The twisted behavior of a rotating electrode atmospheric-pressure argon plasma jet

The twisted behavior of a rotating electrode atmospheric-pressure argon plasma jet is reported and its mechanism is investigated. It is found that the plasma channel turns into a smooth pathway when about 5% of O-2 or 3% of N-2 are added to the main working gas, argon. Further investigation shows that the rotational frequency of the electrode, which can enhance the turbulence of the gas flow, does not affect the appearance of the plasma channel for both pure argon and argon mixed with different amounts of O-2/N-2. The optical emission spectra show that the emission intensities of the transitions from seven excited argon levels to two metastable states decrease dramatically when O-2/N-2 is added. Detailed analyses suggest that when O-2/N-2 is added, both the concentrations of argon in the two metastable states and their lifetimes decrease significantly, which results in a transition of the discharge channel from a turbulent pathway to a smooth pathway. In short, the metastable state of argon rather than the seed electrons plays the key role in the appearance of the plasma channel.