BOLTZMANN-EQUATION ANALYSIS OF ELECTRON SWARM PARAMETERS IN CO2-LASER MIXTURES

Electron swarm parameters in CO2 laser gas mixtures have been analysed for a range of the ratio of electric field to gas number density E/N from 2.83 to 283 Td (E/p0=1-100 V cm-1 Torr-1 at 0 degrees C) by a Boltzmann equation method in which the effect of electron impact ionisation and attachment can be considered properly (Thomas 1969, Tagashira et al. 1977, Taniguchi et al. 1977). Gas mixtures of CO2, N2 and He with concentration ratios of the respective gases of 1:1:8, 1:7:30, 1:1:3 and 1:2:3 are studied. The dissociation and dissociative ionisation processes for CO2 have been taken into account in addition to the electron collision processes considered in a previous study of Lowke et al. (1973). The results show that the present values of the ionisation coefficient and of the ratio of electron diffusion coefficient to mobility for the steady-state Townsend experiment are by about a few tens of percent lower than the previous theoretical values of Lowke et al. at high E/N values, but are in good agreement with recent experimental values of Lakhsminarasimha et al. (1976) for the whole E/N range studied. The excitation coefficient for the vibrational levels, important for the CO2 laser action, and the electron attachment coefficient are also calculated and discussed.