The magnetic diffusivity is a parameter in plasma physics which appears in the magnetic Reynolds number. It has SI units of m²/s and is defined as:
while in Gaussian units it can be defined as
In the above, is the permeability of free space, is the speed of light, and is the electrical conductivity of the material in question. In case of a plasma, this is the conductivity due to Coulomb or neutral collisions: , where
- is the electron density.
- is the electron charge.
- is the electron mass.
- is the collision frequency.
- ^ W. Baumjohann and R. A. Treumann, Basic Space Plasma Physics, Imperial College Press, 1997.