Test-wave measurements of microwave absorption efficiency in a planar surface-wave plasma reactor

A major obstacle for experimental surface-wave (SW) excitation and propagation studies in SW plasma is the self-consistent behaviour of the latter, which does not permit continuous variation of the electron density n(e). In the present study, we demonstrate how this obstacle can be overcome by an independent plasma source, in our case, an inductively coupled plasma (ICP) created by a high-power RF (13.56 MHz) generator. Through a rectangular waveguide short-circuited at its end by a movable plunger, we introduced into the ICP a weak (power less than 20 W) nonionising 2.4 GHz microwave. This permitted us to highlight important SW excitation and propagation phenomena. In particular, we confirmed the existence of the predicted [Jpn. J. Appl. Phys. 36 (1997) 4704] resonance minima in the n(e) dependence of the power reflection coefficient. The influence of the plunger position on the chamber matching was studied systematically and four different coupling aperture geometries were compared.