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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:[1]

\( \eta = \frac{1}{\mu_0 \sigma_0}, \)

while in Gaussian units it can be defined as

\( {\displaystyle \eta ={\frac {c^{2}}{4\pi \sigma _{0}}}}. \)

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: \( \sigma_0=\frac{n_ee^2}{m_e\nu_c} \) , where

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

See also

Electrical resistivity and conductivity


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

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