Influence of external media on the resistance stage of heating of thin wires by high-power current pulse

Summary form only given. As it was shown presently in the wire array experiments residuary basic mass with high-impedance conserved the initial location, and separate wires formed the plasma regions, extended to the axis, instead of a cylindrical shell. This posed the problem of a so-called "cold start" of discharge, the originality of which consists in the necessity to consider at once the four thermodynamic states of the object. The problem of "cold start" is especially important for general understanding of discharge process. A wire explosion in a gaseous and condensed media extends possibilities of study of phase transitions of the wire material. In the present work we studied the influence of the external media on the explosion of micron-size wires by a nanosecond discharge. The copper, nickel and tungsten wires of the diameter d=10-50 /spl mu/m were exploded in vacuum, water and oil by the current pulse with the growth rate of 10/sup 10/-10/sup 11/ A/s. The current pulse with the risetime of 200 ns and the amplitude up to 10 kA was produced by a generator based on a low-inductance capacitor, the discharge voltage being 20 kV. We discuss the experimental results on obtaining the wire explosion images in gaseous and liquid media with the help of hard X-ray radiation of a Z-pinch in the BIN facility diode (270 kA, 150 ns; FIAN). In numerical modeling we used a wide-range semi-empirical equation of state with account of phase transitions and metastable states. In accordance with the nucleation mechanism we estimate the explosion time and the theoretical limits of the energy deposited into the wires at the resistance stage of heating.