Time-resolved measurements of electron and ion densities in low-frequency discharges by high-frequency impedance analysis

Abstract

The densities of ions and electrons as a function of time within low-frequency (100 kHz) glow discharges have been measured using a new technique of impedance measurement and analysis. The technique was used to examine both an electropositive discharge (Ar) at 3 Torr and an electronegative discharge (SF6) at 0.35 Torr. The impedances of the Ar plasmas are influenced by the sheath capacitance and an electron concentration of ∼1016 m−3 in the bulk of the plasma. The impedance of the SF6 discharges is affected by both the electron concentrations and the much higher ion concentrations of 5×1017 m−3 in the bulk. The electron concentration varies from less than 1012 to about 8×1014 m−3 over the cycle due to fast rate constants for electron attachment that may or may not be balanced by electron generation from ionization.