A compound plume with solid and hollow parts formed downstream of an argon plasma jet at atmospheric pressure

Plasma jet is able to produce abundant active species in plasma plume, whose morphology is a key issue for its various application fields. In this paper, we report the first observation of a compound plume with a solid part and a hollow one in an argon plasma jet. Results indicate that the compound plume can only be formed under proper conditions. Integrated emission waveform reveals that the compound plume initiates with periodicity. By fast photography, it is found that after a passage of straight-line propagation, some positive discharges behave as a curved propagation due to the influence of residual ions. Moreover, the solid part comes from negative discharges and the straight-line propagation of positive discharges. In contrast, the hollow part originates from the curved propagation of positive discharges. Optical emission spectroscopy verifies the existence of residual ions. These results can enrich the morphology of plasma plume.