray reflectivity at the carbon K edge, with linearly polarized light, was used to derive quantitative information of film morphology, molecular arrangement, and electronic orbital anisotropies of an ultrathin 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) film on Au(111). The experimental spectra were simulated by computing the propagation of the electromagnetic field in a trilayer system (vacuum/PTCDA/Au), where the organic film was treated as an anisotropic medium. Optical constants were derived from the calculated (through density functional theory) absorption cross sections of the single molecule along the three principal molecular axes. These were used to construct the dielectric tensor of the film, assuming the molecules to be lying flat with respect to the substrate and with a herringbone arrangement parallel to the substrate plane. Resonant soft X-ray reflectivity proved to be extremely sensitive to film thickness, down to the single molecular layer. The best agreement between simulation and experiment was found for a film of 1.6 nm, with flat laying configuration of the molecules. The high sensitivity to experimental geometries in terms of beam incidence and light polarization was also clarified through simulations. The optical anisotropies of the organic film were experimentally determined and through the comparison with calculations, it was possible to relate them to the orbital symmetry of the empty electronic states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗