Intense Electromagnetic Pulses Research Articles

Formation and emission of intense electromagnetic pulses by means of an insulated rod antenna excited by a short-duration high-current relativistic electron beam

The possibility of forming and emitting high-power electromagnetic pulses by means of an insulated rod antenna excited by a short-duration high-current electron beam is studied. It is found experimentally that the amplitude of the emitted pulses and their characteristic period depend on the antenna length. The potentialities of the method proposed as applied to the generation of intense videopulses are discussed.

Kinetic model of the propagation of intense subnanosecond electromagnetic pulse through the lower atmosphere

The propagation of high-amplitude electromagnetic pulses (EMP's) having a pulse length of nanoseconds through the lower atmosphere is studied by using a kinetic model for free electrons. It is shown that an EMP with an amplitude above 1 MV/m can be transported to altitudes of 50 km from the ground without significant energy loss due to the shortness of its pulse length. The distortion of these pulses due to air breakdown and the energy distribution of the electrons in the plasma in the tail of the pulse will also be characterized.

Nonlinear and Kinetic Effects in the Propagation of an Intense Electromagnetic Pulse Through the Atmosphere

Nonlinear and Kinetic Effects in the Propagation of an Intense Electromagnetic Pulse Through the Atmosphere

Temporary acceleration of electrons while inside an intense electromagnetic pulse

A free electron can temporarily gain a very significant amount of energy if it is overrun by an intense electromagnetic wave. In principle, this process would permit large enhancements in the center-of-mass energy of electron-electron, electron-positron and electron-photon interactions if these take place in the presence of an intense laser beam. Practical considerations severely limit the utility of this concept for contemporary lasers incident on relativistic electrons. A more accessible laboratory phenomenon is electron-positron production via an intense laser beam incident on a gas. Intense electromagnetic pulses of astrophysical origin can lead to very energetic photons via bremsstrahlung of temporarily accelerated electrons.

Electron kinetic effects in atmosphere breakdown by an intense electromagnetic pulse.

A physical model is proposed for description of electron kinetics driven by a powerful electromagnetic pulse in the Earth's atmosphere. The model is based on a numerical solution to the Boltzmann kinetic equation for two groups of electrons. Slow electrons (with energies below a few keV) are described in a two-term approximation assuming a weak anisotropy of the electron distribution function. Fast electrons (with energies above a few keV) are described by a modified macroparticle method, taking into account the electron acceleration in the electric field, energy losses in the continuous deceleration approximation, and the multiple pitch angle scattering. The model is applied to a problem of the electric discharge in a nitrogen, which is preionized by an external gamma-ray source. It is shown that the runaway electrons have an important effect on the energy distribution of free electrons, and on the avalanche ionization rate. This mechanism might explain the observation of multiple lightning discharges observed in the Ivy-Mike thermonuclear test in the early 1950's.

Testing Unruh Radiation with Ultraintense Lasers

We point out that using the state-of-the-art (or soon-to-be) intense electromagnetic pulses, violent accelerations that may be suitable for testing quantum field theory in curved spacetime can be realized through the interaction of a high-intensity laser with an electron. In particular, we demonstrate that the Unruh radiation is detectable, in principle, beyond the conventional radiation (most notably the Larmor radiation) background noise, by taking advantage of its specific dependence on the laser power and distinct character in spectral-angular distributions.

Raman self-conversion of femtosecond laser pulses and generation of single-cycle radiation

Stimulated Raman scattering of light in the regime of laser pulse durations shorter than the period of Raman-active vibrational mode $2\ensuremath{\pi}/{\ensuremath{\Omega}}_{R}$ is investigated. Using full equations for the field and the medium polarization, we obtain an insight into the stage of frequency conversion where the slowly varying amplitude approximation is inapplicable. It is found that the laser pulse experiences a continuous downshift of its spectrum, resulting in the formation of an intense single-cycle electromagnetic pulse. The role of the competing processes is analyzed.

Molecules in intense laser fields: Enhanced ionization in a one-dimensional model of H2.

A one-dimensional model of ${\mathrm{H}}_{2}$ is used to examine the nonlinear behavior of a pair of electrons in the presence of intense laser fields and fixed nuclei. We present ionization rates of ${\mathrm{H}}_{2}$ at different frequencies and intensities of short intense electromagnetic pulses by solving exactly the time-dependent Schr\odinger equation for the above system as a function of internuclear distance. Anomalously high ionization rates are found at large critical internuclear separations, akin to similar results found previously in the one-electron molecule ${\mathit{H}}_{2}$${\mathrm{}}^{+}$. Independent one-electron and simultaneous two-electron ionizations are identified from the numerical simulations to occur at different intensities and frequencies. Field-induced barrier suppression models are shown to explain qualitatively the numerical results. \textcopyright{} 1996 The American Physical Society.

Space‐time structure of optical flashes and ionization changes produced by lighting‐EMP

Intense electromagnetic pulses (EMPs) released by lightning discharges produce bright optical emissions at 80–95 km altitudes emitted in a thin (∼30 km) cylindrical shell expanding to radial distances of up to >150 km, lasting for ∼400 µs, and appearing in limb‐view as a thin layer with ∼400 km lateral extent.

Thermonuclear microexplosion ignition by imploding a disk of relativistic electrons

A new ignition concept for thermonuclear reactions is described, in which an electron cloud produced by inductive charge injection and reaching the Brillouin limit, is magnetically compressed inside a long cylindrical solenoid. For sufficiently fast compression, the front of the cloud becomes a relativistically contracted annular disk of high-energy density, which upon impact on a grounded target leads to a cylindrical implosion easily exceeding the power fluxes required for the ignition of thermonuclear microexplosions. Unlike concepts proposed in the past to ignite thermonuclear microexplosions by relativistic electron beams, the energy delivered to the target is not in the form of kinetic particle energy but in the form of an intense electromagnetic pulse.

Nonlinear evolution of Langmuir and electromagnetic pulses in a warm, unmagnetized plasma: modulational instability, integrability and self-focusing in 2 + 1 dimensions

The nonlinear dynamics of wave envelopes modulated in 2 + 1 dimensions is considered for two systems in plasma physics: (i) Langmuir pulses and (ii) intense (but weakly relativistic) electromagnetic (EM) pulses. Using singular perturbation techniques applied to an envelope approximation, both problems are reduced to the two-dimensional nonlinear Schrödinger (2DNLS) system, which describes the dynamics of two coupled slowly varying potentials. The general 2DNLS system exhibits a rich variety of phenomena, including enhanced (compared with ‘longitudinal’ propagation) modulational stability and (1D) soliton formation; decay of 1D solitons over long time scales; self- focusing regimes (determined by a virial-type condition); as well as integrability and 2D solitons. Applying our recent results on the 2DNLS system, we determine which of these phenomena can actually occur here and compute the parameter regimes. (i) The 2DNLS system for the Zakharov equations is modulationally unstable for all parameter values. It also has an integrable sector and a self-focusing regime. (ii) The 2DNLS system describes coupled ‘longitudinal’ and ‘transverse’ modulations of linearly or circularly polarized EM pulses propagating through a warm unmagnetized two-component neutral plasma with arbitrary masses (i.e. electron—positron or electron—ion). The pulse can accelerate particles to weakly (but not fully) relativistic velocities; relativistic, ponderomotive and harmonic effects all contribute to the nonlinear terms. The resulting 2DNLS system does not admit a self-focusing regime. Parameter values leading to an integrable case (the so-called ‘Davey—Stewartson I’ equations, which admit 2D soliton solutions) are computed; however, the required values would not be attainable in a laboratory or astrophysical setting. None the less, the existence of new nonlinear modulational instabilities associated with the second spatial degree of freedom already represents an important potential limitation on any (1 + 1)-dimensional approach to nonlinear evolution and modulational instability of plasma EM waves.

Two-photon Raman processes in spectral ultrabroadening of intense ultrashort light pulses

The spectral evolution of an intense electromagnetic pulse in the course of a coherent two-photon Raman interaction with a medium is analyzed under conditions such that the approximation of slow envelopes is not valid for the field or polarization of the medium. There exist threshold power levels at which a pronounced self-broadening of the field spectrum occurs if the field spectrum includes the frequencies Ω, where Ω=E2 – E1 is the energy difference between the levels involved in the stimulated Raman scattering. The results found here agree with experimental data on the generation of a supercontinuum in various media. In particular, there is agreement in terms of the spectral self-transformation of optical solitons in optical fibers.

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Evidence for whole-beam self-focusing of induced spatially incoherent laser light in large underdense plasma.

The propagation of an intense electromagnetic pulse in a large underdense plasma has been investigated using spatially and temporally incoherent laser light. Spatial incoherence was obtained using the induced spatial incoherence (ISI) technique. The first observation of the occurrence of thermal whole-beam self-focusing with ISI laser light is presented. Thermal imaging with a multiframe x-ray camera (140 ps gate time) was used to record the propagation characteristics of the interaction beam through the plasma. A direct measurement of the self-focusing growth length has been made.

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Nonlinear modulational stability and propagation of an electromagnetic pulse in a two-component neutral plasma

Nonlinear effects are studied including possible modulational instability of an intense electromagnetic pulse propagating through a fully-ionized, unmagnetized plasma. The envelope is shown to evolve over long time scales in general according to a vector form of the well-known cubic nonlinear Schroedinger (NLS) equation. Three distinct nonlinear effects contribute terms cubic in the amplitude and thus can be of comparable magnitude: ponderomotive forces, relativistic corrections, and harmonic generation. Influence of an ambient magnetic field on the nonlinear modulational stability of circularly polarized electromagnetic pulses in a two-component, neutral plasma; the nonlinear modulational stability properties of plasma electromagnetic pulses are extended to include the presence of an ambient magnetic field Bo parallel to the direction of propagation. The positive component may consist of either positrons or singularly charged ions, and specific assumptions or approximations are made concerning the mass ratio of the components. Approximate solutions are derived which describe the evolution of a circularly polarized pulse. The envelope is shown to evolve over long time scales according to the cubic nonlinear Schroedinger (NLS) equation.

Ionospheric accelerator

Ionospheric acceleration of high energy particles by a short wavelength microwave pulse is discussed. The intense electromagnetic waves in an ionospheric (F2) or magnetospheric plasma can be self-trapped above a threshold power. The self-binding property and the consequent self-induced transparency of the triple soliton structure of two electromagnetic waves and a plasma wave allow the propagation of an intense electromagnetic pulse without the severe and wasteful distortion that accompanies low power pulse propagation. The effects of magnetospheric fluctuations on the particle beam transport are considered. The fluctuation-induced transport seems to be within the margin of tolerance for useful beam transport. Orbits of negatively charged particles are stable. While synchrotron radiation loss for electrons is prohibitive, that of muons and antiprotons is negligible. A corresponding terrestrial application is also suggested.

Gramophone, Film, Typewriter

Optical fiber networks. Soon people will be connected to a communication channel which can be used for any kind of media for the first time in history or for the end of history. When films, music, phone calls, and texts are able to reach the individual household via optical fiber cables, the previously separate media of television, radio, telephone, and mail will become a single medium, standardized according to transmission frequency and bit format. Above all, the optoelectronic channel will be immunized against disturbances that might randomize the beautiful patterns of bits behind the images and sounds. Immunized, that is, against the bomb. For it is well known that nuclear explosions may send a high intensity electromagnetic pulse through traditional copper cables and cripple the connected computer network. The Pentagon is capable of truly far-sighted planning. Only the substitution of optical fibers for conducting cables can accommodate the enormous rates and volume of bits that are presupposed, produced, and celebrated by electronic warfare. Then all early warning systems, radars, missile bases, and army headquarters on the opposite coast, in Europe,' will finally be connected to computers, safe from an electromagnetic pulse and able to function when needed. And for the intervening period there is even the by-product of pleasure: people can switch to any medium for their entertainment. After all, optical fibers can transmit any imaginable message but the one that counts-the one about the bomb.

Development of cold electron beam sources for a Raman type free electron laser

Two types of very cold relativistic electron beam sources for Raman FEL experiments have been developed. Using one of them as an electron beam source for a Raman type FEL, intense electromagnetic radiation pulses of about 100 kW were obtained in the millimeter wavelength region with an energy conversion efficiency of about 2%.

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.