Microwave and RF plasmas are finding increasing use in materials processing, plasma chemistry, chemical analysis, and other fields. This is stimulating the search for suitable plasma sources. In the 1970s, electromagnetic surface waves were put to use to sustain plasmas and an efficient microwave device, called a surfatron. was developed for this purpose. Recent work has shown that such discharges can also operate at radio frequencies. A large number of on surface-wave plasmas experimental data have been accumulated-their modelling is well advanced and they have found applications in various fields of research and technology. This paper reviews the physical principles of operation and the design of surface-wave plasma sources. Since the wave launcher is the central component of the source, this review presents a unified description of several compact, efficient. and easy to operate launchers specifically intended for plasma generation that have been developed over the past fifteen years. It is now possible to sustain such plasmas at frequencies ranging from 1 MHz to 10 GHz, in a pressure domain extending from 10-5Torr up to few times atmospheric pressure, and in a rich variety of plasma vessels and reaction chambers.

Long quiescent, stable and reproducible cylindrical plasma columns can be obtained as a result of the propagation of electromagnetic surface waves. The frequency of these waves is of the order of the electron-plasma frequency and it lies in that part (≃ 300-4 000 MHz) of the microwave spectrum where power generators with large enough output powers are readily available, at reasonable cost. Moreover, these waves can be excited very efficiently by using appropriate launching structures such as the surfatron. Such plasmas can, in certain instances, advantageously replace the positive column of DC discharges. This paper reviews the properties of the plasma columns sustained by the azimuthally symmetric surface wave. Special attention is given to the radial and axial electron density distributions, as well as to the radial density distributions of excited (radiative and metastable) atoms. Some demonstrated applications as well as further potential applications are also presented

We report theoretical and experimental investigations of an atmospheric pressure, microwave plasma torch with axial gas injection (torche A injection axiale elements senn'ng the purpose of wavemode conversion and impedance-matching. The device includes features common to various waveguide-fed torches disclosed previously by other authors, but not yet modelled. Our paper provides a simple equivalent circuit description of the torch operation that accounts for its impedance-matching, power transfer to plasma and tuning characteristics, as verified experimentally. From the outcome of the model and using our experimental results, we introduce new features in the torch design that enable one to optimize its performance. We also examine ways of simplifying its structure and operation. design), !t is a wayeg"de-based s!ruc!ure cop,pr[sing b~!h waveguide and so&yiaj

Long plasma columns, in many instances preferable to the positive columns of DC discharges, can be obtained by means of a UHF surface wave propagating along the column. This is possible through the use of a novel wave-launching structure, called a surfatron. The launcher is compact and located on the outside of the dielectric tube containing the plasma. The surfatron is described and analysed in terms of an equivalent circuit theory. Guidelines for its design and operation are given.

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