Thermionic Power Converter

thermionic power converter, also called thermionic generator, thermionic power generator, or thermoelectric engine, any of a class of devices that convert heat directly into electricity using thermionic emission rather than first changing it to some other form of energy.

A thermionic power converter has two electrodes. One of these is raised to a sufficiently high temperature to become a thermionic electron emitter, or “hot plate.” The other electrode, called a collector because it receives the emitted electrons, is operated at a significantly lower temperature. The space between the electrodes is sometimes a vacuum but is normally filled with a vapour or gas at low pressure. The thermal energy may be supplied by chemical, solar, or nuclear sources. Thermionic converters are solid-state devices with no moving parts. They can be designed for high reliability and long service life. Thus, thermionic converters have been used in many spacecraft.

Emission of electrons from a hot plate is analogous to the liberation of steam particles when water is heated. These emitted electrons flow toward the collector, and the circuit can be completed by interconnecting the two electrodes by an external load, shown as a resistor in the figure. Part of the thermal energy that is supplied to liberate the electrons is converted directly into electrical energy, while some of the thermal energy heats the collector and must be removed.