Probe-spectrometry diagnosis of electron temperature in narrow discharge plasma at low pressure

Abstract

A new technique, the two-stage probe-spectroscopic diagnosis method, is proposed to diagnose indirectly the electron temperature in a narrow discharge plasma at low/middle pressure. The first stage includes the diagnosis of electron temperature Te by the double probe method and measurement of the emission spectrum in an ancillary discharge tube. From its emission spectrum, a pair of spectral lines is selected in such a way that the ratio Imq/Inr of their intensities, Imq and Inr, is changed monotonically with gas pressure. The corresponding relation between the electron temperature Te and the ratio Imq/Inr can be obtained in the ancillary discharge tube at certain pressure. During the second stage, the electron temperature in the diagnosed discharge plasma can be determined from its ratio Imq/Inr according to the above relation between Te and Imq/Inr obtained in the ancillary discharge tube. As an example, the electron temperature in a high power flat He–Ne laser is diagnosed using this probe-spectrometry diagnosis technique. The experiments prove that the calculated electron temperature is obviously higher than the actual electron temperature in the low pressure or small size discharge. The principle, method, setup and results of this diagnostic technique are discussed in this paper.