S. A. Chaikovsky

Numerical calculation of the current specific action integral at the electrical explosion of wires

The electrical explosion of aluminum wires is numerically simulated in the magnetohydrodynamic approximation for the current density ranging from 107 to 1010 A/cm2 and times to explosion varying from 10−10 to 10−6 s. It is shown that, at current densities of 108−109 A/cm2, low-temperature explosion conditions change to high-temperature ones, when inertial forces preventing the wire dispersion play a decisive role. This transition is accompanied by a sharp change in the thermodynamic parameters (the temperature and the energy deposited into the wire by the instant of explosion increase by several times), and the action integral for this transition increases smoothly approximately threefold as the explosion characteristics (current density and time to explosion) change by two orders of magnitude. The instant of transition from the low-temperature explosion to the high-temperature one depends on the radial dimensions of an exploding wire and does not depend on the properties of the environment.

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.

''Water bath'' effect during the electrical underwater wire explosion

The results of a simulation of underwater electrical wire explosion at a current density >109A∕cm2, total discharge current of ∼3MA, and rise time of the current of ∼100ns are presented. The electrical wire explosion was simulated using a one-dimensional radiation-magnetohydrodynamic model. It is shown that the radiation of the exploded wire produces a thin conducting plasma shell in the water in the vicinity of the exploding wire surface. It was found that this plasma shell catches up to 30% of the discharge current. Nevertheless, it was shown that the pressure and temperature of the wire material remain unchanged as compared with the idealized case of the electrical wire explosion in vacuum. This result is explained by a “water bath” effect.

Use of vacuum arc plasma guns for a metal puff Z-pinch system

The performance of a metal puff Z-pinch system has been studied experimentally. In this type of system, the initial cylindrical shell 4 cm in diameter was produced by ten plasma guns. Each gun initiates a vacuum arc operating between magnesium electrodes. The net current of the guns was 80 kA. The arc-produced plasma shell was compressed by using a 450-kA, 450-ns driver, and as a result, a plasma column 0.3 cm in diameter was formed. The electron temperature of the plasma reached 400 eV at an average ion concentration of 1.85 · 1018 cm−3. The power of the Mg K-line radiation emitted by the plasma for 15–30 ns was 300 MW/cm.

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

Electrical explosion of metals in fast-rising megagauss magnetic fields

A criterion for the surface explosion of metal conductors in strong magnetic fields with the magnetic induction rising at rates over 4×1013 G/s has been obtained for a current skinning mode: the explosion occurs as the magnetic energy density at the metal surface becomes as high as a factor of 1.5–2 of the sublimation energy density for the metal under normal conditions.

Simulation of the runaway electron beam formed in a discharge in air at atmospheric pressure

A numerical model is proposed which allows one to describe the dynamics of the fast electrons injected from the head of an anode-directed streamer. The model is based on solving numerically 3-dimensional equations of motion of electrons. In the context of the model, the number of electrons which can be injected from the surface of a streamer is determined by the number of electrons in the Debye layer. Results of numerical calculations show that about 10% of the electrons in the Debye layer are switched to the mode of continuous acceleration. The electrons that have not switched to the runaway mode form a residual space charge cloud, whose dimensions are several centimeters, near a streamer. The space charge screens the streamer tip; therefore, the generation of the runaway electron beam does not resume.

Metastable states and their disintegration at pulse liquid heating and electrical explosion of conductors

The regularities of formation of metastable states and their disintegration under pulse liquid heating and electrical heating and explosion of conductors are studied. With a high energy flux density, the phase transitions occur with a high intensity of heat and mass fluxes, leading to spontaneous generation of a new phase and to phase explosion. The basic features of bubble-like disintegration in not uniformly superheated water and alcohol layers on the microheater are found. Regularities of matter disintegration with electrically exploded conductors are obtained. The metastable liquid disintegration is experimentally investigated for characteristic times of matter transfer to a metastable state of 1 to 4 µs; phase transitions during electric conductor explosion are studied at characteristic times of transfer to a metastable state to 200 ns. A common approach to describing the effects with radically different characteristic times of transfer of the matter to a metastable state is developed.

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.

Skin explosion of double-layer conductors in fast-rising high magnetic fields

An experiment has been performed to study the electrical explosion of thick cylindrical conductors using the MIG pulsed power generator capable of producing a peak current of 2.5 MA within 100 ns rise time. The experimental goal was to compare the skin explosion of a solid conductor with that of a double-layer conductor whose outer layer had a lower conductivity than the inner one. It has been shown that in magnetic fields of peak induction up to 300 T and average induction rise rate 3 × 109 T/s, the double-layer structure of a conductor makes it possible to achieve higher magnetic induction at the conductor surface before it explodes. This can be accounted for, in particular, by the reduction of the ratio of the Joule heat density to the energy density of the magnetic field at the surface of a double-layer conductor due to redistribution of the current density over the conductor cross section.