Physics of high-pressure helium and argon radio-frequency plasmas

The physics of helium and argon rf discharges have been investigated in the pressure range from 50 to 760Torr. The plasma source consists of metal electrodes that are perforated to allow the gas to flow through them. Current and voltage plots were obtained at different purity levels and it was found that trace impurities do not affect the shape of the curves. The electron temperature was calculated using an energy balance on the unbound electrons. It increased with decreasing pressure from 1.1 to 2.4eV for helium and from 1.1 to 2.0 for argon. The plasma density calculated at a constant current density of 138mA∕cm2 ranged from 1.7×1011 to 9.3×1011cm−3 for helium and from 2.5×1011 to 2.4×1012cm−3 for argon, increasing with the pressure. At atmospheric pressure, the electron density of the argon plasma is 2.5 times that of the helium plasma.