Plasma parameters define various characteristics of a plasma, an electrically conductive collection of charged and neutral particles of various species (electrons and ions) that responds collectively to electromagnetic forces.
[1] Such particle systems can be studied statistically, i.e., their behaviour can be described based on a limited number of global parameters instead of tracking each particle separately.
[3] All quantities are in Gaussian (cgs) units except energy
For the sake of simplicity, a single ionic species is assumed.
(in the case of a fully ionized atom,
equals to the respective atomic number).
The other physical quantities used are the Boltzmann constant (
In the study of tokamaks, collisionality is a dimensionless parameter which expresses the ratio of the electron-ion collision frequency to the banana orbit frequency.
denotes the electron-ion collision frequency,
is the major radius of the plasma,
denote, respectively, the mass and temperature of the ions, and
Temperature is a statistical quantity whose formal definition is
or the change in internal energy with respect to entropy, holding volume and particle number constant.
A practical definition comes from the fact that the atoms, molecules, or whatever particles in a system have an average kinetic energy.
If the velocities of a group of electrons, e.g., in a plasma, follow a Maxwell–Boltzmann distribution, then the electron temperature is defined as the temperature of that distribution.
For other distributions, not assumed to be in equilibrium or have a temperature, two-thirds of the average energy is often referred to as the temperature, since for a Maxwell–Boltzmann distribution with three degrees of freedom,
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).
Each kelvin (1 K) corresponds to 8.617333262...×10−5 eV; this factor is the ratio of the Boltzmann constant to the elementary charge.
[6] Each eV is equivalent to 11,605 kelvins, which can be calculated by the relation
The electron temperature of a plasma can be several orders of magnitude higher than the temperature of the neutral species or of the ions.
Firstly, many plasma sources heat the electrons more strongly than the ions.
Secondly, 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.
Therefore, equilibration of the temperature happens very slowly, and is not achieved during the time range of the observation.