[Paper Review] Spectroscopic of atmospheric pressure air jet plasma in transverses arc discharge

Valeriy Chernyak, V. V. Naumov+1 more|ArXiv.org|Oct 28, 2004

Plasma Applications and Diagnostics4 references6 citations

TL;DR

This study investigates atmospheric pressure air jet plasma generated by a transverse dc arc discharge using optical emission spectroscopy. By analyzing emission lines and bands from N, O, H, NO, N2, O2, OH, CO, and CN, the authors determine excitation temperatures for electrons (Texc), vibrational (Tv), and rotational (Tr) states, revealing strong non-LTE behavior and significant non-thermal effects in the plasma during its spatiotemporal evolution.

ABSTRACT

Spectroscopic characterization of a specific case of the atmospheric pressure air jet plasma in the transverse cw dc arc discharge of high voltage was done. Within the spectrum of wavelengths from 200 to 1100 nm all remarkable emissions were monitored, and all excited atomic lines of N, O, H and molecular bands of NO, N2, O2, OH, CO, CN were identified. Using relative intensities of analytical CuI lines 510.5, 515.3, 521.8 nm (the product of electrode emission) and N2 2+ -system band at 337.1 nm (the dominating component of plasma-forming gas), the temperature of electronic excitation of free atoms, Texc, and the temperatures of excitation of vibrational and rotational states of molecules, TV and TR, were determined. It was found that there is no local LTE in this arc discharge air plasma during its space/time evolution, and effects of strong non-izothermality have a place in this case.

Motivation & Objective

• To characterize the spectroscopic properties of atmospheric pressure air jet plasma produced by a transverse dc arc discharge.
• To identify and analyze emission lines and molecular bands in the 200–1100 nm range.
• To determine electronic, vibrational, and rotational excitation temperatures using calibrated emission lines.
• To assess the validity of local thermodynamic equilibrium (LTE) assumptions in this high-voltage, atmospheric-pressure plasma system.
• To investigate the spatiotemporal evolution of non-thermal effects in the plasma discharge.

Proposed method

• Optical emission spectroscopy (OES) was performed over the 200–1100 nm wavelength range to capture atomic and molecular emissions.
• Characteristic emission lines of CuI at 510.5, 515.3, and 521.8 nm were used as internal temperature references due to their origin from electrode material.
• The N2 2+ second-positive system band at 337.1 nm was used as the primary reference for plasma-forming gas excitation.
• Excitation temperatures (Texc, Tv, Tr) were calculated from the relative intensities of selected spectral lines and bands.
• Non-LTE conditions were evaluated by comparing Texc, Tv, and Tr, revealing discrepancies inconsistent with LTE assumptions.
• Spatiotemporal evolution of plasma parameters was analyzed to assess dynamic non-thermal behavior.

Experimental results

Research questions

• RQ1 What are the dominant atomic and molecular species present in the atmospheric pressure air jet plasma from a transverse dc arc discharge?
• RQ2 To what extent do the excitation temperatures (electronic, vibrational, rotational) deviate from each other in this plasma system?
• RQ3 Is local thermodynamic equilibrium (LTE) valid in the transverse arc discharge plasma under atmospheric pressure conditions?
• RQ4 How do the spatial and temporal dynamics of the plasma influence the observed non-thermal effects?
• RQ5 What role do electrode material emissions (e.g., CuI lines) play in temperature diagnostics of the plasma?

Key findings

• Atomic emission lines of N, O, and H, along with molecular bands of NO, N2, O2, OH, CO, and CN, were identified across the 200–1100 nm spectrum.
• Excitation temperatures were determined using CuI lines (510.5, 515.3, 521.8 nm) as reference, yielding Texc values consistent with high-energy electron excitation.
• The N2 2+ second-positive system at 337.1 nm served as the dominant reference for molecular excitation, enabling Tv and Tr determination.
• Significant discrepancies between Texc, Tv, and Tr were observed, indicating strong non-LTE behavior in the plasma.
• Non-thermal effects were confirmed through the absence of local thermodynamic equilibrium, especially during the spatiotemporal evolution of the discharge.
• The plasma exhibits pronounced non-isothermality, with distinct temperature gradients across electronic, vibrational, and rotational states.