Study on the electrothermal instability in electrically exploding aluminum wires in air

Experimental and computational results characterizing the evolution of electrothermal instability in electrically exploding aluminum wires in air are presented. Experiments on the electrically exploding aluminum wires are carried out using a compact pulsed power generator. The discharge is synchronized with shadowgraphy and schlieren diagnostics. The intrinsic physical states of the aluminum wires are analyzed to determine the geometric characteristics of potential resistive inclusions. A computational model based on the framework of magnetohydrodynamics with a two-temperature approximation in the multi-fluid regime is established to elucidate the formation of the electrothermal instability. The computational results reveal the evolution of the electrothermal instability from the initial seeds to the prominent perturbations at the late stage of the discharge. The resistive inclusions redistribute the current density, inducing perturbations in the density and temperature within the plasma column. The dependence of temperature increase coefficients on the density and resistivity of the inclusions is discussed. A critical resistivity ratio kηc = 4.5 is proposed for the evolution patterns of the electrothermal instability induced by resistive inclusions. The penetration of resistive inclusions into the ambient air results in a wavy boundary between the exploding products and the surrounding air. The computational results show good agreement with the experimental measurements in terms of the perturbation wavelength, perturbation amplitude, and wire radius. The computational results of different seed types clarify that the resistive inclusions are the dominant seeds for the electrothermal instability, helping to gain an in-depth understanding of the physics of the instability in electrically exploding wires.