Albert R. Mingaleev

Distribution of matter in the current-carrying plasma and dense core of the discharge channel formed upon electrical wire explosion

Distribution of matter in the discharge channel formed upon a nanosecond electrical explosion of a single wire in air and vacuum was studied experimentally. Simultaneous use of optical, UV, and X-ray diagnostics made it possible to distinguish qualitatively different regions of the discharge channel, such as the current-carrying layers and the region occupied by a weakly conducting cold plasma. Several series of experiments with 25-µm-diameter 12-mm-long wires made of different materials were performed. The charging voltage and the current amplitude were varied in the ranges of U0 = 10–20 kV and Imax ∼ 5–10 kA, respectively. Explosion regimes with a current pause and with and without current interruption, as well as with wire preheating in air and vacuum, were studied. Shadow and schlieren images of the discharge channel were obtained using optical probing at the second harmonic of a YAG: Nd+3 laser (λ = 0.532 µm, τ ∼ 10 ns). In the experiments carried out in vacuum, X-ray images of the discharge channel were also obtained using an X-pinch as a point source of probing radiation and UV images were recorded using a four-frame MCP camera.

Analysis of the discharge channel structure upon nanosecond electrical explosion of wires

The structure of the discharge channel during nanosecond wire explosions has been studied using laser probing. Wires of 25μm diameter and 12mm length were exploded in air and vacuum by 10kA current pulse having a 50A∕ns rate of rise. Upon electrical explosion of thin wires in the air, the development of shock waves was observed. The propagation of shock waves was analyzed, and it was possible to draw conclusions on the location of the flow of most of the current in the volume of the discharge channel. This permitted distinguishing between two scenarios (shunting and internal) of the interelectrode gap breakdown development. The scenario depends to a large extent on the properties of the exploding wire material. The same two scenarios are valid upon electrical explosion of wire in vacuum. Moreover, if secondary breakdown develops in the internal scenario, the value of the energy deposition in the wire material during explosion in vacuum may be comparable with that found during explosion in air.

Nanosecond electric explosion of a tungsten wire in different media

The effect of surrounding media of different densities and electric strengths on the heating dynamics of a micron wire during its nanosecond electric explosion is investigated. Tungsten wires with diameters of d = 25–50 μm were exploded in air and water at a current rise time of (dI/dt) ∼ 1010 A/s. The diagnostic complex is described.

Accelerated electrons and hard X-ray emission from X-pinches

The generation of accelerated electrons in the X-pinch minidiode is studied experimentally. It is well known that the explosion of an X-pinch consisting of two or more wires is accompanied by the formation of a minidiode, in which electrons are accelerated. The subsequent slowing down of electrons in the products of wire explosion causes the generation of hard X-ray (HXR) emission with photon energies higher than 10 keV. In this work, the spatial and temporal characteristics of X-pinch HXR emission are studied, the specific features of HXR generation are discussed, and the capability of applying this radiation to point-projection X-ray imaging of various plasma and biological objects is considered. The parameters of the electron beam produced in the X-pinch are measured using a Faraday cup and X-ray diagnostics. The experiments were performed with the XP generator (550 kA, 100 ns) at Cornell University (United States) and the BIN generator (270 kA, 150 ns) at the Lebedev Physical Institute (Russia).

Stratification dynamics and the development of electrothermal instability at the wire explosion

The stratification dynamics at wire explosion of copper and nickel wires (25 and 50 μm) in air is studied under current dwell conditions. Experimental and theoretical data are presented for the stratification of a core due to electrothermal instability. The evolution of strata during the quasi-adiabatic expansion of the core is studied, and it is shown that the elongation of strata and their dynamics are well described in terms of a model of electrothermal instability for conductors with different diameters.

Electric explosion of fine wires: Three groups of materials

Experimental data demonstrating differences in the structures of channels formed during nanosecond discharges through fine wires made of different materials are presented. In addition to the traditional two classes of metals and alloys (the copper and tungsten groups), a new class is proposed to which materials of the nickel type belong. Their properties combine the characteristic properties of the two traditional groups, due to which they occupy an intermediate position between the latter. This manifests itself in the unstable character of explosion, the type of which can change drastically when changing the ambient medium or other conditions. Most of the reported results were obtained at a small setup with maximum values of the current and voltage of 10 kA and 20 kV, respectively, the current rise time being about 300 ns. An attempt is made to construct a scenario of the development of a nanosecond explosion that would make it possible to qualitatively describe the formation of the discharge channel structure. The analysis is based on the recent experimental results indicating that the cores formed in the course of the discharge have a tubular structure.

Hybrid X-pinches

Results from experimental studies of a hybrid X-pinch with an initial configuration in the form of a high-current diode with conical tungsten electrodes spaced by 1–2 mm and connected to one another with 20- to 100-μm-diameter wires are presented. The experiments were carried out at four facilities with a current amplitude from 200 to 1000 kA and front duration from 45 to 200 ns. It is shown that, in spite of their simpler configuration, hybrid X-pinches with a short rise time of the current pulse (50–100 ns) are highly competitive with standard X-pinches in the generated soft X-ray power and the formation of a single hot spot in them is much more stable, while hard X-ray emission is almost absent. The possibility of using hybrid X-pinches as soft X-ray sources for point projection X-ray imaging of plasma objects is considered.

Maximum Energy Deposition During Resistive Stage and Overvoltage at Current Driven Nanosecond Wire Explosion

A wire explosion in a gaseous and condensed media extends possibilities of studying of phase transition of the wire material. The copper and tungsten wires of the diameter of d=25 mum were exploded in vacuum, air, and water by current pulse with the rate increase of ~ 50 A/ns. Energy deposited into the wires at different stages of explosion in the media and maximum voltage reached during wire explosion was estimated from the experiments. Laser probing measurements were performed with the second harmonic of a YAG:Nd+3 laser (lambda=0.53 mum; Deltat=10 ns). Shadow images of the expanding wire materials and shock waves leading the explosion were obtained at different times during the discharge

Overvoltage pulse development upon electrical explosion of thin wires

Experimental data are presented on the electrical explosion of wires of micrometre diameters with a 10 kA current having a rise time rate of up to 50 An s −1 . The influence of circuit and wire parameters and properties of the wire material on the process of possible rupture of current in the circuit and resulting overvoltage at the discharge gap is evaluated. A large amount of experimental data on electrical explosion of wire in various media and in vacuum in the micro- and nanosecond range is analysed. The data are compared with theoretical estimations.

Dynamics of thin exploded-wire plasma with a cold dense core

Ideas are put forward regarding the possibility of a cold dense core, surrounded by a plasma corona, forming near the axis at the initial stage of a nanosecond electric explosion of metal wires, and the influence of such a radial structure on the plasma compression dynamics is discussed. Experimental evidence supporting these suppositions is presented. It includes both indirect confirmations, based on optical and x-ray diagnostics data, and direct observations of the core by new means of x-ray probing employing an X pinch as a source of radiation.