Control of electron recombination rate and electron density inoptically-pumped non-equilibrium plasmas

Abstract

A two-dimensional time-dependent model of non-self-sustained dc andRF discharges is used for the analysis of recent experiments in optically-pumpednon-equilibrium plasmas. The analysis shows that non-self-sustained dc and RFdischarges can be successfully used for measurements of the electron productionrate, electron recombination rate, and electron density in these plasmas. Theinferred rate of electron production per unit volume by the associativeionization mechanism is S0 = 1.0×1015 cm-3 s-1 and S0 = 2.2×1014 cm-3 s-1 inCO/Ar = 2/100 and in CO/N2 = 2/100 plasmas, respectively. The inferredelectron-ion recombination rate coefficients are β>6.0×10-6 cm3 s-1 andβ = (7.5±1.5)×10-6 cm3 s-1 in CO/Ar = 2/100 mixtures atP = 100 Torr and 20 Torr,respectively. In CO/Ar = 2/100 mixtures with a 0.05-0.1 Torr admixture of O2 atP = 100 Torr and 20 Torr, the inferred recombination rate coefficients areβ = (1.5±0.3)×10-8 cm3 s-1 and β = (5.1±2.9)×10-8 cm3 s-1,respectively. Finally, theinferred electron density in optically-pumped CO/Ar/O2 plasmas at the laserbeam axis is ne = (1.7±0.2)×1011 cm-3 at P = 100 Torr andne = (6.2±0.8)×1010 cm-3at P = 20 Torr. These results demonstrate that the electron density in optically-pumped CO/Arplasmas can be controlled and significantly increased by addingsmall amounts (up to ~0.1%) of species such as O2 and NO, which result inthe reduction of the electron-ion recombination rate.