[en] Attenuation of a surface wave is studied experimentally in an unmagnetized cylindrical plasma column sustained by the wave itself. The losses connected with the plasma creation are negligible and the wave propagation is described by the relations for the linear regime. It is shown that a simple theory of collisional attenuation, obtained by extension of the collisionless theory to the case of few collisions, predicts very well the dependence of the attenuation on the electron density, the electron collision frequency, and the geometry of the plasma column. (author)

[en] The propagation of electron surface waves can be used to sustain long plasma columns. The relation between the axial distribution of the electron density observed along the plasma column and the corresponding power distribution of the surface wave that produces it is investigated. It is found that the electron density decreases almost linearly along the plasma column in the direction of the wave propagation. This is explained by assuming that the number of electrons produced over a given axial length is proportional to the wave power absorbed over that same length

[en] The authors report an experimental investigation of the conditions required to sustain a plasma column through the propagation of the m = 1 mode surface wave. It reveals that, given a discharge tube radius a, there corresponds a minimum frequency value of f_m below which the discharge cannot be achieved; conversely, for a given operating frequency f, the tube radius must exceed some minimum value a_m for the plasma to be sustained. These minimum conditions required to obtain the discharge are observed to obey a scaling law of the form (af)_m ≅ const., where the constant is independent of the gas nature and pressure. Theoretically, the dispersion equation of the m = 1 mode wave shows no low frequency cut-off. However, it is found that the specific dependence of the wave attenuation coefficient on the frequency and on the tube diameter can ultimately account for the observed limitations when the wave is used to sustain a plasma. A discharge stability criterion is proposed that recovers the observed scaling laws determining the minimum tube radius and wave frequency values. It is further shown that using a surface wave to sustain a discharge in large diameter tubes (> 50 mm) at 2.45 GHz is bound to yield plasma columns with aximuthal inhomogeneities because the wave then propagates in the m = 1 or higher order modes