This work reports average electron temperature ($T_e$ ) and electron density ($n_e$ ) of an atmospheric argon rotating gliding arc ($RGA$ ), operated in glow-type mode, under transitional and turbulent flows. Both $T_e$ and $n_e$ were calculated near the shortest ($\delta$ ) and longest ($\mathrm{\Delta }$ ) gap between the electrodes, by two different methods using two separate measurements: (1) optical emission spectroscopy ($OES$ ) and (2) physical–electrical. $T_e$ calculated from (a) collisional radiative model ($CRM$ ) ($OES$ ) and (b) BOLSIG+ [physical–electrical, reduced electric field $(\frac{E}{N_o})$ as input], differed each other by 16%–26% at $\delta$ and 6% at $\mathrm{\Delta }$ . $T_e$ was maximum at $\delta$ ($>2$ eV) and minimum near $\mathrm{\Delta }$ (1.6–1.7 eV). Similarly, the $\frac{E}{N_o}$ was maximum near the $\delta$ (5–8 Td) and minimum near $\mathrm{\Delta }$ , reaching an asymptotic value (1 Td). By benchmarking $T_e$ from $CRM$ , the expected $\frac{E}{N_o}$ near $\delta$ was corrected to 3 Td. The calculated $CRM$ intensity agreed well with that of the measured for most of the emission lines indicating a well optimized model. The average $n_e$ near $\delta$ and $\mathrm{\Delta }$ from Stark broadening ($OES$ ) was 4.8–$8.0\times {10}^{21}$ ${\mathrm{m}}^{-3}$ , which is an order higher than the $n_e$ calculated through current density (physical–electrical). $T_e$ and $n_e$ were not affected by gas flow, attributed to the glow-type mode operation. To the best of authors’ knowledge, this work reports for the first time (a) an optimized $CRM$ for $RGA$ s (fine-structure resolved), (b) the poly-diagnostic approach to estimate plasma parameters, and (c) the validation of $\frac{E}{N_o}$ calculated using physical–electrical measurements.

The work investigates the correlation between the plasma characteristics and reactive chemical species generation in an Ar-nonthermal atmospheric pressure plasma-jet (Ar-NTAPPJ) under various operating conditions such as gas flow rate, excitation voltage, and electrode gap and demonstrates the application of such understanding in developing efficient nonthermal plasma systems. The critical plasma parameters such as electron temperature (T _e) and electron density (n _e) under the various operating conditions were estimated using optical emission spectroscopy coupled with the collision radiative model and Stark broadening methods. At optimal setting of 5 LPM gas flow rate, 4 kV excitation voltage, and 6 mm electrode gap resulted in maximum T _e (0.6 eV), enhancing •OH production (0.056 mM) in the liquid phase and OH(A-X) emission in the gas phase, highlighting the significance of operating conditions on building energy efficient plasma systems. The enhanced performance of the optimized Ar-NTAPPJ is demonstrated by taking atrazine as a model herbicide. The degradation performance data was correlated and validated with results obtained from spectroscopic diagnostics. By adequately tuning the operating parameters, four times enhancement in energy yield (∼150 mg kWh⁻¹) was obtained without perturbing the nonthermal plasma mode. In nonthermal mode, to best of the authors knowledge, it is the highest reported energy yield for atrazine degradation. The scalability aspect of the present plasma jet was also investigated by Intensified Charge-Coupled Device camera-based imaging technique. The study establishes the importance of adequate diagnostics in developing efficient next-generation plasma reactors.

The spatially-resolved electron temperature, rotational temperature, and number density of the two metastable Ar $1s$ levels were investigated in a miniature RF Ar glow discharge jet at atmospheric pressure. The $1s$ level population densities were determined from optical absorption spectroscopy (OAS) measurements assuming a Voigt profile for the plasma emission and a Gaussian profile for the lamp emission. As for the electron temperature, it was deduced from the comparison of the measured Ar $2p_i\to 1s_j$ emission lines with those simulated using a collisional-radiative model. The Ar $1s$ level population higher than 10 ${}^{18}$ m ${}^{-3}$ and electron temperature around 2.5 eV were obtained close to the nozzle exit. In addition, both values decreased steadily along the discharge axis. Rotational temperatures determined from OH(A) and N ${}_2$ (C) optical emission featured a large difference with the gas temperature found from a thermocouple; a feature ascribed to the population of emitting OH and N ${}_2$ states by energy transfer reactions involving the Ar $1s$ levels.

A detailed fine-structure resolved collisional radiative model is developed to investigate the laser-produced Mg plasma. The dominant processes linked with the electron impact excitation and de-excitation have been considered explicitly in a very reliable and consistent manner in the present model. The required electron impact excitation cross-sections of Mg for the large number of transitions from the ground state 3s ² ( J = 0) to the 3s3p, 3s4s, 3s3d, 3s4p, 3s5s, 3s4d, 3s5p, 3s6s, 3s5d, and 3s6p excited states and from 3s3p manifolds to the other fine-structure levels of 3s4s, 3s3d, 3s5s, 3s4d, 3s6s, and 3s5d configurations are obtained using the fully relativistic distorted wave approach. To ensure the accuracy of our calculations, where available, the oscillator strengths and cross-sections are compared with previous measurements and other calculations. Further, plasma diagnostics are carried out by coupling the present collisional radiative model with the laser-induced breakdown spectroscopy measurements reported by Delserieys et al (2009 J. Appl. Phys. , 106 , 083304). Five measured intense emission lines of Mg viz 383.3, 470.3, 517.8, 552.8, and 571.1 nm are used and corrected through the self-absorption to extract the plasma parameters i.e. electron temperature and electron density. The obtained plasma parameters at different delay times ranging from 100–700 ns are compared with the results of Delserieys et al (2009 J. Appl. Phys. , 106 , 083304) that were estimated using the Thomson scattering and Boltzmann plot approaches.

Comprehensive collisional radiative (CR) models have been developed for the diagnostic of argon plasma using Ar and Ar⁺ emission lines. The present CR models consist of 42 and 114 fine-structure levels of Ar and Ar⁺, respectively. Various populating and depopulating mechanisms are incorporated in the model. A complete set of electron-impact fine-structure resolved excitation cross-sections for different excited levels in Ar and Ar⁺ are used, which are obtained by employing relativistic distorted wave theory. Along with this, the electron-impact ionization, radiation trapping, diffusion, and three-body recombination are also considered. Further, to demonstrate the applicability of the present CR model, we applied it to characterize the Helicon-plasma utilizing the optical emission spectroscopy measurements. The key plasma parameters, such as electron density and electron temperature, are obtained using their measured Ar and Ar⁺ emission line intensities. Our results are in reasonable agreement with their anticipated estimates. The matching of our calculated intensities of the different Ar and Ar⁺ lines shows excellent agreement with the measured intensities at various powers.