A Characterization of the Electrodynamics of Metals under the Action of Large Electric Currents

An experimental and numerical investigation of the behavior of electrically thin exploding foils is presented that focuses on the influence that the geometry and non-linear material properties have on the electrodynamic behavior of the system. The foil is electrically excited using the first quarter cycle of a 1200 A, 1.7 MHz current source. This high power current pulse was experimentally found to be sufficient to induce solid to vapor phase transitions over the entire bridgefoil. A novel finite element code (FEM) was used to determine the transient thermal and electrical distributions in the (electrically) thin copper foil to the point where a significant portion of the bridgefoil and surrounding region has exceeded the melting temperature. The FEM code solves two non-linear partial differential equations that account for the thermal conductivity, latent heat of fusion, and specific heat (constant volume) of the foil. Contour plots of the foil's electrical and thermal signature indicate that there is the expected focusing of energy dissipation in the vicinity of the corners - an effect that has been experimentally observed. The model predicts that following the onset of melt (over approximately 50% of the bridgefoil), the time-to-burst occurs at time frames that are less than 10% of the time required to induce melt from the onset of the event.