Revisiting The Physics Of High-Current, Foil Opening Switches With Modern Codes

Metal foils have been used extensively as high-power opening switches. The configuration consists of an electrically thin foil between dielectric insulators. The dimensions of the foil fuse are governed by the appliation, the foil material, and the resistivity. The general principle is to Joule heat the metal to vaporization causing a 10 2 increase in resistivity, but limiting it from the plasma state where resistivity drops. We apply modern MHD codes and the most recent EOS and conductivity tables to study the physics of foil opening switches in detail. In the ideal case, all of the tamped foil material follows the liquid/vapor co-existence curve prior to vaporization. Thus, the performance of fuse is largely determined by the accuracy of the resistivity along this path. We present the sensitivity of a fuse calculation to various tables. Further, axisymmetric geometry can lead to uneven heating effectively creating a set of unequal, series resistors that can hinder performance. Finally, there is the question of heat dissipation of the vapor by the insulator layers. ranular tampers (e.g., glass microspheres) have been shown to be more effective than layered polymers (e.g., polyimide films). We speculate that the higher surface area and porosity is responsible for quenching the heat of the vapor. Here, we compare computational results to previous, well-diagnosed experimental studies and explore some new designs.