Theory of Gas Ionization by Intense Electromagnetic Fields

The distribution function of the electrons produced in the interaction between an intense electromagnetic wave and a neutral gas is derived and is shown to be nonequilibrium and anisotropic. By assuming that the time scale of gas ionization is much greater than the field period, it is shown that the electron distribution function formed in microwave and optical discharges has sharp anisotropy affecting the discharge plasma. The anisotropy stimulated by the inequality of average longitudinal and transverse energy of electrons is investigated. Furthermore, the parametric instability stimulated by scattering of incident wave on the density oscillation of plasma under the positive slope of EDF with respect to velocity is studied.