On the reliability of the Bhatnagar-Gross-Krook collision model in weakly ionized plasmas

The ion velocity distribution in weakly ionized plasma with mobility-limited ion flow driven by an electric field is studied numerically, with the assumption that the charge exchange is the dominant mechanism of ion scattering. The calculations are performed using the realistic constant mean free path model and the results are compared with those given by the constant mean free time (Bhatnagar-Gross-Krook) model. The comparison shows that in the regime where the flow velocity is less than or comparable with the thermal velocity of neutrals the two models yield quite similar velocity distributions. Nevertheless, even in this regime, there are quantitative differences that might be important for certain cases. The implications for theoretical investigations in dusty plasmas are discussed.