The effect of pre- and post-mixing N2 on discharge characteristics and production of reactive species in a pulsed-DC Ar plasma jet

Abstract

This study investigated the effects of pre- and post-mixing nitrogen (N2) on the discharge characteristics as well as the production of reactive oxygen and nitrogen species (RONS) in an atmospheric-pressure argon (Ar) pulsed-direct current plasma jet. Plasma is generated by mixing 0%–1% N2 with Ar gas within the gas line (termed as pre-mixing) and in the inter-electrode separation region (termed as post-mixing). Hydrogen peroxide (H 2 O 2 ) and nitrite (NO 2 − ) were measured as markers of reactive oxygen species and reactive nitrogen species, respectively. Both mixing methods produced similar total RONS levels: increasing the N2 fraction reduced H2O2 , while NO2 − peaked at 0.6% N 2 then declined. Despite both methods producing similar RONS concentrations, pre- and post-mixing had differing effects on the intrinsic discharge properties. Pre-mixing produced greater changes in discharge current ( I D ) and power ( P av ), resulting in a decrease by 85.5% and 46.7% from 0% to 1% N2 mixing, respectively. Whereas I D and P av were only moderately affected by post-mixing decreasing by 28.8% and 14.9% from 0% to 1% N 2 mixing, respectively. Electron temperature ( T e ) rose sharply from 1.01 up to 1.55 eV with 1% N2 pre-mixing but only to 1.39 eV with equivalent post-mixing. The gas temperature at the ground electrode increased to 61.2 °C for pre-mixing versus 58.4 °C for post-mixing with 1% N2 . However, post-mixing had a greater effect on diminishing UV photon emission, which significantly decreased H2O2 generation via UV photolysis. These findings demonstrate that although pre- and post-discharge mixing with N2 results in similar levels of plasma jet produced RONS, the method of mixing alters plasma characteristics in different ways that might affect the plasma jet’s performance and safety in certain biomedical applications.