A slapper etonator is a relatively recent kind of a detonator developed in Lawrence Livermore National Laboratory. 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 (for example, PETN or hexanitrostilbene) then delivers the energy and shock needed to initiate a detonation. Normally all the slapper's kinetic energy is supplied only 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 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.