Description
EBWs were developed as a means of detonating multiple explosive charges simultaneously, mainly for use in plutonium-based nuclear weapons in which a plutonium core (called a “pit”) is compressed very rapidly. This is achieved via conventional explosives placed uniformly around the pit. The implosion must be highly symmetrical or the plutonium would simply be ejected at the low-pressure points. Consequently, the detonators must have very precise timing.
An EBW has two main parts: a piece of fine wire which contacts the explosive, and a “strong” source of high-voltage electricity — strong, in that it holds up under sudden heavy load. When the wire is connected across this voltage, the resulting high current melts and then vaporizes the wire in a few microseconds. The resulting shock and heat initiate the high explosive.
This accounts for the heavy cables seen in photos of the Trinity “Gadget”; they had to deliver a large current with little voltage drop, lest the EBW not achieve the phase transition quickly enough.
The precise timing of EBWs is achieved by the detonator using direct physical effects of the vaporized bridgewire to initiate detonation in the detonator’s booster charge. Given a sufficiently high and well known amount of electric current and voltage, the timing of the bridgewire vaporization is both extremely short (a few microseconds) and extremely precise and predictable (standard deviation of time to detonate as low as a few tens of nanoseconds).
Conventional blasting caps use electricity to heat a bridge wire rather than vaporize it, and that heating then causes the primary explosive to detonate. Imprecise contact between the bridgewire and the primary explosive changes how quickly the explosive is heated up, and minor electrical variations in the wire or leads will change how quickly it heats up as well. The heating process typically takes milliseconds to tens of milliseconds to complete and initiate detonation in the primary explosive. This is roughly one to ten thousand times longer and less precise than the EBW electrical vaporization.
Read more about this topic: Exploding-bridgewire Detonator
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