Optical spectroscopy diagnostics of a helium surface wave sustained discharge. I. Experiment

A stationary microwave discharge in helium gas is studied by applying optical spectroscopy (emission and absorption) methods and field radial decay measurements. The discharge is created at the frequency 2375 MHz with an applied power varied between 100 and 200 W; the gas pressure is 0.6 Torr. From optical spectroscopy measurements, the population densities of the 2 1 P, 2 3 P, 4 1 S and 4 3 S excited states, the radial distribution of the 2 1 P and 2 3 P level population and the gas temperature are determined. The range of variation of the electron density along the plasma column is taken from the field radial decay measurements. The experimental data obtained are the basis for developing (in part II of this study) a theoretical model which specifies the kinetics of the processes for production and destruction of excited states under the nonequilibrium plasma conditions studied. The comparison between experimental results presented here and the theoretical results given in part II is extrapolated to the determination of the electron density and the mean electron energy.