ABSTRACT
In a fluid description of plasmas, as well as other media, we use space and time as independent variables in analyzing local densities and bulk velocities, for instance. The actual distribution of particle velocities in a small volume element is assumed a priori to be a Maxwellian locally. Due to the long range of the Coulomb interaction, a charged particle can interact with many other particles simultaneously. This can be true even if we allow for Debye shielding; for sub-thermal velocities any charged particle in plasma is interacting only with other charged particles within its local Debye sphere. Since a fluid description of the plasma in a number of cases reproduces many basic wave properties, the existence of wave-modes in particular, it seems intuitively reasonable to expect some sort of relation between descriptions based on a kinetic and a fluid model.
