FKSPITZ

FKSPITZ = 9e-07

Spitzer parallel thermal conductivity prefactor in CGS.

The Spitzer heat flux along the magnetic field is

\[\mathbf{q} = -\kappa_0 T^{5/2}\, \hat{\mathbf{b}}\hat{\mathbf{b}} \cdot \nabla T\]

where \(\kappa_0 = 9 \times 10^{-7}\) erg cm⁻¹ s⁻¹ K⁻⁷/² is the Spitzer conductivity coefficient for a fully ionized hydrogen plasma. This constant is stored as a plain float (not an astropy Quantity) because it is used directly in normalized code expressions; the associated physical unit are erg cm⁻¹ s⁻¹ K⁻⁷/².

See FN_KAPPA for the conductivity normalization that converts the dimensionless code conductivity back to physical unit.