Classification of Equilibria in Plasmas

Abstract

Plasmas in complete thermodynamic equilibrium only exist in very special conditions like, for example, in the interior of stars. Plasmas are rarely found in equilibrium in laboratory because very often the walls enclosing such plasmas are transparent to the radiation fields over a wide range of frequencies. The radiation escapes and the fulfilling of the Planck radiation law is not achieved. At this point it is not possible to describe the radiation field by a unique temperature. Another source of disequilibrium is that walls have lower temperatures than the inner regions of plasmas and only one thermodynamic temperature does not exist. Other factor that contributes to the instability is the diffusion that causes the out flux of particles, changing the local density of the excited states influencing the production of charged particles for example.