# Magnetic diffusivity

The magnetic diffusivity is a parameter in plasma physics. It appears in the Magnetic Reynolds number. The magnetic diffusivity is defined as:[1]

$\eta = \frac{1}{\mu_0 \sigma_0}$.
• $\mu_0$ is the permeability of free space.
• $\sigma_0$ is the electrical conductivity of the material in question. In case of a plasma, this is the conductivity due to Coulomb or neutral collisions: $\sigma_0=\frac{n_ee^2}{m_e\nu_c}$, where
• $n_e$ is the electron density.
• $e$ is the electron charge.
• $m_e$ is the electron mass.
• $\nu_c$ is the collision frequency.

## References

1. ^ W. Baumjohann and R. A. Treumann, Basic Space Plasma Physics, Imperial College Press, 1997