Spark gap
Usually, the action of ionizing the gas is violent and disruptive, often leading to sound (ranging from a snap for a spark plug to thunder for a lightning discharge), light, and heat.
Their most widespread use today is in spark plugs to ignite the fuel in internal combustion engines, but they are also used in lightning arresters and other devices to protect electrical equipment from high-voltage transients.
The heat of the ionization trail, but more importantly, UV radiation and hot free electrons (both cause the formation of reactive free radicals)[citation needed] ignite a fuel-air mixture inside an internal combustion engine, or a burner in a furnace, oven, or stove.
One might also find small Jacob's ladders mounted on top of ceramic insulators of high-voltage pylons.
Smaller spark gaps are often used to protect sensitive electrical or electronic equipment from high-voltage surges.
These low-cost devices are often used to prevent damaging arcs between the elements of the electron gun(s) within a cathode-ray tube (CRT).
[citation needed] Small spark gaps are very common in telephone switchboards, as the long phone cables are very susceptible to induced surges from lightning strikes.
Spark gaps are sometimes implemented on Printed Circuit Boards in electronics products using two closely spaced exposed PCB traces.
A calibrated spherical spark gap will break down at a highly repeatable voltage, when corrected for air pressure, humidity and temperature.
When a spark gap consists of only two electrodes separated by gas, the transition between the non-conducting and conducting states is governed by Paschen's law.
These limitations on the speed with which discharge may be initiated mean that spark gaps with two electrodes typically have high jitter.
Triggered spark gaps share many similarities with other gas-filled tubes such as thyratrons, krytrons, ignitrons, and crossatrons.
A triggered vacuum gap consists of three electrodes in an airtight glass or ceramic envelope that has been evacuated.
Triggered vacuum gaps are also rad hard because in the non-conducting state they do not contain any gas that could be ionized by radiation.
