Krytron is one of the earliest developments of the EG&G Corporation. It is a cold-cathode gas filled tube intended for use as a very high-speed switch. Unlike most other gas switch tubes, the krytron uses arc discharge to handle very high voltages and currents (several kV and several kA peak), rather than the usual low-current glow discharge. The krytron is a development of the triggered spark gaps originally developed for radar transmitters during World War II.

KN2 "Krytron" switch tube, made by EG&G--approx 25 mm tall

There are four electrodes in a krytron. Two are conventional anode and cathode. One is a keep-alive electrode, arranged to be close to the cathode. The keep-alive has a low positive voltage applied, which causes a small area of gas to ionize near the cathode. High voltage is applied to the anode, but primary conduction does not occur until a positive pulse is applied to the trigger electrode. Once started, arc conduction carries a considerable current. Each krytron also contains a very tiny amount of radioactive material (usually nickel-63) which emits beta particles (high-speed electrons) to make ionization easier. The amount of radiation in a krytron is very small and not harmful.

This design, dating from the late 1940s, is still capable of pulse-power performance which even the most advanced semiconductors cannot match easily. The vacuum-filled version is called a Sprytron and is designed for use in environments where high levels of radiation are present (because the radiation might cause the gas-filled krytron to trigger inadvertently.)

Krytrons and their variations are still manufactured by Perkin-Elmer Components, and used in a variety of industrial and military devices. They are most (in)famous for their use in igniting the exploding-wire detonators in atomic bombs, their original application. They are also used to trigger large flashlamps in photocopiers, lasers and scientific apparatus, as well as firing ignitors for industrial explosives.

References and External Links

• E G & G Electronic Components Catalog, 1994.

• http://homepage.ntlworld.com/electricstuff/pulse.html#Krytron - John Pasley's article about gas-filled switch tubes, Krytron section.
• http://homepage.ntlworld.com/electricstuff/sparkgaps.html#krytron - Photo of a small glass krytron.