Equilibrium properties of Ar/SF6 inductive plasma discharges

Abstract

Large-size, low-pressure, and high-density inductive plasma discharges operated with argon and SF6 gas mixtures are studied experimentally and numerically modelled. The neutral gas and positive ion species are determined from mass spectrometry. The magnitudes and spatial variations of the charged particle densities are obtained from Langmuir probes and from microwave interferometry. A three-fluid, one-dimensional, discharge model is presented, that explains the main features of the data. Most discharges consist of a large electronegative region. The ion density profiles are flat in the bulk plasma, and show strong gradients at the edge. The electron density profiles are less flat, and gradually decrease to about half values near the wall. The electron temperatures and the negative ion concentrations are mostly determined by the ionization, attachment, and recombination rates. These features qualitatively apply to other source geometries and electronegative gas chemistries.