Editing Exploding-bridgewire detonator (section)

== Description ==

EBWs were developed as a means of detonating multiple explosive charges simultaneously, mainly for use in [[Nuclear weapon design#Implosion-type weapon|plutonium-based nuclear weapons]] in which a plutonium core (called a ''[[plutonium pit|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.

An EBW has two main parts: a piece of fine wire which contacts the explosive, and a [[high-voltage]] high-current low-impedance [[electricity]] source; it must reliably and consistently supply a rapid starting pulse. When the wire is connected across this voltage, the resulting high [[current (electricity)|current]] melts and then vaporizes the wire in a few microseconds. The resulting shock and heat initiate the [[high explosive]].<ref name="Cooper"/>

{{gallery
|Image:HD.4G.053 (10540204545).jpg|Trinity Gadget
|File:Trinity-Gadget-Closeup-Detonators.jpg|Closeup of a detonator set.  The EBW is the Y-shaped device with two wires coming in at angles along the surface.  The larger round objects with two wires coming out perpendicular to the surface are diagnostic equipment.
}}

This accounts for the heavy cables seen in photos of the [[Trinity site|Trinity]] "[[The gadget|Gadget]]"; high voltage cable requires good insulation and 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 bridgewire to initiate detonation in the detonator's booster charge. Given a sufficiently high and well-controlled amount of electric current and voltage, the timing of the bridgewire 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 cap]]s 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 bridgewire 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 1,000 to 10,000 times longer and less precise than the EBW electrical vaporization.

[[Image:Exploding-bridgewire detonators in case.png|frame|right|Modern exploding-bridgewire detonators arranged in a tray.]]

=== Use in nuclear weapons ===

Since explosives detonate at typically 7–8 kilometers per second, or 7–8 meters per millisecond, a 1 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&nbsp;mm variation in the detonation wave. This is sufficiently precise for very tight tolerance applications such as nuclear weapon [[explosive lens]]es.<!-- cite to Nuclear Weapons FAQ -->

In the US, due to their use in nuclear weapons, these devices are subject to nuclear control authorities, according to the Guidelines for the Export of Nuclear Material, Equipment and Technology. EBWs are on the [[United States Munitions List]], and exports are highly regulated.<ref name="RISI-Export">{{cite web |url=http://www.teledynerisi.com/1techtopics/pdf/1193.pdf |title=RISI Technical Topics 11-92 ATF Licenses
|archive-url=https://web.archive.org/web/20070226071620/http://www.teledynerisi.com/1techtopics/pdf/1193.pdf |archive-date=26 February 2007 |url-status=dead}}</ref>

=== Civilian use ===

EBWs have found uses outside nuclear weapons, such as the [[Titan IV]] missile,<ref>{{Cite web|url=http://neyersoftware.com/Papers/AIAA96/HVD.htm|title = AIAA 96-2874 Development and Qualification Testing of the High Voltage Detonator}}</ref> safety conscious applications where stray electrical currents might detonate normal blasting caps, and applications requiring very precise timing for multiple point commercial blasting in mines or quarries.<ref name="RISI-Models">{{cite web |url=http://www.teledynerisi.com/products/0products_1ebw_page10.asp |title=Teledyne RISI - Selecting the Right EBW Detonator
|archive-url=https://web.archive.org/web/20090106140347/http://www.teledynerisi.com/products/0products_1ebw_page10.asp |archive-date=6 January 2009}}</ref> EBW detonators are much safer than regular electric detonators because, unlike regular detonators, EBWs do not have primary explosives. Primary explosives such as [[lead azide]] are very sensitive to static electricity, radio frequency, shock, etc.