Experimental and theoretical studies of the electrode impedance effect in capacitive discharges

It is widely acknowledged that one can observe a strong harmonics content in the current of an asymmetric capacitive discharge, even in case of a strongly sinusoidal driving voltage. This particular phenomenon is directly connected to the heating of electrons.\footnote{T. Mussenbrock et al., Phys. Rev. Lett {\bf 101}, 085004 (2008).} It has been shown by means of careful measurements that the increase of certain harmonics indicates an increase of the electron density.\footnote{Y. Yamazawa et al., Jpn. J. Appl. Phys. {\bf 46}, 7453 (2007).} In this paper we revisit these experiments. We also propose a model to study the possibility of controlling the excitation of current harmonics using an external circuit and its effect on the electron density (which is often referred to as the electrode impedance effect).