Development and investigation of a large-diameter helium atmospheric-pressure plasma jet with floating electrode configuration

The discharge behavior of a helium atmospheric-pressure plasma jet (APPJ) in a 10 mm-diameter tube was investigated under various electrode configurations using optical emission spectroscopy (OES), voltage-current characteristics, and electrostatic simulations. The results indicate that the discharge mechanisms differ above and below the ground electrode: the upstream region is mainly initiated by electron avalanches and involves a transient DC-glow-like discharge, whereas the downstream region is dominated by photoionization-assisted streamer propagation. Floating electrodes and insulating tape significantly modify the electric field distribution, influencing local electron dynamics, metastable transport, and plume characteristics. With a larger tube radius and Peltier-based gas pre-cooling, the developed system can generate a stable, relatively cold plasma plume, suggesting potential for localized surface treatment and biomedical applications.