Breakdown dynamics and instability of underwater metallic aerosol bubble atomized by electrical explosion

This study delves into the electrophysical processes and intricate fluid dynamics of an electrical-explosion-induced bubble in water. A fine copper wire is heated up and exploded to dense metallic aerosol (vapor-drop mixture) via a μs-timescale 10 kA current pulse, crossing a wide range of the density-temperature parametric space. High-speed photography along with discharge diagnostics reveals two modes for plasma development (restrike) inside explosion products: gas discharge and volume ionization. Experimental results indicate the metal-insulator transition of metal can easily throttle down circuit current at a moderate degree of vaporization, resulting in a free-expanding metallic aerosol in the presence of a quasi-direct current axial electric field of kV/cm level. After dozens of μs, an anode-directed, “ionization wave” is observed inside the aerosol bubble, propagating with a speed of 3-10 km/s. Remarkably, adjustments in the electric field permit the observation of cathode-directed discharge development. Increasing the charging voltage or wire diameter promotes the overheating degree, accompanied by partial ionized striation of electro-thermal instability. With sufficient high overheating of the wire (ξ > 1), the gas discharge disappears and restrike is dominated by volume ionization.