Photonic Doppler velocimetry of ohmically exploded aluminum surfaces

Abstract

Photonic Doppler Velocimetry (PDV) was used to investigate the exploding surface of coated metal driven by lineal current density increasing at 3×1015 A/m/s. Aluminum-6061 rods were coated with three thicknesses (5, 17, and 41 μm) of Parylene-N and driven to 850 kA in approximately 100 ns, with the metal thicker than the skin depth. According to PDV, the metal surface melts at 85±13 T and expands with a constant acceleration. Then, at a surface magnetic field of 140–180 T, the metal acceleration begins to increase in time. Later, plasma forms on, and is correlated with PDV signal loss from, uncoated aluminum rods, 5-μm-coated rods, and 17-μm-coated rods, while no evidence suggests that plasma forms on 41-μm-coated metal.