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Thermionic emission is the liberation of charged particles from a hot electrode whose thermal energy gives some particles enough kinetic energy to escape the material's surface. The particles, sometimes called thermions in early literature, are now known to be ions or electrons .
This is called thermionic emission. The resulting cloud is negatively charged, and can be attracted to any nearby positively charged object, thus producing an electric current which passes through the vacuum. Space charge can result from a range of phenomena, but the most important are:
The Schottky effect or field enhanced thermionic emission is a phenomenon in condensed matter physics named after Walter H. Schottky. In electron emission devices, especially electron guns , the thermionic electron emitter will be biased negative relative to its surroundings.
From a physical electronic viewpoint, thermionic energy conversion is the direct production of electric power from heat by thermionic electron emission. From a thermodynamic viewpoint, [1] it is the use of electron vapor as the working fluid in a power-producing cycle.
Electron gun from an oscilloscope CRT Setup of an electron gun. 1. Hot cathode.2. Wehnelt cylinder.3. Anode. A direct current, electrostatic thermionic electron gun is formed from several parts: a hot cathode, which is heated to create a stream of electrons via thermionic emission; electrodes generating an electric field to focus the electron beam (such as a Wehnelt cylinder); and one or more ...
In vacuum tubes and gas-filled tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. This is in contrast to a cold cathode , which does not have a heating element.
Thermionic emission In thermionic electron guns , the work function and temperature of the hot cathode are critical parameters in determining the amount of current that can be emitted. Tungsten , the common choice for vacuum tube filaments, can survive to high temperatures but its emission is somewhat limited due to its relatively high work ...
In condensed matter physics, the Nottingham effect is a surface cooling and heating mechanism that occurs during field and thermionic electron emission.The effect is named after physicist Wayne B. Nottingham who explained it in a commentary to 1940 experiments by Gertrude M. Fleming and Joseph E. Henderson.