Study on the optical emission spectrum diagnosing of the low-temperature plasma using a collisional-radiative model based on the detailed-term-accounting approximation

Considering the difficulty of large computation and the characteristic of helicon plasma, a modified collisional-radiative model was proposed for the diagnosis of low-temperature helicon argon plasma. A simplified 47-level is proposed due to the lack of experimental support of transition data at high levels as well as heavy computation to obtain macroscopic parameters of helicon argon plasma, e.g., electron number density ne and electron temperature Te. A creative twice-matching method is proposed in the model because the current double-line intensity ratio method shows significant sensitivity in diagnosing low-temperature electrons. Calculations based on this model shows the spectrum intensity depends on the electron temperature as well as density for low-temperature plasma, especially when it's below 6eV. The twice matching process based on the priori knowledge chooses 15 spectrums cognizable within the wavelength from 680nm to 860nm, adopting the absolute values of the lines to match with the results calculated by the collisional-radiative model. This method greatly reduces the average error to 13.7%. The result indicates that the precision of the electron temperature and density has been improved a lot and the relative errors are 25% and 40%, respectively. Within the accuracy range above, the research shows when RF power is 500-800W and the pressure is 0.5-1.3Pa, the electron number density rises with the increasing RF power and decreases with the increasing magnetic field strength (450-900G) and gas pressure. Moreover, comparing to the number density of electrons, the electron temperature changes less and rises with the decreasing pressure.