Search

The advent of X-pinch based compact radiographs has significantly expanded the application field of pulsed radiography for diagnostics of fast processes. The key point here is the spatial resolution which these radiographs can provide. The method for determining the size of the soft x-ray (SXR) source based on diffraction imaging of opaque metallic wires and their comparison with the diffraction pattern calculated for an extended source in a given spectral range is presented in the paper. The X-pinch source sizes have been measured taking into account the sensitometric characteristic of the film and the scanner characteristics. By this method it has been shown that the diameter of the X-pinch radiation source for current rise rates in the range 0.7–1.35 kA/ns varies slightly for the spectral range hv >3 keV.

Z-pinch experiments with hybrid deuterium gas-puff showed a possibility of efficient production of neutrons and multi-MeV ions. In the experiments on the GIT-12 generator, the total neutron yields are typically above 10 12 at a current of 3 MA. Since the intense pulsed neutron sources are desired for numerous applications as nuclear astrophysics 1 , subcritical experiments 2 , flash neutron radiography 3 , etc., neutron emission from the hybrid Z-pinches deserves to be thoroughly characterized. For this purpose, a comprehensive system of neutron diagnostic is exploited on the GIT-12 generator. Using scintillation detectors, nuclear activation methods, and bubble detectors, the fundamental features of neutron emission, e.g. energy spectrum, angular anisotropy, and number of non-DD reactions are evaluated. The analogous experiments on the HAWK generator allow comparison and scaling of the neutron emission at two different values of the Z-pinch current.

The paper describes a pulsed electron beam accelerator with release of electrons accelerated in a vacuum diode into the atmosphere. The electron energy in the beam is 1 MeV, the average adjustable electron current density is 10–200 А/см2, the average adjustable absorbed dose rate in silicon is 0.2 1011–4 1011 Gy/s, the irradiated area is several square centimeters, and the accelerating voltage pulse duration is adjustable in the range 50–200 ns.

The propagation of a nonlinear magnetic-field diffusion wave generated under the condition of an electrical explosion of flat conductors is investigated in the current skinning mode. Using a MIG terrawatt generator, a number of experiments are performed on electrical explosion of a copper foil, 100 μm in thickness and 5 mm in width, at the current amplitude up to 2.5 MA and its rise rate 100 ns. It is shown that under these conditions a plasma channel is formed by approximately 75-th ns from the current onset. The estimations, made considering the magnetic field enhancement on the foil edges, demonstrate that about 70–80 ns are required for the nonlinear magnetic-field diffusion wave to propagate from the foil edge to its center. A good agreement of the experimental data and the estimates suggested a conclusion that the plasma channel formation is due to the convergence of the nonlinear diffusion wave towards the longitudinal foil axis.

We report the results of investigations aimed at raising the peak output power of a THL-100 visible-range hybrid femtosecond laser system based on a XeF(C − A) photodissociation amplifier. The increase in power was achieved due to the shortening of the pulse duration at the system output by broadening the spectral profile of the second harmonic from 5.3 to 8 nm, which takes place in the transformation of a negatively chirped pulse of the fundamental frequency radiation in a nonlinear KDP crystal. After the KDP the radiation pulse was stretched to 1.8 ps in a prism stretcher and amplified in the XeF(C − A) amplifier. The energy obtained at the amplifier output was 1.2 J. After compression of the amplified output pulse, its duration was equal to 29.4 fs, which means that a peak output power of 40 TW was reached at the output of the laser system.

This paper presents an analysis of the results of an experiment on the explosion of copper foils, which was carried out on the MIG generator that produced a current through the foil at a level of 2 MA with a current pulse rise time of 100 ns. The foil length (along the z axis) was 20 mm, width (along the x axis) 5 mm, and thickness (along the y axis) 250 μm. It was observed that when the foils were exploded in megagauss magnetic fields with the foil current flowing along the z axis, the expansion of the plasma was extremely nonisotropic. The expansion of the foil material along the x axis was suppressed, and it expanded only along the y axis. An analysis of the experimental data carried out using a radiation magnetohydrodynamic code has shown that the nonisotropy of the expansion was associated with an enhancement of the magnetic field at the narrow side of the foil. As a result of the field enhancement, the magnetic pressure at the narrow foil side significantly exceeded the magnetic pressure in the center of the foil surface. Using an HSFC Pro optical camera (providing a frame exposure time of 3 ns), large-scale instabilities with wavelengths of 0.2–0.5 mm were detected on the foil surface. In appearance, these instabilities were similar to those developing in an exploding rod. It was suggested that the most likely cause of the appearance of the plasma structure observed in the experiment was the growth of flute instabilities.

A model has been considered to describe the development of a surface discharge over a conductor electrically exploding in a strong magnetic field. A simulation performed using this model has shown that in the initial stage of the conductor explosion, a plasma layer of several tens of micrometers thick with an electron temperature of several electronvolts is formed on the metal surface. Based on the theory of small perturbations, the development of thermal filamentation instabilities that form in the surface plasma layer has been analyzed. The characteristic growth rates and wavelengths of these instabilities have been determined. The theoretical results were compared with the results of experiments performed on the ZEBRA generator (providing load currents of amplitude about 1 MA and rise time about 100 ns) and on the MIG generator (providing load currents of amplitude about 2 MA and rise time about 100 ns). For the conditions implemented with these generators, the filamentation model gives rise times of thermal filamentation instabilities of tens of nanoseconds at characteristic wavelengths of the order of 100 μm. These values are in good agreement with experimental data, which indicates the adequacy of both the surface discharge development model and the filamentation model.

A set of neutron diagnostics including scintillation time-of-flight detectors, bubble detectors, and several kinds of threshold nuclear activation samples is used to obtain information about the yield and spectrum of the neutrons produced by a deuterium gas-puff z-pinch. The experiments are performed at a current of about 3 MA on the GIT-12 generator at the Institute of High Current Electronics of the Siberian Branch of Russian Academy of Sciences in Tomsk. The average neutron yield in the experiments in 2016 was $2.3 \times 10^{12}$ neutrons per single shot. Using the data obtained with the help of neutron activation diagnostics, the time-of-flight detectors have been absolutely calibrated and the broad energy spectrum of the produced neutrons was evaluated. By the calculations presented in this paper, due to the multi-MeV energies of deuterons generated in the pinch, up to 15% of the total neutron yield could be produced by nuclear reactions of deuterons with a stainless steel vacuum chamber and aluminum components of the diagnostic apparatus inside the chamber.

The paper deals with the soft X-ray backlighting based on the X-pinch as a powerful tool for physical studies of fast processes. Proposed are the unique small-size pulsed power generators operating as a low-inductance capacitor bank. These pulse generators provide the X-pinch-based soft X-ray source (hν = 1–10 keV) of micron size at 2–3 ns pulse duration. The small size and weight of pulse generators allow them to be transported to any laboratory for conducting X-ray backlighting of test objects with micron space resolution and nanosecond exposure time. These generators also allow creating synchronized multi-frame radiographic complexes with frame delay variation in a broad range.

Results of investigation of the parameters of the THL-100 hybrid laser system of visible range developed at the IHCE SB RAS in collaboration with the LPI RAS are presented. The laser system consists of the Ti:Sa Start-480M starting complex and the photodissociation XeF(C-A) amplifier with aperture of 24 cm. The starting complex provides 50-fs spectrally limited radiation pulses with energy of the second harmonic (475 nm) up to 20 mJ and 50-ps positively chirped radiation pulses with energy up to 5 mJ. The active medium of the XeF(CA) amplifier is created in the XeF2/N2 mixture upon exposure to VUV radiation of xenon excited by a highpower electron beam. It is demonstrated that record power of 14 TW is attained by amplification of negatively chirped radiation pulse with duration of 1.6 ps in the XeF(C-A) amplifier, and maximum energy of ~3.2 J is realized by amplification of positively chirped radiation pulse.

The results from the generation and amplification of positively chirped pulses of 0.05 ns duration at a central wavelength of 475 nm in a THL-100 laser system are presented. It is found that the initial complex allows the generation of such radiation pulses with Gaussian intensity profiles and energies of up to 7 mJ. When such pulses with energies of 2–4 mJ are amplified in an XeF(C-A) amplifier, it is possible to achieve a saturation mode and obtain at the output laser beams with energies of up to 3.2 J. The possibility of compressing subnanosecond pulses at a wavelength of 475 nm in a compressor based on diffraction gratings is demonstrated.

Z-pinches have been explored as efficient soft x-ray sources for many years. To optimize x-ray emission, various z-pinch configurations were tested. This paper presents data obtained with a hybrid gas-puff z-pinch imploding onto on-axis wires on a microsecond, multi-megaampere GIT-12 generator. In our previous experiments, the hybrid gas puff, i.e., an inner deuterium gas puff surrounded by an outer hollow cylindrical plasma shell, was used to produce energetic protons, deuterons, and neutrons up to 60 MeV [Klir et al., New J. Phys. 22, 103036 (2020)]. The behavior of the hybrid gas-puff z-pinch on GIT-12 was interpreted as a high-density plasma opening switch with a microsecond conduction time, 3 MA conduction current, nanosecond opening, and up to 60 MV stand-off voltage. These properties can be employed to transfer the current into an on-axis load with a high rise rate. In the recent experiments on GIT-12, we therefore placed single or multiple aluminum wires on the axis of the hybrid gas-puff z-pinch. Before a current sheath arrived at the axis, a coronal plasma was seen around the wire. A rapid increase in x-ray radiation was observed when the coronal plasma imploded onto the axis. The coronal plasma implosion resulted in a long (2 cm), narrow (∼mm) column radiating in the Al K-shell lines. With the single Al wire of 80 μm diameter, the K-shell x-ray output reached 5.5 ± 0.8 kJ in a 0.6 ± 0.1 TW peak power and 7 ± 1 ns pulse. The higher K-shell yield of 12 ± 2 kJ and peak K-shell power of 0.7 ± 0.1 TW were achieved with four 38 μm diameter Al wires. (Their cross section formed the corners of a square with 1 mm side.) The presence of the wires on the axis significantly suppressed ion acceleration and neutron production. Deuterium-deuterium (DD) neutron yields of about 1.2 × 1011 were 20 times smaller than the yields produced in shots without any wire. The DD neutron yield was increased up to 4.5 × 1011 when the Al wire was replaced by a fiber from deuterated polyethylene. A characteristic feature of the experiments with the (CD2)n fiber was a rapid expansion with the velocity approaching 900 km/s.

B-field measurements are crucial for the study of high-temperature and high-energy-density plasmas. A successful diagnostic method, ion deflectometry (radiography), is commonly employed to measure MGauss magnetic fields in laser-produced plasmas. It is based on the detection of multi-MeV ions, which are deflected in B-fields and measure their path integral. Until now, protons accelerated via laser–target interactions from a point-like source have been utilized for the study of Z-pinch plasmas. In this paper, we present the results of the first Z-pinch-driven ion deflectometry experiments using MeV deuterium beams accelerated within a hybrid gas-puff Z-pinch plasma on the GIT-12 pulse power generator. In our experimental setup, an inserted fiducial deflectometry grid (D-grid) separates the imploding plasma into two regions of the deuteron source and the studied azimuthal B-fields. The D-grid is backlighted by accelerated ions, and its shadow imprinted into the deuteron beams demonstrates ion deflections. In contrast to the employment of the conventional point-like ion source, in our configuration, the ions are emitted from the extensive and divergent source inside the Z-pinch. Instead of having the point ion source, deflected ions are selected via a point projection by a pinhole camera before their detection. Radial distribution of path-integrated B-fields near the axis (within a 15 mm radius) is obtained by analysis of experimental images (deflectograms). Moreover, we present a 2D topological map of local azimuthal B-fields B(r,z) via numerical retrieval of the experimental deflectogram.

This paper presents the results of experimental and theoretical studies of imploding metal-puff Z-pinches. The experiments were carried out on the MIG high-current pulse generator at a current level of about 2 MA and a current rise time of about 100 ns. A plasma gun was used to produce a plasma column with a tailored density profile through which the main electromagnetic pulse of the MIG generator was passed. The experiments have shown that pinches of this type, being compressed, are resistant to dynamic magneto-Rayleigh–Taylor (MRT) instabilities. The experimental results were analyzed using one-dimensional radiation magnetohydrodynamic simulations. It has been shown that in a pinch with a tailored density profile, the formation of a high-temperature plasma at the pinch axis and the generation of x-rays occur at the stagnation stage, i.e. under conditions close to Bennett equilibrium. At this stage, flute-like MRT instabilities develop, causing the pinch to decay.

In this paper, we give a review of some most powerful pulsed systems developed at the Institute of High Current Electronics (HCEI), Siberian Branch, Russian Academy of Sciences, and describe latest achievements of the teams dealing with these installations. Besides the presented high-power systems, HCEI performs numerous investigations using much less powerful generators. For instance, last year much attention was paying to the research and development of the intense low-energy (

Deuterium gas-puff z-pinches are very efficient laboratory sources of neutron pulses. Using a novel hybrid gas-puff load on the GIT-12 generator, a significant increase in the neutron yields up to 5.6 × 10 12 is reached. At the same time, a very broad neutron energy spectrum up to energies on the order of tens of MeV is observed. In these experiments, the neutrons are produced not only by the D(d,n)3He (DD) nuclear reaction but also by reactions of multi-MeV deuterons with the experimental hardware. The angular distribution of the neutron fluence and dependence of the fluence on the distance from the z-pinch are measured using neutron activation diagnostics. By this method, a number of produced non-DD neutrons and anisotropy of DD neutron emission are evaluated.

The latest results obtained in THL-100 hybrid femtosecond laser system operating in the visible spectral range are presented and the ways of the peak power increase of the laser beam are discussed.

The first experimental results obtained in visible range using the THL-100 multi-terawatt hybrid laser system after modernization of the starting femtosecond complex and the gas amplifier are reported. The modernization was performed to increase the output beam power at the expense of changing the configuration of the vacuum diode of the electron accelerator used for pumping of the XeF(C-A) amplifier. As a result, the increase of the VUV radiation pumping energy of the active medium of the XeF(C-A) amplifier by 30% is attained. This leads to doubling of the output laser beam energy of the XeF(C-A) amplifier.

The results of experimental studies aimed at increasing the power of THL-100 hybrid laser system are presented. The laser system consists of Ti:Sa front-end, operating at the central wavelength of 950 nm, second harmonic generator (SHG), prism stretcher, gas XeF(C-A) amplifier, and compressor based on fused quartz plates. In these experiments the SH spectrum broadening in a nonlinear crystal was realized, which allows to reduce its pulse duration from 50 to 30 fs. This radiation pulse was extended in the prism stretcher to 1.8 ps and amplified in the XeF(C-A) amplifier. At the output of amplifier 1.2 J energy was obtained. After compression, this laser pulse had duration of 29.4 fs and peak power of 40 TW. It is the second highest peak power value in visible spectrum range.

The efficiency of the X-ray point-projection radiography technique has been demonstrated on a terawatt pulse power generator using a detached compact current generator driving an X-pinch load. This technique has been approved in an experiment on the multiwire-array implosion performed at the Angara-5-1 generator with a peak power as high as 6 TW. The advantage of this experiment over earlier experiments on terawatt generators is in the use of a separate X-pinch driver, which makes it possible to arbitrarily vary the sample probing time. The X-pinch driver is connected to the load unit by means of a flexible low-inductance transmission line. The flexibility of the transmission line is an additional advantage of this technique, since it allows the accuracy of the X-ray radiography system adjustment to be improved and the X-pinch to be located near the plasma load. When compared to the laser method for producing a probe radiation source, the proposed technique features a smaller size, a lower cost of the facility, the absence of high-price optical elements, and a higher efficiency of X-ray generation. Owing to the small size of the synchronized X-pinch driver, it can be transported for use in experiments performed at other research organizations.

A pulsed source of hard X rays for high-speed radiography is described. The source is composed of a line pulse transformer, which is discharged into an accelerating tube with a vacuum diode, producing a high-voltage pulse across the tube with an amplitude of up to 750 kV. The effective energy of X-ray quanta, determined by attenuation in a 5-mm-thick steel plate, is 125 keV. The X-ray dose at a distance of 1 m from the anode is 10 and 15 mR at a 40- and 60-ns full width at half-maximum of the X-ray pulse, respectively. The diameter of the X-ray emitting spot is

Results of experimental and theoretical investigations of the hybrid (solid state/gas) visible-range femtosecond systems THL-100 (IHCE SB RAS) and THL-30 (P.N. Lebedev Physics Institute) based on a Ti : sapphire front end and a photochemical XeF(C–A) amplifier are reported. The front end generates 50-fs optical pulses with the second-harmonic (475 nm) energy of up to 5 mJ. The active medium of the amplifier is produced in a mixture XeF2 – N2 subjected to VUV radiation of xenon excited by an electron beam. The computer model is developed for calculating parameters of the XeF(C – A) amplifier, which is in a good agreement with experiments. In the THL-100 system with the 25-cm output aperture of the XeF(C–A) amplifier, a record visible-range femtosecond radiation peak power of 14 GW was obtained in a 50-fs pulse with the time contrast of above 108. The measured power of an amplified spontaneous emission of the XeF(C–A) amplifier in the angle of 0.2 mrad was 32 W. The result obtained testifies that the hybrid approach to the development of ultrahigh-power systems provides a high time contrast of radiation (greater than 1012 for the projected peak power of 100 TW). In the THL-30 system, prospects for shortening an amplified femtosecond pulse are studied and it is experimentally shown that by compensating a third-order dispersion in a hybrid system one can obtain pulses with duration of at least 27 fs with a recompression of amplified pulses in bulk glass. Also, a new phenomenon was observed of spectrum broadening and self-compression of negatively chirped femtosecond pulses in the visible range under a nonlinear interaction of wide-aperture beams with fused silica. This result opens prospects for development of the new methods of selfcompression for femtosecond pulses that are lacking physical limitations on pulse energy and realisation of self-compression of amplified pulses in the output window of the XeF(C–A) amplifier.

The results of the formation and amplification of positive chirped 0.1 ns laser pulse at a central wavelength of 470 nm in the laser system THL-100 are presented. It is shown that a front-end allows forming a radiation pulse with a Gaussian intensity profile and the energy up to 7 mJ. At amplification in XeF(C-A) amplifier of the pulse with 2-5 mJ energy a saturated mode is realized and 3.2 J output laser beam energy is reached.

The operation of a double-frame soft X-ray backlighting system on the basis of two table-top pulsed power generators and X-pinches is described. The system allows one to obtain two backlighting frames of a fast process with a nanosecond exposure (2–3 ns), a micrometer spatial resolution, and an adjustable delay between the frames. Backlighting registration of electrically exploding single aluminum wires was performed in the spectral range hν > 0.8 keV of the backlighting source using the double-frame system. The jitter time between X-ray pulses was within ±18 ns.

Experiments on a compact pulsed power generator with an amplitude of 200 kA and a 180-ns front width loaded on an X-pinch consisting of four aluminum wires with a diameter of 35 μm have been carried out. Experimental data and the results of calculations performed in the framework of an impact-radiation model have been used to determine parameters (temperature, density, linear mass) of the X-pinch hot spot at the moment of maximum compression. It is established that (i) a pulse of soft X-ray emission from the X-pinch is generated upon almost complete ejection of substance from the hot spot and (ii) hot-spot formation in the X-pinch proceeds under conditions close to the Bennett equilibrium.

THL-100 hybrid femtosecond laser system operating in the visible spectral range and the experimental results obtained by now are presented.

This paper reports on the creation of a THL-100 multi-terawatt hybrid laser system based on a Start-480M titanium-sapphire starting complex and photochemical XeF(C-A) amplifier with a 25-cm aperture. The complex produces 50-fsradiation pulses of energy up to 5 mJ at a second harmonic wavelength of 475 nm. The active medium of the amplifieris created in a XeF 2 /N 2 mixture under vacuum-ultraviolet radiation of electron beam-excited xenon. The results of firstexperiments on femtosecond pulse amplification in the active medium of the XeF(C-A) amplifier are presented todemonstrate that a laser beam peak power of 14 TW has been attained.Keywords: Chirped pulses; Femtosecond pulses; Hybrid (solid/gas) laser system; Photochemical XeF(C-A) amplifier;Second harmonic INTRODUCTIONAt present, the development of ultra-high power laser sys-tems with a pulse duration of 10–100 fs is based mainly onnear-infrared solid-state titanium-sapphire or parametric am-plifiers and amplification of positively chirped pluses, i.e.,stretched in time (0.5–1 ns), by linear frequency modulation(Strickland & Mourou, 1985) with their subsequent com-pression to the initial duration. Stretching of a pulse is re-quired to decrease its power below a threshold at which thebeam is self-focused; in solid-state systems, pulses are nor-mally stretched about 10

For the first time, the regime of a micrometer-size hot spot formation is impemented for an X-pinch in a plasma, which is fed from a current generator based on low-inductance capacitors and rapid current switches. The configurations of X-pinches, which can be used effectively as point sources of soft X-rays with this type of current generator, are determined. A prototype of a small-size radiation source for high-resolution point projection X-ray radiography has been constructed. The main parameters of X-pinch as a radiation source are analyzed and compared with X-pinch parameters in high-voltage setups with shaping lines. An analysis of the data on the operation of X-pinches in generators with different parameters has led to simple relations that can be used to select optimal initial X-pinch parameters.

The results of experiments with a three-ring large-area diode that were conducted on an MIG pulse generator are reported. The MIG generator makes it possible to produce in a matched load electrical pulses up to 2 TW in power with an FWHM of 50–60 ns (1.2–1.4 TW and 80–90 ns in our experiments). In the operating mode of the generator, the current amplitude through the load is 2 MA (the current of a relativistic electron beam) at a diode voltage of ≈ 500 kV. As a load, a large-area vacuum diode with three ring-shaped cathodes is used. It is shown that about 20% of the energy stored in the capacitor bank can be converted to the energy of a relativistic electron beam by matching the output resistance of the MIG generator to the load resistance. When the beam slows down on a condensed foil target, the parameters of the resulting source are the following: the mean energy of X-ray quanta is ≈ 70 keV; irradiated area, 500 cm2; pulse FWHM, 65 ns; energy flux in the spectrum, 2 J/cm2; and percentage of X-ray radiation (10–100 keV) in the flux, ≈ 50%.

Ultrafine materials were produced under conditions of extreme energy effects on the mixture of graphite and Ni-Mn catalysts. For the purpose to obtain various forms of carbon, including diamond-like forms, experiments were performed on a MIG high-current generator with the current amplitude of 2-2.5 MA and current rise time of 100 ns. The composition of the explosion products was studied using x-ray diffraction and x-ray phase analyses, the impedance spectroscopy, optical and scanning electron microscopy, x-ray microanalysis and energy dispersive x-ray analysis and the laser confocal Raman microscopy. It was found that the carbon in the studied materials is in the graphite, diamond-like (the faceted particles or agglomerates of faceted particles in size about or less than 250 nm) and amorphous forms.

Radiography of short-living objects using X-pinch radiation is a new perspective direction in diagnostics developed at the P. N. Lebedev Institute of Physics. High spatial (up to a few tenth of a micrometer) and temporal resolutions (up to 0.1 ns) achieved with the use of the X pinch is extremely interesting to the researches of transient processes and substances in extreme states. The X pinch is produced by two or more crossed wires (with wire diameters up to 30 µm) exploded under the influence of current running through them. Scanning radiation is generated in a dense high-temperature plasma (up to several kiloelectron volts) arising in the region of wire crossing. Among the main requirements on the generator used to create the X pinch are current amplitudes of 150–300 kA and rates of current increase of 1–2 kA/ns. Up to now, these current pulse parameters have been provided only by bulky stationary generators weighing from 300 kg to several tons. In the present paper, a small-size (weighing 70 kg) high-current pulse generator (with current amplitude exceeding 300 kA and pulse rise time of 200 ns) of soft x-ray radiation from high-temperature X-pinch plasma is described.

The paper reports on recent developments in the field of design, manufacturing, and testing of compact capacitive energy stores with an energy transfer time of 100 ns, namely high-voltage pulse capacitors, capacitor-switch assemblies, and artificial forming lines, at the High Energy Density Department of the Institute of High Current Electronics. A characteristic feature of the developments is the possibility to create variously shaped capacitive stores with an energy density of up to 350 J/dm3, low inductance of 10–20 nH, and capability of withstanding pulse currents of up to 100 kA. The devices find application in drivers of hard1 and soft2,3 X-ray sources and can be used in pulse power supply systems of different accelerators.

Since 2006, researches of the X-pinch dynamics have been carried out at the Institute of High Current Electronics (Tomsk, Russia) on compact pulsed power generators (100–250 kA, 110–180 ns) of our own design. Considerable amount of the experimental data was accumulated during these years. It was shown experimentally that at the region of initial cross point of the X-pinch wires a plasma neck with a length of 200–300 microns develops, where a small scale constriction is formed immediately before an X-ray burst producing a "hot spot"1. The "hot spot" size does not exceed 2.5 microns in a spectral range of quantum energies hv > 3 keV for X-pinches consisting of two-four thin Mo or W wires. The full width at half maximum (FWHM) of an x-ray pulse for such X-pinches is less than 2 ns. The measured length of the plasma neck coincides well with that resulting from the numerical simulations of the X-pinch dynamics2. The compact pulsed power generators with X-pinch loads have been tested as a diagnostic tool of the ultrafast physical processes in different researches (electrical explosions of wires and foils, wire array implosions, etc.)3'4. On the base of these generators, a synchronized multiframe complex for radiography with a nanosecond exposure time has been created and tested in the experiments5.

A small low-inductance PC 200-1.5 capacitor with pulsed charging to 200 kV has been developed. In this capacitor, which has an inductance of 1.5 nF, a combined paper-film insulator impregnated with castor oil is employed. To reduce the edge effect in the capacitor, a method of splitting the insulator into thin layers in the region of the plate’s sharp edge by way of mutually shifting the capacitor’s plates. PC 200-1.5 devices were used as peak capacitors at the LTD-100R stage of a high-power pulse generator and allowed the output power to be increased by ∼25%. The service life of these capacitors exceeded 2 × 103 pulses.

Results of works on a fast energy output from a capacitor by using a pseudospark gap are described. For this purpose, an HCEIcap 50-0.1 capacitor was specially designed with a combined paper-film insulation impregnated with a castor oil with three types of films: mylar, polypropylene, and teflon. A TDI1-50K/50 pseudospark gap was modified so that the total circuit inductance did not exceed 10 nH. During tests at 40–45 kV, current pulses of ∼100 kA with a 2.4 × 1012-A/s rise rate were obtained.

Argon K-shell plasma radiation source experiments were carried out on the GIT-12 generator [Bugaev, S.P. et al., 1997, Russian Phys. Journal, 40, 38] for a long (300 ns) implosion regime. The performance of a shell-on-solid-fill double gas puff was characterized in the experiments with and without an external axial magnetic field. The maximum Ar K-shell radiation yield registered in the experiments without an axial magnetic field was at the level of 1100 J/cm. This yield is consistent with the theoretically predicted yield for a short (100 ns) implosion regime. The experiments showed that the initial magnetic field which provides stabilization of the shell-on-solid-fill double gas puff was lower than that required for stabilization of a single annular gas puff. Satisfactory stabilization of the double gas puff was observed at an initial axial magnetic field of 1.4 kG. The maximum Ar K-shell radiation yield registered in the experiments with the axial magnetic field did not exceed 400 J/cm. A sharp reduction of the K-shell yield cannot be explained only by taking into account the energy losses associated with the compression of the axial magnetic field.

The pd reaction (pd → He + γ (5.5 MeV)) is studied in the astrophysical energy collision range of protons with deuterons using the hydrogen liner in the inverse Z-pinch configuration at the pulsed power generator MIG (HCEI, Tomsk). Fundamental characteristics of this and other light-nucleus reactions at ultralow energies are important for problems of basic physics and astrophysics. The knowledge of the energy distribution of the nuclei participating in these reactions is important due to their exponential type of dependence on the collision energy. Two experimental techniques were designed and tested for recovering the energy distribution of liner protons incident on the CD2 target by using optical detectors and ion collectors. It is shown that the combined use of these two techniques could provide relevant information on the energy distribution of the accelerated protons in the liner. The estimates of the upper limits for the astrophysical S factor and effective cross section of the pd reaction in the proton-deuteron collision energy range of 2.7–16.7 keV are obtained: \(\bar S_{pd} (E_{pd} = 10.2 keV) \leqslant 2.5 \times 10^{ - 7} MeV b;\overline \sigma _{pd} (2.7 \leqslant E_{pd} \leqslant 16.7 keV) \leqslant 4 \times 10^{ - 33} cm^2 \).

This paper presents the simulation results of electrical explosion of thin Al wires at a current rise time of several tens of nanoseconds and at a current density of ∼108 A/cm2. Studies include the matter phase transfers and magnetohydrodynamic (MHD) model. A two-dimensional MHD model based on the particle-in-cell method is used to consider the formation of striations and a low-density plasma corona surrounding the wire. The striations are shown to occur through evolving overheat instabilities early in the explosion, when the conductor material is in the liquid or two-phase states. The process results from the decrease in liquid metal conductivity with increasing temperature and decreasing density.

This paper is devoted to measurement of the astrophysical S factor and cross sections of the d + d → 3He + n reaction at ultralow deuteron-collision energies. Formation of the flow of the accelerated deuterons incident on the CD2 solid-state target was made within the scheme of the inverse Z pinch. The liner in the initial state was a hollow supersonic deuterium jet of radius of 15 mm and length of 20 mm. The experiment was carried out at the pulsed high-current accelerator (I=950 kA, τ=80 ns) of the Institute of High-Current Electronics (Tomsk, Russia). Measurement of the deuteron energy distribution was performed through an analysis of the time distributions of the intensity of the liner radiation (Hα and Hβ lines) generated during the liner radial movement from the axis. Recording of this radiation was carried out by optical detectors placed along the direction of the liner moving from its axis. The measured value of the astrophysical S factor for the dd reaction at the average deuteron collision energy E coll=3.69 keV was equal to S(E coll=3.69 keV)=58.2±18.1 keV b. The dd-reaction cross section calculated using the found value of the S factor and known representation of the reaction cross section as the product of the barrier factor and the astrophysical S factor was σ dd n (E coll=3.69 keV)=(1.33±0.41)×10−30 cm2.

A method and results of measurements are presented of the ion energy distribution in a deuterium liner accelerated in the inverse Z-pinch, in which the plasma is accelerated electrodynamically from the liner axis. Knowledge of the deuteron energy distribution is of primary importance for the correct interpretation of the experimental results from the study of the dd-reaction in the range of infralow energies with the use of a liner plasma. Experiments were carried out in a high-current pulsed accelerator (I=950 kA, τ=80 ns) at the Institute of High-Current Electronics of the Siberian Division of the Russian Academy of Sciences (Tomsk, Russia). In the initial state, the liner is a supersonic hollow deuterium jet 32 mm in diameter and 20 mm in length. The liner parameters were measured with the help of optical detectors of H α and H β deuterium lines and magnetic probes arranged in a radial direction (along the direction the liner expansion). In addition, scintillation spectrometers and BF3 counters were used to measure the intensity of the neutron flux produced in the d + d → 3He + n reaction. The results obtained by simultaneously analyzing the data from magnetic probes, optical detectors, and neutron detectors point to the possibility of using a rather simple method for measuring the parameters of the liner accelerated up to energies of 3–6 keV.

The Z-pinch experiments with deuterium gas-puff surrounded by an outer plasma shell were carried out on the GIT-12 generator (Tomsk, Russia) at currents of 2 MA. The plasma shell consisting of hydrogen and carbon ions was formed by 48 plasma guns. The deuterium gas-puff was created by a fast electromagnetic valve. This configuration provides an efficient mode of the neutron production in DD reaction, and the neutron yield reaches a value above 1012 neutrons per shot. Neutron diagnostics included scintillation TOF detectors for determination of the neutron energy spectrum, bubble detectors BD-PND, a silver activation detector, and several activation samples for determination of the neutron yield analysed by a Sodium Iodide (NaI) and a high-purity Germanium (HPGe) detectors. Using this neutron diagnostic complex, we measured the total neutron yield and amount of high-energy neutrons.

This paper is devoted to examination of the possibility of using deuterium inverse Z-pinch for investigation of the dd reaction at ultralow deuterium collision energies. The experiment was carried out at the Institute of High-Current Electronics (Tomsk) using the high current accelerator (the current pulse amplitude is 850 kA, the high-voltage pulse duration is ∼ 80 ns). The characteristic data of the deuterium liner accelerated by the inverse Z-pinch process up to (2.8– 7.2)×10 7 cm/s were measured for the first time. The character and values of γ and neutron radiation occurred during the liner acceleration process were examined. The application of fast scintillator neutron detectors with definite size and a deuterium target located at distances more than 140 mm from the liner axis was demonstrated to allow reliable time separation of “useful” events from background events.