Abstract
Theoretical and experimental results are reported for the dispersion relations found for electromagnetic wave propagation along a coaxial line partially filled with an annular plasma column. Using the slow wave approximation it had been predicted by Napoli and Swartz and Pinder and Foulds that such a structure should support a backward wave and that this backward wave would be virtually unaffected if the inner conductor is withdrawn. The exact analysis which is here reported shows that whilst the backward wave is present without the inner conductor it is no longer present when the inner conductor is inserted. The absence of the backward wave in the coaxial line was also shown by the experiment that was performed. The experiment was performed with a novel standing wave detector which was developed for this purpose. For the theoretical aspect of this work a technique for solving certain types of differential equations was developed. The theory when applied to a multi-layered model of a plasma also failed to show the presence of the backward wave for the coaxial line arrangement.