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.

Study of radiative characteristics of Al metal-puff Z-pinches has been carried out in the experiments on the GIT-12 generator. The generator was operated in a microsecond mode that provides 4.7-MA current with the current rise time of 1.7 μs in a short-circuit load at a charging voltage of 50 kV. A Z-pinch load under investigation consisted of a metal puff surrounded by a plasma shell. The Al metal puff was created on the axis by evaporation of the electrode substance in a vacuum arc discharge. The outer plasma shell was formed at a diameter of 350 mm with the help of 48 plasma guns. Measurements of the radiation power and yield were carried out with a set of x-ray vacuum diodes and photoconducting detectors. During the experiments, the data on the Al K-shell radiation power and yield were obtained for two different configurations of the Al metal-puff Z-pinches and for a case, when the Al metal puff was used without the outer plasma shell. The experimental data were compared to the theoretical predictions of an expected K-shell yield at a certain current level in order to estimate the efficiency of a new type of K-shell plasma radiation source. Performance of the Al metal-puff Z-pinch with the outer plasma shell as a K-shell plasma radiation sources was also compared with that of the gas-puff-on-wire array and planar wire array loads operating in the microsecond implosion regime. Up to now, the highest Al K-shell radiation power and yield were achieved in our previous experiments with planar wire arrays: 200 GW/cm and 6.5 kJ/cm, respectively. These radiation parameters were reached at the peak implosion current of 3.6 MA. The maximum Al K-shell radiation power and yield observed in the experiments with Al metal-puff Z-pinches with the outer plasma shell were 400 GW/cm and 4.5 kJ/cm, however the peak implosion current was only 2.4 MA. This means that the efficiency of the K-shell plasma radiation source based on the Al metal-puff with the outer plasma shell is significantly higher.

Z-pinch experiments with a hybrid configuration of a deuterium gas puff have been carried out on the HAWK (NRL, Washington, DC) and GIT-12 (IHCE, Tomsk) pulsed power generators at 0.7 MA and 3 MA currents, respectively. On GIT-12, neutron yields reached an average value of 2 × 1012 neutrons, and deuterons were accelerated up to an energy of 30 MeV. This was 50 times the ion energy provided by the generator driving voltage of 0.6 MV and the highest energy observed in z-pinches and dense plasma foci. To confirm these unique results independently on another device, we performed several experimental campaigns on the HAWK generator. Comparison of the experiments on GIT-12 and HAWK helped us to understand which parameters are essential for optimized neutron production. Since the HAWK generator is of a similar pulsed power architecture as GIT-12, the experiments on GIT-12 and HAWK are important for the study of how charged-particle acceleration scales with the current.

Acceleration of ions to multi-MeV energies is investigated in various plasma devices to better understand processes in astrophysical plasmas and to develop efficient accelerators for a variety of applications. This paper reports the production of proton, deuteron, and electron beams in a z-pinch—a cylindrically symmetric plasma column that is compressed by its own magnetic field. For this work, the GIT-12 pulsed-power generator was used to drive a novel configuration of z-pinch that dramatically enhanced ion acceleration associated with disruption of the current by instabilities in the compressed plasma. During the disruption of 3 MA current, hydrogen ions were accelerated up to at least 50 MeV, which is almost a hundred-times the ion energy provided by the generator driving voltage of 0.6 MV. Under optimal conditions, the total numbers of hydrogen ions with energies above 20 and 50 MeV were 4 × 1013 and 1011, respectively. Accelerated deuterons produced one 20 ns (full width at half maximum) pulse of fast neutrons via D(d, n)3He and other nuclear reactions. A maximum neutron output of (1.0 ± 0.2) × 1012 neutrons/sr was observed downstream, i.e., in the anode to cathode direction. In this direction, the maximum neutron energy reached 58 ± 7 MeV. Both ion and neutron beams in our experiment reached an end-point energy of about 60 MeV, which is the highest value observed in pulsed-power devices. A localized peak voltage of ≳60 MV was driven by the inductive energy that was stored around the plasma column and that was extracted during a sub-nanosecond current drop. Considering the natural occurrence of current-carrying columns in laboratory and space plasmas, the current interruption observed in z-pinches could represent a more general physical process that contributes to the efficient conversion of magnetic energy into the energy of particle beams in various plasmas.

Mega-ampere dense plasma foci and deuterium gas-puff z-pinches can accelerate deuterons to multi-MeV energies. Diagnostic measurements of the properties of these ions provide information about ion acceleration in z-pinch plasmas. In particular, the results from ion pinhole cameras seem to be useful for the discussion of ion acceleration mechanisms. Recently, we have used various configurations of ion pinhole cameras in deuterium gas-puff experiments on the GIT-12 generator at the Institute of High Current Electronics in Tomsk and on the HAWK generator at the US Naval Research Laboratory in Washington. The stack of radiochromic films and CR-39 solid-state nuclear track detectors recorded deuterons with energies up to 30 MeV. From our ion diagnostics, we obtained the spatial distribution of the ion source and the ion-beam divergence during the ion emission. This ion-beam divergence was found to decrease with increasing deuteron energy. At 20 MeV, the divergence of each of the individual micro-beams that composed the ion source was on the order of 10 mrad. The deflection of each micro-beam due to the azimuthal magnetic and/or radial electric fields resulted in radial stripes observed by the beam-profile detectors. By analyzing the ion pinhole images, we found that the deuterons were emitted both from a central spot and from a ring-shaped region with a rather large diameter, on the order of 1 cm. The origin and particular diameter of this ring is attributed to the geometry of the electrodes and to the distribution of the current density before the disruption.

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.

The work is devoted to studying a “zippering” effect arising in a process of Al metal-puff liner implosions on the pulse power generator GIT-12 (the load current of 4.7 MA with the rate of 3 kA/ns and the current rise time of 1.7 μs). Since a “zippering”” effect is a consequence of an initial distribution of a conductive substance of a liner plasma shell, consideration of a liner compression dynamics along its height gives an idea about an initial compression conditions of a plasma shells. An influence of a “zippering” effect on an Al K-shell radiation output power is considered. The relationship between a “zippering” effect and a density gradient of the Al metal-puff liners along its axis for various plasma gun designs is considered. An inclination angle of a plasma shell outer boundary varies depending on a plasma gun design. If a plasma jet flows out from a hole in the plasma gun anode, a liner shell with a traditional inclination angle is formed at which a plasma shell expands from cathode to anode. If cathode and anode of a plasma gun are located in the same plane, a liner shell with an inverse inclination angle is formed at which the plasma shell expands from anode to cathode.

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 5.6×1012 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.

Studies of K-shell plasma radiation sources were performed on the GIT-12 generator (4.7 MA, 1.7 μs). In the experiments, a new type of load configuration was used to form the Z-pinch plasma – a gas puff with an outer plasma shell. Noble gases neon and argon were used as working gases. The gas puff consisted of two cascades: a hollow cylindrical shell outside and a solid jet inside. The outer plasma shell was created with the help of plasma guns located on a diameter of 350 mm. A distinctive feature of these studies is that the experiments with the plasma radiation source were carried out in the microsecond implosion regime usually leading to a significant decrease in the efficiency of generation of K-shell x-rays. The use of the Z-pinch load of a new type significantly improved the efficiency of the microsecond plasma radiation source. As a result of optimization of the initial gas-puff parameters, a neon K-shell radiation yield of 14.7 kJ/cm at a peak implosion current of 3.5 MA was achieved. In experiments with argon gas puffs, the radiation yield reached 1.9 kJ/cm at a peak implosion current of 3.1 MA.

The acceleration of hydrogen ions up to 35 MeV is observed in the z-pinch experiments on the GIT-12 generator at a 3 MA current and 0.6 MV driving voltage. High ion energies are obtained with a novel configuration of a deuterium gas-puff z-pinch. In this configuration, a hollow cylindrical plasma shell is injected around an inner deuterium gas puff to form a homogeneous, uniformly conducting layer between electrodes at the initial phase of z-pinch implosion. The stable implosion at the velocity up to 650 km s(-1) is important to deliver more current onto the z-pinch axis. Magnetohydrodynamic instabilities become apparent first at stagnation. After the disruptive development of m = 0 instabilities, similar to 20 ns pulses of high-energy photons, neutrons, electrons, and ions are observed. The average neutron yield is 2 x 10(12). The ion emission is characterized by various diagnostic techniques including those based on the usage of neutron-producing samples. When a large neutron-producing sample is placed onto the axis below a cathode mesh, the neutron yield is increased up to (1.1 +/- 0.3) x 10(13). Considering a similar to 130 kJ energy input into z-pinch plasmas and magnetic field, this implies the neutron production efficiency of similar to 10(8) neutrons per one Joule of the z-pinch energy.

Acceleration of high energy ions was observed in z-pinches and dense plasma foci as early as the 1950s. Even though many theories have been suggested, the ion acceleration mechanism remains a source of controversy. Recently, the experiments on the GIT-12 generator demonstrated acceleration of ions up to 30 MeV from a deuterium gas-puff z-pinch. High deuteron energies enable us to obtain unique information about spatial, spectral and temporal properties of accelerated ions. In particular, the off-axis ion emission from concentric circles of a ∼1 cm diameter and the radial lines in an ion beam profile are germane for the discussion of acceleration mechanisms. The acceleration of 30 MeV deuterons can be explained by the fast increase of an impedance with a sub-nanosecond e-folding time. The high (>10 Ω) impedance is attributed to a space-charge limited flow after the effective ejection of plasmas from m = 0 constrictions. Detailed knowledge of the ion acceleration mechanism is used with a neutron-producing catcher to increase neutron yields above 1013 at a current of 2.7 MA.

The acceleration of hydrogen ions up to 35 MeV is observed in the z-pinch experiments on the GIT-12 generator at a 3 MA current and 0.6 MV driving voltage. High ion energies are obtained with a novel configuration of a deuterium gas-puff z-pinch. In this configuration, a hollow cylindrical plasma shell is injected around an inner deuterium gas puff to form a homogeneous, uniformly conducting layer between electrodes at the initial phase of z-pinch implosion. The stable implosion at the velocity up to 650 km s−1 is important to deliver more current onto the z-pinch axis. Magnetohydrodynamic instabilities become apparent first at stagnation. After the disruptive development of m = 0 instabilities, ∼20 ns pulses of high-energy photons, neutrons, electrons, and ions are observed. The average neutron yield is 2 × 1012. The ion emission is characterized by various diagnostic techniques including those based on the usage of neutron-producing samples. When a large neutron-producing sample is placed onto the axis below a cathode mesh, the neutron yield is increased up to (1.1 ± 0.3) × 1013. Considering a ∼130 kJ energy input into z-pinch plasmas and magnetic field, this implies the neutron production efficiency of ∼108 neutrons per one Joule of the z-pinch energy.

The experiments have been carried out on the GIT-12 generator to characterize the effect of the anode and cathode meshes installed on the path of the gas flow on the initial gas density distribution, the gas-puff implosion dynamics, and the resulting radiative characteristics of the Ne K-shell plasma radiation source (PRS) operated in the microsecond implosion regime. The experiments showed that the obstacles located directly on the way of the main gas flow have the greatest influence on the gas distribution in the interelectrode gap of the generator. At all other factors being the same, the presence or absence of the anode and cathode meshes changed significantly the implosion dynamics and radiative characteristics of the Ne K-shell PRS. In our experiments, we observed two-fold decrease in the K-shell radiation yield and more than four-fold decrease in the K-shell radiation power. These observations should be taking into account in development of the gas-puff loads for Z-pinch experiments.

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.

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.

Characteristics of Z-pinch plasma radiation in the form of a double shell neon gas puff with outer plasma shell are investigated in the microsecond implosion mode. Experiments are performed using a GIT-12 mega-joule generator with load current doubler having a ferromagnetic core at implosion currents up to 5 MA. Conditions for matching of the nonlinear load with the mega-ampere current multiplier circuit are determined. The load parameters (plasma shell characteristics and mass and geometry of gas puff shells) are optimized on the energy supplied to the gas puff and n energy characteristics of radiation. It is established that the best modes of K-shell radiation in neon are realized for such radial distribution of the gas-puff material at which the compression velocity of the shell is close to a constant and amounts to 27–30 cm/μs. In these modes, up to 40% of energy supplied to the gas puff is converted into K-shell radiation. The reasons limiting the efficiency of the radiation source with increasing implosion current are analyzed. A modernized version of the energy supply from the current doubler to the Z-pinch is proposed.

A novel configuration of a deuterium z-pinch has been used to generate a nanosecond pulse of fast ions and neutrons. At a 3 MA current, the peak neutron yield of (3.6 ± 0.5) × 1012 was emitted within 20 ns implying the production rate of 1020 neutrons/s. High neutron yields resulted from the magnetization of MeV deuterons inside plasmas. Whereas deuterons were trapped in the radial direction, a lot of fast ions escaped the z-pinch along the z-axis. A large number of >25 MeV ions were emitted into a 250 mrad cone. The cut-off energy of broad energy spectra of hydrogen ions approached 40 MeV. The total number of >1 MeV and >25 MeV deuterons were 1016 and 1013, respectively. Utilizing these ions offers a real possibility of various applications, including the increase of neutron yields or the production of short-lived isotopes in samples placed in ion paths. On the basis of our experiments with various samples, we concluded that a single shot would have been sufficient to obtain GBq positron activity of 13N isotopes via the 12C(d,n)13N reaction. Furthermore, the first z-pinch generated neutron radiograph produced by ≈20 ns pulses is presented in this paper.