The results of experiments on measuring the magnetic field from the azimuthal component of the current during the explosion of thin wires in high-current generators are presented. The discharge was excited by high-voltage pulses of 20 kV, 500 ns, with current up to 8 kA. Laser, X-ray tenegrams from other similar experiments are given. An assumption is made that the appearance of strata in such discharges is caused by the appearance of the spiral component of the current in the discharge, which leads to the splitting of the plasma column of the discharge into strata under the action of the Ampere forces between the resulting current coils.

The paper presents the results of experimental studies of the operation of hybrid X-pinches on a modified high-current KING generator. The KING generator is a portable pulse current generator based on four low-inductive pulse capacitors. The output assembly of the generator was modified for greater diagnostic access to the load, which led to an increase in the inductance of the entire circuit and an increase in the duration of the current rise. A series of experiments with hybrid X-pinches with Al, Cu, and Mo wires with a diameter of 25 μm was carried out on the modified KING generator (200–260 kA, 220–280 ns, 45 kV). In experiments, it was shown that such a modification of the generator led to the stable formation of bright soft x-ray sources in X-pinches, suitable for use in point-projection radiography with a spatial resolution of about 10–15 μm.

We consider the coherent properties of short-wavelength radiation generated by high-current nanosecond discharges. The first part of the paper is concerned with the feasibility of using a plasma soft X-ray radiation source, the X-pinch, proposed at the Lebedev Physical Institute in the late 1970s as part of the inertial thermonuclear fusion program based on high-current nanosecond discharges. Experimental studies of the X-pinch suggest that a high-temperature plasma with extreme parameters is produced in it, which emits a high- power electromagnetic pulse in a broad wavelength range, with the X-ray radiation source (1 keV10 keV) possessing unique parameters. Its dimensions are so small (<1 mu m) that the radiation it emits is spatially coherent. When it was used in projection radiography, phase contrast was observed in images of low-absorbing objects. The results of assessing the applicability of the wave approximation in image analysis and simulations of the intensity distribution in images using Fresnel integrals are presented. In the second part of the paper, we analyze a new physical phenomenon, also discovered at the Lebedev Physical Institute, related to the production of a short (<2 ns), narrowly directed electromagnetic radiation pulse in the pre-breakdown stage of a high-current discharge on the surface of a ferrite, 50% of the energy spectrum of which lies in the X-ray region (hv > 1 keV) with an energy of similar to 0.6 mJ and average power of similar to 0.3 MW. The pulse propagates parallel to the ferrite surface towards the anode with a low angular divergence of <2 degrees. The high radiation directivity in the absence of special optical devices and the quadratic dependence of the energy flux density transferred by a detected radiation pulse on the length of the working part of the ferrite prism indicate with a high probability its coherent nature. We discuss the possible mechanism for generating radiation, which involves the excitation of short-term magnetization of ferrite sections as a result of the passage of an exciting electromagnetic pulse over the surface of a ferrite prism during the formation of a longitudinal electric field in the interelectrode gap and subsequent coherent addition of elementary waves. The total radiation from the entire surface as a result of interference is concentrated in a small spatial region, which explains the high intensity and directionality of the radiation.

To study the spatial distribution of the intensity of an X-ray source of electric discharge plasma, a new-type coded aperture, which is a structure of intersecting mutually perpendicular transparent and opaque strips with the widths selected using a random number generator, has been used. The radiation passed through the coded aperture has produced a complex pattern of the coded image, which has been recorded on a Fuji TR fluorescent imaging plate without a protective coating. A mathematical procedure based on the iterative method of solving an incorrectly posed problem given by the Fredholm integral equation of the first kind has been applied to reconstruct the spatial distribution of plasma radiation intensity from this pattern. It has been shown that the use of the coded aperture not only has increased significantly the light intensity of the recording system in comparison with a pinhole camera, but also has made it possible to obtain a spatial resolution of the discharge plasma no worse than the resolution of the pinhole camera. The applicability of the developed iterative method for both sources close to point ones and extended emitting objects has been demonstrated.

Over the many decades of studying the electric explosion of thin wires (EEW), researchers have developed and accepted certain notions about this process. Despite the lack of proof behind certain established assertions and, sometimes, their contradiction with the results of recent experiments, they are still widely used to describe and interpret new data. In the first place, this concerns the concept that the EEW is a fast evaporation of metal as a result of the dissipation of Joule energy inside it. Another fundamental notion that is used during the analysis of the experimental results and in model calculations is the uniform distribution of matter along the cross section of the wire core during the explosion. To date, the nature and mechanism of the appearance of strata, i.e., the periodicity observed in many images of the EEW, remain unexplained. Using the traditional notions of the EEW, even in experiments conducted at a high level, does not allow one to correctly interpret the obtained results and, as a whole, does not facilitate the progress in understanding the complicated physics of the process of wire explosion. Therefore, the traditional concepts of the EEW have long required a revision. This work summarizes the results of modern research in this area and considers its relation to the previous works. It also proposes new approaches to the studies of the EEW dynamics and to the understanding of the processes of energy transformation in matter during its rapid heating by the electric current.

The results of studying instabilities in flat aluminum 4-μm-thick foils exploded using the GVP generator with a short circuit current of 10 kA and a current rise time of 350 ns are presented. The dynamics of foil destruction during the explosion was studied using laser probing. During the experiments, it was ascertained that in the presence of the two-dimensional structure of foil, the growth rates of instabilities and their nature depend on the foil orientation relative to the direction of current flow. The conditions are cleared up, under which during the explosion of foils with two-dimensional inherent structures, the development of instabilities is slowed down.

Based on numerical simulation, the electrical processes during pulsed electric fields passage through dielectrics insulator with high permeabilities µ and permittivities ε were analyzed. It is shown that the passage of short intense voltage pulses causes a ferrite cylinder magnetization in a narrow submillimeter layer near the dielectric surface. As the magnetization region reaches an opposite electrode, the layer as a whole is tightened to the cylinder axis. In this case, the magnetization wavefront in the surface layer moves with velocity c . The analysis performed made it possible to construct a model explaining the formation of a narrowly directed short pulse of coherent electromagnetic radiation in the prebreakdown discharge stage over the surface of solid dielectric with high magnetic permeability µ. The model is based on the excitation of short-term magnetization of the ferrite surface in forming a field in the interelectrode gap and subsequent coherent addition of elementary waves forming resulting radiation.

The technique in experimental studies of the spectral composition of X rays of hybrid X-pinch plasma with wires of 13 Al aluminum, 42 Mo molybdenum, and 47 Ag silver is described and the results are presented. The experiments were performed in the energy range from 0.5 to 15 keV using detectors based on lithium fluorides LiF(Mg, Ti). The electron temperatures of plasma for aluminum, molybdenum, and silver were Т е ≈ 0.35, 0.48, and 0.40 keV, respectively. The energy of hard radiation of hybrid X pinches was measured for the first time.

The results of a study of the electrical explosion of aluminum foils with an artificial periodic surface structure created by laser engraving are presented. Experiments were carried out on pulsed high-current generators BIN (270 kA, 300 kV, 100 ns) and KING (200 kA, 40 kV, 200 ns) with Al foil of thicknesses 16 and 4 μm, respectively. Images of the exploded foils were recorded by point projection radiography in the radiation from hybrid X-pinches. It is found that the application of an artificial periodic structure to the foil leads to a much more uniform and well-defined periodic structure of the exploded foil. Images recorded in the UV range using a microchannel-plate-intensified detector show that the radiation from a surface-modified foil is more uniform along the entire length and width of the foil than that from a foil without modification.

— A technique for studying the spatial structure of hybrid X-pinch plasma objects in the X-ray range is described, and main experimental results are presented. The spectral characteristics of X-ray sources of plasma objects have been measured. The investigations have been carried out using thermoluminescent detectors based on lithium fluorides LiF(Mg, Ti).

Описана методика и приведены основные экспериментальные результаты исследования пространственной структуры плазменных объектов гибридного Х-пинча в диапазоне рентгеновского излучения. Представлены результаты измерений спектральных характеристик источников рентгеновского излучения плазменных объектов. Исследования проведены с использованием термолюминесцентных детекторов на основе фторидов лития LiF(Mg, Ti).

The results of the study of radiation produced by the electrical explosion of Al foil with a thickness of 4 μm with an artificial periodic structure of periodic holes with 50–400 μm steps created by laser engraving are presented. The experiments were carried out on a KING pulse high-current generator (220 kA, 40 kV, 300 ns). Images of exploded foils were recorded using pinhole cameras with a 20 μm aperture on a four-frame microchannel plate camera with 5 ns temporal resolution. In experiments on the electrical explosion of thin foils, it was shown that the application of an artificial periodic structure to the foil leads to a much more uniform radiation in the UV spectrum range along the entire length and width of the foil. Uniform radiation was observed from 20 to 70 ns. It is shown that such radiation can be used for the imaging of test objects or plasma objects like exploded wires.

Results of laser probing of products of electrical explosion of thin molybdenum wires in air (20 kV, 10 kA, 350 ns) are presented. Shadow and interferometric images of the discharge gap were obtained simultaneously using probing radiation at two wavelengths (λ1 = 1064 nm and λ2 = 532 nm). Comparison of images revealed that an increase in the probing wavelength results in substantial increase in transparency of the so-called core, the most long-lived and relatively dense remnants of the wire material, at a relatively late stage of expansion (one microsecond and more after beginning of current). These observations can be explained if we consider that the core material to a large extent consists of small, on the order of one hundred nanometers, particles, scattering from which obeys the Rayleigh dependence on wavelength (~λ–4). Presented results show that scattering should certainly be taken into account when analyzing the data of shadow and interferometric probing in studies of electrical explosion of wires.

This paper presents characteristic features of the explosion of thin flat foils for currents and pulse risetimes ranging from 8 kA at 350 ns to 1000 kA at ∼100 ns. Foils made of aluminum, copper, nickel, and titanium with thicknesses of 1–100 µm are tested. Various diagnostics in the optical, UV, and x-ray spectral ranges are used to image the exploding foils from initial breakdown to complete destruction or pinching. It is shown that foil explosion is a complex process that depends on many factors, but features common to all foils are found that do not depend on the parameters of the generators or, accordingly, on the energy deposited in the foil: for example, the breakdown of flat foils under different conditions occurs at the edges of the foil. For the first time, the formation of a precursor over the central part of the foil is shown, which significantly changes the dynamics of the foil explosion.

For the first time observed that at the initial stage of a high-current discharge, a low-divergence short (<2 ns) electromagnetic pulse is formed over a ferrite surface. The 50% part of the energy spectrum of this pulse lies in the region of sufficiently hard x-ray radiation (hν > 1 keV) with an energy of 0.6 mJ and an average power of 0.3 MW. The radiation propagates parallel to the surface in the anode direction with the angle divergence <2°. The high directionality of the radiation in absence of the aperture-limiting devices for the radiation beam and the quadratic dependence of the spatial radiation energy flux density on the length of working part of the ferrite prism points to the coherent nature of the observed radiation. A possible generation mechanism of the radiation is proposed. It is based on the short-lived magnetization of the ferrite plots by a high-power electromagnetic pulse and the subsequent coherent interference of unit waves irradiated by these plots.