Line-pair method cannot be applied to wide-range electron temperature Te and density Ne diagnostics of plasmas in the state of non-equilibrium. Although the method using multi-emission lines is suitable, little has been reported for the low-pressure plasma measurement. We proposed the optical emission spectroscopic (OES) diagnostic method for the low-pressure argon plasma. In this presentation, the applicability for the microwave discharge argon plasma is reported.
Based on the Ar collisional-radiative (CR) model, the dominant elementary possesses were extracted for the excitation kinetics for several excited states. And, the excitation-kinetic model for the OES diagnostics was established. As a result, the diagnostic model was obtained. In the model, input parameter is 15 optical emission lines (wavelength range: 340.7 – 912.5nm). Possible measurement range is 1.0 ≤ Te [eV] ≤ 3.8, and 1.0 × 109 ≤ Ne [cm-3] ≤ 5.0 × 1012.
In order to examine the validity of the proposed method, microwave discharge argon plasma was diagnosed with (A) probe measurement: (A-1) under the assumption that the electron density distribution function (EEDF) is Maxwellian, (A-2) together with the measurement of the EEDF by the Druyvesteyn’s method, and equivalent Te measurement; and (B) OES measurement by the present proposed method at points (from the center of the waveguide) = 10, 14, and 18 cm, with the microwave power = 100, 300, and 500 W.
Concerning Ne diagnosis, the trend of Ne determined with the scheme (B) was in good agreement with the scheme (A-1). Meanwhile, as for Te diagnosis, it was difficult to evaluate, because the result of the scheme (B) reached the limit value of root-finding range in the numerical procedure. However, at least, the result of (A-1) is considered to be reasonable. And by using input with arbitrary shaped EEDF is measured by the OES measurement, and the resultant improvement of the diagnostic result can be expected.