A short video to accompany this material Basic Plasma Parameters can be found here

Consider an idealized plasma consisting of an equal number of electrons, with mass *m***_{e }**and charge

**(here,**

*-e***denotes the**

*e**magnitude*of the electron charge), and ions, with mass

*m***and charge**

_{i}**. We do not necessarily demand that the system has attained thermal equilibrium, but nevertheless use the symbol to denote a**

*+e**kinetic temperature*measured in energy units (

*i.e.*, joules). Here,

**is a particle speed, and the angular brackets denote an ensemble average.**

*v*The kinetic temperature of species ** S** is essentially the average kinetic energy of particles of this species. In plasma physics, kinetic temperature is invariably measured in

*electron-volts*(1 joule is equivalent to 6.24×10

^{18 }eV).

Quasi-neutrality demands that

where *n***_{s}** is the number density (

*i.e.*, the number of particles per cubic meter) of species

**.**

*S*Assuming that both ions and electrons are characterized by the same ** T** (which is, by no means, always the case in plasmas), we can estimate typical particle speeds via the so-called

*thermal speed.*

Note that the ion thermal speed is usually far smaller than the electron thermal speed:

Of course, ** n** and

**are generally functions of position in a plasma.**

*T*