A krytron is a specialized electronic device for the extremely fast switching (e.g., 5 nanosecond) of moderately high power electrical pulses. It is a member of the subclass of cold cathode trigger devices in the broader class of pulse power switching devices. While there are multiple applications, the strategically sensitive, dual-use reason that they are under tight export controls is that they are a building block for the triggering mechanisms of many nuclear weapons. The speed and reliability of switching distinguish it rather than its absolute power switching ability; a typical krytron impulses up to approximately 3000 amperes and 5000 volts.
Physically, it is a gas-filled tube, with the gas kept ionized because the tube contains a small radioactive source, usually a beta emitter. It has four electrodes, two for the triggering impulse and two for the power load to be transferred.
Non-nuclear applications include photographic flash lighting and laser welding.