Trigatron
Encyclopedia
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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,...
switch designed for high current and high voltage, (usually 10-100 kV and 20-100 kA, though devices in the mega-ampere range exist as well). It has very simple construction and in many cases is the lowest cost high energy switching option. It may operate in open air, it may be sealed, or it may be filled with a dielectric gas
Dielectric gas
A dielectric gas, or insulating gas, is a dielectric material in gaseous state. Its main purpose is to prevent or rapidly quench electric discharges. Dielectric gases are used as electrical insulators in high voltage applications, e.g...
other than air. The dielectric gas may be pressurized, or a liquid dielectric
Liquid dielectric
A liquid dielectric is a dielectric material in liquid state. Its main purpose is to prevent or rapidly quench electric discharges. Dielectric liquids are used as electrical insulators in high voltage applications, e.g. transformers, capacitors, high voltage cables, and switchgear...
(eg. mineral oil
Mineral oil
A mineral oil is any of various colorless, odorless, light mixtures of alkanes in the C15 to C40 range from a non-vegetable source, particularly a distillate of petroleum....
) may be substituted to further extend the operating voltage. Trigatrons may be rated for repeated use (over 10,000 switching cycles), or they may be single-shot, destroyed in a single use.
A trigatron has three electrodes. The heavy main electrodes are for the high current switching path, and a smaller third electrode serves as the trigger. During normal operation, the voltage between the main electrodes is somewhat lower than the breakdown voltage
Breakdown voltage
The breakdown voltage of an insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive.The breakdown voltage of a diode is the minimum reverse voltage to make the diode conduct in reverse...
corresponding to their distance and the dielectric between them (usually air, argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
-oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, or sulfur hexafluoride
Sulfur hexafluoride
Sulfur hexafluoride is an inorganic, colorless, odorless, and non-flammable greenhouse gas. has an octahedral geometry, consisting of six fluorine atoms attached to a central sulfur atom. It is a hypervalent molecule. Typical for a nonpolar gas, it is poorly soluble in water but soluble in...
). To switch the device, a high voltage pulse is delivered to the triggering electrode. This ionizes the medium between it and one of the main electrodes, creating a spark which shortens the thickness of non-ionized medium between the electrodes. The triggering spark also generates ultraviolet light and free electrons in the main gap. These lead to the rapid electrical breakdown
Electrical breakdown
The term electrical breakdown or electric breakdown has several similar but distinctly different meanings. For example, the term can apply to the failure of an electric circuit....
of the main gap, culminating in a low resistance electric arc
Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...
between the main electrodes. The arc will continue to conduct until current flow drops sufficiently to extinguish it.
The triggering electrode is most often mounted through a hole in the center of the positive main electrode. The undrilled main electrode is the negative electrode. When switching high currents, the electrodes undergo considerable heat stress, as they are directly involved in the electric arc. This causes the surfaces to undergo gradual vaporization, so some designs incorporate methods to easily adjust the distance between the electrodes or to actually replace the electrodes. The main electrodes are typically fabricated from brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
, or alloys of copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
and tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
for longer electrode life.
Glass trigatrons are often enclosed in a woven wire mesh, to provide protection from fragmentation if the device explodes due to internal overpressure.
Trigatrons find many different uses in pulsed power
Pulsed power
Pulsed power is the term used to describe the science and technology of accumulating energy over a relatively long period of time and releasing it very quickly thus increasing the instantaneous power.-Overview:...
applications. For example, they were used in early radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
modulators to feed the high-power pulses into the magnetrons, for use with slapper detonator
Slapper detonator
A slapper detonator, also called exploding foil initiator , is a relatively recent kind of a detonator developed in Lawrence Livermore National Laboratory...
s, or for triggering a Marx generator
Marx generator
A Marx generator is an electrical circuit first described by Erwin Otto Marx in 1924. Its purpose is to generate a high-voltage pulse. Marx generators are often used to simulate the effects of lightning on power line gear and aviation equipment....
.