Keren Lin

<jats:title>Abstract</jats:title> <jats:p>The discharge behavior of a helium atmospheric-pressure plasma jet in a 10 mm diameter tube was investigated under various electrode configurations using optical emission spectroscopy, 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.</jats:p>