Neutral density profiles in argon helicon plasmas

We present an analysis of laser-induced fluorescence and emission spectroscopy profile measurements of the excited states of neutral argon for two different helicon source pressures. Through use of a collisional-radiative model that calculates excited state profiles based on measured electron densities, electron temperatures, and the measured edge neutral pressure, the ground state neutral density profile is determined for each pressure case. The results demonstrate that it is possible to extract the ground state neutral density profile from such measurements and that the degree of ionization at the center (r = 0) of a helicon source plasma can vary significantly for a small change in source pressure.