David J. Mayhall

Theory of intense electromagnetic pulse propagation through the atmosphere

A set of fluid equations is derived to describe the interaction of a very strong electromagnetic pulse with a weakly ionized plasma. These equations are used to investigate the dynamic behavior of an intense electromagnetic pulse propagating through the atmosphere. Results show that the amount of energy transmitted through the medium depends very strongly on the initial energy of the pulse and such characteristics and its frequency, its shape, and its length. In addition, a pulse was propagated through an air filled waveguide to verify the acuracy of the theoretical model. The theory also predicts very accurately the pulse breakdown threshold.

Propagation of intense microwave pulses in air and in a waveguide

The state of research on intense electromagnetic pulse propagation in air and in waveguides is reviewed. Some results obtained from recent investigations of the propagation of intense electromagnetic pulses in the atmosphere and in an air-filled waveguide when the field strength is above the threshold for air breakdown are presented. It is shown how the air breakdown affects the shape of the pulse. In addition, the accuracy of the calculational models is discussed, comparing calculations with experimental data. >

Computer simulation of nonlinear coupling of high-power microwaves with slots

Numerical calculations are used to determine the effects of air breakdown on the coupling of intense microwave pulses passing through enclosed slot apertures. The calculations are based on Maxwells equations and a set of electron-fluid equations. Variations in the energies of microwaves transmitted through slot apertures as a function of incident-field intensity and aperture size are addressed. Results show that air-breakdown threshold energies in apertures have a functional dependence on pressure similar to that of air-breakdown threshold energies in the atmosphere. >

Modeling the propagation of long, intense microwave pulses in mixtures of air and SF/sub 6/

Self-consistent equations-Maxwells equations and the electron fluid transport equations-are used to study the interaction of long, intense microwave pulses with gases. The threshold for breakdown is a factor of seven higher in SF/sub 6/ than in air. This difference is attributed to the fact that SF/sub 6/ is an insulator. When SF/sub 6/ was mixed with air, the breakdown threshold increased with the increase in the percentage of SF/sub 6/. Introducing 5-10% of SF/sub 6/ in air increased the breakdown threshold by a factor of 3-4. The electron density and conductivity and the plasma frequency increased as the pulse intensity increased. The growth rates of the electron density and conductivity were much higher in air than in SF/sub 6/. >

Physical Phenomena Induced by Passage of Intense Electromagnetic Pulses (Including CO2 Lasers) through the Atmosphere

The electron fluid equations are combined with Maxwell’s equations to investigate the physical phenomena that occurs when short, intense electromagnetic pulses (including the CO2 laser pulse) interact with the atmosphere. The phenomena of “tailed erosion” occurs when the pulse intensity exceeds the air-breakdown threshold. In some cases, the erosion of the pulse occurs first in the middle of the pulse and then occurs in the tail of the pulse. In addition, we discovered that the amount of the energy that a pulse carries through the atmosphere is independent of whether it is propagating vertically upward from the Earth’s surface or vertically downward toward the Earth’s surface, provided the distance the pulse travels is the same for both directions of the propagation.

Modeling the interaction of intense electromagnetic pulses with gaseous media

Results obtained from recent theoretical investigations of the interaction of intense electromagnetic pulses with gases when the field strength is above the threshold for avalanche breakdown are presented. It is shown how the breakdown affects the shapes of the pulses. In addition, the accuracy of the calculational models is discussed by comparing some calculations with experimental data. It is noted that this is not a comprehensive review of the field of microwave breakdown. >

High-power microwave bandwidth broadening by air breakdown

Abstract not available.

Calculational prediction of ultrawideband electromagnetic pulses by laser-initiated air avalanche switches

Abstract not available.

One‐dimensional, nearly time‐harmonic simulation of laser propagation and breakdown in the atmosphere

For a number of years, we have numerically investigated intense microwave pulse propagation in the atmosphere. For short pulses (<20 ns), full‐wave electron fluid computer codes were used. These codes have been impractical for pulses longer than several hundred cycles due to memory limitations. To overcome such limitations, nearly time‐harmonic, one‐ and two‐dimensional (1D and 2D), electric field envelope codes were developed and applied to atmospheric and laboratory microwave situations. In this work, we extend the 1D code, based on cascade ionization, to frequencies for CO2 and neodymium glass laser pulses. We consider plane‐wave propagation and breakdown in the lower atmosphere (0–10 km of altitude) for several incident electric field amplitudes, waveshapes, and pulse lengths. Electric field waveshapes and electron density spatial profiles are shown. Breakdown thresholds are computed for pulse lengths from 0.1–10 ns for square and Gaussian pulses. These thresholds are compared to a published analytic ...

One-dimensional Plane Wave Simulation Of Laser Beam Propagation And Breakdown In The Atmosphere

For several years, numerical simulation of intense microwave and laser beam propagation in the atmosphere has been conducted at Lawrence Livermore National Laboratory. For very short pulses of 20 ns or less, full-wave electron fluid computer codes have investigated atmospheric propagation, as well as propagation in low-pressure, air-filled waveguides. These one- and two-dimensional codes solved time-dependent equations for electron number, momentum, and energy conservation self-consistently with Maxwell`s curl equations. Because of machine limitations, these codes, which resolve variations within a wave cycle, have been impractical for pulses longer than several hundred cycles. A one-dimensional, time-harmonic, envelope electron fluid code has been developed for calculation of long-pulse, cascade ionization microwave and laser beam effects in the atmosphere. In this investigation, the authors consider envelope code calculations for incident pulses from 0.1--100 ns in the laser wavelength regime for propagation in the lower atmosphere. Both CO{sub 2} and neodymium glass laser wavelengths are addressed. Square pulse breakdown electric field thresholds are calculated and compared with analytic predictions from the literature. Gaussian envelope thresholds are also calculated. Propagated and tail-eroded electric field waveshapes and electric density and energy profiles for several incident amplitudes, waveshapes, and pulse lengths will be presented.