Principle and application of a thermal probe to reactive plasmas

A thermal probe for plasma diagnostics is introduced. The method is based upon measuring the equilibrium temperature of a conducting sphere as a function of its applied bias. The resulting temperature–voltage characteristic is processed using a theoretical model that accounts for charge and thermodynamic balance.

The thermal probe is capable of detecting negative ions and shows sensitivity to certain chemical reactions. Measurements performed in Ar, Ar/SF6, and O2 show good agreement among the plasma parameters using thermal and Langmuir probes.