Modification of the electron velocity distribution function in weakly ionized plasmas by nonisotropic elastic-scattering processes

After a brief presentation of a technique for solving Boltzmann's equation in multiterm approximation in the presence of nonisotropic elastic and (conservative) inelastic collisions of the electrons with gas atom or molecules, the results of a systematic study of the impact of a nonisotropic scattering in elastic collisions are reported. By using an appropriate distribution for the scattering angle, the effects on isotropic (i.e. energy) distribution, total anisotropy of the velocity distribution and some transport and rate coefficients are investigated for a model plasma, from mainly forward to mainly backward scattering. The results are then compared with those found for isotropic scattering. A particular large impact has been found, for istance, on energy distribution and some macroscopic quantities for narrow forward scattering, while the classical two-term approximation especially is found to fail for backward scattering. The results are qualitatively explained by considering the balance between energy gain by the field and collisional dissipation and the modifications produced when changing the anisotropy of elastic scattering