Physics:Magnetic diffusivity

Short description: A parameter in plasma physics

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:

[math]\displaystyle{ \eta = \frac{1}{\mu_0 \sigma_0} }[/math],

while in Gaussian units it can be defined as

[math]\displaystyle{ \eta = \frac{c^2}{4\pi\sigma_0} }[/math].

In the above, [math]\displaystyle{ \mu_0 }[/math] is the permeability of free space, [math]\displaystyle{ c }[/math] is the speed of light, and [math]\displaystyle{ \sigma_0 }[/math] is the electrical conductivity of the material in question. In case of a plasma, this is the conductivity due to Coulomb or neutral collisions: [math]\displaystyle{ \sigma_0=\frac{n_ee^2}{m_e\nu_c} }[/math], where

• [math]\displaystyle{ n_e }[/math] is the electron density.
• [math]\displaystyle{ e }[/math] is the electron charge.
• [math]\displaystyle{ m_e }[/math] is the electron mass.
• [math]\displaystyle{ \nu_c }[/math] is the collision frequency.

See also

• Electrical resistivity and conductivity