Estimating electron temperature and density using improved collisional-radiative model in high-density RF argon plasma

H Horita,S Shinohara,D Kuwahara,H Akatsuka

doi:10.1063/5.0050215

Abstract

It is crucial to measure the electron density (ne) and temperature (Te) for applications such as developing small helicon sources in plasma thrusters. Hence, this study developed a method based on an optical emission spectroscopic (OES) measurement without disturbance or contamination for helicon plasma produced using argon gas. The argon collisional-radiative (CR) model was used to describe the excitation number density in plasma as a function of ne and Te. Each number density ratio was surveyed as a function of ne and Te. From these results, contours of two number densities, i.e., two excitation energy levels, were drawn on an ne–Te plane. By applying various contour pairs, ne and Te were determined from the intersection point of two contours whose values were taken from the experimental intensities. Finally, we compared the new OES measurements with the CR model for various intensity ratios and found a way to select a valid intensity ratio that is in good agreement with the ne and Te derived by the probe method.

Highlights

We found a way to select the intensity ratio pairs necessary to reduce the difference between our CR model (65 energy levels) and the results of the probe method by a factor of 2–3
The value of ne could not be derived for certain values of PRF in the chosen only for the previous model12 (CR1) data analysis because the two contours from the experimental intensity ratio did not intersect each other
It is found that ne increases with increasing PRF at all flow rates in the double probe measurement

Summary

Introduction

Various engineering applications use plasma sources. To develop these sources further, it is necessary to know their discharge properties, such as electron density ne, electron temperature Te, and neutral density, which indicate discharge characteristics.Previous work in this field includes the development of advanced electric satellite thrusters. To explore deep space, a spacecraft must have a long lifetime and an efficient and reliable thruster. To develop these sources further, it is necessary to know their discharge properties, such as electron density ne, electron temperature Te, and neutral density, which indicate discharge characteristics. Previous work in this field includes the development of advanced electric satellite thrusters.. The electrodeless helicon thruster, which is a plasma thruster, shows promise owing to its unlimited lifetime and expected high density. Electrodeless plasma discharges have already been established, plasma acceleration is still being developed, using methods such as rotating magnetic field (RMF) acceleration method and m = 0 coil acceleration method, where m is the circumferential mode

Methods

Results

Conclusion