The influence of the tube diameter on the properties of an atmospheric pressure He micro-plasma jet

In the present study, a single electrode micro-plasma jet working in helium flow was investigated. The aim of our study was to clarify the influence of the tube diameter on the discharge ignition and sustaining voltage, as well as on nitrogen rotational temperature, helium excitation temperature and electron density. The diameter of the micro-tubes was varied in the range of 80–500 µm. A sinusoidal voltage with a frequency of 6 kHz was applied to ignite and sustain the plasma jet. Both the ignition and sustaining voltage monotonically increased with the decreasing diameter of the tube. The gas temperature of the plasma in the capillary tube estimated by the rotational temperature of the N₂ second positive system remained below 500 K and depended weakly on tube diameter, while the excitation temperature of He and electron density, n_e, increased as the tube diameter decreased. (paper)