The energy balance of a plasma in partial local thermodynamic equilibrium

The energy balance for electrons and heavy particles constituting a plasma in partial local thermodynamic equilibrium is derived. The formulation of the energy balance used allows for evaluation of the source terms without knowledge of the particle and radiation transport situation, since most of the contributions that arise from that situation (diffusion, local capture of radiation, etc.) are taken into account in the nonequilibrium term. The small correction for the contribution of the loss of excited states, which is slightly overestimated in this approach, can usually be neglected. The overpopulation factor, which can often be evaluated from measurements of the pressure, electron density, and temperature, becomes one of the most important plasma parameters; in the energy balance it accounts for most of the phenomena which may be difficult to evaluate otherwise. As an illustration, some rate coefficients are given for an argon plasma, and the evolution of the several terms of the electron energy equation in a flowing cascaded arc is discussed