Anomalous Behavior of Electrically Exploding Aluminum Foils Under Vacuum

The electrical explosion characteristics of partially confined square shaped aluminum foils have been investigated under vacuum down to 10^-4 mbar. In contrast to its behavior near atmospheric pressure, an anomalous rise has been observed in the current flowing through the foil after burst. The peak voltage developed across the foil, which is proportional to the dielectric strength of expanded vapor, has also been found to be decreasing under vacuum. More serious effects have been observed at vacuum levels from 100 to 0.05 mbar, where no signatures of foil explosion were detected. The effect of vacuum on the expansion rate of exploded metal plasma was estimated by measuring the velocity of a thin dielectric sheet placed over it and found to be significantly reduced in vacuum. The possible cause for this behavior appears to be the formation of a low-resistance breakdown channel parallel to metal foil, initiated by the ionization in released adsorbed gas molecules or in partially evaporated metal vapors in the presence of self-generated magnetic field over the heated foil surface.