Since explosives detonate at typically 7–8 kilometers per second, or 7–8 meters per millisecond, a 1 millisecond delay in detonation from one side of a nuclear weapon to the other would be longer than the time the detonation would take to cross the weapon. Modern exploding-bridgewire detonators arranged in a tray. This is roughly 1,000 to 10,000 times longer and less precise than the EBW electrical vaporization. The heating process typically takes milliseconds to tens of milliseconds to complete and initiate detonation in the primary explosive. 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. 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).Ĭonventional blasting caps use electricity to heat a bridge wire rather than vaporize it, and that heating then causes the primary explosive to detonate. 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. This accounts for the heavy cables seen in photos of the Trinity " Gadget" high voltage cable requires good insulation and they had to deliver a large current with little voltage drop, lest the EBW not achieve the phase transition quickly enough. The larger round objects with two wires coming out perpendicular to the surface are diagnostic equipment. The EBW is the Y-shaped device with two wires coming in at angles along the surface. The resulting shock and heat initiate the high explosive. When the wire is connected across this voltage, the resulting high current melts and then vaporizes the wire in a few microseconds. Consequently, the detonators must have very precise timing.Īn EBW has two main parts: a piece of fine wire which contacts the explosive, and a high-voltage high-current low-impedance electricity source it must reliably and consistently supply a rapid starting pulse. The implosion must be highly symmetrical or the plutonium would simply be ejected at the low-pressure points. This is achieved via conventional explosives placed uniformly around the pit. Description ĮBWs 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. The Fat Man Model 1773 EBW detonators used an unusual, high reliability detonator system with two EBW "horns" attached to a single booster charge, which then fired each of the 32 explosive lens units. The EBW was invented by Luis Alvarez and Lawrence Johnston for the Fat Man–type bombs of the Manhattan Project, during their work in Los Alamos National Laboratory. The slapper detonator is a more recent development along similar lines. This has led to their common use in nuclear weapons. Exploding with more precise timing after the electric current is applied, by the process of exploding wire method. EBWs use a different physical mechanism than blasting caps, using more electricity delivered much more rapidly. The exploding-bridgewire detonator ( EBW, also known as exploding wire detonator) is a type of detonator used to initiate the detonation reaction in explosive materials, similar to a blasting cap because it is fired using an electric current.
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