Diagnostics of low-pressure discharge argon plasma by multi-optical emission line analysis based on the collisional-radiative model

Abstract

This work is focused on diagnostics of electron temperature (1.0 eV–3.8 eV) and electron density (1.0 × 109 cm−3–5.0 × 1012 cm−3) of low-pressure (133 Pa) discharge argon plasma by optical emission spectroscopic (OES) measurement. The diagnostic method using multi-emission lines was analyzed. First, the excitation-kinetic models were obtained by extracting dominant kinetic processes based on the collisional-radiative model. Then, the diagnostic equations for wide range of electron temperature and density were proposed to describe the approximate excitation kinetic balance of several excited levels. 15 optical emission lines (wavelength range: 340.7 nm–912.3 nm) were selected for OES measurement. RMS of the theoretical relative error was found to be 5.96% for electron temperature, while 32.6% for electron density. The diagnostics of 2.45 GHz microwave plasma was demonstrated by the proposed method and by the probe method. The electron density results by the proposed method were in good agreement with the probe method.

Optical Emission Spectroscopic (OES) analysis for diagnostics of electron density and temperature in non-equilibrium argon plasma based on collisional-radiative model

“…In order to realize such an OES measurement, following two conditions must be satisfied in the modeling of the excitation kinetics [74]:…”

“…Based on these approximations, dominant terms are to be extracted from the RHS of Equations (8) -(9) [39,[72][73][74]. If the above model is made to cover a wide range of the electron temperature and density, too many parameters must be extracted from the summation of the RHS of these equations.…”

“…In the meantime, when strictness is given priority, the parameter Θ becomes too large to incorporate the elementary processes, which deteriorates practicality of the model. Therefore, after due consideration on the measurement purpose and the characteristics of the object, the practical model of the excitation kinetics must be constructed under the assumption of the appropriate range of electron temperature and density as well as the threshold value Θ [72][73][74].…”

“…Consequently, it is considered to be put to practical use still now. This scheme is now being expanded to the microwave discharge argon plasma with its discharge pressure several Torr [74]. A novel model with the lower threshold value Θ is also being developed for the purpose of enlargement of applicable range of the plasma parameters [72][73][74].…”

Optical Emission Spectroscopic Measurement of Argon Low-Pressure Inductively Coupled Plasma Based on the Optimization Algorithm of Plasma Diagnostic Model

“…Furthermore, there are few reports on the differences caused by the data analysis method on OES measurement. Some types of OES measurements of T e or N e for nonequilibrium low-temperature plasma have been proposed, e.g., the dominant elementary process extraction method [24]- [26], line-pair method [3], [27], and excitation temperature conversion method [28]. The dependence of diagnostic results on the spectrum analysis methods of OES measurements is interesting for the improvement of OES measurements.…”