Effect of magnetic field on optical emission from cold atmospheric pressure micro-plasma jet

Abstract

Application of magnetic field can affect the charge particle dynamics, plasma constituents, and optical emissions from a cold atmospheric pressure micro-plasma jet. The present study focuses on the effect of an externally applied transverse magnetic field (B) on optical emissions from the plasma jet and the resulting particle behavior inside the plasma. Detailed experiments are performed to look at Hα, Hβ, He, and other emission lines from which the electron density (ne) and electron excitation temperature (Texc) are determined as a function of B. Reactive O2 and N2 species (RONS) that are important for biomedical applications are identified and the effect of B on them is investigated. The discharge is modeled using fluid theory, which predicts the temporal evolution of plasma parameters both during nascent and time to saturation (ts) values. It is observed that ts of ne reduces as B is increased. Besides the Lorentz force, strong B invokes the Zeeman effect and also contributes to the broadening of emission lines, thereby altering ne and Texc. The observed phenomena can be explained from the cross field transport and the dependence of Larmor radius and cyclotron frequency upon B. It is found that finite Larmor radius effect and the satisfaction of collisionally broadened ion cyclotron resonance condition can alter the emission intensities of RONS. Furthermore, the incidence of charged RONS on a specified surface area could be controlled by B.