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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.

The validity of actinometry to monitor oxygen atom concentration in O2-N2 microwave discharges created by surface wave is investigated. The plasma is created with a gas flow in a quartz tube of inner diameter 16 mm at pressures in the Torr range. First, it is shown that the reliability of actinometry can be deduced from the longitudinal profile of the actinometry signal. Second, absolute concentrations of oxygen atoms are estimated from the experimental actinometry signal and agree satisfactorily with concentrations simultaneously measured by vacuum ultraviolet (VUV) absorption downstream from the plasma. Moreover, upon varying the nitrogen percentage (0%–100%), it is evidenced that the actinometry signal is proportional to the concentration measured by VUV absorption. Furthermore, it is evidenced that the oxygen dissociation rate is only 2% in pure oxygen plasmas, while it reaches 15% (433 MHz) or 30% (2450 MHz) for mixtures containing more than 20% of nitrogen. This drastic increase in [O] upon the addition of N2 is extensively discussed and, finally, attributed to a decrease in the recombination frequency of oxygen atoms on the quartz wall, in the presence of nitrogen.

We investigate a source of H atoms generated by a low-pressure surface wave discharge (2.45 GHz). We study the influence of microwave power both on the discharge characteristics on the H atom density, which has been measured by actinometry. Dissociation levels of H2 are much higher (75%) at low microwave power than at high power (10%). Unlike what has been found in oxygen surface wave plasmas, discharge characteristics depend strongly on microwave power, due to an important coupling between discharge equilibrium and kinetics of the atomic hydrogen. These results are explained taking into account the effect of discharge tube wall temperature on atomic recombination. The wall recombination probability gamma is estimated as a function of the microwave power: it ranges from 6*10-3 to 6*10-2, which is very high in comparison with values determined previously under post-discharge conditions.

This paper reports on an experiment in argon discharges produced by surface waves at 2.45 GHz. A self-consistent description of these discharges at low pressure ( p < 10 Torr) is presented. Characteristics such as the electron density, the maintaining electric field (E), the collision frequency for momentum transfer Y and the mean power required for maintaining the electron-ion pair 8 are determined as functions of the product of the pressure and the plasma diameter. In particular, scaling laws are verified for v and 8. It is concluded that experimental surface-wave discharges behave similarly to positive-column discharges.

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