Radiation of an antenna in a compressible magnetoplasma.
Radiation of monofrequency antenna in compressible magnetoplasma expressing far field as sum of modal plane waves
PLANE WAVE↗
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Results for “ELECTROMAGNETIC RADIATION”
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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Radar detection of radiation-induced ionization in air
A millimeter wave measurement system has been developed for remote detection of airborne nuclear radiation, based on electromagnetic scattering from radiation-induced ionization in air. Specifically, methods of monitoring radiation-induced ionization of air have been investigated, and the ionized air has been identified as a source of millimeter wave radar reflection, which can be utilized to determine the size and strength of a radiation source.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Experimental performance of a low-power MPD ARC thrustor.
Low power MPD arc thrustor design and performance with radiation cooled electromagnets and permanent magnets
RADIATION COOLING↗
Simulation of radiation from lightning return strokes: The effects of tortuosity
A Monte Carlo simulation has been developed for the electromagnetic fields radiated from a tortuous lightning channel. This was done using a piecewise linear model for the channel and employing for each element the field radiated by a traveling wave on an arbitrarily oriented filament over a conducting plane. The simulation reproduces experimental data reasonably well and had been used to study the effects of tortuousity on the fields radiated by return strokes. Tortuosity can significantly modify the radiated waveform, tending to render it less representative of the current pulse and more nearly unipolar than one would expect based on the theory for a long straight channel. In the frequency domain the effect of tortuosity is an increase in high frequency energy as compared with an equivalent straight channel. The extent of this increase depends on the mean length of the elements comprising the channel and can be significant.
Levine, D. M.↗
Simulation of radiation from lightning return strokes - The effects of tortuosity
A Monte Carlo simulation has been developed for the electromagnetic fields radiated from a tortuous lightning channel. This was done using a piecewise linear model for the channel and employing for each element the field radiated by a traveling wave on an arbitrarily oriented filament over a conducting plane. The simulation reproduces experimental data reasonably well and has been used to study the effects of tortuosity on the fields radiated by return strokes. Tortuosity can significantly modify the radiated waveform, tending to render it less representative of the current pulse and more nearly unipolar than one would expect based on the theory for a long straight channel. In the frequency domain the effect of tortuosity is an increase in high frequency energy as compared with an equivalent straight channel. The extent of this increase depends on the mean length of the elements comprising the channel and can be significant.
Levine, D. M.↗
On the motion and radiation of charged particles in strong electromagnetic waves. I - Motion in plane and spherical waves
Charge particle motion and radiation in strong plane and spherical electromagnetic waves with nonthermal astrophysical applications
Gunn, J. E.↗
A dynamic analysis of the radiation excitation from the activation of a current collecting system in space
Current collecting systems moving in the ionosphere will induce electromagnetic wave radiation. The commonly used static analysis is incapable of studying the situation when such systems undergo transient processes. A dynamic analysis has been developed, and the radiation excitation processes are studied. This dynamic analysis is applied to study the temporal wave radiation from the activation of current collecting systems in space. The global scale electrodynamic interactions between a space-station-like structure and the ionospheric plasma are studied. The temporal evolution and spatial propagation of the electric wave field after the activation are described. The wave excitations by tethered systems are also studied. The dependencies of the temporal Alfven wave and lower hybrid wave radiation on the activation time and the space system structure are discussed. It is shown that the characteristics of wave radiation are determined by the matching of two sets of characteristic frequencies, and a rapid change in the current collection can give rise to substantial transient radiation interference. The limitations of the static and linear analysis are examined, and the condition under which the static assumption is valid is obtained.
Wang, J.↗
High-frequency instability of the sheath-plasma resonance
Coherent high frequency oscillations near the electron plasma frequency (omega approx. less than omega sub p) are generated by electrodes with positive dc bias immersed in a uniform Maxwellian afterglow plasma. The instability occurs at the sheath-plasma resonance and is driven by a negative RF sheath resistance associated with the electron inertia in the diode-like electron-rich sheath. With increasing dc bias, i.e., electron transit time, the instability exhibits a hard threshold, downward frequency pulling, line broadening and copious harmonics. The fundamental instability is a bounded oscillation due to wave evanescence, but the harmonics are radiated as electromagnetic waves from the electrodes acting like antennas. Wavelength and polarization measurements confirm the emission process. Electromagnetic waves are excited by electrodes of various geometries (planes, cylinders, spheres) which excludes other radiation mechanisms such as orbitrons or beam-plasma instabilities. The line broadening mechanism was identified as a frequency modulation via the electron transit time by dynamic ions. Ion oscillations at the sheath edge give rise to burst-like RF emissions. These laboratory observations of a new instability are important for antennas in space plasmas, generation of coherent beams with diodes, and plasma diagnostics.
Stenzel, R. L.↗
High-frequency instability of the sheath-plasma resonance
Coherent high-frequency oscillations near the electron plasma frequency are generated by electrodes with positive dc bias immersed in a uniform Maxwellian afterglow plasma. The instability occurs at the sheath-plasma resonance and is driven by a negative RF sheath resistance associated with the electron inertia in the diodelike electron-rich sheath. With increasing dc bias, i.e., electron transit time, the instability exhibits a hard threshold, downward frequency pulling, line broadening, and copious harmonics. The fundamental instability is a bounded oscillation caused by wave evanescence, but the harmonics are radiated as electromagnetic waves from the electrodes acting like antennas. Wavelength and polarization measurements confirm the emission process. Electromagnetic waves are excited by electrodes of various geometries (planes, cylinders, spheres), which excludes other radiation mechanisms such as orbitrons or beam-plasma instabilities. The line-broadening mechanism has been identified as a frequency modulation via the electron transit time by dynamic ions. Ion oscillations at the sheath edge give rise to burstlike RF emissions. These laboratory observations of a new instability are important for antennas in space plasmas, generation of coherent beams with diodes, and plasma diagnostics.
Stenzel, R. L.↗
Electromagnetic cloak to restore the antenna radiation patterns affected by nearby scatter
We have theoretically verified the feasibility of the concept of mantle cloak for very high frequency (VHF) antenna communications. While the applicability of the concept has been demonstrated for an infinitely long cylindrical obstacle and infinitely long electric source [Y.R. Padooru, A.B. Yakovlev, and P.-Y. Chen and Andrea Alù, J. Appl. Phys., 112, 104902, (2012)], the use of this cloak in realistic conditions is not straightforward. In this paper as an electric source we consider a typical VHF monopole antenna mounted on ground plane together with a metallic cylindrical obstacle. The both ground plane and obstacle affect the antenna radiation scattering. Nevertheless, we could show that the mantle cloak can bee successfully applied to restore the radiation patterns of antenna even when the source, the cylindrical metallic obstacle, and the ground plane have finite length. We have studied the antenna adaptation in the presence of the cloaked obstacle and found that the complete radiation system is still functional in the bandwidth that is reduced only by 11%.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Continuum radiation and electron plasma oscillations in the distant geomagnetic tail
ISEE-3 electric field measurements are used to examine the properties of electromagnetic continuum radiation in the distant geomagnetic tail. Continuum is observed in all the tail's plasma regions and in the magnetosheath. The power spectrum at 210 R sub E is nearly identical to that at 40 R sub E, indicating that the tail cavity forms a reasonably loss-free waveguide. The angular distribution exhibits both anisotropy, which is similar to that observed nearer the earth, and isotropy for high frequencies (greater than 31.6 kHz) in the magnetosheath and for low frequencies (equal to or less than 17.8 kHz) in the tail lobes and boundary layer. Isotropic radiation suggests that, in addition to the near earth source, continuum is also generated over a large spatial region in the tail. Electrostatic electron plasma oscillations are also detected in the distant tail, and these could represent the local source of the continuum.
Coroniti, F. V.↗
Radiative flux opens new window on climate research
For several decades, global satellite observations have been made of the rate at which electromagnetic energy (radiative flux) is emerging from the top of the atmosphere of our planet in the spectral range of about 0.2-50.0 microns. At the same time, models have been developed to infer the radiative flux at the surface from the values observed by the satellites at the upper boundary. The balance of incoming and outgoing radiative flux (radiation budget) at both boundaries, determines the net gain or loss of the radiative energy within an atmospheric column. Climate researchers can use the radiative flux as a tool to validate climate models, separate the radiative impact of clouds from surface and atmosphere contributions, and to understand the global hydrological cycle. When applied to physical processes occurring at the surface, information on the radiative flux has the potential to substantially advance our understanding of the transport of heat, moisture, and momentum across the surface/atmosphere interface. Geophysicists of many disciplines stand to benefit from efforts to improve the use of this latter untapped resource. Oceanographers can improve the representation of the selective absorption of radiation in the oceans; biologists and ecologists can improve their models for carbon dioxide exchange and biological heating in oceans; agronomists can model more realistically biomass and crop yields; and environmentalists can obtain better assessment of natural resources of radiation.
Pinker, R. T.↗
On the electromagnetic fields, Poynting vector, and peak power radiated by lightning return strokes
The initial radiation fields, Poynting vector, and total electromagnetic power that a vertical return stroke radiates into the upper half space have been computed when the speed of the stroke, nu, is a significant fraction of the speed of light, c, assuming that at large distances and early times the source is an infinitesimal dipole. The initial current is also assumed to satisfy the transmission-line model with a constant nu and to be perpendicular to an infinite, perfectly conducting ground. The effect of a large nu is to increase the radiation fields by a factor of (1-beta-sq cos-sq theta) exp -1, where beta = nu/c and theta is measured from the vertical, and the Poynting vector by a factor of (1-beta-sq cos-sq theta) exp -2.
Krider, E. P.↗
Ionizing radiation
The penetrating ionizing space radiations are found to be extremely diverse in the energy range of both their particulate and their electromagnetic components. Radiation terms and measures and ionizing radiation classes and sources are presented. Whole body radiation effects are examined, including radiation intensity and rate effectiveness factors. Radiation effects on specific body systems, such as blood, skin, visual, and reproductive systems are also discussed.
Warren, S.↗
Characteristics of quasi-unipolar electromagnetic pulses formed in the interaction of high-power laser pulses with nanoscale targets
A new method is suggested for generating quasi-unipolar electromagnetic IR and terahertz pulses. The method is based on synchronous acceleration of electrons combined to a dense bunch with a charge of up to several tens nanocoulombs, which are forced out from a nanoscale target under an action of a high-power, sharp-leading edge laser pulse. The electromagnetic bunch moving in a field of laser radiation can generate high-power electromagnetic pulses with various spectral composition including terahertz and IR ranges. A physical mechanism underlying the formation of generated quasi-unipolar pulses of electromagnetic radiation is determined and numerically studied. The pulse characteristics are found by numerical simulation, such as amplitude and duration dependences on the angle between the pulse propagation direction and laser beam axis. It is established that in modern laser installations, the amplitudes of quasi-unipolar pulses may reach relativistic values. Reflection of a unipolar pulse from an ideally reflecting surface is numerically analysed. It is shown that the pulse retains its unipolar profile in this case. (paper)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Dipole radiation in moving media.
Propagation and radiation of waves excited by electric dipole in dispersionless uniaxial moving medium
ELECTROMAGNETIC RADIATION↗