Modeling of atmospheric-pressure plasma columns sustained by surface waves

Abstract

A self-consistent two-dimensional fluid-plasma model coupled to Maxwell's equations is presented for argon discharges sustained at atmospheric pressure by the propagation of an electromagnetic surface wave. The numerical simulation provides the full axial and radial structure of the surface-wave plasma column and the distribution of the electromagnetic fields for given discharge operating conditions. To describe the contraction phenomenon, a characteristic feature of high-pressure discharges, we consider the kinetics of argon molecular ions in the charged-particle balance. An original feature of the model is to take into account the gas flow by solving self-consistently the mass, momentum, and energy balance equations for neutral particles. Accounting for the gas flow explains reported discrepancies between measured and calculated plasma parameters when assuming the local axial uniformity approximation. In contrast to the low-pressure case, the latter approximation is shown to be of limited validity at atmospheric pressure. The gas temperature is found to be a key parameter in modeling surface-wave discharges sustained at atmospheric pressure. It determines the radial and the axial structure of the plasma column. The calculated plasma parameters and wave propagation characteristics using the present two-dimensional fluid model are in good agreement with our set of experimental data.

Absorption spectroscopy measurements of resonant and metastable atom densities in atmospheric-pressure discharges using a low-pressure lamp as a spectral-line source and comparison with a collisional-radiative model

“…8 displays the axial distribution of the values of L at the discharge axis obtained for the Ar I 763.51 nm and 738.39 nm lines and of the plasma glow diameter, taken as the half-width of the H β line lateral profile [5,6]. The value of L increases with z, as does the glow diameter in surface-wave sustained discharges [5,6,32], depending critically on the absorption line examined: taking L as the plasma glow diameter appears, therefore, inappropriate, as discussed further in relation with Fig. 10.…”

“…However, when gas pressure is increased above 1 kPa, the discharge becomes affected by the phenomenon of radial contraction [3][4][5][6]: the plasma glow retracts farther and farther away from the tube wall as pressure is increased, tending to be centered at the tube axis as a single and radially nonuniform filament of maximum brightness at the discharge axis. To estimate L then, we proceed as follows: the values of I 0 and I t are recorded transversally (x coordinate) to the tube axis, i.e.…”

“…The kinetics of rare-gas plasmas sustained at gas pressures higher than approximately 1 kPa is considerably dependent upon the presence of metastable and resonant-state atoms [1][2][3][4][5][6]. For instance, metastable-state atoms, with their high excitation-energy levels and population density, provide an efficient intermediate state for twostep ionization of neutrals through electron collisions (X + e → X m + e; X m + e → X + + e + e where X m designates atoms in a metastablestate).…”

Study of laser induced plasma grating dynamics in gases

“…The relaxation time in the diatomic gases is less than 100 ps, which is radically different from the atomic gases, where the electron lifetime exceeds 1 ns. Very slow plasma decay in the case of argon is explained by the fact that the electron recombination proceeds through the long lived Rydberg states [28] with a very low ionization potential. It is possible that in our experiment the intensity of the probe is sufficient to re-ionize the Argon atoms in Rydberg states, which would explain the longevity of the plasma grating in this case.…”

Experimental Characterization of a Surfaguide Fed Plasma Antenna

“…On the basis of these studies, several surface-wave plasma sources have been developed: in [5], [8] a surface wave is launched by a capacitive coupling applying an intense field between a copper ring placed around the tube and a ground plane. The surfaguide is another device, first proposed in [12] and illustrated in several papers [13]- [17], which could be used as a plasma source, and it is by far the simplest of the surface-wave launchers: it is a wave-guide device able to excite a surface wave that propagates along the tube axis providing the power required to ignite the plasma.…”