Exploding Foil Initiator (EFI) Modes of Operation Determined Using Down-Barrel Flyer Layer Velocity Measurement

Abstract

Exploding Foil Initiator (EFI) flyer layer velocities measured down the barrel of an EFI are presented. Flyer velocity was shown to be proportional to supply voltage and of a similar order to other studies previously conducted. Bridge volume ejection was shown to be proportional to capacitor voltage. Current density increased with respect to capacitor voltage up to a point of saturation between 2400 V and 3000 V (evidenced electrically). Beyond the saturation voltage, high voltages demonstrated sustained energy delivery at a reduced current. This work indicates that control of active bridge volume or electrical supply signal may enable more closely controlled EFI flyer layer ejection behavior, and it demonstrates the relevance of using current per active bridge (specific current) as a metric to describe EFI electrical performance with relevance to dynamic response of the EFI. The impulse delivered by an EFI can be modulated via manipulation of the firing circuit input signal giving rise to system behavior variation.

Modeling of the exploding foil initiator and related circuitry for the variable mode of operation

“…The analytical calculation steps described herein build upon the observations of Borman et al 13 and can be broadly broken down into three phases: a time iterated phase determining the state of the bridge; an energy calculations phase that determines the transfer of the remaining energy from the capacitor; and a solution phase reporting flyer ejection information (i.e., fire/no fire; velocity).…”

“…11,12 James 12 also identifies the time at which the explosive acquires the maximum amount of energy from the initial shock to be of importance in critical energy calculations. This instant can be identified using the time of arrival, from analytical calculation (Section 2.1), or via empirical measurement, 13 in addition to time of arrival duration (ToAD).…”

“…Flyer-explosive interaction has been observed to be of importance when considering system behavior. The work of Borman et al 13 utilized an experimental technique to measure the velocity of ejected material from the barrel at high speed with the pellet removed for a range of initial capacitor voltages. This work sought to understand the mode of operation of the EFI in greater detail for the purpose of controlling and modifying this behavior in line for selective deflagration or detonation modes of operation.…”

“…Deflagration has been identified as achievable using the EFI. 16,17 From the observations and postulations presented by Borman et al, 13 analytical and numerical models have been developed and are presented herein and compared with the data of Borman et al 13 The full experimental procedure has been presented previously, 13 and hence will not be reproduced here; however, where additional processing to the raw data collected has taken place, such processes will be described.…”

Investigation of Electrically Heated Exploding Foils in Reactive Al/Ni Multilayer

“…When high current pulse is passing through metallic foil or wire in short time, the state of foil or wire changes from solid to vapor rapidly, resulting plasma with high temperature and pressure by ionized vapor. The plasma created by metallic foil or wire has many applications in electrical guns (EGs) [1][2][3][4], exploding foil initiator (EFIs) [5][6][7][8][9], exploding wire initiator. The high pressure generated by plasma can accelerate plastic flyers to km/s, which can initiate explosion or investigate impacting performance of materials.…”