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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). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Experiments on studying the effect of pulsed superhigh currents and soft X-ray emission (SXR) on the plasma production on the surface of current-carrying electrodes are carried out at the Angara-5-1 facility. The linear current density was about 1 MA/cm, and the SXR power flux density reached ~0.8 TW/cm2 in the spectral range of 50–500 eV. The current rise time to the maximum was ~100 ns. It is shown that under the conditions of our loads, plasma formed during ablation of the material from the surface of the electrodes moves symmetrically towards the middle of the interelectrode gap at a speed of up to 90–95 km/s. It is found that the effect of pulsed superhigh currents and SXR emission on the plasma production on metal electrodes with a layer of organic matter leads to earlier production of plasma from organic matter and, accordingly, to faster (at higher rates) filling of the interelectrode gap with this plasma. Under intense irradiation with soft X‑ray emission, the plasma from the electrodes expands at a speed of up to 150 km/s. [ABSTRACT FROM AUTHOR]

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 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 ~10 TW with a pulse duration FWHM ~ 5 ns were obtained, compared to the parameters of SXR pulses upon compression of single tungsten arrays: ~ 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). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In electromagnetic generators of the terawatt range with current pulse of 1–30 MA, electric explosion of the surface of current-carrying electrodes takes place. One of the options for protecting the electrodes is covering the current-carrying surface with different materials. In this work, we present experimental data and results of numerical simulations of the processes that take place in a thick-walled heterophase electrode during the passage of current with a high linear density. The amplitude value of the linear current density in the simulations was of 2.8 MA/cm. The results of the simulations of the processes that occur in the electrodes during the passage of current with high linear density are in qualitative agreement with experimental data. [ABSTRACT FROM AUTHOR]

Compression of a fiber array with a deuterated target mounted on its axis is studied at the Angara-5-1 facility (3.5 MA, 100 ns). Cylindrical arrays with an initial diameter of 12 mm made from polypropylene fibers with a diameter of 13.4 µm are used. The number of fibers varied from 30 to 120. The target with the density of 0.08–0.2 g/cm3 and the diameter of 1 mm was made on the basis of deuterated polyethylene. A 10‑frame ultra-high-speed X-ray camera, optical slit scans, an integral X-ray pinhole camera, vacuum X-ray diodes, a crystal spectrograph, and neutron detectors are used to measure the plasma parameters in the Z‑pinch. It is found that the dynamics of plasma compression and evolution of local plasma formations, which are sources of neutrons and soft X-ray emission in the energy range of E > 150 eV, depend on the load configuration: the number of fibers, diameter, and density of the deuterated target. Efficient compression of the liner plasma, high concentration and temperature of the compressed target state, as well as the highest neutron yield (8 × 109 neutron/pulse) are observed in experiments with arrays with the fiber number of 60, inside which the target with the diameter of 1 mm and density of 0.2 g/cm3 was placed. The electron density and temperature of the hot plasma in local formations are estimated as ne ≈ 1021 cm–3, Te ≈ 1 keV, respectively. The average neutron energy was 2.6 ± 0.2 MeV. The intensity of the plasma formation [in µg/(cm2 ns)] of polypropylene fibers under the action of the discharge current of the facility is determined in experiments with fiber arrays. [ABSTRACT FROM AUTHOR]

The formation of plasma on the surface of a current-carrying electrode of a high-current facility when a current flows through it with a linear density of up to 4 MA/cm and is coated with lead foil or ceramic is studied. The propagation velocity of a dense plasma from a stainless steel electrode is 2–10 km/s, and when the electrode is coated with lead, it is 1–6 km/s. In these experiments, there is no load typical for such facilities—a source of intense X-ray radiation. The plasma propagation from ceramic-coated electrodes starts 200 ns later than that for metal electrodes. [ABSTRACT FROM AUTHOR]

The generation of accelerated electron beams in a high-current Z-pinch formed by the implosion of wire cylindrical tungsten arrays on an Angara-5-1 facility is studied. The most intense characteristic and bremsstrahlung X-ray radiation of fast electrons is recorded from the central region of the pinch at the pin-ching stage. The transverse size of the radiation source in the characteristic tungsten radiation Lα is ~1.5‒1.8 mm, which is close to the transverse size of the radiation source in the soft X-ray emission (1‒1.5 mm). The current of accelerated electrons generated during the implosion of the wire array and the formation of a pinch is on the order of the Alfvén current (IA). This result is consistent with the estimate of the current of accelerated electrons made from the measured characteristic radiation intensity Lα of tungsten under the assumption that the mean free path of fast electrons in a pinch is on the order of its length. [ABSTRACT FROM AUTHOR]

The implosion of combined loads consisting of an outer wire (fiber) array and inner cylindrical target was studied experimentally at the Angara-5-1 facility (3.5 MA, 100 ns) at currents of up to 3.5 MA. The experiments were carried out with 12- and 20-mm-diameter outer arrays made of 15-μm-diameter aluminum wires, composite arrays made of aluminum wires and 25-μm-diameter kapron fibers, and arrays made of kapron fibers with a 1-μm-thick aluminum coating. The number of wires varied from 10 to 40. The targets were made of agar-agar or low-density deuterated polyethylene. The parameters of the Z-pinch plasma were determined using the Angara-5-1 diagnostic complex, which included optical streak cameras, X-ray frame cameras, X-ray detectors, X-ray pinhole cameras, neutron detectors, and a mica-crystal X-ray spectrograph. It is established that the plasma compression dynamics and the formation of local plasma structures generating neutrons depend on the load configuration: the array diameter, the number of wires (fibers), and the diameter and density of the target. The most efficient compression and the highest plasma parameters (the compression ratio and plasma temperature), as well as the highest neutron yield, were achieved in experiments with 12-mm-diameter aluminum wire arrays inside which a 1-mm-diameter deuterated target with a mass density of 0.3 g/cm3 was installed As a result of collision of the bulk of the array mass with the inner target, a compact pinch with a diameter of ≈0.5 mm forms. The pinch formation is accompanied by the generation of a soft X-ray pulse. The development of MHD instabilities in the pinch plasma results in the formation of multiple hot spots (HSs) on the pinch axis with a typical size of 200–300 μm and an electron temperature of 0.4–0.7 keV. The HS formation is accompanied by emission of neutrons with a mean energy of 2.7 ± 0.2 MeV. The maximum neutron yield achieved in these experiments was 2.6 × 1010 neutrons/shot. [ABSTRACT FROM AUTHOR]

Experiments on the acceleration of a flyer by a magnetic field make it possible to study the dynamic characteristics of matter on submicrosecond time scales. Megabar pressures at the Angara-5-1 facility are produced using the magnetic field of the current with a linear density of up to 5 MA/cm. In the previous experiments on the acceleration of a duralumin flyer, velocities of up to 10 km/s were achieved. The flyer motion was recorded by means of laser shadowgraphy. In this work, the efficiency of momentum transfer from a duralumin flyer to an initially immobile tungsten target was studied. From the kinematic parameters of the flyer motion before the impact and the motion of the flyer together with the target after the impact, the fraction of the flyer mass that transfer the momentum to the target was estimated. It is established that almost the entire mass of the flyer is involved in the impact process. [ABSTRACT FROM AUTHOR]

Experiments on the creation of megabar pressures and acceleration of metal flyers by the pressure of a pulsed magnetic field are being carried out at the Angara-5-1 facility. Velocities of up to 10 km/s were achieved. The velocities of flyers were recorded using the VISAR laser interferometer (velocity interferometer system for any reflector). The issues of the electromagnetic compatibility of the VISAR with the Angara-5-1 facility are considered, since the operation of this facility causes electromagnetic interference and when the magnetic self-isolation is established in the vacuum transmission lines, X-ray bremsstrahlung is generated and influences the optics, fiber-optic cables, and photomultipliers. The suppression of these two sources of interference made it possible to reliably register the VISAR signals and determine the velocity of a flyer. [ABSTRACT FROM AUTHOR]

The acceleration of a flyer by a magnetic field allows studying the dynamic characteristics of matter in submicrosecond processes. At the Angara-5-1 facility, pressure is created by a magnetic field of the current with the linear current density of up to 5 MA/cm. The velocity of up to 10 km/s was obtained in the first experiments on acceleration of a duralumin flyer 1 mm thick. Two methods are used for registration of the flyer velocity: laser shadow photography and VISAR interferometric method. This paper presents the results of experiments on determining the velocity of a flyer by the VISAR method. Particular attention is paid to the problem of suppression of spurious signals in the VISAR registration system. The first problem was electromagnetic interference emerging when the Angara-5-1 facility is activated, when megavolt voltages and megaampere currents are generated within a hundred nanoseconds. The second problem was bremstrahlung radiation emerging when magnetic self-isolation is established in vacuum transmission lines. This radiation affects the optics, fiber optic cables, and photomultipliers. The suppression of these two sources of interference ensured the reliable registration of the VISAR signals. The results obtained by the two laser methods—shadow photography and VISAR—coincide with each other and with the results of numerical simulation of flyer acceleration. The experimental results and simulation results are compared. [ABSTRACT FROM AUTHOR]

Abstract: Radiological methods of treatment of malignant tumors are widespread in medical practice. In addition to the type of radiation and dose and fractionation of the radiation regime, the dose rate is one of the factors that affects the effectiveness of treatment. The therapeutic dose rate lies in the range of tens of mGy/s. At modern high-current accelerators of relativistic electron beams, a significant increase in the dose rate to hundreds of MGy/s is achievable, which is more than 108 times greater than the therapeutic dose rate. It is difficult to predict the nature of processes in tissues and its cells at such radiation intensities. To determine the effect of extreme dose rate on the radiosensitivity of tissues at the Angara-5-1 facility, experiments were conducted to determine the lethal dose (LD50/30) for laboratory mice. Our result on the study of the LD50/30 dose (~100 MGy/s) allows us to make a conclusion about a possible higher lethal dose than the power range of the doses used for medical purposes. [ABSTRACT FROM AUTHOR]

The output unit of the Angara-5-1 installation was upgraded in order to increase megabar pressure. Upgrading was carried out taking into account those fact that pressure was created using the magnetic field of the current flowing through the specimen. To increasing the power impulse acting on the flyer from the side of the magnetic field, variants of increasing the time duration of the magnetic field were considered by controlled current shorting (crowbar). In accordance with the mathematical simulation when extending the current pulse, it is possible to increase the flyer velocity by a factor of two. [ABSTRACT FROM AUTHOR]

Preliminary results are presented for the parameters of flyer used in experimental studies of material properties in the shock-wave compression of a sample by a magnetic field. [ABSTRACT FROM AUTHOR]

By means of the electrostatic expansion of a cylindrical wire array by an additional electrode, quasi-spherical arrays with a radius of 8–12 mm and a mass of 200–400 μg consisting of 30–60 tungsten wires 6 μm in thickness are formed. The compression of Z pinches formed by these arrays was performed by a current of 3–4 MA with a rise time of 100 ns in the Angara-5-1 facility. It has been shown that the central part of this array forms a region hotter than its edges and that for cylindrical arrays. [ABSTRACT FROM AUTHOR]

Results are presented from experimental studies of hard X-ray (HXR) emission in the photon energy range above 20 keV from dense radiating Z-pinch plasmas. The work is aimed at revealing the nature of fast-electron (electron beam) generation during the implosion of cylindrical and conical wire arrays in the Angara-5-1 facility at currents of up to 3 MA. It is found that the plasma implosion zippering caused by the inclination of wires affects the parameters of the HXR pulse emitted during the implosion of a conical array. It is shown that HXR emission correlates well with the decay of the plasma column near the cathode in the stagnation phase. HXR images of the pinch are produced by the bremsstrahlung of fast electrons generated during plasma column decay and interacting with plasma ions and the anode target. It is found that the use of conical arrays makes it possible to control the direction of plasma implosion zippering and the spatiotemporal and energy parameters of the pinch X-ray emission, in particular the X-ray yield. For wire array with diameters of 12 mm and linear masses of 200–400 μg/cm, the current of the fast electron beam is 20 kA and its energy is 60 J, which is about 1/500 of the energy of the main soft X-ray pulse. [ABSTRACT FROM AUTHOR]

Results are presented from experimental studies of the generation of hard X-ray (HXR) emission with photon energies above 20 keV during the implosion of wire arrays in the Angara-5-1 facility. An analysis of X-ray images of the Z-pinch shows that the dimensions and spatial structures of the emitting regions are different for hard and soft X rays. It is found that the HXR emission peak is delayed with respect to the soft X-ray (SXR) one. The dependence of the HXR power on the material, initial diameter, and mass (implosion time) of the wire array is determined. It is shown that the HXR intensity in the spectral range >50 keV is several orders higher than the emission intensity in the high-energy tail of the SXR spectrum (assuming that this spectrum is thermal). A comparison of the time evolution and spatial localization of the HXR and SXR sources during the implosion of wire arrays indicates the presence of a new superthermal phenomenon that differs qualitatively from the processes determining the peak power of the SXR pulse. Possible mechanisms that can be responsible for the generation of HXR pulses are considered. [ABSTRACT FROM AUTHOR]

A qualitative model of the dynamics of a multiterawatt radiating Z-pinch with cold start and high rate of current rise is proposed. The model is used to analyze discharges with currents I ∼ 2–5 MA (with dI/dt > 1013 A/s) through uniform or structured plasma-producing loads, including wire arrays. The most important consequence of cold start is that spatially nonuniform plasma production is prolonged to almost the entire current rise time. Under these conditions, the Ampére force begins to play a dominant role in the plasma dynamics before the plasma-producing load is completely transformed into an accelerated plasma. The results of computations of wire-array vaporization are presented. A formula is proposed for estimating the highest attainable velocity of plasma flow into a heterogeneous liner driven by the Ampére force. It is shown that local imbalance between radial motion of the produced plasma and supply of the plasma-producing substance to be ionized leads to axially nonuniform breakthrough of magnetic flux into the liner, which precedes plasma collapse. The magnetic-flux breakthrough gives rise to a chaotic azimuthal–axial plasma structure consisting of radial plasma jets of relatively small diameter, which is called a radial plasma rainstorm. The breaking-through azimuthal magnetic flux obstructs further current flow in the breakthrough region. Analyses of Z-pinch implosion based on the theory of Rayleigh–Taylor instability or the snowplow model are incorrect under the plasma-rainstorm conditions. The processes taking place in a stagnant Z-pinch include conversion of the energy carried by the current-generated magnetic field into turbulent MHD flow of the ion component of the plasma, its convective mixing with magnetic field, heating, energy transfer from ions to electrons, and emission from the plasma. Under typical experimental conditions, emission plays a key role in the energy balance in an imploding pinch. Z-pinch is modeled by an electric-circuit component that has a time-dependent nonlinear impedance and consumes the magnetic energy supplied by a generator through a magnetically insulated transmission line (MITL). The peak power reached in the circuit is comparable to the peak soft X-ray power output emitted by the pinch in terms of magnitude and timing. Optimum matching conditions are formulated for the generator–MITL–pinch circuit. © 2004 MAIK “Nauka/Interperiodica”. [ABSTRACT FROM AUTHOR]

A method for determining the substance density distribution in the plasma produced by a current-driven implosion of multiwire tungsten liners at the Angara-5-1 facility is described. This method is based on the X-ray probing of plasma with radiation from a point source. As a source of this radiation, an X pinch is used. The time resolution (<2 ns) was determined by the X pinch. The probing of both the liner peripheral and near-axial regions is considered. The plasma-attenuated X-pinch radiation was detected using photographic film and p–i–n diodes in the first and second approach, respectively. The spatial resolutions (over the object) in both cases were determined by the sizes of the X pinch and p–i–n diodes and amounted to 4 and 44 μm, respectively. The design of the X-pinch and the dependence of its radiation characteristics (the burst time moment and the radiation-pulse power and duration) on the electric and design parameters of the circuit and load are described. The experimental data on the X-pinch radiation spectrum in the range of photon energies of 1–20 keV and the results of studying the substance-density distribution inside liners during the current-driven implosion at the Angara-5-1 facility are presented. [ABSTRACT FROM AUTHOR]

The set of diagnostic techniques used at the Angara-5-1 facility that make it possible to study the processes which accompany the ultrafast current-driven implosion of liners is described. This set includes electric methods and methods for the detection of various radiations. The liner-plasma shapes are visualized by detecting the intrinsic liner radiation in various wavelength ranges and actively probing liners in the visible and X-ray regions. Examples of the results of studying the current-driven implosion of cylindrical arrays of tungsten wires at the Angara-5-1 facility are presented. [ABSTRACT FROM AUTHOR]

Prolonged plasma creation in heterogeneous liners, in which the liner substance is separated into two phase states (a hot plasma and a cold skeleton), is investigated both experimentally and theoretically. This situation is typical of multiwire, foam, and even gas liners in high-current high-voltage facilities. The main mechanisms governing the rate at which the plasma is created are investigated, and the simplest estimates of the creation rate are presented. It is found that, during prolonged plasma creation, the electric current flows through the entire cross section of the produced plasma shell, whose thickness is comparable with the liner radius; in other words, a current skin layer does not form. During compression, such a shell is fairly stable because of its relatively high resilience. It is shown that, under certain conditions, even a thick plasma shell can be highly compressed toward the discharge axis. A simplified numerical simulation of the compression of a plasma shell in a liner with prolonged plasma creation is employed in order to determine the conditions for achieving regimes of fairly compact and relatively stable radial compression of the shell. © 2001 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]