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

Abstract

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.

Modelling of diamond deposition microwave cavity generated plasmas

“…Such a solution can be attempted either in the frequency domain or in the time domain [20,21,[66][67][68][69]. The solution methods using a wave propagation analysis based on a set of dispersion equations in the frequency domain were developed for a large number of plasma structures such as surface-wave discharges [66,[70][71][72] or magnetized plasmas [5,18,[72][73][74]. As far as MW cavity systems are concerned, both frequency [75][76][77][78][79] and time domain [20] approaches were used to investigate the EM field in the cavity.…”

Travelling-wave-sustained discharges

“…Whereas the interferogram method and the field radial decay method are based on measurements of the properties of the wave which produces the discharge, the test-wave method involves measurements of the dispersion behaviour of small amplitude test waves. Suggested in a very early study [131] it has been recently developed precisely [132] involving the new knowledge on the dispersion behaviour of SWs in inhomogeneous collisional plasmas.…”

Spectroscopic investigation of an expanding surface wave produced plasma

“…The propagation of surface waves in the presence of longitudinal density gradients has been treated at length in the literature. [5][6][7][8][9][10] Only little effort, however, has been devoted to the investigation of surface waves that are expanding into a region with lowered gas pressure. Such kinds of discharges are not only interesting from a theoretical point of view, but also important for applications.…”