Experimental Observation of the Stratified Electrothermal Instability on Dielectric-Coated Thick Aluminum

The first direct observation of the stratified electrothermal instability on the surface of thick metal is reported. Aluminum rods coated with 70 um Parylene-N were driven to 1 MA in approximately 100 ns, with the metal thicker than the skin depth. The dielectric coating suppressed plasma formation, prolonging the observability of discrete azimuthally-correlated stratified structures perpendicular to the current. Assuming blackbody emission, radiometric calculations indicate strata are temperature perturbations that grow exponentially with rate 0.04/ns in 3000 - 10,000 K aluminum.