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This page is intended as a "cheat sheet" or brief overview of basic plasma physics concepts.


====== Plasma viscous flow (electrical conductivity and diffusion) ======
When forces are applied to a plasma (or any fluid) in the presence of a damping force (viscosity, friction, collisions, etc), the plasma achieves a steady-state velocity (i.e. terminal velocity) with the form

$\left< v \right> = \text{constants} * F_{orces}$.  

If the forces are electromagnetic, the process is called electrical conductivity (or resistivity).  If the forces are pressures and density gradients, the process is called diffusion.  The two cases can also be mixed.

==== Electrical conductivity ====

Terminal velocities associated with electromagnetic forces is called electrical conductivity.  

In terms of current, it has the form

$J= n \mu F_{orces} = \sigma \frac{F_{orces}}{e} $

where $\mu$ (the mobility) is a collection of constants (mass, viscosity, charge, etc) and $\sigma$ is the **electrical conductivity** (constant or tensor).  

Electrostatic form,

$ J  = \sigma E $

Electromagnetic form,

$  J   = \sigma \left( E + v \times B \right) $ [[https://w3.pppl.gov/~jchen/books/JDCallen/chap6.pdf|callen_ch6]]

==== Diffusion ====

Diffusion is the terminal velocity due to pressure and density gradients.  

$\Gamma = n v = D \nabla n$

where $\Gamma$ is the flux and $D$ is the set of constants that make up the diffusion coefficient.

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