High fidelity studies of exploding foil initiator bridges, Part 3: ALEGRA MHD simulations

Abstract

Abstract. Simulations of high voltage detonators, such as Exploding Bridgewire (EBW) and Exploding Foil Initiators (EFI), have historically been simple, often empirical, one-dimensional models capable of predicting parameters such as current, voltage, and in the case of EFIs, flyer velocity. Experimental methods have correspondingly generally been limited to the same parameters. With the advent of complex, first principles magnetohydrodynamic codes such as ALEGRA and ALE-MHD, it is now possible to simulate these components in three dimensions, and predict a much greater range of parameters than before. A significant improvement in experimental capability was therefore required to ensure these simulations could be adequately verified. In this third paper of a three part study, the experimental results presented in part 2 are compared against 3-dimensional MHD simulations. This improved experimental capability, along with advanced simulations, offer an opportunity to gain a greater understanding of the processes behind the functioning of EBW and EFI detonators.

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

“…The plume front (A) of arriving material demonstrably differed in shape as a result of bridge geometry modification. It is proposed that this is the reason for differing behavior prediction concerning peripheral regions of the flyer and bridge between this study and that of Neal and Garasi 32 . The advantage of the numerical model presented herein is its ability to solve without the requirement for supercomputer access (as with Neal and Garasi 32 ), whilst still predicting comparable ToAD.…”

Numerical Analysis on Acceleration Process and Shock Initiation of Parylene C−Cu Flyer in Exploding Foil Initiator

“…Therefore, minus sign (À ) was taken in equation (6). Since p J is much larger than p 0 , so the latter is negligible, and D J equals to D 0 , then equation ( 6) was deduced as (7) Introducing a parameter ξ, the equations of weak detonation were simplified as (8) If assuming the electro-explosion of exploding foil is realized in a moment, namely D!∞, then ξ equals to 1, and equation ( 8) was reduced to (9) Compared with typical explosives, polytropic exponent of metal vapor is no longer equals to 3, Riemann constant must be considered: (10) Due to α ¼ 6 u + c, shock pressure and sound speed were written as (11) (12) According to Newton's Second Law, equation of motion can be described as (13) where m f , s f are the mass and effective area of flyer, respectively. Inserting equation ( 11) and ( 12) into equation ( 13), it will be transformed as (14) Joining with initial conditions u(0) = 0 and x(0) = l, the relationship between flyer velocity and time can be obtained by integral calculus as (15) Meanwhile, the flight trajectory x(t) can be obtained as (16) where h b is the thickness of the bridge foil.…”

“…In an EFI, it is clear that plastic flyer plays an important role, which transfers the energy from metal vapors to secondary explosives. Traditionally, polyimide film was used as a flyer, because of its excellent mechanical properties, thermal stability, and dielectric strength [7][8][9]. In recent years, parylene C is becoming a potential choice.…”

Characterization of Plasma Formation and Mass Ejection in Exploding Foil Initiators

“…This magnetic reconnection transfers kinetic energy to the plasma, ejecting it and the flyer layer up the barrel in the top layer of the EFI's laminar structure. This sequence has been demonstrated using a magnetohydrodynamic model of EFI operation [18].…”