A. V. Shishlov

Study of the strata formation during the explosion of a wire in vacuum

The formation of strata during fast electrical explosions of aluminum wires at current densities of (1–1.4)×108 A/cm2 has been studied experimentally. To observe the strata, the soft x radiation generated at the hot point of an x-pinch was used. It has been revealed that strata are formed before the voltage collapse, that is, at the stage of heating of the wire metal. Two wire explosion modes were realized: with and without cutoff of the current carried by the exploding wire. Analysis of the experimental results shows that the stratification is most probably due to the thermal instability that develops as a consequence of the increase in metal resistivity with temperature.

Wire explosion in vacuum: Simulation of a striation appearance

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.

Study of metal conductivity near the critical point using a microwire electrical explosion in water

Electrical explosion of aluminum and tungsten microwires in water was studied both experimentally and numerically. The experimental range of currents through the wire was 0.1–1 kA for explosion times of 40–300 ns and current densities up to 1.5×108 A/cm2. The experimental results were interpreted on the basis of magnetohydrodynamical simulation with various metal conductivity models. A comparison of the experimental and numerical results allows the conclusion to be drawn that the metal conductivity models used in this work are adequate.

Long time implosion experiments with double gas puffs

Long time implosion experiments with argon double gas puffs have been conducted on the GIT-12 [S. P. Bugaev et al., Izv. Vyssh. Uchebn. Zaved., Fiz. 40, 38 (1997)] generator at the current level of 2.2–2.4 MA. A double gas puff was used as one of the alternative ways to improve implosion stability at implosion times from 230 to 340 ns. The results of these experiments were compared with two-dimensional snowplow simulations. The experiments and the simulations show that the final pinch is sufficiently stable when the inner-to-outer shell mass ratio is greater than 1. The maximum argon K-shell yield obtained in the experiments is 740 J/cm with 220 GW/cm radiation power. At the long implosion times, the K-shell yield obtained in the double gas puff implosion is twice the K-shell yield of a 4-cm-radius single gas puff, with more than an order of magnitude increase in radiation power.

The K-shell radiation of a double gas puff z-pinch with an axial magnetic field

A double shell z -pinch with an axial magnetic field is considered as a K -shell plasma radiation source. One-dimensional radiation-hydrodynamics calculations performed suggest that this scheme holds promise for the production of the K -shell radiation of krypton ( h ν ≈ 12–17 keV). As a first step in verifying the advantages of this scheme, experiments have been performed to optimize a neon double-shell gas puff with an axial magnetic yield for the K -shell yield and power. The experiments show that the application of an axial magnetic field makes it possible to increase the K -shell radiation power and reduce the shot-to-shot spread in the K -shell yield. Comparisons between the experiments and modeling are made and show good agreement.

An experimental study of the effect of Rayleigh-Taylor instabilities on the energy deposition into the plasma of a Z pinch

The mechanism for the heating of the plasma of a Z pinch due to the generation of toroidal magnetic structures (magnetic bubbles) which are formed in the plasma as a result of the penetration of the azimuthal magnetic field into the gas puff plasma was investigated experimentally. The experiments were performed with single-shell and double-shell gas puffs (60/30 mm in diameter) on the IMRI-4 generator (I/sub max/=350 kA, T/4=1.1 /spl mu/s). The gases used for the gas puff material were neon, argon, and krypton. Electrical investigations have shown that the final resistance of the plasma depends on the linear mass of the gas puff and equals to /spl sim/0.06/spl divide/0.1 /spl Omega/, which coincides in the order of magnitude with the prediction of the theory of an enhanced energy deposition into the plasma of a Z pinch. Probing of the plasma was carried out with a YAG:Nd/sup 3+/ laser with a wavelength of 532 nm, a pulse energy of the order of 30 mJ, and a pulse full-width at half-maximum of /spl sim/5 ns. Polarimetry has shown that at the stage of stagnation of a Z pinch, there are regions inside the plasma column where the radial distribution of the electron density has a local minimum. The rotation of the polarization plane of the electromagnetic wave probing the plasma suggests that some portion of the azimuthal magnetic field of the Z pinch is captured by the current loop (a magnetic bubble is formed). The magnetic field inside the magnetic bubble is, on the average, 600/spl divide/800 kG and coincides in the order of magnitude with the magnetic field near the pinch boundary.

Deuterium gas puff Z-pinch at currents of 2 to 3 mega-ampere

Deuterium gas-puff experiments have been carried out on the GIT-12 generator at the Institute of High Current Electronics in Tomsk. The emphasis was put on the study of plasma dynamics and neutron production in double shell gas puffs. A linear mass density of deuterium (D2) varied between 50 and 85 μg/cm. Somewhat problematic was a spread of the D2 gas at a large diameter in the central anode–cathode region. The generator operated in two regimes, with and without a plasma opening switch (POS). When the POS was used, a current reached a peak of 2.7 MA with a 200 ns rise time. Without the POS, a current rise time approached 1500 ns. The influence of different current rise times on neutron production was researched. Obtained results were important for comparison of fast deuterium Z-pinches with plasma foci. Average DD neutron yields with and without the POS were about 1011. The neutron yield seems to be dependent on a peak voltage at the Z-pinch load. In all shots, the neutron emission started during stagnat...

The Effects of Preheating of a Fine Tungsten Wire and the Polarity of a High-Voltage Electrode on the Energy Characteristics of an Electrically Exploded Wire in Vacuum

Results obtained from experimental and numerical studies of tungsten wires electrical explosion in vacuum are presented. The experiments were performed both with and without preheating of the wires using positive or negative polarity of a high-voltage electrode. Preheating is shown to increase energy deposition in the wire core due to a longer resistive heating stage. The effect was observed both in single wire and wire array experiments. The evolution of the phase state of the wire material during explosion was examined by means of a one-dimensional numerical simulation using a semiempirical wide-range equation of state describing the properties of tungsten, with allowance made for melting and vaporization

Electric explosion of fine tungsten wires in vacuum

A study is made of the breakdown of a fine wire during its electric explosion in vacuum. The problem of how the wire diameter, the rate of energy deposition in the wire, and the insulation of the electrode surface near the electrode-wire contact influence the wire explosion and the accompanying breakdown is investigated experimentally. The wire explosion was performed at a positive polarity of the high-voltage electrode. A current density growth rate of 6×1011–5×1016 A/(s cm2) is achieved. It is shown that the breakdown along a wire is similar in many respects to the gas breakdown. The insulation of the wire surface makes it possible to avoid breakdown and to increase the deposited energy to values sufficient for the wire sublimation.

Electrical explosion of conductors in the high-pressure zone of a convergent shock wave

The effect of the environmental pressure on the electrical explosion of a conductor (fine tungsten wire of diameter 30 μm) in an insulating liquid (distilled water) is studied. The pressure in the water is produced by exploding a multiwire array with the test conductor on its axis. Along with the experiment, the magnetohydrodynamic simulation of the explosion is carried out. It is shown that a high pressure produced in the explosion zone retards the electrical explosion of the conductor and, consequently, increases the explosion energy.