Thermodynamics is the science which concerns itself with the properties and behavior of bodies in a state of thermal equilibrium. In a dense medium interparticle collisions lead to the rapid establishment of equilibrium conditions. Conversely, in a tenuous plasma, in which collisions are rare, large deviations from equilibrium can persist for a long time. As we shall see below, in fully ionized plasmas the probability of collisions between particles decreases rapidly with increasing temperature. Thus, we can say that dense, cold, and (in particular) weakly ionized plasmas are in thermal equilibrium as a rule. The properties of such plasmas can be described by thermodynamics. On the other hand, tenuous, fully ionized hot plasmas can exist for relatively long times in a nonequilibrium condition. In these cases a thermodynamic description of the plasma state is not valid.
KeywordsThermal Energy Thermal Equilibrium Momentum Space Electrostatic Energy Electron Volt
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