The Quasi-hydrodynamic Approximation
In the conducting-fluid model a number of forces which act on the plasma are related to the pressure force. In an ordinary gas of neutral particles pressure transfer takes place solely by means of collisions. Thus, the pressure force acts only at densities high enough so that frequent collisions occur. An approximate method for describing equilibrium and gas motion in terms of a pressure is called the hydrodynamic approximation. The hydrodynamic approximation can also be applied to dense plasmas just as for any dense gas. However, it turns out that even in tenuous plasmas in which collisions do not play a significant role, one can imagine a pressure that acts on each particle at right angles to the magnetic field. The physical mechanism for pressure transfer is however, quite different from that in the dense-plasma situation. The mechanism in question is associated with the interaction of the drift current and the magnetization current.
KeywordsFrequent Collision Pressure Force Plasma State Magnetization Current Drift Current
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