Two-Fluid Description of Plasmas

Abstract

We have learnt in Chapter one that an electrically quasi-neutral system of negative and positive charges qualifies to be a plasma and that a plasma exhibits cooperative phenomena on certain spatial and temporal scales. Some of the consequences of the quasi-neutral nature of a plasma can be studied by treating each of its constituent components as a fluid. Thus, at this level of description, an electron — proton plasma consists of two fluids — the electron fluid and the proton fluid. Each fluid is allowed to have charge density fluctuations about the overall mean density. This is the most significant deviation from the MHD description. The charge density fluctuations produce current density fluctuations. The associated electric and magnetic fields can be determined from Maxwell’s equations. The space and time dependences of these fields can manifest themselves in the forms of longitudinal and transverse waves (Chen 1974; Melrose 1986).