Abstract
The particle velocity created in beds of both low-density inert sugar and explosive PETN as a function of distance from an exploding bridgewire was measured using optical velocimetry and a silvered PMMA window. As expected, more violent bridge-bursts (from a greater-stored-energy capacitive discharge unit) resulted in greater particle velocities and a better supported compaction wave in sugar. In all cases, ramp waves, not shocks, were observed in the inert sugar. Large window velocities were observed for very powerful bursts (up to 270 m/s), but bursts required for stochastic detonator operation conditions resulted in sugar/PMMA window velocities of only 8–10 m/s 0.85 mm from the bridge location. In contrast, after a distance of only 0.65 mm, a building shock wave was observed in PETN under both threshold and reliable firing conditions. Subsequently a hot-spot-driven shock-to-detonation (SDT) process was observed prior to full detonation. The measured buildup process accounts for approx 66% of the so-called excess transit time (ETT) between the observed and theoretical total function time for the particular exploding-bridge-wire (EBW) detonator studied. The remainder must occur in the powerful output pellet region. In contrast to a common understanding, the ETT is found to be a weak function of the discharge energy. Thus, the operation of the detonator after a bridge-burst energy-to-powder reaction transition process is found to be hot-spot-driven SDT in both the low- and high-density pellets.
Highlights
The exploding bridgewire (EBW) detonator was invented in Los Alamos toward the end of the Second World War [1]
It is clear that the imposed velocities are significant (70–270 m/s) suggesting relatively high pressures are acting on the powder bed
It has been shown that the electrical explosion of thin gold wires by the application of high currents and voltages from a capacitor discharge unit generates strong ramp waves in thin low-density sugar pressings
Summary
The exploding bridgewire (EBW) detonator was invented in Los Alamos toward the end of the Second World War [1]. The aim was to create a safe detonator with highly repeatable functioning time (less than 1 μs of jitter) coupled to a powerful explosive booster output. This was achieved by discharging a high-voltage capacitor across a short, very fine gold wire to create a shock wave, gold plasma, and arc next to a pellet of low-density (≈ 50% of theoretical maximum density, TMD) PETN (2,2-bis[(nitrooxy)methyl]propane-1,3-diyl dinitrate). The exploding of the wire, called bridge-burst, was discovered to reproducibly detonate the low-density PETN (the initial pressing or IP) by some mechanism, and by cou-. This paper will concentrate on PETN since it is the most commonly used future research may study other explosives
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