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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Electromagnetic Ion Cyclotron Waves in the High Altitude Cusp: Polar Observations

High-resolution magnetic field data from the Polar Magnetic Field Experiment (MFE) show that narrow band waves at frequencies approximately 0.2 to 3 Hz are a permanent feature in the vicinity of the polar cusp. The waves have been found in the magnetosphere adjacent to the cusp (both poleward and equatorward of the cusp) and in the cusp itself. The occurrence of waves is coincident with depression of magnetic field strength associated with enhanced plasma density, indicating the entry of magnetosheath plasma into the cusp region. The wave frequencies are generally scaled by the local proton cyclotron frequency, and vary between 0.2 and 1.7 times local proton cyclotron frequency. This suggests that the waves are generated in the cusp region by the precipitating magnetosheath plasma. The properties of the waves are highly variable. The waves exhibit both lefthanded and right-handed polarization in the spacecraft frame. The propagation angles vary from nearly parallel to nearly perpendicular to the magnetic field. We find no correlation among wave frequency, propagation angle and polarization. Combined magnetic field and electric field data for the waves indicate that the energy flux of the waves is guided by the background magnetic field and points downward toward the ionosphere.

Le, Guan↗
NASA NTRS2005

Electromagnetic Ion Cyclotron Waves in the High-Altitude Cusp: Polar Observations

High-resolution magnetic field data from the Polar Magnetic Field Experiment (MFE) show that narrow-band waves at frequencies approx. 0.2-3 Hz are a permanent feature in the vicinity of the polar cusp. The waves have been found in the magnetosphere adjacent to the cusp (both poleward and equatorward of the cusp) and in the cusp itself. The occurrence of waves is coincident with depression of magnetic field strength associated with enhanced plasma density, indicating the entry of magnetosheath plasma into the cusp region. The wave frequencies are generally scaled by the local proton cyclotron frequency and vary between 0.2 and 1.7 times local proton cyclotron frequency. This suggests that the waves are generated in the cusp region by the precipitating magnetosheath plasma. The properties of the waves are highly variable. The waves exhibit both left-handed and right-handed polarization in the spacecraft frame. The propagation angles vary from nearly parallel to nearly perpendicular to the magnetic field. We find no correlation among wave frequency, propagation angle, and polarization. Combined magnetic field and electric field data for the waves indicate that the energy flux of the waves is guided by the background magnetic field and points downward toward the ionosphere.

Le, G.↗
NASA NTRS1972

Method of characteristics for supersonic flow of a guiding centre plasma.

A study of the compressive magneto-acousic waves in a guiding centre plasma shows that the wavefront that emerges point disturbance after a finite time is a simple oblate spheroid with the axis of revolution parallel to the field lines. Thus, in a steady three-dimensional supersonic flow of guiding centre plasma a simple analytic exprencan be obtained to represent the characteristic surfaces. From a proper linear combination of the governing macroscopic equations, the characteristic equation is obtained. It represents the propagation of disturbances on the characteristic surface. The characteristic theory can be used to study the interaction of the solar wind with the moon and possibly with other planetary bodies.

Whang, Y. C.↗
NASA NTRS2021

Lower-Hybrid Drift Waves and Their Interaction With Plasmas in A 3D Symmetric Reconnection Simulation With Zero Guide Field

We investigate lower-hybrid drift waves (LHDW) in symmetric magnetic reconnection with zero guide field using three-dimensional particle-in-cell simulations. The long-wavelength mode with develops in the bifurcated electron current layer around the X-line within the width of the electron meandering motion from the mid-plane, where is the ion (electron) gyroradius. The short-wavelength mode with develops in the separatrix region downstream of the electron outflow jet, producing electron vortices in the background flow frame. Electrons follow the E × B drift with corrections from the diamagnetic drift and are heated inside the vortices with diverging electric fields. In the vortices, ions have comparable E × B and inertia drifts, which together mostly cancel the diamagnetic drift. Toward the center of diverging field vortices, ions are decelerated, leading to a decrease in the perpendicular temperature, while the loss of low-energy ions results in an increase in the parallel temperature. Parallel electric fields exist as a combination of the LHDW wave field projected to the magnetic field direction and the penetration of whistler waves that are mainly outside of the LHDW layer. The magnetic flux tube is twisted in the vortices. The twist may potentially lead to slippage reconnection, as indicated by the non-uniform parallel potential variation across field lines, while the periodic variations of the twisting directions are a limiting factor.

Shan Wang↗
NASA NTRS2024

‘Trapped Wave’ Resonances in Jets From Plug Nozzles

An experimental study is conducted investigating the characteristics of ‘trapped wave’ (TW) resonance tones occurring with nozzles having a center plug. The pressure fluctuation spectral peaks due to these ‘guided’ or ‘trapped’ waves when the nozzle contains a center plug occur at nondimensional frequencies that are an order of magnitude larger than those noted with simple round nozzles. It appears that the exit gap width of the plug nozzle is the characteristic length-scale that dictates the corresponding TW frequencies. The results of this study further our understanding of this phenomenon as it relates to other complex nozzle geometries.

instability↗
NASA NTRS1995

Calculated coupling efficiency between an elliptical-core optical fiber and an optical waveguide over temperature

To determine the feasibility of coupling the output of a single-mode optical fiber into a single-mode rib waveguide in a temperature varying environment, a theoretical calculation of the coupling efficiency between the two was investigated. Due to the complex geometry of the rib guide, there is no analytical solution to the wave equation for the guided modes, thus, approximation and/or numerical techniques must be utilized to determine the field patterns of the guide. In this study, three solution methods were used for both the fiber and guide fields; the effective-index method (EIM), Marcatili's approximation, and a Fourier method. These methods were utilized independently to calculate the electric field profile of each component at two temperatures, 20 C and 300 C, representing a nominal and high temperature. Using the electric field profile calculated from each method, the theoretical coupling efficiency between an elliptical-core optical fiber and a rib waveguide was calculated using the overlap integral and the results were compared. It was determined that a high coupling efficiency can be achieved when the two components are aligned. The coupling efficiency was more sensitive to alignment offsets in the y direction than the x, due to the elliptical modal field profile of both components. Changes in the coupling efficiency over temperature were found to be minimal.

Tuma, Margaret L.↗
NASA NTRS2023

Nonlinear Fast Magnetosonic Waves in Solar Prominence Pillars

We investigate the properties of nonlinear fast magnetosonic (NFM) waves in a solar prominence, motivated by recent high-resolution and high-cadence Hinode/SOT observations of small-scale oscillations in a prominence pillar. As an example, we analyze the details of the 2012 February 14 Hinode/SOT observations of quasi-periodic propagating features consistent with NFM waves, imaged in emission in Ca II and in the far blue wing of Hα. We perform wavelet analysis and find oscillations in the 1-3 min period range. Guided by these observations, we model the NFM waves with a three-dimensional magnetohydrodynamics (3D MHD) model, extending previous 2.5D MHD studies. The new model includes the structure of the high-density, low-temperature material of the prominence pillar embedded in the hot corona, in both potential and non-force-free sheared magnetic field configurations. The nonlinear model demonstrates the effects of mode coupling and the propagating density compressions associated with linear and NFM waves. The guided fast magnetosonic waves, together with density compressions and currents, are reproduced in the 3D pillar structure. We demonstrate or the first time the dynamic effects of the Lorentz force due to the magnetic shear in the non-force-free field on the pillar structure and on the propagation of the waves. The insights gained from the 3D MHD modeling are useful for improving coronal seismology of prominence structures that exhibit fast MHD wave activity.

Leon Ofman↗
NASA NTRS1997

Design of Layered Ridge Dielectric Waveguide for Millimeter and Sub-Millimeter Wave Circuits

Design rules for Layered Ridge Dielectric Waveguide (LRDW) are presented for the first time through simple figures and closed form equations. The Effective Dielectric Constant (EDC) method is used to develop the design rules that account for typical circuit specifications such as higher order mode suppression, dispersion, attenuation, and coupling between adjacent transmission lines. Comparisons between the design of LRDW, image guide, and millimeter-wave dielectric ridge guide are made.

Ponchak, George E.↗
NASA NTRS1974

Hollow-cylinder waveguide isolators for use at millimeter wavelengths

A semiconductor waveguide isolator consisting of a hollow column of a semiconductor mounted coaxially is considered in a circular waveguide in a longitudinal dc magnetic field. An elementary and physical analysis based on the excitation of plane waves in the guide and a more rigorous mode matching analysis are presented. These theoretical predictions are compared with experimental results for an InSb isolator at 94GHz and 75 K.

Kanda, M.↗
NASA NTRS1974

Hollow-cylinder waveguide isolators for use at millimeter wavelengths

The device considered in this study is a semiconductor waveguide isolator consisting of a hollow column of a semiconductor mounted coaxially in a circular waveguide in a longitudinal dc magnetic field. An elementary and physical analysis based on the excitation of plane waves in the guide and a more rigorous mode-matching analysis (MMA) are presented. These theoretical predictions are compared with experimental results for an InSb isolator at 94 GHz and 75 K.

Kanda, M.↗
NASA NTRS1994

Magnetospheric filter effect for Pc 3 Alfven mode waves

We present a ray-tracing study of the propagation of Pc 3 Alfven mode waves originating at the dayside magnetopause. This study reveals interesting features of a magnetospheric filter effect for these waves. Pc 3 Alfven mode waves cannot penetrate to low Earth altitudes unless the wave frequency is below approximately 30 mHz. Configurations of the dispersion curves and the refractive index show that the gyroresonance and pseudo-cutoff introduced by the heavy ion O(+) block the waves. When the O(+) concentration is removed from the plasma composition, the barriers caused by the O(+) no longer exist, and waves with much higher frequencies than 30 mHz can penetrate to low altitudes. The result that the 30 mHz or lower frequency Alfven waves can be guided to low altitudes agrees with ground-based power spectrum observations at high latitudes.

Zhang, X.↗
NASA NTRS1995

Magnetospheric filter effect for Pc 3 Alfven mode waves

We present a ray-tracing study of the propagation of Pc 3 Alfven mode waves originating at the dayside magnetopause. This study reveals interesting features of magnetospheric filter effect for these waves. Pc 3 Alfven mode waves cannot penetrate to low Earth altitudes unless the wave frequency is below approximately 30 mHz. Configurations of the dispersion curves and the refractive index show that the gyroresonance and pseudo-cutoff introduced by the heavy ion O(+) block the waves. When the O(+) concentration is removed from the plasma composition, the barriers caused by the O(+) no longer exist, and waves with much higher frequencies than 30 mHz can penetrate to low altitudes. The result that the 30 mHz or lower frequency Alfven waves can be guided to low altitudes agrees with ground-based power spectrum observation at high altitudes.

Zhang, X.↗
NASA NTRS2004

Electrical Transfer Function and Poling Mechanisms for Nonlinear Optical Polymer Modulators

Electro-Optic Polymers hold great promise in increased electro-optic coefficients as compared to their inorganic corollaries. Many researchers have focused on quantum chemistry to describe how the dipoles respond to temperature and electric fields. Much work has also been done for single layer films to confirm these results. For optical applications, waveguide structures are utilized to guide the optical waves in 3 layer stacks. Electrode poling is the only practical poling method for these structures. This research takes an electrical engineering approach to develop poling models and electrical and optical transfer functions of the waveguide structure. The key aspect of the poling model is the large boundary charge density deposited during the poling process. The boundary charge density also has a large effect on the electrical transfer function which is used to explain the transient response of the system. These models are experimentally verified. Exploratory experiment design is used to study poling parameters including time, temperature, and voltage. These studies verify the poling conditions for CLDX/APC and CLDZ/APEC guest host electro optic polymer films in waveguide stacks predicted by the theoretical developments.

Watson, Michael Dale↗
NASA NTRS1982

Whistlers

Theoretical models of ionospheric whistler phenomena are reviewed and compared with experimental data. Whistlers were characterized as lightning discharges through a dispersive medium in 1919, with the first observed appearance of whistler noises detected in telephone communications. Magneto-ionic theory is used to characterize whistlers, with the Appleton-Hartree equations applied to the wave fields arising from lightning interactions with ionospheric plasma. Large values of the refractive index or slow propagation speeds give rise to the whistler mode, i.e., propagation of the wave through plasmas of any density. Propagation through the ionosphere is examined with the Snell's law, and account is taken of absorption and the necessity of obtaining full-wave solutions. Finally, theories are under development to explain the occurrence of ducting, i.e., guiding of the whistler wave by field-aligned plasma density irregularities.

Park, C. G.↗