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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

A nonlinear analysis of the terahertz serpentine waveguide traveling-wave amplifier

A nonlinear model for the numerical simulation of terahertz serpentine waveguide traveling-wave tube (SW-TWT) is described. In this model, the electromagnetic wave transmission in the SW is represented as an infinite set of space harmonics to interact with an electron beam. Analytical expressions for axial electric fields in axisymmetric interaction gaps of SW-TWTs are derived and compared with the results from CST simulation. The continuous beam is treated as discrete macro-particles with different initial phases. The beam-tunnel field equations, space-charge field equations, and motion equations are combined to solve the beam-wave interaction. The influence of backward wave and relativistic effect is also considered in the series of equations. The nonlinear model is used to design a 340 GHz SW-TWT. Several favorable comparisons of model predictions with results from a 3-D Particle-in-cell simulation code CHIPIC are presented, in which the output power versus beam voltage and interaction periods are illustrated. The relative error of the predicted output power is less than 15% in the 3 dB bandwidth and the relative error of the saturated length is less than 8%.The results show that the 1-D nonlinear analysis model is appropriate to solve the terahertz SW-TWT operation characteristics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Instabilities of a circularly polarized wave with trapped particles in an isotropic plasma

The structure and stability of a transverse electromagnetic wave propagating with a velocity lower than the speed of light in an unmagnetized plasma are considered. The stationary finite-amplitude wave is described by exact solutions to the Vlasov-Maxwell equations. However, unlike the well-known electrostatic analog, the Bernstein-Greene-Kruskal wave, the wave structure is determined to a large extent by the presence of trapped particles with a shear of transverse velocities, without which the existence of waves with a refraction index larger than unity is impossible. It is shown that the main origin of the wave instability is the longitudinal motion of trapped particles relative to the background plasma. Expressions for the growth rates in the main instability regimes are found under definite restrictions on the wave parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1983

Electromagnetic lower hybrid waves in the solar wind

An analysis of electromagnetic lower hybrid waves or hybrid whistlers that propagate nearly perpendicular to the magnetic field lines in the solar wind is described. Doppler-shifted, these waves have a broadband nature when observed in the spacecraft frame depending on the direction of propagation and the supersonic flow velocity of the wind. Lower hybrid waves can energize ions normal to the interplanetary magnetic field. They may occasionaly be responsible for the observed temperature anisotropy in high speed streams and possibly for the acceleration of heavier ions such as the oxygen ions, alpha particles, etc. These modes are probably driven unstable by the anisotropic halos of the solar wind electron distributions exhibiting 'heat flux' profiles.

Marsch, E.↗
DOE OSTI2015

Surface wave and linear operating mode of a plasma antenna

The relation between the propagation conditions of a surface electromagnetic wave along a finiteradius plasma cylinder and the linear operating mode of a plasma antenna is investigated. The solution to the dispersion relation for a surface wave propagating along a finite-radius plasma cylinder is analyzed for weakly and strongly collisional plasmas. Computer simulations of an asymmetrical plasma dipole antenna are performed using the KARAT code, wherein the dielectric properties of plasma are described in terms of the Drude model. The plasma parameters corresponding to the linear operating mode of a plasma antenna are determined. It is demonstrated that the characteristics of the plasma antenna in this mode are close to those of an analogous metal antenna.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Microwave Absorption Properties of Cobalt-Zirconium Doped Strontium Hexaferrites in Ku-Frequency Band

In this article, microwave electromagnetic properties of doped strontium hexaferrites have been investigated in Ku microwave frequency band (12.4–18 GHz), along with their performance as microwave absorbing materials. Vector network analyzer has been used for characterization of cobalt-zirconium substituted strontium hexaferrites Sr(CoZr){sub x}Fe{sub (12−2x)}O{sub 19} (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0), synthesized using sol-gel method. Real parts of permittivity and permeability have shown very small variations up to 16 GHz. There has been a dip in spectrum of real part of permittivity and a peak in spectrum of real part of permeability at the same frequency in 16–18 GHz range for every composition. Regarding the electromagnetic wave absorption, all the six prepared compositions have potential (≥90% absorption) for usage in suppressing electromagnetic pollution. The composition with x = 1.0 has achieved the highest −10 dB absorption bandwidth from 15 to 18 GHz frequency. The realization of absorbing materials with maximum absorption is related to the phenomenon of impedance matching and high electromagnetic losses. The correlation of absorption peaks with attenuation constant, wave impedance and complex thickness has also been studied.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2007

Impact of Ring Current Ions on Electromagnetic Ion Cyclotron Wave Dispersion Relation

Effect of the ring current ions in the real part of electromagnetic ion Cyclotron wave dispersion relation is studied on global scale. Recent Cluster observations by Engebretson et al. showed that although the temperature anisotropy of is energetic (> 10 keV) ring current protons was high during the entire 22 November 2003 perigee pass, electromagnetic ion cyclotron waves were observed only in conjunction with intensification of the ion fluxes below 1 keV by over an order of magnitude. To study the effect of the ring current ions on the wave dispersive properties and the corresponding global wave redistribution, we use a self-consistent model of interacting ring current and electromagnetic ion cyclotron waves, and simulate the May 1998 storm. The main findings of our simulation can be summarized as follows: First, the plasma density enhancement in the night MLT sector during the main and recovery storm phases is mostly caused by injection of suprathermal plasma sheet H + (approximately < 1 keV), which dominate the thermal plasma density. Second, during the recovery storm phases, the ring current modification of the wave dispersion relation leads to a qualitative change of the wave patterns in the postmidnight-dawn sector for L > 4.75. This "new" wave activity is well organized by outward edges of dense suprathermal ring current spots, and the waves are not observed if the ring current ions are not included in the real part of dispersion relation. Third, the most intense wave-induced ring current precipitation is located in the night MLT sector and caused by modification of the wave dispersion relation. The strongest precipitating fluxes of about 8 X 10(exp 6)/ (cm(exp 2) - s X st) are found near L=5.75, MLT=2 during the early recovery phase on 4 May. Finally, the nightside precipitation is more intense than the dayside fluxes, even if there are less intense waves, because the convection field moves ring current ions into the loss cone on the nightside, but drives them out of the loss cone on the dayside. So convection and wave scattering reinforce each other in the nightside, but interfere in the dayside sector.

Khazanov, G. V.↗
DOE OSTI2024

Patterned dielectric back contact design for GaAs thermophotovoltaic devices

-Patterned-dielectric back contact structures in optoelectronic devices are designed to boost the reflectance of light from the device back surface while retaining a low-resistance pathway for electrical conductance. Their reduced light absorption at near- and sub-bandgap photon energies leads to improved luminescence in light-emitting diodes, greater photon recycling, voltage, and efficiency in photovoltaic cells, and greater recuperation of unabsorbed sub-bandgap light in thermophotovoltaic (TPV) systems. However, diffraction from the patterned features can deflect incident light in propagation directions that lead to light trapping and parasitic absorption in the cell. Here, in this article, we use rigorous coupled-wave analysis (RCWA) to study three-dimensional diffractive scattering of electromagnetic waves by periodic metal point-contact gratings on 1.42-eV GaAs TPV cells, to analyze their effect on unwanted sub-bandgap absorption in order to achieve higher TPV system efficiency. Solutions of Maxwell's equations calculated using RCWA are compared to measured sub-bandgap reflectance in experimental GaAs TPV devices with varying metal point-contact diameters and spacing. Modeling and experiments indicate decreased total reflectance due to these diffractive effects for a small point contact diameter of 1 μm, and this effect is much stronger at higher contact coverage fractions.

14 SOLAR ENERGY↗
DOE OSTI2016

Trivelpiece-Gould modes in a uniform unbounded plasma

Trivelpiece-Gould (TG) modes originally described electrostatic surface waves on an axially magnetized cylindrical plasma column. Subsequent studies of electromagnetic waves in such plasma columns revealed two modes, a predominantly magnetic helicon mode (H) and the mixed magnetic and electrostatic Trivelpiece-Gould modes (TG). The latter are similar to whistler modes near the oblique cyclotron resonance in unbounded plasmas. The wave propagation in cylindrical geometry is assumed to be paraxial while the modes exhibit radial standing waves. The present work shows that TG modes also arise in a uniform plasma without radial standing waves. It is shown experimentally that oblique cyclotron resonance arises in large mode number helicons. Their azimuthal wave number far exceeds the axial wave number which creates whistlers near the oblique cyclotron resonance. Cyclotron damping absorbs the TG mode and can energize electrons in the center of a plasma column rather than the edge of conventional TG modes. The angular orbital field momentum can produce new perpendicular wave-particle interactions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1986

COMLINK proposal for future missions of tethered satellite

The quality of the communications links between satellites was tested. The interaction between the VLF and ELF waves, generated by the conducting tether, and the SHF and YHF electromagnetic waves, generated by the 20/30 GHz transmitters were investigated. The ionspheric electron density irregularities was measured by means of phase-coherent RF transmission between the two vehicles. The motion of the tethered satellite was observed through the Doppler link established between the shuttle and the satellite. The technology and deployment of spaceborne antennas of large diameter was tested.

Sciarrino, F.↗
NASA NTRS1996

Measurement of Noise Produced by a Plasma Contactor Operating in Ground Based Facilities

Methods to measure electric field fluctuations accurately in a plasma with an active monopole antenna are described. It is shown that the conductive surfaces of the antenna must be adequately isolated from the ambient plasma and that the monopole must be sufficiently short to avoid antenna amplifier saturation. Experimental results illustrate that the noise produced by plasma contactor operation and sensed by the antenna is due to plasma phenomena and is not induced by laboratory power supplies. A good correlation is shown between the current fluctuations in the contactor electrical circuit and the noise detected by the antenna. A large body of experimental data support the conclusion that the majority of noise sensed by the antenna at frequencies less than 1 MHz is due to current fluctuations (electrostatic waves) in the plasma adjacent to the antenna and not to electromagnetic wave radiation. Caution is suggested when comparing antenna noise measurements to conventional specifications for radiated emissions.

Snyder, Steve↗
DOE OSTI2019

Dyakonov surface waves at the interface of nanocomposites with spherical and ellipsoidal inclusions

The dispersion properties of different types of surface electromagnetic waves which are supported by the interface of two nanocomposite materials with inclusions of different shape are studied theoretically and numerically. Both nanocomposites are made of doped n-type semiconductor inclusions which are evenly distributed in a transparent dielectric matrix. First nanocomposite contains semiconductor inclusions of spherical shape and can be represented as isotropic material with scalar effective dielectric permittivity. Second nanocomposite contains semiconductor inclusions of ellipsoidal shape and can be modeled as a uniaxial anisotropic crystal with two different principal effective permittivity components. Influence of physical and geometrical parameters of the nanocomposites on dispersion properties of surface waves is studied. It is shown that when dissipations in the semiconductor inclusions are taken into account the angular spectrum of Dyakonov surface wave existence becomes wider, and several dispersion curves of surface modes can simultaneously exist.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1980

Generation and injection of e.m. waves in space plasma by means of a long orbiting tether

The generation and injection of electromagnetic waves in space plasma by means of a long orbiting tether are considered. The objectives include an estimation of the portions of the primary electrodynamic power developed by the tether that goes to excite each of various wave generation and injection mechanisms expected to be present during a tether's orbital flight, an evaluation of the signal levels associated with each one of the mechanisms above, and verification of their detectability with state-of-the-art instrumentation on the Earth surface or elsewhere. The generation and injection of Alfven waves and electron whistler waves were identified as the most relevant mechanisms activited by the electrodynamic tether. The physical mechanisms that govern these two families of phenomena were investigated and the ratio between the power that goes in Alfven waves and in whistlers was derived. The analysis of the possible production of accelerated electrons by the electrodynamic tether was initiated.

Source record↗
NASA NTRS1992

On the convergence of the coupled-wave approach for lamellar diffraction gratings

Among the many existing rigorous methods for analyzing diffraction of electromagnetic waves by diffraction gratings, the coupled-wave approach stands out because of its versatility and simplicity. It can be applied to volume gratings and surface relief gratings, and its numerical implementation is much simpler than others. In addition, its predictions were experimentally validated in several cases. These facts explain the popularity of the coupled-wave approach among many optical engineers in the field of diffractive optics. However, a comprehensive analysis of the convergence of the model predictions has never been presented, although several authors have recently reported convergence difficulties with the model when it is used for metallic gratings in TM polarization. Herein, three points are made: (1) in the TM case, the coupled-wave approach converges much slower than the modal approach of Botten et al; (2) the slow convergence is caused by the use of Fourier expansions for the permittivity and the fields in the grating region; and (3) is manifested by the slow convergence of the eigenvalues and the associated modal fields. The reader is assumed to be familiar with the mathematical formulations of the coupled-wave approach and the modal approach.

Li, Lifeng↗
DOE OSTI2026

Unitary Qubit Lattice Algorithms for Plasma Physics

This final technical report summarizes research conducted under DOE Award DE-SC0021653 to develop unitary Quantum Lattice Algorithms for modeling electromagnetic wave propagation and scattering in complex media, including plasmas. The project developed and validated quantum-inspired formulations of Maxwell's equations that preserve unitary evolution and can be evaluated on classical high-performance computing systems while providing a foundation for future quantum-computing implementations. Major accomplishments include the development of two- and three-dimensional algorithms for electromagnetic scattering; scalable, distributed-memory implementations demonstrated on the Perlmutter supercomputer; formulations for nonlinear lossless fluid dynamics and cold, lossless, inhomogeneous magnetized plasmas; and an explicit quantum algorithm for a time-discretized Lorenz model. Simulations reproduced a range of characteristic wave phenomena, including transient effects that are not readily apparent in conventional frequency-domain studies, demonstrating the effectiveness of the proposed approach for modeling complex electromagnetic and plasma systems. The work establishes a unified theoretical and computational framework for quantum and quantum-inspired simulation and provides a foundation for future implementation on fault-tolerant quantum systems.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Modulating surface acoustic wave generation through superconductivity

Surface acoustic waves (SAWs), with their five orders-of-magnitude slower propagation velocity, allow for considerably shorter wavelengths at the same frequency compared to electromagnetic waves. The short wavelengths allow for device miniaturization and on-chip integration. The generic design of these devices involves piezoelectric substrates with comb-like arrays of Al or Au electrodes known as interdigitated transducers (IDTs) deposited on the surface. However, Al and Au both have shortcomings at the cryogenic temperatures required for quantum applications, namely, the formation of two-level systems and the lack of superconductivity perpetuating Ohmic losses, respectively. In this work, SAWs are generated in the high-MHz to low-GHz range using niobium nitride (NbN) interdigitated transducers and Bragg reflectors. We demonstrate the fabrication of acoustic devices through photolithography and reactive ion etching. The sharp transition between superconducting and normal states and the corresponding change in SAW transmission allows for fine control of the “on” (superconducting) and “off” (normal) states of NbN, with a ΔT = 1 K separating the transmission minimum and maximum. We demonstrate a 16× difference in transmission between the “on” and “off” states of the device. The SAW transmission behavior mirrors the change in resistance of NbN at its T c . These findings open up new possibilities for the integration of NbN SAW resonators into existing quantum architectures based on NbN and a method for adjusting transmission properties independent of applied voltage.

36 MATERIALS SCIENCE↗
NASA NTRS2003

Self-Consistent Model of Magnetospheric Ring Current and Electromagnetic Ion Cyclotron Waves: The May 2-7, 1998, Storm

Complete description of a self-consistent model for magnetospheric ring current interacting with electromagnetic ion cyclotron waves is presented. The model is based on the system of two kinetic equations; one equation describes the ring current ion dynamics, and another equation describes the wave evolution. The effects on ring current ions interacting with electromagnetic ion cyclotron waves, and back on waves, are considered self-consistently by solving both equations on a global magnetospheric scale under non steady-state conditions. In the paper by Khazanov et al. [2002] this self-consistent model has only been shortly outlined, and discussions of many the model related details have been omitted. For example, in present study for the first time a new algorithm for numerical finding of the resonant numbers for quasilinear wave-particle interaction is described, or it is demonstrated that in order to describe quasilinear interaction in a multi-ion thermal plasma correctly, both e and He(+) modes of electromagnetic ion cyclotron waves should be employed. The developed model is used to simulate the entire May 2-7, 1998 storm period. Trapped number fluxes of the ring current protons are calculated and presented along with their comparison with the data measured by the 3D hot plasma instrument Polar/HYDRA. Examining of the wave (MLT, L shell) distributions produced during the storm progress reveals an essential intensification of the wave emissions in about two days after main phase of storm. This result is well consistent with the earlier ground-based observations. Also the theoretical shapes and the occurrence rates for power spectral densities of electromagnetic ion cyclotron waves are studied. It is found that in about 2 days after the storm main phase on May 4, mainly non Gaussian shapes of power spectral densities are produced.

Khazanov, G. V.↗
NASA NTRS2000

Development of a Methodology for Conducting Hall Thruster EMI Tests in Metal Vacuum Chambers of Arbitrary Shape and Size

While the closed-drift Hall thruster (CDT) offers significant improvement in performance over conventional chemical rockets and other advanced propulsion systems such as the arcjet, its potential impact on spacecraft communication signals must be carefully assessed before widespread use of this device can take place. To this end, many of the potentially unique issues that are associated with these thrusters center on its plume plasma characteristics and the its interaction with electromagnetic waves. Although a great deal of experiments have been made in characterizing the electromagnetic interference (EMI) potential of these thrusters, the interpretation of the resulting data is difficult because most of these measurements have been made in vacuum chambers with metal walls which reflect radio waves emanating from the thruster. This project developed a means of assessing the impact of metal vacuum chambers of arbitrary size or shape on EMI experiments, thereby allowing for test results to be interpreted properly. Chamber calibration techniques were developed and initially tested at RIAME using their vacuum chamber. Calibration experiments were to have been made at Tank 5 of NASA GRC and the 6 m by 9 m vacuum chamber at the University of Michigan to test the new procedure, however the subcontract to RIAME was cancelled by NASA memorandum on Feb. 26. 1999.

Gallimore, Alec D.↗
DOE OSTI2014

Determination of the onset time in polarization power ratio Z/H for precursor of Sumatra earthquake

Determination of onset time precursors of strong earthquakes (Mw > 5) and distance (d < 500 km) using geomagnetic data from Geomagnetic station KTB, Sumatra and two station references DAV, Philippine and DAW, Australia. separate techniques are required in its determination. Not the same as that recorded in the kinetic wave seismograms can be determined by direct time domain. Difficulties associated with electromagnetic waves seismogenic activities require analysis of the transformed signal in the frequency domain. Determination of the frequency spectrum will determine the frequency of emissions emitted from the earthquake source. The aim is to analyze the power amplitude of the ULF emissions in the horizontal component (H) and vertical component (Z). Polarization power ratio Z/H is used for determining the sign of earthquake precursors controlled by the standard deviation. The pattern recognition polarization ratio should be obtained which can differentiate emissions from seismogenic effects of geomagnetic activity. ULF emission patterns generated that seismogenic effect has duration > 5 days and the dominance of emission intensity recorded at the Z component and for the dominance of the emission intensity of geomagnetic activity recorded in the component H. The result shows that the onset time is determined when the polarization power ratio Z/H standard deviation over the limit (p ± 2 σ) which has a duration of > 5 days.

58 GEOSCIENCES↗