Multiphase Foamlike Structure of Exploding Wire Cores

Abstract

X-ray backlighter images (radiographs) of current-induced explosions of $7.5--25\ensuremath{\mu}\mathrm{m}$ diam metal wires show for the first time $\ensuremath{\mu}\mathrm{m}$ scale, time-resolved details of a persistent foamlike liquid-vapor structure of the expanded wire core. Experiments with refractory and highly resistive metals, with current rising to 2--5 kA per wire in 350 ns, show that a substantial portion of the wire material is not vaporized but remains in a condensed state. As the current damps out, the remaining liquid phase material coalesces into separate droplets.