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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Electron Trapping from Interactions between Laser-Driven Relativistic Plasma Waves

Interactions of large-amplitude relativistic plasma waves were investigated experimentally by propagating two synchronized ultraintense femtosecond laser pulses in plasma at oblique crossing angles to each other. The electrostatic and electromagnetic fields of the colliding waves acted to preaccelerate and trap electrons via previously predicted, but untested injection mechanisms of ponderomotive drift and wake-wake interference. High-quality energetic electron beams were produced, also revealing valuable new information about plasma-wave dynamics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Dynamical Control of Broadband Coherent Absorption in ENZ Films

Interferometric effects between two counter-propagating beams incident on an optical system can lead to a coherent modulation of the absorption of the total electromagnetic radiation with 100% efficiency even in deeply subwavelength structures. Coherent perfect absorption (CPA) rises from a resonant solution of the scattering matrix and often requires engineered optical properties. For instance, thin film CPA benefits from complex nanostructures with suitable resonance, albeit at a loss of operational bandwidth. In this work, we theoretically and experimentally demonstrate a broadband CPA based on light-with-light modulation in epsilon-near-zero (ENZ) subwavelength films. We show that unpatterned ENZ films with different thicknesses exhibit broadband CPA with a near-unity maximum value located at the ENZ wavelength. By using Kerr optical nonlinearities, we dynamically tune the visibility and peak wavelength of the total energy modulation. Our results based on homogeneous thick ENZ media open a route towards on-chip devices that require efficient light absorption and dynamical tunability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Mode-conversion of the extraordinary wave at the upper hybrid resonance in the presence of small-amplitude density fluctuations

In spherical tokamaks, the electron plasma frequency is greater than the electron cyclotron frequency. Electromagnetic waves in the electron cyclotron range of frequencies are unsuitable for directly heating such plasmas due to their reduced accessibility. However, mode-conversion of the extraordinary wave to the electron Bernstein wave (X-B mode-conversion) at the upper hybrid resonance makes it possible to efficiently couple externally-launched electromagnetic wave energy into an overdense plasma core. Traditional mode-conversion models describe an X-mode wave propagating in a potential containing two cutoffs that bracket a single wave resonance. Often, however, the mode-conversion region is in the edge, where turbulent fluctuations and blobs can generate abrupt cutoffs and scattering of the incident X-mode wave. We present a new framework for studying the X-B mode-conversion which makes the inclusion of these fluctuations analytically tractable. In the new approach, the high- field cutoff is modelled as an infinite barrier, which manifests as a boundary condition applied to a wave equation involving only one cutoff adjacent to the resonance on the low-field side. The new model reproduces the main features of the previous approach, yet is more suitable for analyzing experimental observations and extrapolating to higher dimensions. We then develop an analytical estimate for the effect of small-amplitude, quasi-monochromatic density fluctuations on the X-B mode-conversion efficiency using perturbation theory. We find that Bragg backscattering of the launched X-mode wave reduces the mode-conversion efficiency significantly when the fluctuation wavenumber is resonant with the wavenumber of the incident X-mode wave. These analytical results are corroborated by numerically integrating the mode-conversion equations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Method and apparatus of wide-angle optical beamsteering from a nanoantenna phased array

An optical beam-steering apparatus is provided. The apparatus includes one or more optical waveguides and at least one row of metallic nanoantenna elements overlying and electromagnetically coupled to a respective waveguide. In each such row, individual nanoantenna elements are spaced apart along an optical propagation axis of the waveguide so that there is an optical propagation phase delay between successive pairs of nanoantenna elements along the row. The apparatus also includes a respective single electric heating element in thermal contact with each of the waveguides. Each heating element is arranged to heat, substantially uniformly, at least that portion of its waveguide that directly underlies the corresponding row of nanoantenna elements.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Photoacoustic Sounds from Meteors.

High-speed photometric observations of meteor fireballs have shown that they often produce high-amplitude light oscillations with frequency components in the kHz range, and in some cases exhibit strong millisecond flares. We built a light source with similar characteristics and illuminated various materials in the laboratory, generating audible sounds. Models suggest that light oscillations and pulses can radiatively heat dielectric materials, which in turn conductively heats the surrounding air on millisecond timescales. The sound waves can be heard if the illuminated material is sufficiently close to the observer’s ears. The mechanism described herein may explain many reports of meteors that appear to be audible while they are concurrently visible in the sky and too far away for sound to have propagated to the observer. This photoacoustic (PA) explanation provides an alternative to electrophonic (EP) sounds hypothesized to arise from electromagnetic coupling of plasma oscillation in the meteor wake to natural antennas in the vicinity of an observer.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Real-time time-dependent density functional theory in Quantum Espresso and related codes

A set of subroutines that interact with an existing computer program, Quantum Espresso (QE), that takes a set of electronic orbitals from QE and propagates them forward in time in response to a number of perturbations. These perturbations include the motion of ions and a wide spectrum of applied electromagnetic fields (e.g., static magnetic fields, slowly-varying electric fields, x-rays, etc.). From the time evolution of the electronic orbitals comes time-varying values of physical observables like the electronic charge and current densities and atomic forces. These are further post-processed to yield properties of interest like stopping powers, conductivities, and the dynamic structure factor. The electronic orbitals are described in a plane wave basis and the equations of motion are carried out using a unitary or approximately unitary time propagation algorithm. Related work will include subroutines for interfacing this capability, as well as others that already exist within QE, with a fork of QE that is more extensible and modular.SAND2019-12611 M Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.

Baczewski, Andrew↗
DOE OSTI2019

Cylindrical and plane surface electromagnetic waves in laser technology of silicon surface texturing with a double femtosecond pulse

This paper presents experimental results of laser modification of the surface of monocrystalline silicon under the influence of a double femtosecond laser pulse with varying delays less than or close to the electron–phonon interaction time, as well as the results of numerical simulation of the photoexcitation of a semiconductor in the approximation of dielectric constant. It is shown that the excitation of cylindrical surface waves not only precedes the excitation of plane surface electromagnetic waves, but is also a determining factor in the cumulative change in the dielectric constant of the medium and the creation of conditions for the excitation of plane surface electromagnetic waves.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Suppressing the numerical Cherenkov radiation in the Yee numerical scheme

The next generation of laser facilities will routinely produce relativistic particle beams from the interaction of intense laser pulses with solids and/or gases. Their modeling with Particle-In-Cell (PIC) codes needs dispersion-free Maxwell solvers in order to properly describe the interaction of electromagnetic waves with relativistic particles. A particular attention is devoted to the suppression of the numerical Cherenkov instability, responsible for the noise generation. It occurs when the electromagnetic wave is artificially slowed down because of the finite mesh size, thus allowing for the high energy particles to propagate with super-luminous velocities. In the present paper, we show how a slight increase of the light velocity in the Maxwell's equations enables to suppress this instability while keeping a good overall precision of calculations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Minimal model for spoof acoustoelastic surface states

Similar to textured perfect electric conductors for electromagnetic waves sustaining artificial or spoof surface plasmons we present an equivalent phenomena for the case of sound. Aided by a minimal model that is able to capture the complex wave interaction of elastic cavity modes and airborne sound radiation in perfect rigid panels, we construct designer acoustoelastic surface waves that are entirely controlled by the geometrical environment. Comparisons to results obtained by full-wave simulations confirm the feasibility of the model and we demonstrate illustrative examples such as resonant transmissions and waveguiding to show a few examples of many where spoof elastic surface waves are useful.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Optical modeling and physical performances evaluations for the JT-60SA ECRF antenna

The purpose of this work is the optical modeling and physical performances evaluations of the JT-60SA ECRF launcher system. The beams have been simulated with the electromagnetic code GRASP® and used as input for ECCD calculations performed with the beam tracing code GRAY, capable of modeling propagation, absorption and current drive of an EC Gaussion beam with general astigmatism. Full details of the optical analysis has been taken into account to model the launched beams. Inductive and advanced reference scenarios has been analysed for physical evaluations in the full poloidal and toroidal steering ranges for two slightly different layouts of the launcher system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Polyimide dynamically compressed to decomposition pressures: Two-wave structures captured by velocimetry and modeling

We performed a series of six plate impact experiments on polyimide and modeled them using new reactant and products equations of state combined with an Arrhenius rate model. The first experiment was diagnosed with embedded electromagnetic velocity gauges through which we directly observed attenuation of the lead shock to an approximately constant state over a propagation distance of roughly 4 mm. Simulated gauge profiles were in excellent qualitative agreement with experiment and suggested a sluggish chemical reaction that did not proceed to completion. The remaining five experiments were conducted in a transmission geometry and diagnosed velocimetrically at the sample/window interface. All five of these yielded profiles with a sharp shock followed by a more gradual approach to maximum interface velocity that was “rounded” to varying degree. These profiles proved difficult to interpret unambiguously due to the convolution of the reactive wave upon first shock with reflection of the lead wave and reshock or release by the window. Comparison with thermochemical calculations strongly suggests that the point of maximum interface velocity corresponds to the equilibrium reshock or release locus. We discuss the implications of this point for the practice of impedance matching based on the reflected Hugoniot of reactive materials such as polymers. The reactant and thermochemical products equations of state are developmental SESAME tables 97710 and 97720, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Full-wave simulations on helicon and parasitic excitation of slow waves near the edge plasma

Helicon waves are thought to be promising in various tokamaks, such as DIII-D, because they can penetrate reactor-grade high-density cores and drive the off-axis current with higher efficiency. In the frequency regime ~476 MHz, both slow electrostatic and fast electromagnetic helicon waves can coexist in DIII-D. If the antenna parasitically excites the slow mode, these waves can propagate along the magnetic field line into the scrape-off layer (SOL). Although the importance of the misalignment of the Faraday screen and the electron density in the SOL on the excitation and propagation of slow modes is well known, the conditions for minimizing slow mode excitation have yet to be optimized. Using the Petra-M simulation code in the 2D domain, we analyze the effects of the misalignment of the antenna in the poloidal direction, the misalignment of the Faraday screen in the toroidal direction, and the density in front of the antenna on slow mode generation. Our results suggest that the misalignment of the Faraday screen is a critical factor in reducing the slow mode and that the misalignment angle should be below ~5° to minimize the slow wave excitation. When the electron density is higher than 3.5 x 10 18 m –3 in the SOL, the generation of the slow mode from the antenna is minimized and unaffected by the misalignment of the Faraday screen.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Revised formulation of the macroscopic maxwell theory

A modified version of the macroscopic Maxwell theory is developed with the purpose of removing some of the current contradictions and inconsistencies. One of the crucial problems of the current electromagnetic theory concerns the concept of energy. It appears that energy which has a clearly defined physical significance in all fields of physics has not been properly incorporated into the Maxwell-Lorentz theory. Therefore, the electromagnetic energy in a dissipative system as interpreted in the current version of the theory is not « energy » in the same sense as one usually interprets this concept in classical mechanics. The main object of this investigation is, therefore, to clarify the meaning of energy and to suggest a revised version in which the concept of energy is incorporated in accordance with the logical requirements of the theory. The proposed version is based on an assumption that the « electrical energy » both in nondissipative and dissipative media has a meaning only to the extent to which the electrical field theory can be developed as a theory of a dynamical system. This assumption leads to a formulation of a principle which states that the energy densityU e of an electrical field in an absorbing medium is determined solely by the electrical intensityE and is, therefore, independent of any parameter which represents absorption. The proposed version differs from the traditional theory in the interpretation of the dielectric constant and of conductivity. Further, the dielectric constant is considered to be independent of conductivity in the sense that a change in conductivity does not produce a corresponding alteration of the dielectric constant. Part I of this investigation deals with the fundamentals of the proposed reformulated version. These fundamentals are then applied in Part II to the generalization of Brillouin’s theory of wave propagation and group velocity to absorbing media.

DIELECTRICS↗
DOE OSTI2015

Formation of a hybrid plasmonic waveguide mode probed by dispersion measurement

Hybrid waveguides, i.e., dielectric waveguides combined with plasmonic waveguides, have great potential for concomitantly exhibiting subwavelength confinement and long range propagation, enabling a highly integrated photonic circuit. We report the characterization of hybrid waveguide modes excited in Si/SiO{sub 2}/Al films, by dispersion measurement using angle-resolved electron energy-loss spectroscopy. This experiment directly verifies the formation of the hybrid waveguide mode with a strongly localized electromagnetic field in a 6-nm-thick SiO{sub 2} layer. The results clearly describe the characteristic behavior of the hybrid waveguide mode, which depends on the effective index of the constituent dielectric waveguide and the surface plasmon-polariton modes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Tunable ultrasonic phononic crystal controlled by infrared radiation

A tunable phononic crystal based ultrasonic filter was designed by stimulating the phase of the polymeric material embedded in a periodic structure using infrared radiation. The acoustic filter can be tuned remotely using thermal stimulation induced by the infrared radiation. The filter is composed of steel cylinder scatterers arranged periodically in a background of bulk poly (N-isopropylacrylamide) polymer hydrogel. The lattice structure creates forbidden bands for certain sets of mechanical waves that cause it to behave as an ultrasonic filter. Since the bandstructure is determined by not only the arrangement of the scatterers but also the physical properties of the materials composing the scatterers and background, modulating either the arrangement or physical properties will alter the effect of the crystal on propagating mechanical waves. Here, the physical properties of the filter are varied by inducing changes in the polymer hydrogel using an electromagnetic thermal stimulus. With particular focus on the k{sub 00}-wave, the transmission of ultrasonic wave changes by as much as 20 dBm, and band widths by 22% for select bands.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Electromagnetic scattering problems -Numerical issues and new experimental approaches of validation

Electromagnetic scattering problems, thus the question how radiated energy spreads when impinging on an object, are an essential part of wave propagation. Though the Maxwell’s differential equations as starting point, are actually quite simple,the integral formulation of an object’s boundary conditions, respectively the solution for unknown induced currents can only be solved numerically in most cases.As a timely topic of practical importance the scattering of rotating wind turbines is discussed, the numerical description of which is still based on rigorous approximations with yet unspecified accuracy. In this context the issue of validating numerical solutions is addressed, both with reference simulations but in particular with the experimental approach of scaled measurements. For the latter the idea of an incremental validation is proposed allowing a step by step validation of required new mathematical models in scattering theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Simultaneous Trapping of Electromagnetic Ion Cyclotron and Magnetosonic Waves by Background Plasmas

Electromagnetic ion cyclotron waves and fast magnetosonic waves are found to be simultaneously modulated by background plasma density: both kinds of waves were observed in high plasma density regions but vanished in low-density regions. Theoretical analysis based on Snell's law and linear growth theory has been utilized to investigate the physical mechanisms driving such modulation. It is suggested that the modulation of fast magnetosonic waves might be due to trapping by plasma density structures, which results from the conservation of the parameter Q during their propagation. In this study Q = nr sin ψ , with n as the refractive index, r as the radial distance, and ψ as the wave azimuthal angle. As for electromagnetic ion cyclotron waves, the modulation might be owed to the ion composition difference between different plasma density regions. Our results indicate the alternative mechanism for the simultaneous appearance of electromagnetic ion cyclotron waves and fast magnetosonic waves (rather than wave excitations of both two wave emissions), which might take combined effects on the evolution of radiation belt electrons.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Comparison of equilibrium ohmic and nonequilibrium swarm models for monitoring conduction electron evolution in high-altitude EMP calculations

Here, atmospheric electromagnetic pulse (EMP) events are important physical phenomena that occur through both man-made and natural processes. Radiation-induced currents and voltages in EMP can couple with electrical systems, such as those found in satellites, and cause significant damage. Due to the disruptive nature of EMP, it is important to accurately predict EMP evolution and propagation with computational models. CHAP-LA (Compton High Altitude Pulse-Los Alamos) is a state-of-the-art EMP code that solves Maxwell inline images equations for gamma source-induced electromagnetic fields in the atmosphere. In EMP, low-energy, conduction electrons constitute a conduction current that limits the EMP by opposing the Compton current. CHAP-LA calculates the conduction current using an equilibrium ohmic model. The equilibrium model works well at low altitudes, where the electron energy equilibration time is short compared to the rise time or duration of the EMP. At high altitudes, the equilibration time increases beyond the EMP rise time and the predicted equilibrium ionization rate becomes very large. The ohmic model predicts an unphysically large production of conduction electrons which prematurely and abruptly shorts the EMP in the simulation code. An electron swarm model, which implicitly accounts for the time evolution of the conduction electron energy distribution, can be used to overcome the limitations exhibited by the equilibrium ohmic model. We have developed and validated an electron swarm model previously in Pusateri et al. (2015). Here we demonstrate EMP damping behavior caused by the ohmic model at high altitudes and show improvements on high-altitude, upward EMP modeling obtained by integrating a swarm model into CHAP-LA.

54 ENVIRONMENTAL SCIENCES↗