Extended Boltzmann analysis of electron swarm experiments

We present a method for generalizing the traditional two-term Legendre expansion solution of the Boltzmann equation in the context of electron swarm experiment analysis. The method is applied to the calculation of the distribution function and transport coefficients in ${\mathrm{N}}_2$ and in two model cases. We find that the two-term approximation is of limited validity for the cases considered here, and that four to eight terms in the Legendre series are required for convergence of the transport coefficients to the accuracy required for the determination of cross sections from swarm experiments.