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:

$\eta ={\frac {1}{\mu _{0}\sigma _{0}}}$,

while in Gaussian units it can be defined as

$\eta ={\frac {c^{2}}{4\pi \sigma _{0}}}$.

In the above, $\mu _{0}$ is the permeability of free space, $c$ is the speed of light, and $\sigma _{0}$ is the electrical conductivity of the material in question. In case of a plasma, this is the conductivity due to Coulomb or neutral collisions: $\sigma _{0}={\frac {n_{e}e^{2}}{m_{e}\nu _{c}}}$, where

• $n_{e}$ is the electron density.
• $e$ is the electron charge.
• $m_{e}$ is the electron mass.
• $\nu _{c}$ is the collision frequency.

See also

• Electrical resistivity and conductivity