Electron kinetics in atomic and molecular plasmas

In the first part of this paper we briefly review some basic concepts of kinetic theory. The concept of the velocity distribution function is first introduced and its meaning is discussed. Then, the Boltzmann equation is presented on physical grounds and it is shown that the fluid equations are its moments. In the second part, the Boltzmann equation for free electrons in a low-temperature plasma is analysed. It is shown how this equation can approximately be solved for electrons under a HF field of frequency ω (including the particular case of a dc field, which corresponds to the limit ω = 0) by using a first-order double expansion in spherical harmonics in velocity space and a Fourier series in time. The electron transport parameters, particle balance and energy balance are analysed from a general point of view. Finally, an application to argon and nitrogen is given. The effects of changes in the field frequency on the electron energy distribution function, transport parameters and power balance are discussed. The importance of the coupling between the electron and the vibrational kinetics in N₂ is emphasized.