Optical observations of plasma formation and wire core expansion of Au, Ag, and Cu wires with 0-1 kA per wire

Explosions of Au, Ag, and Cu wires (1 cm long, 13-25 mum diameter, with/without insulating coatings) driven by a current pulser (4.5 kA peak, rise time 350 ns) were studied. Diagnostics included three channels of Schlieren imaging and two channels of shearing interferometry using the second harmonic of a Nd:YAG laser (lambda=532 nm, 5 ns pulse width). The formation of a plasma shell around the neutral wire core was observed relatively late in time compared to the voltage collapse time. The corresponding plasma density was measured. From the refractive index of the wire core, some properties of the wire core material will also be discussed. The expansion rates of exploding wires were measured by interferometry and compared to the previously reported results. Two-wire experiments were also performed. The merging of the plasma at an increased plasma density was observed between two wires. The effects of the plasma shell on the wire expansion are discussed. (C) 2004 American Institute of Physics.