ABSTRACT
Plasma is a relatively complex medium, consisting of a mixture of free electrons and ions, susceptible to electric and magnetic forces in addition to those acting also on classical neutral gases or fluids. Although this chapter is dealing mainly with plasma media, it may be instructive first to summarize some basic equations and results for the simpler case dealing with neutral fluids and gases, in order to demonstrate how classical continuum mechanics forms the basis of the description also of plasma dynamics. In the absence of creation or loss of particles, any medium will follow a continuity equation in terms of velocity field and mass density. A fluid has to follow Newton’s second law, giving a force equal to mass times an acceleration. An equation of state, relating pressure to, for instance, mass density, can be obtained from thermodynamics and statistical mechanics.
