Slapper detonator
Encyclopedia
Detonator
A detonator is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the latter two being the most common....
developed in Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...
. It is an improvement of the earlier exploding-bridgewire detonator
Exploding-bridgewire detonator
The exploding-bridgewire detonator is a type of detonator used to initiate the detonation reaction in explosive materials, similar to a blasting cap in that it is fired using an electric current...
; 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
PETN
Pentaerythritol tetranitrate , also known as PENT, PENTA, TEN, corpent, penthrite , is the nitrate ester of pentaerythritol. Penta refers to the five carbon atoms of the neopentane skeleton.PETN is most well known as an explosive...
or hexanitrostilbene
Hexanitrostilbene
Hexanitrostilbene , also called JD-X, is a heat resistant high explosive developed at the Naval Ordnance Laboratory in the 1960s. Other names include 1,1'-bis[2,4,6-trinitrobenzene]; 1,2-bis--ethylene; hexanitrodiphenylethylene.It is commercially produced by oxidizing trinitrotoluene with a...
) then delivers the energy and shock needed to initiate a detonation
Detonation
Detonation involves a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations are observed in both conventional solid and liquid explosives, as well as in reactive gases...
. Normally all the slapper's kinetic energy is supplied only by the heating (and hence expansion) of the plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
(the former foil) by the current passing through it, though constructions with a "back strap" to further drive the plasma forward by magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
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 thousands amperes of electric current through it, usually from a capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
charged to several thousands volts. The switching may be done by a spark gap
Spark gap
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the voltage difference between the conductors exceeds the gap's breakdown voltage, a spark forms,...
or a krytron
Krytron
The krytron is a cold-cathode gas filled tube intended for use as a very high-speed switch, and was one of the earliest developments of the EG&G Corporation. It is somewhat similar to thyratron...
.
Usually the construction consists of an explosive booster
Explosive booster
An explosive booster acts as a bridge between a low energy explosive and a low sensitivity explosive such as TNT. It increases the explosive shockwave from an initiating explosive to the degree sufficient to detonate the secondary charge.Unlike C4 plastic explosive, not all explosives can be...
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
Kapton
Kapton is a polyimide film developed by DuPont which can remain stable in a wide range of temperatures, from -273 to +400 °C...
or PET film
PET film (biaxially oriented)
BoPET is a polyester film made from stretched polyethylene terephthalate and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties and electrical insulation.A variety of companies manufacture boPET and other...
, with a thin strip of metal (typically aluminum or gold) 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.
- 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.
- The explosive can be pressed to higher density
- Very insensitive explosives can be initiated directly.
In a variant called laser detonator the vaporization can be caused by a high-power laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
pulse delivered over-the-air or coupled by an optical fiber
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
; this is reportedly used as a safety detonator in some mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
operations and quarries
Quarry
A quarry is a type of open-pit mine from which rock or minerals are extracted. Quarries are generally used for extracting building materials, such as dimension stone, construction aggregate, riprap, sand, and gravel. They are often collocated with concrete and asphalt plants due to the requirement...
. Typically a 1-watt solid-state laser is used.
The slapper detonators are frequently used in modern weapon designs and aerospace technology.
For the description of the required firing system, see Firing system for exploding-bridgewire detonator.