# Degree of ionization

The **degree of ionization** (rarely also **degree of ****ionization** ) is a term from physics that is used specifically in plasma physics .

In plasma physics it is used to categorize plasmas and to describe different properties. It can assume values between zero (completely neutral) and one (completely ionized, all electrons are free). However, the degree of ionization is not a simple quotient (e.g. in percent ) of two particle numbers or densities : Since atoms and molecules can be ionized several times and there are different ionization energies in gas mixtures , the individual parts of the gas contribute differently to the degree of ionization.

A frequently used mathematical formalism based on these considerations for determining the degree of ionization of a gas as a function of temperature , particle density and ionization energy is provided by the Saha equation .

## Further information

- Ulrich Stroth: Plasma Physics . 1st edition. Vieweg + Teubner, Wiesbaden 2011, ISBN 978-3-8348-1615-3 .