Magnetic diffusivity
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. See also

 Electrical resistivity and conductivity

References

Plasma parameters