Feasibility of using a one-temperature model for determining plasma’s temperature by measuring its refractive index

Abstract

In this paper, the feasibility of using a one-temperature model to determine plasma’s temperature by measuring its refractive index is studied based on the consideration that many plasma flow fields are not in local thermodynamic equilibrium (LTE). We compare the refractive indices between the one- and the two-temperature models of an arc plasma, in order to discuss the applicability of the one-temperature model in optical diagnosis. We found that the applicability is determined by the pressure, the temperature ratio between electrons and heavy particles, the probe wavelength, and the chosen optical method’s refractive index measurement precision. Consequently, a common model is deduced to describe the refractive index of plasma whether it be in LTE or not. In a word, this study is crucial to better apply optical methods based on measurements of the refractive index to diagnose plasma flow fields.