A slapper detonator, also called exploding foil initiator, is a relatively recent kind of a detonator developed by Lawrence Livermore National Laboratory, US Patent No. 4,788,913. It is an improvement of the earlier exploding-bridgewire detonator; instead of directly coupling the shock wave from the exploding wire, the expanding plasma 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 the explosive then delivers the energy and shock needed to initiate a detonation. Normally all the slapper's kinetic energy is supplied only by the heating of the plasma by the current passing through it, though constructions with a "back strap" to further drive the plasma forward by magnetic field exist too. This assembly is quite efficient; up to 30% of the electrical energy can be converted to the slapper's kinetic energy. The initial explosion is usually caused by explosive vaporization of a thin metal wire or strip, by driving several thousand amperes of electric current through it, usually from a capacitor charged to several thousand volts. The switching may be done by a spark gap or a krytron. Usually the construction consists of an explosive 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 or PET film, with a thin strip of metal 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. Advantages over explosive-bridgewire detonators include:
The foil does not come in contact with the explosive, which reduces the risk of corrosion of the foil or chemical reactions between the foil and explosive producing unstable compounds, and secondarily further reduces the risk of accidental electrical ignition of the explosive.
The energy to fire the detonator is quite low
The slapper pellet impacting an area of explosives rather than a single point as in an EBW is more reliable and efficient at initiating detonation.
