Effect of diffraction on the electrodynamic characteristics of two-dimensional coaxial Bragg resonators

The electrodynamic properties of coaxial two-dimensional Bragg resonators with two-dimensional distributed feedback are analyzed. These resonators are made of coaxial waveguide sections with doubly periodic corrugation, which provides coupling and mutual scattering of four partial waves. Two of them propagate along the waveguide, while the other two propagate in the transverse (azimuthal) direction. It is shown that the high azimuthal index selectivity of two-dimensional Bragg resonators may be related to a qualitative difference in topology of the dispersion characteristics of azimuth-symmetric and asymmetric normal waves propagating in infinite waveguides of such a geometry. For the finite-length systems used as two-dimensional Bragg resonators, the eigenmode spectrum is found for two types of boundary conditions that correspond to the limiting cases of perfectly matched (open) systems and, conversely, of systems closed for the extraction of transverse electromagnetic fluxes. Perimeter-to-length ratios of the resonator at which the Q factor of the fundamental azimuth-symmetric mode is greater than those of the other modes are determined. The applicability domain of the geometrical approach, which was earlier applied to two-dimensional Bragg resonators, is discussed.     

Powerful Cherenkov oscillators with 2D distributed feedback

The feasibility of using 2D distributed feedback based on 2D planar and coaxial Bragg structures for generating spatially coherent radiation from rectilinear ribbon and tubular electron beams is studied. One-section and sectional Cherenkov masers are analyzed. In the former design, a 2D Bragg structure acts as a resonator and a periodic slow-wave system simultaneously. In the latter (sectional) design, radiation is synchronized in a 2D Bragg structure that is placed at the cathode end of the interaction space and couples longitudinal and transverse (azimuthal) wave flows. The wave is amplified by the electron beam mainly in the fairly long middle section. The output (collector) part contains a standard 1D Bragg structure that partially reflects the amplified radiation toward the cathode and closes the feedback circuit. It is shown that dissipation introduced into the 2D Bragg structure of the sectional design makes it possible to increase one of the transverse sizes of the system to ∼10³ wavelengths with the energy exchange efficiency and one-frequency masing mode stability remaining the same. With such an overdimension, the millimeter-wave radiation integral power may reach a gigawatt level.     

The kinetics of low-temperature oxidation of cobalt nanoparticles in porous media

The kinetics of oxidation of Co nanoparticles used in heterogeneous catalysis in silica gels and alumina with various porous structures was studied at room temperature. A mathematical model describing processes in the system was suggested. The experimental observations were qualitatively explained.     

The simulation of a free-electron laser amplifier with a ribbon relativistic electron beam

An amplifier based on a high-power free-electron planar laser operating at a wavelength of 4 mm is simulated. The system is built around the U-3 accelerator, which forms a ribbon relativistic electron beam with an energy of up to 1 MeV and a total operating current of up to 2 kA. The simulation uses various approaches, including the direct numerical simulation of the Maxwell equations and particle motion equations by means of the PIC-code KARAT. The approaches are shown to give close results.     

High-Power Free-Electron Masers Based on Linear Induction Accelerators

Radiophysics and Quantum Electronics - We review the results of theoretical and experimental studies of high-power free-electron masers (FEMs), which are performed jointly by the Joint Institute...     

使用分子量级前躯体制备CuInSe_2及其合金并应应用用于光伏发电(英文)

黄铜矿铜铟硒化合物CuInSe2及其与硫或嫁的合金CuIn(Se,S)2或CuInGa(Se,S)2,即所说的CIGS,已通过20%的实验室规模器件光电转换效率展示了其地面光伏应用的巨大潜力。为了减少初始资金成本,提高材料利用率,科研工作者们已经尝试了许多努力通过非真空制程沉积CIGS。这些制程包括电镀工艺,基于颗粒(浆或纳米颗粒)的制程和基于分子量级前趋体的制程。原则上,分子量级前趋体可以使组分元素达到充分混合,可以最大程度地实现组份在基板不同区域的均一分布。这对于一个复杂的涉及到五个主要元素的化合物系统尤为重要。从这个角度来看,分子前趋体的方法具有大面积均匀沉积铜铟镓硒的巨大潜力。这篇综述将着重讨论使用分子前趋体沉积铜铟镓硒制程的最新发展。     

“Nonresonant” Capture Regime in Microwave Amplifiers

We study a new regime of electron–wave interaction in microwave amplifiers and demonstrate its efficiency for a wide class of devices. A mildly relativistic millimeter-wave free-electron maser is calculated as a particular system implementing this regime.     

Simulation of selective characteristics of two-dimensional planar Bragg resonators

Employing direct numerical simulation, we show the adequacy of using the geometrical-optics approximation for describing electrodynamic characteristics of two-dimensional planar Bragg resonators. High selectivity of such resonators with respect to two coordinates is confirmed for large Fresnel parameters. It is shown that in accordance with analytical results, the frequencies of the highest-Q modes lie near the frequency of exact Bragg resonance in the absence of defects of periodicity. The simulation results are in good agreement with the results of “cold” electrodynamic tests. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 10, pp. 906–916, October 2006.