Ignitrons

Unlike a mercury arc rectifier, which needs multiple anodes to keep the arc alive, the ignitron has only one anode. The arc thus extinguishes after each period of conduction, but the ignitron has an igniter. The tip of the igniter dips into the mercury pool, and is specially shaped and made of a semiconducting material such as silicon carbide.

Smaller ignitrons are glass and air cooled, larger ones are metal and water cooled.

An example of an ignitron is the AJ5101.