Optical investigation of a plasma jet generated by water electrodes at atmospheric pressure

A quartz tube tightly surrounded by transparent water electrodes is employed to generate an argon plasma jet at atmospheric pressure. By using electrical and optical diagnosis, the discharge characteristic of the plasma jet is investigated. With the increasing of the gas flow rate, the plasma jet undergoes the transition from laminar to turbulent flow. It is found that the length of the plasma jet increases first and then decreases when the gas flow rate increases from 0.5 L/min to 5.0 L/min. The discharge is composed of several wide low amplitude pulses at the rising voltage edge and one narrow high amplitude pulse at the falling voltage edge. Optical emission spectroscopy is used to diagnose the plasma parameters. It is found that the excited electron temperature and the electron density increase with the increasing of the gas flow rate. These results are analyzed qualitatively.