Plasma transport coefficients in a magnetic field by direct numerical solution of the Fokker--Planck equation

Significant departures from standard transport coefficients [e.g., Sov. Phys. JETP 6, 338 (1958)] have been found for the electron current and heat flux in a fully ionized plasma. These have been discovered by carrying out a direct and accurate numerical solution of the linearized Fokker--Planck equation using a Cartesian tensor expansion of the distribution function. The results, which were carried out for plasmas of various atomic numbers, show the presence of major inaccuracies (errors of up to 65%) in Braginskii coefficients β/sub X/, kappa/sub perpendicular/, and kappa/sub X/ (as conventionally defined) for Hall parameters ωtau in the range 0.3< or approx. =ωtau< or approx. =30. Surprisingly, α/sub X/ and β/sub perpendicular/ are found to depend on tau/(ωtau)2/sup //3 and 1/(ωtau)5/sup //3, and not on tau/(ωtau) and 1/(ωtau)2, respectively, as ωtau→infinity. An analytic expansion for large ωtau verifies this result, showing that the relatively cold unmagnetized electrons in the distribution function play a dominant role in the cross-field transport. The numerical results are fitted to within 15% to a polynomial in ωtau for various values of Z