Spitzer resistivity

The Spitzer resistivity (or plasma resistivity) is an expression describing the electrical resistance in a plasma, which was first formulated by Lyman Spitzer in 1950. The Spitzer resistivity of a plasma decreases in proportion to the electron temperature as formula_1. 
The inverse of the Spitzer resistivity formula_2 is known as the Spitzer conductivity formula_3.
Formulation.
The Spitzer restitivity is classical model of electrical resistivity based upon electron-ion collisions and it is commonly used in plasma physics. The transverse Spitzer resistivity is given by:
and the parallel Spitzer resistivity by:
where formula_6 is the ionization of nuclei, formula_7 is the electron charge, formula_8 is the electron mass, formula_9 is the Coulomb logarithm, formula_10 is the electric permittivity of free space, formula_11 is Boltzmann's constant, and formula_12 is the electron temperature in kelvins. The two resistivities correspond to current perpendicular and parallel to a strong magnetic field (the collision rate is small compared to the gyrofrequency). In an unmagnetized case the resistivity is formula_13.
In CGS units, the expression is given by:
For arbitrary formula_6,
where
Disagreements with observation.
Measurements in laboratory experiments and computer simulations have shown that under certain conditions, the resistivity of a plasma tends to be much higher than the Spitzer resistivity. This effect is sometimes known as "anomalous resistivity" or "neoclassical resistivity." It has been observed in space and effects of anomalous resistivity have been postulated to be associated with particle acceleration during magnetic reconnection. There are various theories and models that attempt to describe anomalous resistivity and they are frequently compared to the Spitzer resistivity.