Spectral properties of the high-temperature plasma obtained by exposing a nickel layer to a source of high-power X-ray radiation (a power of 6–10 TW with a duration of 7–10 ns) based on a Z-pinch, formed during implosion of tungsten multi-wire arrays at the Angara-5-1 facility, are studied. In this case, the Z‑pinch radiation heats the target and turns it into the hot plasma, and the same radiation probes the target plasma to determine the spectral dependence of the transmission of this plasma. An original scheme is proposed for measuring the incident, transmitted and self-emission of a target simultaneously in one experiment in the frame mode using a grazing incidence diffraction spectrograph. Using laser shadow imaging, experimental data are obtained on the velocity of the plasma expansion on the irradiated and back sides of the target, which reached 100 km/s. Targets made of thin Ni layers deposited on a mylar film are studied. An irradiation-induced multiple increase in the transmission of the target plasma in the EUV range is observed compared to the transmittance of the target in the cold state. The dependence of the absorption spectrum of the plasma and the accompanying self-radiation of the target on the power and shape of the heating pulse is studied. The measurement results are compared with numerical calculations performed using the RALEF-2D two-dimensional radiation code, which has been repeatedly used previously to simulate similar experiments. The shape of the spectral dependence of the transmission in the experiment and calculation is similar in the range of ∼30–200 Å, but the model plasma transmission (∼0.8–0.9) is higher than that obtained using a spectrograph and X-ray multi-frame photography (∼0.5–0.6).

The results of research on the creation of a powerful source of soft X-ray radiation (SXR, hν > 100 eV) based on the Z-pinch of compact nested arrays are presented. One of the applications of such an SXR source can be radiation ablation of targets made of various substances in experiments on high-energy density physics and extreme states of matter, which are currently being actively carried out worldwide. Experiments are carried out on plasma implosion of combined nested arrays with different ratios of array radii at a discharge current level of up to 3.5 MA at the pulse power facility Angara-5-1. The outer array consisted of fibers of a substance with a low atomic number (polypropylene) and the inner array consisted of a substance with a high atomic number (tungsten). It is shown that in the case of nested arrays of this design, it is possible to obtain a significant ( 1.4 times) increase in the peak SXR power compared to single W arrays with the same parameters as the W array in the inner array. At the same time, spectral data obtained using a “flat field” grazing incidence spectrograph demonstrate a significant decrease in the fraction of tungsten ions in the trailing plasma around the pinch of nested arrays. By optimizing the linear mass of the outer array and its radius, powerful and short SXR pulses with amplitude of 10 TW, energy of 130 kJ and duration of 4–5 ns are obtained. This made it possible to increase the incident power density and fluence on the target up to 1.55 TW/cm2 and 17 kJ/cm2, respectively, in experiments on extreme states of matter currently being carried out at the facility.

Experiments on compression of cascade tungsten wire arrays with reduced inductance at the final stage of pinching aimed at increasing the specific concentration of plasma energy of the high-current Z‑pinches were carried out. The experiments were conducted at the Angara-5-1 facility at load current of up to 4 MA. The highest radiation power per unit pinch length were obtained using the cascade wire arrays in which mass per unit length of the inner wire array with reduced inductance was in the range between 1 and 1.5 that of the outer wire array. The soft X-ray radiation power of P 11 TW was obtained from the 1-cm-long pinch. The specific yield of the soft X-ray radiation was in the range of 130–140 kJ/cm. The total and specific powers of the pinch radiation obtained upon compression of the cascade load with reduced inductance exceeded the total and specific powers of the pinch radiation obtained by compression of a “standard” wire array with a length of 1.6 cm with the same parameters (7–8 TW and 5 TW/cm, respectively). The yield of the soft X-ray radiation did not change upon reduction in the length of the emitting pinch from 1.6 to 0.6 cm. The compression dynamics of such a load is indicative of an increased role played by the magnetic field of the current flowing in the inner cascade in interaction of the cascades. A variant of using interaction of the cascade-array shells via the magnetic field of the inner-cascade current as applied to the scheme of the statistical “hohlraum” with indirect irradiation of spherical targets is proposed. The scheme enables entrainment of part of the current by the inner wire array that confines the statistical “hohlraum.” In this case, interaction of cascades allows using nearly entire kinetic energy of the accelerated outer shell for generation of radiation in the statistical “hohlraum” by two forming near-electrode pinches.

This work is devoted to the reconstruction of Z-pinch plasma emission spectra in the wavelength range of less than 10 Å recorded by using a crystal x-ray spectrograph at the Angara 5-1 mega-ampere facility. The spectrograph JA-1 used in experiments has a cylindrical mica crystal with dimensions of 50 × 40 mm2 and radius of curvature of 100 mm. Registration of spectra is performed on the photographic film UF-4 with dimensions of 30 × 10 mm2. To reconstruct the spectra, the previously developed method based on iterative approximation of a true spectrum shape while minimizing a residual between experimental and calculated spectrograms is used. The calculated spectrogram was obtained taking into account the instrumental function of the spectrograph. To define the instrumental function a virtual Monte-Carlo model in the Geant4 toolkit has been developed. This model takes into account the interaction of radiation with the mica crystal using dynamical theory of diffraction. A true spectrum of Z-pinch plasma radiation is reconstructed for a 16 mm high load made of two nested cylindrical wire liners. External liner with a diameter of 12 mm has 40 Al wires with a diameter of 18 μm. The internal liner with a diameter of 5 mm has 4 W wires with a diameter of 6 μm. The W wires have a sputtered layer of Re that is 0.5 μm thick.

This work is devoted to the development of a method for the reconstruction of plasma extreme UV (EUV) spectra recorded by a three frame grazing incidence spectrograph (GIS-3D). The spectrograph provides registration of radiation reflected from the diffraction grating (DG) on a three-frame detector based on a microchannel plate with a scintillator screen and registration on a CCD camera, with an exposure time of one frame of ∼1.5 ns. DG has a gold-coated spherical concave form with a radius of curvature of 2 m and dimensions of 30 × 40 × 10 mm3. In this case, radiation is incident on the DG at a grazing angle of 2°; the DG period is 1.66 µm. The new single-pass method for the reconstruction of plasma EUV spectra was developed, which solves the inverse problem of decomposing experimental signals into separate contributions from each of the diffraction orders, followed by the reconstruction of the true plasma spectrum. Using the developed method, the possibility of finding a close approximation to the shape of a DG groove profile based on a priori information about the recorded spectra was demonstrated. In order to test and demonstrate the efficiency of this method, several experimental EUV spectra obtained at the Z-pinch facility Angara-5-1 with a current of ∼3-4 MA through loads made of either tungsten wires or polypropylene fibers were reconstructed. In addition, to test the single-pass method, the transmittance of EUV in cold aluminum was measured in the wavelength range of 3-35 nm, and it has a good match with the Henke database.

The results of experiments on the study of the generation of high-power pulsed soft X-ray (SXR) emission with a photon energy higher than 100 eV (in the spectral range with wavelengths λ shorter than 120 Å) during the plasma implosion of nested arrays of mixed composition with different ratios of array radii carried out on a pulse power facility Angara-5-1 with a discharge current level of up to 3.5 MA are presented. The outer array consisted of fibers of a substance with a low atomic number (plastic), and the inner array consisted of a substance with a high atomic number (tungsten, W). In the case of nested arrays of this design, a significant increase in the peak SXR power was obtained compared to single tungsten arrays with the same parameters as for the tungsten array in the inner array. By optimizing the linear mass of the outer array and the ratio of array radii, powerful SXR pulses were prepared with a high pulse power up to 18 TW, pulse energy of ~140 kJ and short pulse duration of ~5 ns. It is shown that by optimizing the linear mass of the outer array (fiber array) it is possible to achieve ~90% conversion of the electromagnetic energy pumped into the vicinity of the array into X-ray emission pinch energy. In this case, the fraction of the kinetic energy of the plasma implosion into the emission energy is not higher than 30%. In shots optimal over the output SXR power, an increase in the fraction of the X-ray emission energy in the spectral range of λ ∈ (30, 40) Å was recorded that is 30–100% than that in single tungsten arrays with similar parameters.

A digital model of a grazing-incidence X-ray spectrograph and methods for reconstruction of soft X-ray spectra of a Z-pinch plasma at the Angara-5-1 facility in the 2–40 nm range have been developed. The main problems hindering reliable qualitative and quantitative reconstruction of the initial Z-pinch X-ray spectra are the superposition of signals from different diffraction orders and the complex form of the device instrumental function. Two techniques for reconstructing the spectrum are presented. In the first one, a digital model of the spectrograph was developed in the Geant4 Monte Carlo simulation toolkit, taking into account the geometry of the experiment and the processes of interaction of X-ray radiation with a diffraction grating. In this model, taking into account the specific shape of the groove profile of the diffraction grating and the differential method for solving the diffraction problem, the X-ray intensity distribution in different diffraction orders depending on the wavelength is calculated. Using the developed model of the spectrograph, its instrumental function was calculated. The second technique does not use a specific grating groove shape, but, based on the analysis of calibration spectrograms, it constructs a dispersion relation and allows one to reconstruct the spectrum. At the end of the work, the results of reconstruction by the first and second techniques are compared and fairly good agreement between the spectra obtained by different techniques is shown.

The results of experiments on the study of plasma compression of nested wire arrays of mixed composition and the generation of powerful pulses of soft x-ray radiation (SXR), carried out on a pulse power facility Angara-5-1 at a current level of up to 3 MA, are presented. Based on the latest experimental data on the intensity of plasma formation of various substances m ˙ (in μ g(cm 2 ns) −1 ) (Mitrofanov et al 2020 Plasma Phys. Rep. 46 1150–80) and on the features of the dynamics of plasma compression in nested arrays (Mitrofanov et al 2018 Plasma Phys. Rep. 44 203–35), a nested wire array design has been developed which makes it possible to obtain a high peak SXR power in comparison with the known designs of single and nested tungsten wire arrays. During the implosion of nested arrays of mixed composition, consisting of plastic fibers and tungsten wires, shorter and more powerful SXR pulses were obtained with a maximum peak power P SXR max ∼ 10 TW with a full width at half maximum (FWHM) duration of ∼5 ns compared to the parameters of SXR pulses upon compression of single tungsten arrays: P SXR max ∼ 5 TW and FWHM ∼ 10 ns. Thus, under the conditions of our experiments, we have shown the possibility of a twofold increase in the peak SXR power during compression of nested arrays by optimizing their design.

The results of experiments on the effect of soft X-ray radiation (SXR) on thin mylar films of micron thickness are presented. The main result of the research is the development and testing of an adaptive filter-a filter made of mylar (hereinafter, My) film with time-varying transparency. This film is necessary for profiling the multi-terawatt soft X-ray radiation pulse in the experiments on radiation ablation of the targets made of layers of some metals (e.g., Al, Ni, In, Sn, Au, Bi, etc.), currently being carried out at the Angara-5-1 facility. Such a film absorbs almost all the energy of the preliminary pulse (the so-called "pre-pulse") and becomes "transparent" by the time the main terawatt radiation pulse occurs. The distance between this film and the target under study is chosen so as not to damage the target by the spreading filter substance during its radiation heating. Thus, the target layer initial density at the time of its irradiation by the main SXR radiation pulse will increase significantly. The use of an adaptive filter makes it possible to determine the change in the target layer transparency in a wider range of the initial values of its density and to reduce the influence of the target expansion dynamics on the accuracy of measuring its spectral transparency.

The results of experiments on increasing the specific energy density of high-current Z-pinch plasma by using various compression modes are presented. The experiments were carried out with cascade wire cylindrical loads at the Angara-5-1 facility with a current in the load of up to 4 MA. The experiments used loads both with a reduced inductance at the final stage of pinch compression and loads that make it possible to implement a transient compression mode from a cascade scheme to a composite Z-pinch scheme. When cascade arrays, which have a reduced inductance at the final stage of compression, are compressed, the specific power of soft X-ray emission is higher than 5 TW/cm, which corresponds to the radiation power with a pinch of a standard length of 1.6 cm at the level of 8–9 TW. The specific total X-ray emission yield is about 150 kJ/cm for a total emission yield at a level of 90–95 kJ. The compression dynamics of such a load indicates a significant role of the magnetic field of the current flowing through the inner cascade in the interaction of the cascades. It is shown that in the transient compression mode from a cascade array to a composite Z‑pinch, the outer array of a material with a relatively low atomic number (Al) provides a high kinetic energy flux density, while the inner array of a small diameter made from a material with a high atomic number (W) allows one to increase the radiation power three times.

In this paper, we consider an experimental procedure for searching for the stimulation of de-excitation of nuclear isomer (SDNI) of 186 m Re (the isomer spontaneous half-life is T 1/2 = 2 × 10 5 yr) in a high-current Z-pinch plasma. On the basis of the recently obtained results of observing SDNI for 186 m Re in a laser plasma, the possibility of observing SDNI for 186 m Re in a Z-pinch plasma with an electron temperature of ~1 keV at the Angara-5-1 setup is shown. The design of a liner, a set of metal wires with the 186 m Re isomer whose electric explosion produces a Z-pinch, the method for introducing the 186 m Re isomer into the liner, and the method for detecting SDNI for 186 m Re in a Z-pinch plasma are discussed.

Experiments aimed at investigation of X-ray self-emission of plasma of heated targets consisting of layers of different materials (Mylar, polypropylene, In, Sn, and Au) exposed to the action of energy flux of X‑ray radiation (the so-called energy exposure of the target) of up to 10 kJ/cm2 were carried out. A Z-pinch induced by implosion of a tungsten wire-array by current of up to 4 MA in Angara-5-1 facility was used as a source of high-power X-ray radiation. The temporal dynamics of intensity of self-emission of heated targets was studied. In the process, contribution of expanding layer of a material with high atomic number Z to self-emission of the target dominates that of a Mylar film with effective charge Zeff ≈ 4.5. It is demonstrated that the 1/e decay time of target emission depends on expansion dynamics of target plasma. The latter, in turn, depends on orientation of the layer characterized by high atomic number relative to the source of radiation. New data on spectral composition of self-emission of targets and its changes with time is obtained. This data is compared with the results of numerical simulation of target heating and scatter by means of RALEF-2D two-dimensional radiation gas-dynamic code.

The paper presents the results of experiments with the compression of the plasma of double multiwire arrays of mixed composition and the generation of powerful soft X-ray radiation (SXR) pulses carried out on the powerful electrophysical facility Angara-5-1 at a discharge current of up to 3 MA. Based on the latest experimental data on the production rate $$\dot {m}$$ of different plasmas (in μg/(cm2 ns)) [1] and on specificities of the dynamics of plasma compression in nested arrays [2], a nested array was designed, which makes it possible to obtain a high SXR peak power in comparison with the optimal (in terms of radiation power) designs of single and nested tungsten wire arrays. By selecting substances with different plasma production rates, it was possible to reduce the level of magnetohydrodynamic instabilities at the final stage of compression of the inner array. This made it possible to reduce the radiation pulse duration and increase the SXR power. Using implosion of nested arrays of mixed composition, consisting of plastic fibers and tungsten wires, shorter and more powerful SXR pulses with a maximum peak power $$P_{{{\text{SXR}}}}^{{{\text{max}}}}$$ ~10 TW with a pulse duration FWHM ~ 5 ns were obtained, compared to the parameters of SXR pulses upon compression of single tungsten arrays: $$P_{{{\text{SXR}}}}^{{{\text{max}}}}$$  ~ 5 TW and FWHM ~ 10 ns. Thus, we have shown the possibility of a twofold increase in the peak SXR power during compression of nested arrays under the conditions of our experiments by optimizing their design. One of the results of this work was finding the optimal parameters of the nested arrays and the prediction of the peak SXR power for experiments at powerful electrophysical facilities, differing from with substantially different levels of discharge current, 4–26 MA (Angara-5-1, Julong-1, and ZR).

The results of the studies of the compression of the plasma of cone-cylindrical nested arrays of mixed composition at current flow through them of up to 3 MA at the Angara-5-1 facility are presented. The outer array of the nested array is a conical array of thin nylon fibers or tungsten wires, while the inner one is a cylindrical tungsten wire array. The implosion of current in this type of nested arrays is a unique opportunity for simulating the interaction of magnetized plasma flows with a strong magnetic field. In the space between the inner and outer arrays, the super-Alfvén plasma flow from the outer array collides with the magnetic field of the discharge current through the inner array. As a result of this interaction in the space between arrays, different plasma flow modes are implemented: pre-Alfvén (Vr < VА), super-Alfvén (Vr > VА), and a mode with the formation of the transition region—a shock wave (SW) between arrays, depending on the ratio of the plasma formation rates of arrays of nested array and on the ratio of their radii. The SW region formation in the space between arrays occurs near the inner array, where the kinetic pressure of the plasma flow from the outer array is balanced by the magnetic pressure of the discharge current of the inner array. New experimental data was obtained on the features of the SW region formation near the surface of the inner array and the nature of its change during the interaction. The use of an external conical array enabled us to obtain the SW position depending on the ratio of radii of the outer and inner arrays in one shot. It is shown that the interaction of plasma flows of the outer conical array with the magnetic field of the inner cylindrical array leads to a significant decrease in the zipper-effect at the final stage of plasma compression of the inner array and the pinch formation. The obtained experimental results are compared with the results of simulating the plasma motion between the arrays using the three-dimensional radiation-magnetohydrodynamic code MARPLE3D.