A novel cold plasma jet generated by capillary atmospheric dielectric barrier discharge

An easy-operated and effective scheme is presented to generate a novel kind of atmospheric cold plasma millimeter jet. The jet operates with many kinds of working gas at atmosphere pressure, such as Ar, He and N-2, in a capillary quartz dielectric barrier discharge (DBD) system powered by a pulsed power source with a frequency of 33kHz and variable voltage of 1-12kV. Via an CCD imager, the initial discharge filaments in the DBD gap are found to be transformed into diffusion discharge or glow-like discharge by the flowing gas through the DBD gap, and a plasma jet formed in the outlet of the capillary is viewed simultaneously. The critical velocity of the gas flow for the plasma jet formation is determined to be 3-8m/s for different working gases by a well-designed enthalpy probe. The jet range for a special gas can be changed by the increase of the gas flow velocity while the jet range for different gases varies a lot and the helium jet takes the longest range of about 44mm when the helium flows at a velocity of about 20m/s. Beyond the velocity limit of 20m/s for laminar helium flow, the jet of helium plasma becomes torrent and unstable and its range turns shorter. Based on the OES analysis of He plasma jets, it is determined that the excitation temperature of He jets lay in the range 2000K-3000K, which is much lower than the excitation temperature of a normal arc plasma torch and hints that the jet is cold especially when compared to the arc plasma torch.