"breakdown" of stratified electrical explosion products: Plasma development and its mechanical effect

The physical image of breakdown dynamics inside striations is depicted. High-speed photography along with electrophysical and spectral diagnostics reveals three modes for plasma development in Cu wire explosion: current cutoff, initial breakdown (with quenching), and main breakdown (with re-strike). The growth of spatial heterogeneity by electrothermal instability (ETI) provides a stratified structure before the initial breakdown. The characteristic wavelength of the strata is <100 μm for thinner wires (d = 90/130 μm) but in mm level for thicker ones (d = 240/290 μm). By increasing the stored energy from 200 to 220 J, the 290-μm-diameter Cu wire experiences a transition from current cutoff to initial breakdown, with a deposited energy of 2.64 and 3.10 eV/atom. Although the energy is not sufficient to vaporize the wire, axial micro-plasma-channels develop among bright layers (higher temperature but lower density), forming a crossed low-conductive "plasma-network"connecting two electrodes. If the residual energy is enough, the scenario (main breakdown) would be similar to "streamer-spark transition"and enhance the expansion of discharge channel. Two paralleled wires are exploded simultaneously but only one establishes main breakdown; therein, three stronger shock waves are detected, namely, two for vaporization and one for breakdown.