Effects of Liquid Composition on Cold Atmospheric Plasma Jet Discharge characteristics studied using Collisional Radiative Model

Plasma–liquid interactions are becoming an increasingly important topic in the field of plasma science and technology. The interaction of non-equilibrium plasmas with a liquid is crucial in numerous applications, where the composition and conductivity of liquids vary significantly. Studying the effects of liquid composition on plasma properties, such as the electric field distribution, discharge behaviour, and the production of reactive species, is therefore essential. Numerous investigations have demonstrated that the formation of reactive species is highly dependent on the electrical conductivity and composition of the liquid. Nevertheless, the understanding of the impact of liquid composition on the performance of cold atmospheric plasma (CAP) jet for liquid treatment applications is currently limited.

In this work an effort has been made to study the impact of liquid composition on a bipolar pulsed powered CAP jet discharge characteristics using Collisional Radiative (CR) Model. The CAP jet, based on dielectric barrier discharge (DBD), is tuned for applied voltage, frequency, power consumption, and gas flow rate. Using optical emission spectroscopy (OES), key plasma properties are examined and reactive species generated are analysed when plasma contacts with differing composition and conductivities of liquids like deionized (DI) water, tap water, seawater, waste water. The CR model along with the Line ratio method and deviation parameter (Δ) is employed to extract the electron temperature (T_e) and electron density (n_e) from the spectra, while the cross-section data sourced from Open-ADAS. Our findings indicate that varying liquid composition significantly influences plasma behaviour. High conductivity liquids enhance the electric field at the plasma-liquid interface, resulting in increased electron densities. Conversely, lower conductivity liquids like DI water produce more diffuse plasmas with lower electron densities.

The results highlight the critical role of liquid composition in determining the efficiency and characteristics of CAP jets. This study provides a foundational understanding of plasma-liquid interactions, insights for optimizing plasma systems for specific applications.