THE EFFECT OF MOLECULAR-IONS ON THE PLASMA PARAMETERS IN A MEDIUM PRESSURE RARE-GAS RADIO-FREQUENCY DISCHARGE POSITIVE-COLUMN

A rare gas positive column plasma theory that takes into account the effect of various chemical processes on the production, loss, and interconversion of metastable and ion species is developed and compared with experimental results. The experimental measurements have been made in a 4 cm i.d. radio frequency (rf) discharge tube for He, Ne, and Ar. An electrostatic triple probe was used to monitor the electron temperature and plasma density, and a mass spectrometer was used to analyze the ion species. The results show that the molecular ion becomes important when gas pressure is above 1 Torr in the Ar and Ne plasmas. For a He plasma, the molecular ion always plays an important role in the plasma process. Good agreement has been observed between present model and experiments.