Anomalous Quasi TE11 Mode Absorption in the Afterglow of a Positive Column Occupying a Long Guide Cylindrical Wave

Experimental observations of reflection and transmission of a cw wave propagating in the quasi TE11 mode in a cylindrical wave guide filled with a time decaying plasma are presented. The discharge column occupies, with the exception of a thin layer of quartz, the entire cross-section of the wave guide. The transmitted wave displays a series of optima whose relative amplitudes increase with decreasing electron density. With regard to phase separation, frequency and pressure variation the extrema seem to fit a simple theoretical model, which, however, fails to explain the absorption mechanism, the latter being also associated with a reversed cross-modulation not explainable by the Ramsauer effect.