Skin electric explosion in double-layer conductors with a low-conductivity deposited layer

The experiments on explosion of cylindrical conductors aimed at comparison of plasma formation during skin explosion of homogeneous and double-layer conductors with an external layer with a lower conductivity are carried out on a high-current MIG generator (current amplitude up to 2.5 MA and current rise time 100 ns). The generator is loaded with cylindrical copper conductors with a diameter of 3 mm on the cathode part of which a titanium layer of thickness 20, 50, and 80 μm is deposited in vacuum. This type of loading makes it possible to compare the behaviors of the homogeneous and double-layer conductors in identical conditions. It is shown that using the double-layer structure of the conductor with an external layer of thickness 20–80 μm with a lower conductivity, which is obtained by vacuum arc deposition, higher values of magnetic induction (as compared to homogeneous conductor) can be attained on its surface prior to plasma formation and spread.     

Visualization of the large-scale vortex structures in excited turbulent jets

The present work is a part of the more common research aimed at establishing the role of large-scale vortex structures in the mechanism of noise generation by subsonic turbulent jet. The work presents the results of photography and videography of fast non-stationary processes in a circular subsonic jet under lateral acoustic excitation by harmonical source located upstream in a stilling chamber. Jet velocity varied in the range of 40–200 m/s (M=0.12–0.6).     

Theory of cluster systems in plasma-like media

The conditions of existence of stable formations of charged particles (clusters) moving in a plasma-like medium are discussed in this paper. The interaction of clusters is considered in the framework of a one-dimensional model. It is shown that the stability of a cluster depends strongly on the number of particles that form part of it. When two clusters moving with respect to each other interact, they break up if the relative velocity is fairly low. Fast-moving clusters hardly interact with each other.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 83–87, May, 1987.     

Mechanisms of metallic nanoparticle generation during an electric explosion of conductors

The mechanisms of conductor fracture and the generation of metallic nanoparticles during an electric explosion are discussed. The fracture of polycrystalline conductors with a crystallite size smaller than 100 nm during rapid introduction of energy is shown to occur due to its localization at grain boundaries. The dynamics of the explosion products (droplets, vapor) flying into a buffer gas is numerically simulated in terms of the mechanics of heterogeneous media with allowance for condensation and evaporation. The calculated size distributions of particles agree with the experimental distributions both qualitatively and quantitatively.     

Imitation of wave processes by generating an electric explosion of conductors in nonuniformly heated materials

A new method for imitating wave processes in nonuniformly heated materials by means of the electroexplosion of conductors was proposed. The problem of a planar high-current discharge initiated by the explosion of a foil in the air was solved in the 1D approximation of magnetic radiation gas dynamics with regard to the dependence of the conductivity of the foil on the density and temperature of the material during electroexplosion, a dependence that characterizes the specifics of the state of the material in various areas of the phase diagram. The main parameters of the electroexplosion setup were selected. A special construction of the loading unit was developed, which eliminates the effect of current contraction in a planar conductor and ensures a uniform distribution of current over the foil and, consequently, a uniform distribution of the pressure pulse momentum over the surface area of loading. A method for imitating the temperature profile in the sample was proposed. A procedure for measuring the integral pressure pulse momentum under conditions of intense electromagnetic disturbances was developed.     

Visualisation and analysis of large-scale vortex structures in three-dimensional turbulent lid-driven cavity flow

In this paper, large eddy simulation (LES) of a three-dimensional turbulent lid-driven cavity (LDC) flow at Re = 10,000 has been performed using the multiple relaxation time lattice Boltzmann method. A Smagorinsky eddy viscosity model was used to represent the sub-grid scale stresses with appropriate wall damping. The prediction for the flow field was first validated by comparing the velocity profiles with previous experimental and LES studies, and then subsequently used to investigate the large-scale three-dimensional vortical structures in the LDC flow. The instantaneous three-dimensional coherent structures inside the cavity were visualised using the second invariant (Q), Δ criterion, λ₂ criterion, swirling strength (λ_ci) and streamwise vorticity. The vortex structures obtained using the different criteria in general agree well with each other. However, a cleaner visualisation of the large vortex structures was achieved with the λ_ci criterion and also when the visualisation is based on the vortex identification criteria expressed in terms of the swirling strength parameters. A major objective of the study was to perform a three-dimensional proper orthogonal decomposition (POD) on the fluctuating velocity fields. The higher energy POD modes efficiently extracted the large-scale vortical structures within the flow which were then visualised with the swirling strength criterion. Reconstruction of the instantaneous fluctuating velocity field using a finite number of POD modes indicated that the large-scale vortex structures did effectively approximate the large-scale motion. However, such a reduced order reconstruction of the flow based on the large-scale vortical structures was clearly not as effective in predicting the small-scale details of the fluctuating velocity field which relate to the turbulent transport.     

Collisionless damping of surface oscillations and the possibility of its inversion in plasma-like media

We have developed a quantum theory of collisionless damping of surface plasmons under conditions of weak spatial dispersion of the permittivity of the medium and demonstrate the possibility of appearance of their instability as the interface between the media is crossed by a monoenergetic flow of charged particles. Institute of Radiophysics and Electronics of the National Academy of Sciences, Khar’kov, Ukraine; Research and Design Institute “Molniya” of the Ukraine Ministry of Education, Khar'kov, Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 6, pp. 735–746, June, 1998.     

Phase composition and defect substructure of nickel alloyed with boron and copper by electric explosion of conductors

Using methods of electron microscopy, we have discovered that combined electroexplosive alloying of nickel with boron and copper gives rise to a multilayer structure. An outer amorphous crystalline layer incorporating 2–3 nm nickel-and copper-boride, oxide, and boride-oxide crystallites is formed on the alloyed surface. The intermediate (subsurface) layer 1–2 μm thick is made up of NiB ₁₂ and Ni ₄ B ₃ crystallites 120–130 nm in size, with boron-and copper-oxide particles observed along the grain boundaries. The underlying thick layer exhibits a cellular Ni-Cu-B melt crystallization structure grading initially into a high-rate dendritic crystallization structure and then into a granular structure. The electroexplosive alloying process is found to bring into existence a high scalar dislocation-density substructure in nickel crystallites both in the alloyed zone and in the adjacent heat-affected zone. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 3–7, March 2007.     

Generation of large-scale radiative vortex structures at stagnation of pulsed plasma jets in air

Large-scale vortex structures forming when pulsed plasma jets of the capillary discharge stagnate in atmospheric air are investigated. It is shown that injection of high-enthalpy plasma jets into air may effectively generate electromagnetic radiation from the optical range: the energy yield of radiation reaches 20–37% of the total energy content of the plasma. The radiation pulse has a complex time waveform including micro-and nanosecond components.     

Interaction of electromagnetic oscillations with charged particle flows in nonuniform plasma-like structures

A hydrodynamic theory is developed of the interaction of electromagnetic oscillations with a monoenergetic charged particle beam propagating through a structure consisting of plasma and dielectric layers bounded by perfectly conducting planes. It is shown that, in such a system, plasma oscillations are excited due to the transformation of space charge oscillations of the particle flow into plasma oscillations at the layer boundaries. The regions of generation and decay of plasma oscillations are determined.     

Electrical explosion of conductors in the high-pressure zone of a convergent shock wave

The effect of the environmental pressure on the electrical explosion of a conductor (fine tungsten wire of diameter 30 μm) in an insulating liquid (distilled water) is studied. The pressure in the water is produced by exploding a multiwire array with the test conductor on its axis. Along with the experiment, the magnetohydrodynamic simulation of the explosion is carried out. It is shown that a high pressure produced in the explosion zone retards the electrical explosion of the conductor and, consequently, increases the explosion energy.     

Wave dynamics of electric explosion in solids

A mathematical model of an electric explosion is developed that consistently describes the expansion of the explosion channel with regard to the parameters of the discharge circuit of a high-voltage pulse generator, radiation, and propagation of stress waves in a solid. The dynamics of conversion of the stored energy to a wave and the formation of mechanical stresses due to electric explosion in a solid immersed in a liquid are considered. In the context of electro-discharge destruction of hard materials, the resulting stress field and the relationship between the discharge circuit parameters and characteristics of the wave are analyzed and the most efficient discharge modes are determined.     

高斯涡旋光束在自由空间传输中电场和磁场的偏振奇点

利用矢量菲涅尔衍射积分公式, 以高斯涡旋光束为例, 推导出傍轴高斯涡旋光束在自由空间传输过程中电场分量和磁场分量的解析表达式, 详细研究了自由空间中电场和磁场的偏振奇点变化规律. 结果表明, 高斯涡旋光束在自由空间传输中, 存在二维和三维电场和磁场的偏振奇点, 其位置一般不重合. 改变光束束腰宽度比、 振幅比以及传输距离, 偏振奇点出现移动. 在二维电场和磁场中, 当满足一定条件时, 会有V点产生.     

The effect of floating-potential conductors on the electric field near overhead transmission lines

The use of helicopters as platforms equipped with infrared and UV detection, digital cameras and other inspection equipment is an effective method of increasing the efficiency and effectiveness of transmission line inspection. However, as a 'floating-potential conductor' near to a high-voltage transmission line, a helicopter causes distortion of the local electric field, with regions of high electric field near the helicopter's surface where the curvature is high. In this paper, these fields are investigated both by calculation and experimentally, using a simple metal sphere, and then a model of a helicopter, placed near to a short length of energized transmission line conductor.     

Three-dimensional vortex solitons in self-defocusing media

We demonstrate that families of vortex solitons are possible in a bidispersive three-dimensional nonlinear Schr?dinger equation. These solutions can be considered as extensions of two-dimensional dark vortex solitons which, along the third dimension, remain localized due to the interplay between dispersion and nonlinearity. Such vortex solitons can be observed in optical media with normal dispersion, normal diffraction, and defocusing nonlinearity.     

First indication of ampere tension in solid electric conductors

An empirical law for the mechanical force between two current-elements, originally deduced by Ampère from a series of classical experiments, asserts that an electric current flowing along a straight wire should place the wire in tension. The existence of longitudinal Ampère forces at solid-liquid conductor interfaces has been demonstrated by various investigators during the past 160 years. This letter contains the first report of pulse currents creating sufficient tension to cause fracture in hot copper and aluminum wires.     

Algebraic bright and vortex solitons in defocusing media

We demonstrate that spatially inhomogeneous defocusing nonlinear landscapes with the nonlinearity coefficient growing toward the periphery as (1+|r|(α)) support one- and two-dimensional fundamental and higher-order bright solitons, as well as vortex solitons, with algebraically decaying tails. The energy flow of the solitons converges as long as nonlinearity growth rate exceeds the dimensionality, i.e., α>D. Fundamental solitons are always stable, while multipoles and vortices are stable if the nonlinearity growth rate is large enough.     

Vortex glass and vortex liquid in oscillatory media

We study the disordered, multispiral solutions of two-dimensional oscillatory media for parameter values at which the single-spiral/vortex solution is fully stable. Using the complex Ginzburg-Landau (CGLE) equation, we show that these states, heretofore believed to be static, actually evolve extremely slowly. This is achieved via a reduction of the CGLE to the evolution of the sole vortex coordinates. This true defect-mediated turbulence occurs in two distinct phases, a vortex liquid characterized by normal diffusion of spirals, and a slowly relaxing, intermittent, "vortex glass."