A. CENIAN (a), A. CHERNUKHO (b), V. BORODIN (b) and G. SLIWINSKI (a) (a) Instiiute of Fluid-Flow Machines, Polish Academy of Sci., 80-952 Gdansk, ul. Fiszera 14. Poland. (b) A. V. Luikov Heat and MassTransfer Institute, Belarus AcademyofSci.. 220072 Minsk, 15 P. Brovki str.. Belarus. AbstractThe chemistry of a pure CO, glow discharge is modelled as a first step in description of C 0 2 lasers plasma-chemical reactions. The equilibrium conversion of CO, into CO strongly depends on E/N ratio. It grows from few percent for E/N = 2 x V cmz to more then 70% for E/N -9x V cm2. The X, values are only slightly influenced by the change of electron density and temperature.,The role of ions and of the CO(a3n) excited electronic state in recombination of CO as well as of heterogeneous recornbination is studied. The time required to reach the steady-state concentrations of chemical species in the system varies from few seconds for high E / N values up to hours in the other end of investigated region; it increases with the fall of discharge current and with the fall of E/N. Satisfactory agreement with experimental data is achieved.

In the paper we have modelled plasma-chemical reactions in the C 0 2 low pressure, DC excited lasers. A good agreement of theoretical and experimental results has been achieved. It has been proved that neglect of reactions with electronic excited species or heterogeneous recombination leads to almost 50% overestimation of GO2 equilibrium conversion. The relation of C 0 2 equilibrium conversion to the reduced field E / N , pressure and current density depends on discharge conditions and mainly on the role played in discharge by ambipolar diffusion. This role decreases with an increase of the discharge diameter and of the mixture convection velocity. The CO, equilibrium conversion increases with growth of E / N and j and with decrease of pressure for discharges in small, sealed-off laser systems. The CO, equilibrium conversion is not always a monotone function of p in large, convection cooled lasers. It does not depend so much on E / N as the electron temperature alone if conversions in different mixtures are compared.

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The Langmuir-probe diagnostic of a plasma is studied using a particle-in-cell Monte Carlo model. The electron-density, temperature, and potential profiles are determined for a probe immersed in an Ar plasma. The model is verified using the low-pressure results of Sternovsky et al. [J. Appl. Phys. 94, 1374 (2003)]. It was proved that the ion to electron temperature ratio may not be constant in the sheath–presheath region.