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Aslapper detonator, also calledexploding foil initiator (EFI), is adetonator developed byLawrence Livermore National Laboratory, US Patent No. 4,788,913 (Filed 1971, Granted 1988). It is an improvement over the earlierexploding-bridgewire detonator. Instead of directly coupling theshock wave from the exploding wire (as the bridgewire does), the expandingplasma from an explosion of a metal foil drives another thin plastic or metal foil called a "flyer" or a "slapper" across a gap, and its high-velocity impact on anexplosive (for example,PETN orhexanitrostilbene) then delivers the energy and shock needed to initiate adetonation. Normally all the slapper'skinetic energy is supplied by the heating (and hence expansion) of the plasma (the former foil) by the current passing through it, though constructions with a "back strap" to further drive the plasma forward bymagnetic field also exist. This assembly is quite efficient; up to 30% of the electrical energy can be converted to the slapper's kinetic energy. The device's name is derived from the English word "slap".
The initial explosion is usually caused by explosive vaporization of a thin metal wire or strip, by driving several thousand amperes ofelectric current through it, usually from acapacitor charged to several thousand volts. The switching may be done by aspark gap or akrytron.
Usually the construction consists of anexplosive booster pellet, against which a disk with a hole in the center is set. Over the other side of the disk, there is a layer of an insulating film, for example,Kapton orPET film, with a thin strip of metal (typicallyaluminum orgold) foil deposited on its outer side. A narrowed section of the metal then explosively vaporizes when a current pulse passes through it, which shears the mylar foil and the plasma ball pushes it through the hole, accelerating it to very high speed. The impact then detonates the explosive pellet.
Slapper detonators are frequently used in modern weapon designs and aerospace technology.
Advantages over explosive-bridgewire detonators include:
In a variant calledlaser detonator the vaporization can be caused by a high-powerlaser pulse delivered over-the-air or coupled by anoptical fiber; this is reportedly used as a safety detonator in somemining operations andquarries. Typically a 1-wattsolid-state laser is used.