The impact of surface imperfections on aluminum rods pulsed with extreme current

The electrothermal instability (ETI) is a Joule heating-driven instability that instigates runaway heating on conductors driven to high current density, altering the 3D evolution of material expansion. Most metals include complex distributions of imperfections (voids, resistive inclusions) which seed ETI. To simplify comparison with modeling and theory, experiments examined growth of ETI from relatively void/inclusion free, 99.999% pure, diamond-turned, 1 mm-diameter aluminum rods, which are pulsed with 1 MA of current in 100 ns. Aluminum surfaces included a variety of deliberately machined and well-characterized perturbations, including 10-micron-scale quasi-hemispherical voids, or “engineered” defects (ED), and sinusoidal patterns of varying wavelength and amplitude. This talk will describe how the details of 2D and 3D surface perturbations drive instabilities, which will be compared to theoretical predictions and simulations.