Excitation of surface electrostatic waves in semibounded layered superconductors by a nonrelativistic electron beam

Excitation of potential surface waves by a nonrelativistic electron beam traveling in a vacuum space near the boundary of a layered superconductor is studied theoretically. Dispersion relations for surface waves at an arbitrary angle between superconductor layers and interface are obtained. Allowance is made for an arbitrary direction of wave propagation in the interfacial plane. Increments of kinetic and hydrodynamic instabilities are found. It is shown that absolute instability may occur.     

Excitation of a wake field by a relativistic electron bunch in a semi-infinite dielectric waveguide

A wake field excited by a relativistic electron bunch in a semi-infinite metal waveguide filled with a dielectric consists of the Vavilov-Cherenkov radiation, the “quenching”-wave field, and transient radiation, which interfere with each other. An exact analytic expression for the transient component of the field of a thin relativistic annular bunch is derived for the first time. The evolution of the space distribution of a field excited by a finite-size electron bunch is numerically calculated. The excitation of the wake field by a periodic train of electron bunches in a finite-length waveguide is studied.     

Mathematical modeling of the cathodoluminescence of excitons generated by a narrow electron beam in a semiconductor material

A mathematical model of the cathodeluminescence of free excitons excited by a narrow electron beam in a semiconductor material is described and investigated. The model is based on an analytical solution to equations of the three-dimensional diffusion of excitons. It is shown that the model can be used to estimate the diffusivity of excitons from experimental time-of-flight measurements of samples coated with a lightproof mask with round apertures. The parameters of gallium nitride were used in the modeling.     

Excitation of low-frequency oscillations via interaction of a high-current relativistic electron beam with a radial ion flux

The nonlinear excitation of low-frequency oscillations in the case when an ion flux is radially injected into the drift chamber where a tubular relativistic electron beam propagates is studied. A mechanism behind low-frequency ion oscillations is discussed.     

Shaping of the cross section of a nonrelativistic high-current electron beam by means of return current leads

Calculation results and experimental data on shaping the cross-section of a nonrelativistic (10–30 keV) high-current (up to 25 kA) electron beam are presented. A circular beam is successfully transformed into a beam with a quasi-rectangular cross section. Transformation is carried out using flat buses or circular pins as return current leads over a short (4 cm) section of the beam transport channel. The distance between the edge of the beam and the leads is comparable to its radius, and the external guiding magnetic field is comparable to the self-magnetic field of the beam. The calculation results are compared with the experimental data.     

Excitation of microwave by an annular electron beam in a plasma-filled dielectric lined waveguide

An axial relativistic electron beam passing through a slow wave structure is unstable to an electromagnetic perturbation whose phase velocity equals the velocity of the beam. This phenomenon of Cherenkov emission is the basis of all traveling wave tubes. In this paper an excitation of Cherenkov radiation by a thin annular relativistic electron beam in a plasma-filled dielectric-lined waveguide is analysed by use of the self-consistent linear theory. The effect of the thin annular electron beam on the beam-wave interaction is completely described by a jump condition. The dispersion equation and the simultaneous condition of the beam-wave interaction are derived. Finally, the growth rate of the wave is obtained, and the effect of the background plasma density and the electron beam radius on the growth rate of the wave are presented.This work is supported by National Natural Science Foundation of China.     

Self-trapped excitons in rare-gas dimers and solids

The excited electron states in isolated rare-gas dimers are described by a model Hamiltonian with appropriate simplifications for the short-range terms. Then the energies of self-trapped excitons are obtained by including solid state effects. The results are compared with the available transient absorption spectroscopy measurements.     

Polarization effects of electron current settling when the cerenkov radiation is excited by a nonrelativistic electron beam in an open dielectric resonator

We study the effect of electron current settling of a strip nonrelativistic electron beam (EB) on the Cerenkov radiation (CR) in a metal-dielectric channel formed by the metal surface and the surface of a rectangular open dielectric resonator having isotropic properties and operated at millimeter wavelengths (3.6–5.8 mm). The choice of this channel was substantiated by theoretical studies of the CR energy density. We experimentally examined several effects, including the neutralization of the dielectric surface dipole charge by electrons, the accumulation of electron charge at the dielectric surface, and the influence of the electron charge on the EB and CR. Conclusions are drawn on the prospects of using short pulses of EB and special metal-dielectric diffraction gratings for the excitation of CR. Institute of Radioengineering and Electronics, Ukrainian National Academy of Sciences, Kharkov, Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 4, pp. 491–505, April, 1997.     

Excitation of waves in magnetoactive plasma by a strongly “spread” inhomogeneous electron beam

The stability of beam-plasma systems is studied assuming that the distribution of beam-electrons in the velocity space corresponds to the first period of the quasilinear relaxation. The necessary condition is derived for the usual quasilinear equations to be applicable within the whole period of quasilinear relaxation.The authors wishes to thank Dr. R. Klíma for his interest in this paper.     

Excitation of a cylindrical cavity by a helical current and an axial electron beam current

The explicit expressions (in the Vainshtein and Markov forms) are derived for the excitation of a cylindrical cavity with perfectly conducting walls and with impedance end faces. Excitation of a cylindrical cavity and a cylindrical waveguide with a preset nonuniform axial electron-beam current and a helical current with a variable pitch, which is excited by a concentrated voltage source and is loaded by a preset pointlike matched load, is considered. For the helical current, the integro-differential equation is formulated. The traveling-wave tube (TWT) is simulated in the preset beam current approximation taking into account the nonuniform winding of the spiral coil, nonuniform electron beam, and losses.     

Conduction electron effective-mass in a field of excitons in semiconductors

The interaction of an electron with excitations of an exciton gas in a semi-conductor is considered in the intermediate coupling theory, to explain the recently observed enhancement of the electron effective mass in germanium in a field of real excitons.     

Electron polarization in nonrelativistic nondegenerate magnetized electron gas

For a nondegenerate nonrelativistic electron system, taking account of the minimum of its total energy, the population of the Landau electron levels by electrons with intrinsic magnetic moments parallel and antiparallel to the external magnetic field is determined, as a function of the external magnetic field strength H. The results are then compared with analogous data obtained by other authors without taking the minimum of the system’s total energy into account. Brestsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 14–19, February, 1997.     

The processes of formation and nonstationary dynamics of a virtual cathode in a nonrelativistic electron beam in the decelerating field (two-dimensional approximation)

We present the results of studies within the framework of a two-dimensional numerical model of nonlinear nonstationary processes in a nonrelativistic electron beam in the mode of formation of a virtual cathode in the decelerating field without focusing of the electrons by a magnetic field (low-voltage vircator). The results of numerical simulation were qualitatively confirmed by the experiment. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 10, pp. 843–852, October 2006.     

Two-dimensional diffusion and cathodoluminescence of excitons generated by an electron beam in a semiconductor material: Results of mathematical modeling

Mathematical models of the two-dimensional diffusion and cathodoluminescence of excitons excited by an electron beam in a semiconductor material have been studied and are described. It is shown that the obtained models can be used to estimate the coefficients of exciton diffusion and mobility by means of the results of experimental measurements of the cathodoluminescence decay. Parameters typical of gallium nitride were used in the modeling.