Some observations on the slab-line cavity developed for the excitation of electrodeless discharge sources

The design approach which leads to a simple new cavity structure, the slab-line cavity, for a microwave-excited electrodeless discharge light source, is outlined. The magnitude of the microwave impedance of a low-pressure neon electrodeless discharge was found to vary between 0.5 and 4 k Omega depending on the gas pressure and incident microwave power. The microwave results obtained show the difficulties in evaluating the system performance and in particular in the use of microwave power as an independent variable to describe the electrodeless discharge tube behaviour in any microwave cavity.