Perfecting Braginskii's eletron transport coefficients for high collisionality plasmas

It is known that Braginskii's transport coefficients for the heat flow and frictional force are in error up to 65\% for some finite values of $x=\Omega \tau$ and have significant error in the large-$x$ limit.~\footnote{E. M. Epperlein and M. G. Haines, Phys. Fluids {\bf 29}, 1029 (1986).} Here $\Omega$ is the electron-cyclotron frequency, and $\tau$ is the electron-ion collision time. In this work, we find fitting formulas which are practically exact (less than 1\% error) for the whole range of $x$ and $Z$, the ion charge, checked up to $Z$=100. The new fitting formulas are based on calculations with 160 moments (Laguerre polynomials)~\footnote{J.-Y. Ji and E. D. Held, Phys. Plasmas {\bf 13}, 102103 (2006); {\bf 15}, 102101 (2008).} for $x<100$ and on the asymptotic form for large $x$-values.