Electron temperature

If the velocities of a group of electrons, e.g. in a plasma, follow a Maxwell-Boltzmann distribution, then the electron temperature is well-defined as the temperature of that distribution. For other distributions, two-thirds of the average energy is often referred to as the temperature, since for a Maxwell-Boltzmann distribution with three degrees of freedom, $langle\; E\; angle\; =\; (3/2)\; langle\; k\_BT\; angle$.

The SI unit of temperature is the kelvin (K), but using the above relation the electron temperature is often expressed in terms of the energy unit electronvolt (eV). 1 K corresponds to 8.617343(15)×10^-5 eV; this factor is the ratio of the Boltzmann constant to the elementary charge.

The electron temperature of a plasma can be several orders of magnitude higher than the temperature of the neutral species or of the ions. This is a result of two facts. First, many plasma sources heat the electrons more strongly than the ions. Second, atoms and ions are much heavier than electrons, and energy transfer in a two-body collision is much more efficient if the masses are similar.