Dispersion studies of surface-wave-produced discharges with a view to diagnostics

Dispersion of surface-wave-produced plasmas and field behaviour outside the discharges are studied under the influence of collisions and radial and axial density inhomogeneities, the latter density, both in WKB and eigenfunction treatment, is carried through for a cylindrical discharge configuration. The trends of joint influences can be approximated by an extrapolation from WKB treatment, avoiding the large numerical effort of an accurate two-dimensional code. Some consequences for radiophysics diagnostics are pointed out. Whereas standard methods of phase measurements are only weakly affected, amplitude measurements are more subject to various influences. Therefore, potential extensions of methods using test waves of various frequencies can yield additional and improved information on the collision frequency and on the value of the radial inhomogeneity index. A procedure is suggested and exemplified with measurements at a helium discharge.