On the use of the line-to-continuum intensity ratio for determining the electron temperature in a high-pressure argon surface-microwave discharge

This work presents an experimental study of argon microwave discharges maintained by a surface wave at 2.45 GHz, at atmospheric pressure and under low flow, in a capillary tube. Emission spectroscopy techniques are used to characterize these discharges. Special attention is paid to the determination of the electron temperature by using the line-to-continuum intensity ratio method. We show that, even in situations very close to local thermal equilibrium, simple substitution of the excitation temperature T exc by the electron temperature T e in the equation governing the line radiation emitted by a plasma should not be done. Causes for such an assertion are analysed and a parametric study is conducted to determine the sensitivity of the proposed method. This method is then applied to provide T e from experimental data corresponding to an atmospheric pressure argon plasma produced by a surface microwave.