On the Cutoff Distance and the Classical Energy-Averaged Electron-Ion Momentum Transport Cross Section in Ideal and Nonideal Plasmas

The wide use of a speed-independent distance as a cutoff impact parameter together with Rutherford's scattering formula, within the cutoff theory, to account for charge screening in plasma environment embodies a clear inconsistency. A new physically justified choice of the cutoff distance is introduced and used to derive a closed form expression for the effective momentum transport cross section. A simple approximation for the present Coulomb logarithm, free of special functions, is also presented and assessed. A comparison with experimentally recovered data for the reduced Coulomb conductivity showed better agreement and better physical behavior of the present expressions compared with previous cutoff expressions in the literature.