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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Attenuation of Bragg backscattering of electromagnetic waves from density fluctuations near the region of polarization degeneracy in magnetoactive plasma

Specific features of Bragg backscattering under conditions of strong polarization degeneracy near the cutoff surface in an anisotropic medium are studied analytically and numerically. It is shown that the linear interaction of normal waves can substantially affect wave scattering by suppressing the amplification of Bragg backscattering near the cutoff region in the case of weak coupling between normal waves.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Recovery of the characteristics of plasma turbulence from the radial correlation backscattering diagnostics

Signals of the backscattering radial correlation Doppler diagnostics of plasma density fluctuations in the presence of the cutoff of the probing wave are analyzed theoretically with allowance for the curvature of magnetic surfaces. The scattering of the probing electromagnetic wave is considered in the linear (Born) approximation with respect to the amplitude of fluctuations. Using the Wentzel−Kramers−Brillouin approach, analytical expressions for the scattered signal and the correlation function of two scattered signals corresponding to oblique probing at different frequencies are derived. A criterion is obtained for the tilt angle of the antenna pattern at which the two-point turbulence correlation function can be measured directly. A method is proposed to recover the spectrum of plasma density fluctuations from the data on the radial wavenumbers even if this criterion is violated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Surface Plasmon Resonances of an Axially Magnetized Plasma Column in the Presence of Collisional Loss

Surface plasmon resonances arising in the course of scattering of an H-polarized plane electromagnetic wave by an axially magnetized plasma column are analyzed. Main attention is paid to the behavior of these resonances in the presence of collisional loss in the magnetoplasma filling the scatterer. The frequencies, Q factors, and amplitude coefficients of the electromagnetic field of multipole surface plasmon resonances of different orders are found, and conditions under which the collisional loss in the plasma completely suppresses a given resonance are determined.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Linear Transformation of Electromagnetic Wave Beams of the Electron-Cyclotron Range in Toroidal Magnetic Configurations

The field structure of quasi-optical wave beams tunneled through the evanescence region in the vicinity of the plasma cutoff in a nonuniform magnetoactive plasma is analyzed. This problem is traditionally associated with the process of linear transformation of ordinary and extraordinary waves. An approximate analytical solution is constructed for a rather general magnetic configuration applicable to spherical tokamaks, optimized stellarators, and other magnetic confinement systems with a constant plasma density on magnetic surfaces. A general technique for calculating the transformation coefficient of a finite-aperture wave beam is proposed, and the physical conditions required for the most efficient transformation are analyzed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Incoherent Scattering of Electromagnetic Waves by Langmuir Fluctuations Trapped in a Plasma Density Well

Incoherent scattering of a probing wave by Langmuir fluctuations trapped and enhanced near a local minimum of the electron density (plasma density well) in plasma with a parabolic density profile is considered. Steady-state amplitudes of fluctuations are calculated for arbitrary velocity distribution functions of plasma particles with allowance for electron collisions. It is shown that quasi-periodic oscillations with two characteristic scales can be present in the spectrum of the plasma line. The smaller scale is due to the wellknown effect of discretization of the spectrum of Langmuir fluctuations in a plasma density well. The larger scale is associated with the generation of scattered waves in two spatial regions and subsequent interference of these waves at the exit from the density well. Oscillations with this scale are more stable under unsteady plasma conditions and can be more often observed in experiments. The results of this work can be used to experimentally determine the plasma parameters, such as the electron collision frequency and the size and lifetime of the plasma density well.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Model of Metamaterial Based on Graphene Scrolls and Carbon Nanotubes with Negative Refractive Index

The structure of a new metamaterial with negative permittivity and permeability that is made of periodically positioned graphene/boron nitride nanoscrolls and carbon nanotubes is proposed. The parameters of the metamaterial structure with a negative refractive index for the frequency of an electromagnetic wave within the visible range (namely, from near infrared to yellow) are calculated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

On second-harmonic generation in nonuniformly magnetized media

This paper presents a theoretical study of new effects of double-frequency optical signal generation in magnetic media with a nonuniform magnetization distribution. The study is based on the hydrodynamic approximation of the motion of conduction electrons in the field of an electromagnetic wave and equations for the mean electron spin. Within this approach, the mechanisms of the toroidal moment effect, which was experimentally discovered earlier in a system of magnetic particles with a vertical magnetization distribution as well as in a multilayered magnetic system (which is a collinear nonuniform magnetic system), are demonstrated. A new effect that appears due to the presence of equilibrium spin currents in a nonuniform magnetic system is studied in detail. This effect was predicted from the symmetry and can occur only in noncollinearly magnetized media. It is shown that this effect has a resonance nature with a resonance at a pump frequency equal to the plasma frequency of conduction electrons. Estimates of the susceptibility at the double frequency for the parameters of nickel and the typical scale of variation in the magnetization, which is equal to 10 nm, show that the susceptibility near the frequency of the plasma resonance at the chosen parameters is on the order of 10{sup –9} esu, which holds up a hope of the experimental detection of this effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Analysis of an Electromagnetic Wave with Circular Electron Beam Interaction in a Slow-Wave System of “Ribbed-Metal-Rod” Type

The interaction of an electromagnetic wave and external annular electron beam in a slow-wave system (SWS) of ribbed-metal-rod type was analyzed and expressions for the equivalent parameters of inductance and capacitance of the structure were found. A dispersion equation describing the excitation of axisymmetric electric waves in the SWS was derived in the impedance approximation. The dispersion characteristics and coupling coefficient have been modeled depending on the geometry of the rod and dielectric permittivity of the material filling the grooves in the SWS structure.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

A Phase Switch for Electromagnetically Induced Gratings in a Medium with Λ Atoms

We have theoretically studied the possibility of using the phenomenon of phase switching of coherent population trapping for creating a switch of light propagation direction in electromagnetically induced gratings in a medium with Λ-atoms. The permissible region of this effect application is determined and the parameters are found which ensure the obtaining of a high-efficiency scheme of the spatial redistribution of probing field intensity on atomic density gratings.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

End-to-end GPU acceleration of low-order-refined preconditioning for high-order finite element discretizations

In this article, we present algorithms and implementations for the end-to-end GPU acceleration of matrix-free low-order-refined preconditioning of high-order finite element problems. The methods described here allow for the construction of effective preconditioners for high-order problems with optimal memory usage and computational complexity. The preconditioners are based on the construction of a spectrally equivalent low-order discretization on a refined mesh, which is then amenable to, for example, algebraic multigrid preconditioning. The constants of equivalence are independent of mesh size and polynomial degree. For vector finite element problems in H(curl) and H(div) (e.g., for electromagnetic or radiation diffusion problems), a specially constructed interpolation–histopolation basis is used to ensure fast convergence. Detailed performance studies are carried out to analyze the efficiency of the GPU algorithms. The kernel throughput of each of the main algorithmic components is measured, and the strong and weak parallel scalability of the methods is demonstrated. The different relative weighting and significance of the algorithmic components on GPUs and CPUs is discussed. Results on problems involving adaptively refined nonconforming meshes are shown, and the use of the preconditioners on a large-scale magnetic diffusion problem using all spaces of the finite element de Rham complex is illustrated.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Radar Wind Profiler (RWP) and Radio Acoustic Sounding System (RASS) Instrument Handbook

The radar wind profiler (RWP) is an active remote-sensing instrument that can routinely, and virtually unattended, observe wind and turbulence in the troposphere through scattering from clear-air irregularities of the atmospheric refractive index (Gage and Balsley 1978). The principle of Doppler radars in general is based on sending electromagnetic pulses in the vertical and several tilted directions (vertical and oblique beams) and measuring the signal that is scattered back by atmospheric turbulence at all heights and received at the antenna. The RWPs provides measurements of backscattered signal strength and wind profiles nominally between 0.1 km and 6 km. The RWP operation assumes that the wind field is homogeneous over the spatial separation of the antenna beams, which is a safe assumption under stable atmospheric conditions. However, the wind may be different between the beams due to significant changes in the wind field, resulting in erroneous wind calculations. Therefore, the radial measurements are averaged over a sufficient time period to validate the assumption of homogeneity.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Advancing Pre-college Science and Mathematics Education

With support from the US Department of Energy, Office of Science, Fusion Energy Sciences, and General Atomics, an educational and outreach program primarily for grades G6-G13 was developed using the basic science of plasma and fusion as the content foundation. The program period was 1994 - 2015 and provided many students and teachers unique experiences such as a visit to the DIII-D National Fusion Facility to tour the nation’s premiere tokamak facility or to interact with interesting and informative demonstration equipment and have the opportunity to increase their understanding of a wide range of scientific content, including states of matter, the electromagnetic spectrum, radiation & radioactivity, and much more. Engaging activities were developed for classroom-size audiences, many made by teachers in Build-it Day workshops. Scientist and engineer team members visited classrooms, participated in science expositions, held workshops, produced informational handouts in paper, video, online, and gaming-CD format. Participants could interact with team members from different institutions and countries and gain a wider view of the world of science and engineering educational and career possibilities. In addition, multiple science stage shows were presented to audiences of up to 700 persons in a formal theatre setting over a several day period at Science & Technology Education Partnership (STEP) Conferences. Annually repeated participation by team members in various classroom and public venue events allowed for the development of excellent interactive skills when working with students, teachers, and educational administrative staff members. We believe this program has had a positive impact in science understanding and the role of the Department of Energy in fusion research on thousands of students, teachers, and members of the general public through various interactive venues.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2016

Correlation of Noise Signature to Pulsed Power Events at the HERMES III Accelerator.

The HERMES III accelerator, which is located at Sandia National Laboratories' Tech Area IV, is the largest pulsed gamma X-ray source in the world. The accelerator is made up of 20 inductive cavities that are charged to 1 MV each by complex pulsed power circuitry. The firing time of the machine components ranges between the microsecond and nanosecond timescales. This results in a variety of electromagnetic frequencies when the accelerator fires. Testing was done to identify the HERMES electromagnetic noise signal and to map it to the various accelerator trigger events. This report will show the measurement methods used to capture the noise spectrum produced from the machine and correlate this noise signature with machine events.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Distributed Temperature Profiles of Silicon Carbide Catalyst Bed in a Microwave Reactor using Fiber-optic Sensor

Microwave heating is of great interest for reducing greenhouse gas emissions of catalytic chemical conversion processes because it can heat up the reactants rapidly and efficiently and accelerate reaction rates. In microwave-assisted catalytic thermochemical conversion processes, accurate internal temperature measurement would help facilitate effective process control. Metallic thermocouples interfere and spark in the microwave heating environment, so they are not an option. Infrared pyrometers typically provide a single temperature value by averaging over a finite surface area of the catalyst bed. In this work, we use fiber-optic sensors passing through the catalyst bed to provide more accurate temperatures along the height of the catalyst bed. The fiber optic sensors are immune to the electromagnetic microwave radiation and provide temperature profiles along their length. Here, custom fiber-optic sensors were coupled to the optical distributed temperature sensing devices to measure the temperature profiles along the height of the catalyst bed at high temperatures with ~1 mm spatial resolution. The sensing devices use optical frequency domain reflectometry (OFDR) technique for distributed temperature measurement. This work shows the temperature profiles along the height of the silicon carbide powder catalyst bed in the variable and fixed frequency microwave reactors.

Thapa, Juddha↗
DOE OSTI2016

AN EMPIRICAL DETERMINATION OF THE INTERGALACTIC BACKGROUND LIGHT FROM UV TO FIR WAVELENGTHS USING FIR DEEP GALAXY SURVEYS AND THE GAMMA-RAY OPACITY OF THE UNIVERSE

We have previously calculated the intergalactic background light (IBL) as a function of redshift from the Lyman limit in the far-ultraviolet to a wavelength of 5 μ m in the near-infrared range, based purely on data from deep galaxy surveys. Here, we use similar methods to determine the mid- and far-infrared IBL from 5 to 850 μ m. Our approach enables us to constrain the range of photon densities by determining the uncertainties in observationally determined luminosity densities and spectral gradients. By also including the effect of the 2.7 K cosmic background photons, we determine upper and lower limits on the opacity of the universe to γ -rays up to PeV energies within a 68% confidence band. Our direct results on the IBL are consistent with those from complimentary γ -ray analyses using observations from the Fermi γ -ray space telescope and the H.E.S.S. air Čerenkov telescope. Thus, we find no evidence of previously suggested processes for the modification of γ -ray spectra other than that of absorption by pair production alone.

79 ASTRONOMY AND ASTROPHYSICS↗