Harmonic generation of microwave frequencies in plasmas

The ability of RF plasma discharges to generate harmonics of the source frequency was reported as early as 1950s by Margenau and Hartmann [1]. Experiments by Krenz and Kino [2] measured up to seventh harmonic in a spherical discharge with considerable efficiencies. Since the Ions and heavy species are usually slow in responding to a high-frequency signal it is the dynamics of electrons that determine the overall discharge characteristics. The equation of motion that governs the electron dynamics in a plasma discharge and the relation between the current and electron velocity is non-linear. These two factors lead to creation of harmonics of the input frequency. In this work we study the physics of harmonic generation in a microdischarge using a computational model. The model is based on fluid description of plasma. A discharge which is electrostatically excited by a microwave frequency source is simulated and its response is measured. The model is used to provide insights into the non-linear process in the plasma that leads to the creation of higher order harmonics. Microdischarges and large-size discharges are analyzed for their ability to produce harmonics. \\[4pt] [1] H. Margenau and L.M. Hartman, ``Theory of high frequency gas discharges. II - Harmonic components of the distribution function.'' Phys. Rev. 73, 309 (1948).\\[0pt] [2] J.H. Krenz and G.S. Kino, ``Harmonic Generation and Parametric Oscillations in Plasma,'' Journal of Applied Physics 36, 8 (1965)