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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 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Optimizing searches for electromagnetic counterparts of gravitational wave triggers

With the detection of a binary neutron star system and its corresponding electromagnetic counterparts, a new window of transient astronomy has opened. Due to the size of the sky localization regions, which can span hundreds to thousands of square degrees, there are significant benefits to optimizing tilings for these large sky areas. The rich science promised by gravitational wave astronomy has led to the proposal for a variety of proposed tiling and time allocation schemes, and for the first time, we make a systematic comparison of some of these methods. We find that differences of a factor of 2 or more in efficiency are possible, depending on the algorithm employed. For this reason, with future surveys searching for electromagnetic counterparts, care should be taken when selecting tiling, time allocation, and scheduling algorithms to optimize counterpart detection.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Radiation by a laser-driven flying-focus electron wave packet

An exact solution of the Dirac equation in the presence of an arbitrary electromagnetic plane wave is found, which corresponds to a focused electron wave packet, with the focus of the wave packet moving at the speed of light in the opposite direction of the average momentum of the electron wave packet (unless the plane wave is so intense to reflect the electron). The photon spectrum emitted by such an electron wave packet in the presence of a linearly polarized plane wave is studied both analytically and numerically. The spectrum is also compared with the one emitted by a single-momentum, plane-wave electron in the case of the electron being initially counterpropagating (on average for the flying-focus case) with the plane wave and within the locally constant field approximation. It is found that if the electron flying-focus wave packet is focused beyond a Compton wavelength, the angular distribution of the emitted radiation along the magnetic field of the electromagnetic plane wave is broader than for an electron with definite momentum. Corresponding the maximum value of the photon yield on the transverse plane is smaller in the flying-focus electron case. This could represent an experimental signature of a laser-driven flying-focus electron wave packet.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Design of a finline antenna for current drive in TST-2

A novel “finline” antenna was designed to excite lower-hybrid waves (LHWs) for plasma current drive at 2.45 GHz in the TST-2 spherical tokamak. A periodic fin array acts as a transmission line for electromagnetic surface waves. Cold tests confirmed propagation of the electromagnetic surface wave on the fin array which was dominantly Transverse Magnetic (TM). Unlike the conventional waveguide array “grill” antenna, the finline antenna requires only two ports to feed all the elements, and calculations show that there is little reflection regardless of the plasma conditions in front of the antenna. Characteristics of the microwave transmission on the fin array were investigated using a three-dimensional full-wave simulation and the fin geometry was tuned to achieve the desired refractive index. Coupling to LHWs under typical TST-2 scrape-off layer conditions was confirmed by the simulation. Finally, to demonstrate LHW excitation, the finline antenna was energized in the presence of a plasma generated by another 200 MHz LH antenna. The x-ray radiation showed strong enhancement during the finline antenna pulse which indicated successful generation of fast electrons by LHWs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Exact solution of the DeWitt-Brehme-Hobbs equation in copropagating electromagetic and gravitational waves

An accelerated charge interacts with its own electromagnetic field, a phenomenon known as electromagnetic radiation reaction. The DeWitt-Brehme-Hobbs (DWBH) equation describes the motion of a charged mass in the presence of combined electromagnetic and gravitational fields, taking into account electromagnetic radiation-reaction effects. Here, we find the first exact analytical solution of the DWBH equation in the case of a charged mass in the presence of copropagating and otherwise arbitrary electromagnetic and gravitational plane waves. As a consequence of the Penrose limit, the scenario considered here can be seen as a local limit around ultrarelativistic trajectories in a general curved spacetime. Finally, the paradigmatic example of an electromagnetic wave in the presence of a constant-amplitude gravitational wave is worked out explicitly and it is shown how the presence of the gravitational wave can qualitatively change electromagnetic radiation-reaction effects.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Electron acceleration during the decay of nonlinear Whistler waves in low-beta electron-ion plasma

Relativistic electron acceleration through dissipation of a nonlinear, short-wavelength, and monochromatic electromagnetic whistler wave in low-beta plasma is investigated by utilizing a one-dimensional fully relativistic electromagnetic particle-in-cell code. The nonlinear (large-amplitude) parent whistler wave decays through the parametric instability which enhances electrostatic ion acoustic waves and electromagnetic whistler waves. These waves satisfy the condition of three-wave coupling. Through the decay instability, the energy of electron bulk velocity supporting the parent wave is converted to the thermal energy perpendicular to the background magnetic field. Increase of the perpendicular temperature triggers the electron temperature anisotropy instability which generates broadband whistler waves and heats electrons in the parallel direction. The broadband whistler waves are inverse-cascaded during the relaxation of the electron temperature anisotropy. In lower-beta conditions, electrons with a pitch angle of about 90° are successively accelerated by inverse-cascaded whistler waves, and selected electrons are accelerated to over a Lorentz factor of 10. The result implies that the nonlinear dissipation of a finite-amplitude and short-wavelength whistler wave plays an important role in producing relativistic nonthermal electrons over a few MeV especially at lower beta plasmas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

The Schrödinger formalism of electromagnetism and other classical waves—How to make quantum-wave analogies rigorous

This paper systematically develops the Schrödinger formalism that is valid also for gyrotropic media where the material weights W=( ε χ χ* μ )≠ W-bar are complex. This is a non-trivial extension of the Schrödinger formalism for non- gyrotropic media (where W= W-bar ) that has been known since at least the 1960s (Wilcox, 1966; Kato, 1967). Here, Maxwell’s equations are rewritten in the form i∂{sub t}Ψ=MΨ where the selfadjoint (hermitian) Maxwell operator M=W{sup -1} Rot |{sub ω≥0}=M* takes the place of the Hamiltonian and Ψ is a complex wave representing the physical field (E,H)=2Re Ψ. Writing Maxwell’s equations in Schrödinger form gives us access to the rich toolbox of techniques initially developed for quantum mechanics and allows us to apply them to classical waves. To show its utility, we explain how to identify conserved quantities in this formalism. Moreover, we sketch how to extend our ideas to other classical waves.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Systematic errors in low-latency gravitational wave parameter estimation impact electromagnetic follow-up observations

Among the most eagerly anticipated opportunities made possible by Advanced LIGO/Virgo are multimessenger observations of compact mergers. Optical counterparts may be short-lived so rapid characterization of gravitational wave (GW) events is paramount for discovering electromagnetic signatures. One way to meet the demand for rapid GW parameter estimation is to trade off accuracy for speed, using waveform models with simplified treatment of the compact objects’ spin. We report on the systematic errors in GW parameter estimation suffered when using different spin approximations to recover generic signals. Component mass measurements can be biased by >5σ using simple-precession waveforms and in excess of 20σ when non-spinning templates are employed. This suggests that electromagnetic observing campaigns should not take a strict approach to selecting which LIGO/Virgo candidates warrant follow-up observations based on low-latency mass estimates. For sky localization, we find that searched areas are up to a factor of ∼2 larger for non-spinning analyses, and are systematically larger for any of the simplified waveforms considered in our analysis. Distance biases for the non-precessing waveforms can be in excess of 100% and are largest when the spin angular momenta are in the orbital plane of the binary. We confirm that spin-aligned waveforms should be used for low-latency parameter estimation at the minimum. Including simple precession, though more computationally costly, mitigates biases except for signals with extreme precession effects. Our results shine a spotlight on the critical need for development of computationally inexpensive precessing waveforms and/or massively parallel algorithms for parameter estimation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Quasicrystalline structures and uses thereof

This invention relates generally to devices constructed from quasicrystalline heterostructures. In preferred embodiments, two or more dielectric materials are arranged in a two- or three-dimensional space in a lattice pattern having at least a five-fold symmetry axis and not a six-fold symmetry axis, such that the quasicrystalline heterostructure exhibits an energy band structure in the space, the band structure having corresponding symmetry, which symmetry is forbidden in crystals, and which band structure comprises a complete band gap. The constructed devices are adapted for manipulating, controlling, modulating, trapping, reflecting and otherwise directing waves including electromagnetic, sound, spin, and surface waves, for a pre-selected range of wavelengths propagating within or through the heterostructure in multiple directions.

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

Quasicrystalline structures and uses thereof

This invention relates generally to the field of quasicrystalline structures. In preferred embodiments, the stopgap structure is more spherically symmetric than periodic structures facilitating the formation of stopgaps in nearly all directions because of higher rotational symmetries. More particularly, the invention relates to the use of quasicrystalline structures for optical, mechanical, electrical and magnetic purposes. In some embodiments, the invention relates to manipulating, controlling, modulating and directing waves including electromagnetic, sound, spin, and surface waves, for pre-selected range of wavelengths propagating in multiple directions.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Quasicrystalline structures and uses thereof

This invention relates generally to the field of quasicrystalline structures. In preferred embodiments, the stopgap structure is more spherically symmetric than periodic structures facilitating the formation of stopgaps in nearly all directions because of higher rotational symmetries. More particularly, the invention relates to the use of quasicrystalline structures for optical, mechanical, electrical and magnetic purposes. In some embodiments, the invention relates to manipulating, controlling, modulating and directing waves including electromagnetic, sound, spin, and surface waves, for pre-selected range of wavelengths propagating in multiple directions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Quasicrystalline structures and uses thereof

This invention relates generally to the field of quasicrystalline structures. In preferred embodiments, the stopgap structure is more spherically symmetric than periodic structures facilitating the formation of stopgaps in nearly all directions because of higher rotational symmetries. More particularly, the invention relates to the use of quasicrystalline structures for optical, mechanical, electrical and magnetic purposes. In some embodiments, the invention relates to manipulating, controlling, modulating and directing waves including electromagnetic, sound, spin, and surface waves, for pre-selected range of wavelengths propagating in multiple directions.

Steinhardt, Paul Joseph↗
DOE OSTI2021

Quasicrystalline structures and uses thereof

This invention relates generally to the field of quasicrystalline structures. In preferred embodiments, the stopgap structure is more spherically symmetric than periodic structures facilitating the formation of stopgaps in nearly all directions because of higher rotational symmetries. More particularly, the invention relates to the use of quasicrystalline structures for optical, mechanical, electrical and magnetic purposes. In some embodiments, the invention relates to manipulating, controlling, modulating and directing waves including electromagnetic, sound, spin, and surface waves, for pre-selected range of wavelengths propagating in multiple directions.

Steinhardt, Paul Joseph↗
DOE OSTI2023

Quasicrystalline structures and uses thereof

This invention relates generally to the field of quasicrystalline strictures. In preferred embodiments, the stopgap structure is more spherically symmetric than periodic structures facilitating the formation of stopgaps in nearly all directions because of higher rotational symmetries. More particularly, the invention relates to the use of quasicrystalline structures for optical, mechanical, electrical and magnetic purposes. In some embodiments, the invention relates to manipulating, controlling, modulating and directing waves including electromagnetic, sound, spin, and surface waves, for pre-selected range of wavelengths propagating in multiple directions.

Steinhardt, Paul Joseph↗
DOE OSTI2016

Effects of electromagnetic wiggler and ion channel guiding on equilibrium orbits and waves propagation in a free electron laser

In this paper, an analysis of equilibrium orbits for electrons by a simultaneous solution of the equation of motion and the dispersion relation for electromagnetic wave wiggler in a free-electron laser (FEL) with ion-channel guiding has been presented. A fluid model has been used to investigate interactions among all possible waves. The dispersion relation has been derived for electrostatic and electromagnetic waves with all relativistic effects included. This dispersion relation has been solved numerically. For group I and II orbits, when the transverse velocity is small, only the FEL instability is found. In group I and II orbits with relatively large transverse velocity, new couplings between other modes are found.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

High-performance terahertz wave absorbers made of silicon-based metamaterials

Electromagnetic (EM) wave absorbers with high efficiency in different frequency bands have been extensively investigated for various applications. In this paper, we propose an ultra-broadband and polarization-insensitive terahertz metamaterial absorber based on a patterned lossy silicon substrate. Experimentally, a large absorption efficiency more than 95% in a frequency range of 0.9–2.5 THz was obtained up to a wave incident angle as large as 70°. Much broader absorption bandwidth and excellent oblique incidence absorption performance are numerically demonstrated. The underlying mechanisms due to the combination of a waveguide cavity mode and impedance-matched diffraction are analyzed in terms of the field patterns and the scattering features. The monolithic THz absorber proposed here may find important applications in EM energy harvesting systems such as THz barometer or biosensor.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

The role of higher-order modes on the electromagnetic whistler-cyclotron wave fluctuations of thermal and non-thermal plasmas

Two fundamental challenging problems of laboratory and astrophysical plasmas are the understanding of the relaxation of a collisionless plasmas with nearly isotropic velocity distribution functions and the resultant state of nearly equipartition energy density with electromagnetic plasma turbulence. Here, we present the results of a study which shows the role that higher-order-modes play in limiting the electromagnetic whistler-like fluctuations in a thermal and non-thermal plasma. Our main results show that for a thermal plasma the magnetic fluctuations are confined by regions that are bounded by the least-damped higher order modes. We further show that the zone where the whistler-cyclotron normal modes merges the electromagnetic fluctuations shifts to longer wavelengths as the β{sub e} increases. This merging zone has been interpreted as the beginning of the region where the whistler-cyclotron waves losses their identity and become heavily damped while merging with the fluctuations. Our results further indicate that in the case of nonthermal plasmas, the higher-order modes do not confine the fluctuations due to the effective higher-temperature effects and the excess of suprathermal plasma particles. The analysis presented here considers the second-order theory of fluctuations and the dispersion relation of weakly transverse fluctuations, with wave vectors parallel to the uniform background magnetic field, in a finite temperature isotropic bi-Maxwellian and Tsallis-kappa-like magnetized electron–proton plasma. Our results indicate that the spontaneously emitted electromagnetic fluctuations are in fact enhanced over these quasi modes suggesting that such modes play an important role in the emission and absorption of electromagnetic fluctuations in thermal or quasi-thermal plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗