Thermions – en

30-second summary

Thermions

Thermions are electrically charged particles or ions that are emitted by a heated conducting material via thermionic emission. The electrons emitted from the cathodes of electron tubes (such as cathode ray tubes) are thermions.

Thermionic emission (archaically known as the Edison effect) is the flow of charged particles (electrons or ions) called thermions from an electrode, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface.

This process is crucially important in the operation of a variety of electronic devices (vacuum tubes) and can be used for electricity generation (such as thermionic converters) or cooling.

thermions

Thermions

Thermions are electrically charged particles or ions that are emitted by a heated conducting material via thermionic emission. The electrons emitted from the cathodes of electron tubes (such as cathode ray tubes) are thermions.

Thermionic emission (archaically known as the Edison effect) is the flow of charged particles (electrons or ions) called thermions from an electrode, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface. This process is crucially important in the operation of a variety of electronic devices (vacuum tubes) and can be used for electricity generation (such as thermionic converters) or cooling.

diode
The Edison effect in a diode tube. A diode tube is connected in two configurations; one has a flow of electrons and the other does not.

A thermionic energy converter is a device consisting of two electrodes placed near one another in a vacuum. One electrode is normally called the cathode or emitter, and the other is called the anode or plate. The hot cathode can be a metal filament, a coated metal filament, or a separate structure of metal or carbides or borides of transition metals.

Ordinarily, electrons in the cathode are prevented from escaping from the surface by a potential-energy barrier. When an electron starts to move away from the surface, it induces a corresponding positive charge in the material, which tends to pull it back into the surface. To escape, the electron must somehow acquire enough energy to overcome this energy barrier. At ordinary temperatures, almost none of the electrons can acquire enough energy to escape. However, when the cathode is very hot, the electron energies are greatly increased by thermal motion. At sufficiently high temperatures, a considerable number of electrons are able to escape. The liberation of electrons from a hot surface is called thermionic emission. Vacuum emission from metals tends to become significant only for temperatures over 1,000 K (730 °C; 1,340 °F).

The electrons that have escaped from the hot cathode form a cloud of negative charges near it called a space charge. If the plate is maintained positive with respect to the cathode by a battery, the electrons in the cloud are attracted to it. As long as the potential difference between the electrodes is maintained, there will be a steady current flow from the cathode to the plate. A thermionic generator is like a cyclic heat engine, and its maximum efficiency is limited by Carnot’s law. It is a low-Voltage high current device where current densities of 25-50 (A/cm2) have been achieved at a voltage from 1-2V. The energy of high-temperature gases can be partly converted into electricity if the riser tubes of the boiler are provided cathode and anode of a thermionic generator with the interspace filled with ionized cesium vapor.

thermions

header - logo

The primary purpose of this project is to help the public to learn some exciting and important information about electricity and magnetism.

Privacy Policy

Our Website follows all legal requirements to protect your privacy. Visit our Privacy Policy page.

The Cookies Statement is part of our Privacy Policy.

Editorial note

The information contained on this website is for general information purposes only. This website does not use any proprietary data. Visit our Editorial note.

Copyright Notice

It’s simple:

1) You may use almost everything for non-commercial and educational use.

2) You may not distribute or commercially exploit the content, especially on another website.