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

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