Harmonic Generation in Ionized Nitrogen

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Abstract
The effect of collisions on the generation of harmonics in ionized molecular nitrogen subjected to an alternating electric field is examined theoretically. The electron distribution function is approximated by a function containing four undetermined parameters. The Boltzmann transport equation is then used to obtain a set of kinetic equations for these parameters. The kinetic equations are used to determine the harmonic generation in a uniform ionized gas subjected to a homogeneous alternating electric field. The nonlinearity which must be present in the kinetic equations in order to produce harmonics is assumed to arise from velocity-dependent electron-molecule collision frequencies. It is shown that the principal harmonic generated is the third harmonic. An expression for the third harmonic current density is obtained. Available elastic and inelastic cross-section data are used to apply the general result to the case of ionized nitrogen, and the results are compared with two related microwave discharge experiments.