Characterization of Plasma Formation and Mass Ejection in Exploding Foil Initiators

To aid exploding foil initiator (EFI) design, better prediction of ejecta momentum through either mass or velocity prediction is required. A numerical model was developed to calculate the mass of material converted to plasma within the confined region of an EFI bridge during the change of state under an electrical stimulus from a discharging capacitor. Optimization is facilitated through the increased understanding of plasma evolution in current EFI designs, including the impact of this on both current delivery to the bridge and overall unit efficiency. The plasma regions were formed in key regions within the bridge, termed $P_{A}$ (ground side of EFI) and $P_{B}$ (high-voltage side of EFI) in this work. Different regions were dominant in mass ejection for different operating voltages. A trend is identified wherein the bridge exhibits an optimum threshold between the capacitor energy being utilized for mass conversion to plasma and that used for acceleration of this mass. It is postulated that, through geometric design modification, this threshold can be adjusted to deliver the momentum threshold of the explosive for which an EFI may be designed.