Electromagnetic vibrator: An initiator of air breakdown in the subcritical field of a quasi-optical microwave beam

The subject of investigation is the resonance properties of cylindrical electromagnetic vibrators with different diameters and spherically rounded ends acting as initiators of air breakdown in the subcritical field of a quasi-optical microwave beam. The vibrator is placed both in the field of a traveling electromagnetic wave and at the antinode of the field above a screen inserted in the microwave beam. The shortening of the half-wave vibrator that governs its ability to initiate air breakdown, the field at the top-pole of this vibrator, and a tolerance on its resonance length are found from experimental data.     

The electromagnetic radiation from sources above an ideally conducting expanding sphere

Electromagnetic fields are considered which are created by external currents of the traveling-wave type above an ideally conducting expanding sphere. A specific calculation is carried out, and the shape of the pulse is discussed as a function of the parameters of the problem.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 2, pp. 211–220, February, 1972.The author thanks V. N. Krasil'nikov for the stated problem, and A. A. Andronov and V. I. Semenova for discussing the results of the work.     

Small-angle approximation for an ion beam in an external electromagnetic field

A small-angle approximation method is formulated for a curvilinear ion beam propagating in an electromagnetic field. The effects of particle velocity scatter and multiple elastic scattering on the beam path in a magnetic field, the electric field of a cylindrical capacitor, and mutually orthogonal electric and magnetic fields are considered. An analytical model for beam power compression is developed.     

Deeply undercritical microwave discharge excited by the field of a quasi-optical electromagnetic beam in a supersonic air jet

Electric discharge in a supersonic air jet is studied. It is ignited in a linearly polarized quasi-optical microwave electromagnetic beam the initial field intensity of which is much lower than the breakdown level. Electric breakdown is initiated by a tubular electromagnetic vibrator, one end of which has spikes and is covered by a quartz tube. Atmospheric air enters into a low-pressure working chamber through the inner channel of the vibrator. As a result, an immersed supersonic air jet forms in the chamber at the outlet from the quartz tube. A microwave discharge ignited in this jet is “attached” to aft spikes of the vibrator. The energy deposit into the discharge plasma and the effective area of energy interaction between the discharge and excited microwave field are estimated from the temperature and stagnation pressure distributions in the wake of the discharge.     

Flow of an electrically conducting bubble liquid in the field of an electromagnetic force

Physical processes accompanying the flow of a conducting bubble liquid in crossed electric and magnetic fields are considered. Based on the general equations of mechanics of multiphase media, we develop a one-dimensional model of the flow of and heat exchange in a compressible bubble liquid when the phases are not in thermal and velocity equilibrium. The model is numerically investigated. It is demonstrated that, when the bubble liquid flows along the electromagnetic force vector, the bubbles lag behind the carrying flow and are compressed and warmed up. This causes oscillations of the bubble volume, as well as oscillations of the parameters of both the disperse and carrying phase. In particular, the compression of the bubbles reduces the volumetric gas content, as well as increases the effective conductivity of the flow and the electromagnetic force in the downstream direction. This sets conditions for crisis of the bubble flow when the electromagnetic force expels the bubbles against the main stream. On the basis of the solutions obtained, the efficiency of a gas compressor is calculated.     

Diffraction of a plane electromagnetic wave by a slot in a conducting screen of arbitrary thickness

A 2D theoretical model of the diffraction of a plane electromagnetic wave by a slot in a perfectly conducting screen is constructed based on the partial domain method. The Tikhonov regularization is used to solve a system of algebraic equations for the slot-mode amplitudes. This makes it possible to extend the domain of applicability of the theory to conducting screens of arbitrary thickness and to significantly increase the accuracy of solution in the cases when the slot width and the screen thickness are comparable to the wavelength of the diffracted radiation. The absence of a continuous passage to the limit of an infinitesimal screen thickness from the case of an arbitrarily small finite thickness is demonstrated. The boundary conditions for the energy-flux vector are considered. A concept of the energy potential that is convenient for the computer calculations of the energy-flux lines of 2D diffraction fields is introduced.     

The electromagnetic field of a guided Gaussian beam

An electromagnetic wave traveling along a dielectric slab between two parallel, plane conductors is analyzed for a special case that is particularly relevant to guided laser beams employed in integrated optics. The beam is assumed to have an approximate gaussian field dependence along the y-direction, defined to be transverse to the direction of propagation and to the normal to the conductor planes. Approximate expressions for the field in a well collimated beam are derived. Asymptotic approximations, valid far away from the focus of a beam that is not necessarily well collimated, are also derived. It is found that the TE and TM guided gaussian beams are not linearly polarized. This is unlike the case for the usual waveguide modes whose fields are constant along the y direction. It is also found that the guided gaussian beam must have a focus and that the divergence from focus is more rapid than for a similar gaussian beam in free space.     

On the propagation of a paraxial beam of charged particles in an external electromagnetic field

A small-angle approximation method as applied to a curvilinear beam of relativistic particles in mutually orthogonal uniform magnetic and nonuniform electric fields is elaborated. Analytical solutions to the paraxial equation for curvilinear beams of charged particles are obtained.     

Diffraction of a plane electromagnetic wave by a slot in a conducting screen with a transverse dielectric layer

The problem of diffraction of a plane electromagnetic wave by a slot in a planar perfectly conducting arbitrary thick screen with an infinite planar dielectric layer passing through the slot transversely to the screen is solved rigorously. In each of the field existence domains (two domains on either side of the screen and the interior of the slot), the solution is represented as an expansion in piecewise harmonic or exponential modes that allow for reflection and refraction at the boundaries of the dielectric layer. It is found that a set of functions describing such modes is complete enough to construct a solution satisfying all boundary conditions of the diffraction problem. The procedures of solution construction for the case at hand and for the same diffraction structure without the dielectric layer are compared.     

The electromagnetic field in the plasma jet of a microwave plasmatron

A coaxial microwave plasmatron operating at a frequency of 10 GHz is investigated. The microwave field distribution in the plasma jet of the plasmatron is studied using a vibrating string as a small perturbation source. The phase structure of the microwave field inside the plasma is found to differ from that on the outer side of the plasma jet boundary. A slow surface electromagnetic wave propagating along the plasma jet is observed.     

The electromagnetic field above a two-dimensional inhomogeneous structure. Boundary conditions

Summary The induction problem in the case of an inhomogeneous two-dimensional conductor presenting a vertical contact between two media of diverse resistivity is considered. TheE andH polarizations are treated in a similar way. The general solutions of the Helmholtz equation in the atmosphere is constructed. Far above the conductivity contrast the asymptotic form of the anomalous electromagnetic field is analytically found. It is proved that in theE-polarization case the asymptotic behaviour of the anomalous field differs very much from the generally assumed one. The conclusion of this paper is that in theE-polarization case the boundary conditions widely utilized in numerical computations are incorrect.

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Riassunto Si considera il problema dell'induzione nel caso di un conduttore bidimensionale inomogeneo che presenta un contatto verticale tra due mezzi di diversa resistività. Le polarizzazioniE eH sono trattate in modo simile. Si costruisce la soluzione generale dell'equazione di Helmholtz nell'atmosfera. Molto al di sopra del contrasto di conduttività, la forma asintotica del campo elettromagnetico anomalo è trovata analiticamente. Si prova che, nel caso della polarizzazioneE, il comportamento asintotico del campo anomalo differisce molto da quello generalmente considerato. La conclusione di questo lavoro è che nel caso della polarizzazioneE le condizioni al limite ampiamente usate nei calcoli numerici non sono corrette.

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Резюме Рассматривается проблема индукции в сличае неоднородното двумерного проводинка, представляющего вертикальный контакт между двумя средами с различными сопротивлениями.Е-иН-поляризации трактуются обычным образом. Конструируется общее решеиие уравнения Гельмгольца в атмосфере. Аналитически получена асимптотическая форма аномального електромагнитного поля значительно выше контраста проводимости. Доказывается, что в случаеЕ-поляризации асимптотическое поведение аномального поля сильно отличается от обычного поведения. В работе делается заключение, что в случаеЕ-поляризации граничные условия, широко используемые при численных вычислениях, не являются корректными.

     

Interaction of space-charge waves in an electron beam with electromagnetic waves in a longitudinal magnetic field

The effect of space charge on the interaction between an electron beam and an electromagnetic wave in a longitudinal magnetic field has been considered. The equations describing the interaction processes have been formulated within the two-dimensional linear theory and solved using the dispersion-equation approach and the successive approximation method.     

Quantum modulation of an electron beam in the field of opposite electromagnetic waves

The quantum modulation of an electron beam in the field of opposite electromagnetic waves, at a frequency equal to the difference of the wave frequencies, and its harmonics, is obtained. The depth of the modulation becomes of order one at relatively small intensities of the laser fields (including a real spreading of the beam). In the case of equal frequencies of the waves (when the Kapitza-Dirac effect occurs particles form a beam. An experiment for obtaining a modulated beam of particles at the frequencies of the laser radiation, and its harmonics, as well as for bunching of particles in the field of a standing wave is suggested.     

Specificity of multiwave interaction of an electronic beam and electromagnetic field in a relativistic diffractive generator

The mechanisms of self-consistent interaction of tubular relativistic electronic beams with the fields of super-dimensional periodic structure of a relativistic diffractive generator have been studied in the area of 2π-type oscillations of fundamental mode. Numerical analysis was carried out with the use of the matrix multimode method in its nonstationary variation. The electromagnetic field profiles, their mode structure, and their radiation spectrum have been studied. The conditions for generating frequency stabilization concerned with the longitudinal resonance of the surface spatial harmonics and volume resonance at the cutoff frequency of the E _0n mode of cylindrical waveguide have been revealed.