Comparison of Langmuir probe and spectroscopic electron temperature measurements

Abstract

Deals with an experimental confirmation of the deviation from LTE in a low density argon plasma and of the applicability of the theory on the deviation from LTE developed by Griem. The excitation temperature determined spectroscopically using relative intensities of the resonance lines 4000-7000 AA of argon atoms was compared with the electron temperature measured by a conventional Langmuir probe. As a result it was found that the excitation temperature was 1000- 1500 degrees C higher than the electron temperature and that the difference between them increased along the radius of the plasma stream. It implies that the plasma was not in LTE. In fact the excitation temperature determined from relative populations of the 5p states of the argon atoms was found to agree quite well with electron temperature across the plasma stream.