Krytron

The krytron is a high speed switch, which turns on in about 10 microseconds to handle high currents at high voltages. This makes them useful for initiating nuclear explosions. The Wikipedia informs us that QUOTE One prominent case [ of smuggling them ] UNQUOTE was that of Richard Kelly Smyth. It does not mention that Smyth was exporting them to Jews in Israel.

Krytron ex Wiki
QUOTE
Krytrons and their variations are manufactured by Perkin-Elmer Components and used in a variety of industrial and military devices. They are best known for their use in igniting exploding-bridge wire and slapper detonators in nuclear weapons, their original application, either directly (sprytrons are usually used for this) or by triggering higher-power spark gap switches. They are also used to trigger thyratrons, large flash lamps in photocopiers, lasers and scientific apparatus, and for firing igniters for industrial explosives.

Export restrictions
Because of their potential for use as triggers of nuclear weapons, the export of krytrons is tightly regulated. A number of cases involving the smuggling or attempted smuggling of krytrons have been reported, as countries seeking to develop nuclear weapons have attempted to procure supplies of krytrons for igniting their weapons. One prominent case was that of Richard Kelly Smyth.

Krytrons and sprytrons handling voltages of 2,500 V and above, currents of 100 A and above, and switching delays of under 10 microseconds are typically suitable for nuclear weapon triggers.
UNQUOTE
The export restrictions are a little surprising. They do not sound difficult to make. Their short lifetime is not an issue in nuclear explosions. Once is all it needs.

 

Exploding Bridge wire
QUOTE
The exploding-bridge wire 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 in that it is fired using an electric current. EBWs use a different physical mechanism than blasting caps, using more electricity delivered much more rapidly, and explode in a much more precise timing after the electric current is applied. This has led to their common use in nuclear weapons. The slapper detonator is a more recent development along similar lines.

History
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 Fat Man Model 1773 EBW detonators used an unusual, high reliability detonator systems with two EBW "horns" attached to a single booster charge, which then fired each of the 32 explosive lens units. Description
EBWs 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. This is achieved via conventional explosives placed uniformly around the pit. The implosion must be highly symmetrical or the plutonium would simply be ejected at the low-pressure points. Consequently, the detonators must have very precise timing.

Description
An EBW has two main parts: a piece of fine wire which contacts the explosive, and a “strong” source of high-voltage electricity — strong, in that it holds up under sudden heavy load. When the wire is connected across this voltage, the resulting high current melts and then vaporizes the wire in several microseconds. The resulting shock and heat initiate the high explosive.

This accounts for the heavy cables seen in photos of the Trinity “Gadget”; they had to deliver a large current with little voltage drop, lest the EBW not achieve the phase transition quickly enough.

The precise timing of EBWs is achieved by the detonator using direct physical effects of the vaporized bridge wire to initiate detonation in the detonator’s booster charge. Given a sufficiently high and well known amount of electric current and voltage, the timing of the bridge wire 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).

Conventional blasting caps use electricity to heat a bridge wire rather than vaporize it, and that heating then causes the primary explosive to detonate. Imprecise contact between the bridge wire 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. The heating process typically takes milliseconds to tens of milliseconds to complete and initiate detonation in the primary explosive. This is roughly one to ten thousand times longer and less precise than the EBW electrical vaporization.

Use in nuclear weapons
Since explosives detonate at typically 7–8 kilometers per second, or 7–8 meters per millisecond, a one 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. The time precision and consistency of EBWs (0.1 microsecond or less) are roughly enough time for the detonation to move 1 millimeter at most, and for the most precise commercial EBWs this is 0.025 microsecond and about 0.2 mm variation in the detonation wave. This is sufficiently precise for very low tolerance applications such as nuclear weapon explosive lenses.

Due to their common use in nuclear weapons, these devices are subject to the Nuclear Control Authorities in every state, according to the Guidelines for the Export of Nuclear Material, Equipment and Technology. In the US, EBWs are on the US State Department Munitions Control List, and exports are highly regulated.
UNQUOTE
Microsecond timing sounds about right for these things.

 

Slapper Detonators
QUOTE
A slapper detonator, also called exploding foil initiator (EFI), is a relatively recent kind of a detonator developed in Lawrence Livermore National Laboratory. It is an improvement of the earlier exploding-bridge wire 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.

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 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 (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.

Advantages over explosive-bridge wire detonators include:

In a variant called laser detonator the vaporization can be caused by a high-power laser pulse delivered over-the-air or coupled by an optical fiber; this is reportedly used as a safety detonator in some mining operations and quarries. 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-bridge wire detonator.
UNQUOTE
This is some of the engineering that goes into making these things work. The American offerings did just that. Aum Shinrikyo, a very well funded Japanese terrorist outfit tried and failed.

 

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Updated on 23/06/2018 21:29