The resistance stage of heating of wires by high-power current pulse in different external media

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=25 μm were exploded in open air and water by the current pulse with the growth rate of 1010-1011 A·s-1. The current pulse with the rise-time 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. Electrical parameters of the discharge were measured, and wire resistance and energy deposition versus time were determined. 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 an X-pinch in the BIN facility diode (270 kA, 150 ns; P.N.Lebedev Institute). Exploded wires were placed outside the BIN vacuum chamber and images were registered on the film without magnification. Spatial resolution was limited by film grain structure, and reached 20-30 mm. Spectral range of the imaging radiation (15-30 keV) was determined by vacuum chamber window material, film sensitivity and thickness of the media where wire was exploded. Temporal resolution was about 10-20 ns and depended on X-pinch wire material and thickness. Shadow laser probing was performed with a second harmonic of the YAG:Nd+3. Shadow and schlieren images of the 25 μm tungsten exploding wire as far as of shock waves in its vicinity were obtained in the different moments of the discharge. The features of imaged shock waves propagated in the corona and in surrounding air show their correlation with the initial state of the wire surface and with the existence in the discharge another wire. (author)