ABSTRACT
For the transport processes comparatively long time scales and smooth spatial profiles of plasma parameters and fields are typical. For such conditions the collisions of plasma particles result in the formation of some sort of equilibrium state between the particles and the local and instantaneous values of the external fields. This partial equilibrium can significantly differ from thermodynamic equilibrium. In other words, an average particle is representative for description of the behavior of all the plasma particles in a given place and moment. The particles of each species can be described in terms of their density, mean velocity (or momentum), and mean energy. Such averaged description is usually called a fluid approximation, and the closed set of equations for these values known as fluid, or transport equations.
