Effect of Die Pattern on Explosively Formed Fuse Performance

Explosively formed fuse (EFF) devices are opening switches for high explosive pulsed power (HEPP) applications. Such switches have been operated at currents up to 25 MA, voltages up to 500 kV, and power over 3 TW in our large-scale HEPP systems. The switch consists of a conducting foil that is driven by high explosives into a dielectric die consisting of extrusion anvils and gaps that separate them. The switch develops resistance as the foil is extruded. We have conducted tests with many foils, and many die materials and patterns. We have also performed calculations using both 2-D hydrodynamic (hydro) and magneto-hydrodynamic (MHD) codes of switches with the different die patterns. Dies with more massive corners at each extrusion position develop resistance faster, and tend to have more pronounced features in the resulting R(t) curves. In addition, the explosive drive is important as is the shape and density of the anvil bottom. These data and calculations will be discussed, along with what we have learned from MHD calculations. To date, we have been unable to calculate accurate R(t) curves accurately from first principles with MHD codes, but have gained increased insight into performance.