Density evolution of a copper wire during nanosecond timescale underwater explosions

We present high-contrast X-ray images (∼30 μm space and ∼10 ns time resolution) of ns-timescale underwater electrical explosions of copper wires to the low density limit of ∼1 g/cm³, using a rod-ring electron diode as a source of X-rays. The radial density distribution, obtained by inverse Abel transform analysis of the X-ray images, is reproduced by one dimensional magneto-hydrodynamic (MHD) simulations using the SESAME equations of state and a modified Bakulin, Kuropatenko, and Luchinskii conductivity model for copper. These modifications are introduced by matching the experimental and simulated current and voltage waveforms and the radial wire expansion. For our ns-timescale copper wire underwater electrical explosions, the X-ray images display no MHD and thermal instabilities.