Senditron

A senditron is a quick acting switch able to carry very high currents - up to several thousand amps.

The cathode, anode and auxiliary electrode consist of mercury pools. It uses a capacitive igniter. The ignition electrode extends down into the mercury pool and is insulated from it by a thin coating of dielectric material. A high voltage applied to the ignition electrode causes a small amount of electron emission. At this stage a high voltage momentarily applied to the auxiliary electrode causes ionisation of the mercury vapour which then starts the main discharge.