Electric probe diagnostics in thermal plasmas: Double probe theory and experimental results

Electric probes can be advantageously applied to the study of nonequilibrium induced in thermal plasmas by the presence of cold boundaries, since the interpretation of experimental data does not require any assumption about the thermodynamic state of the plasma. An experimental setup and procedure are described which allow accurate measurements of the electron temperature profiles in the near-wall region of wall stabilized, atmospheric pressure, argon dc arcs. An extension of the classical double floating probe theory was developed to include asymmetries in collecting areas and nonuniformities in the plasma. Excellent agreement between the measured probe characteristics and the analytical relationship was obtained.