Transport phenomena in plasmas can be promoted by external and by internal forces. In a spatially homogeneous plasma under the influence of external forces a drifting of the electrons can occur. This motion induced by external forces is referred to as mobility. Since the electrons have mass and electric charge, their motion implies transport of mass and conduction of electricity when acted upon by an external electric field. On the other hand, in a spatially inhomogeneous plasma, collisions cause the electrons to drift from the high-pressure to the low-pressure regions. The existence of pressure gradients is associated with the existence of either density gradients or temperature gradients, or both. This motion of the electrons, induced by internal pressure gradients, is called diffusion. Since the electrons also have kinetic energy associated with their random thermal motion, their drift implies the transport of thermal energy and therefore heat conduction. When the plasma is spatially inhomogeneous and is also acted upon by external forces, then the particle flux is due to both diffusion and mobility.
KeywordsBoltzmann Equation Velocity Space Collision Frequency Conductivity Tensor Collision Term
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