Temperature Profiles in Argon Induction Plasmas: Theory and Experiment

A comparison is made between recent temperature measurements of argon induction plasmas which include cases of annular geometry and calculations based on the one-dimensional Elenbaas-Heller equation. Exact numerical solutions, as well as approximate closed-form solutions derived from a two-zone model are used. Good agreement is obtained for the central portion of the plasma column with the exact method for all reported power inputs and with the approximate method for medium power input. Near the walls, however, the experimental temperatures are considerably higher for all geometries and power inputs. It is argued that here electron diffusion causes an overpopulation of electrons and thus an overestimation of gas temperatures when Saha equilibrium is assumed.