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

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.