A two-dimensional model of He/O2 atmospheric pressure plasma needle discharge**Project supported by the National Natural Science Foundation of China (Grant No. 11465013), the International Science and Technology Cooperation Program of China (Grant No. 2015DFA61800), and the Natural Science Foundation of Jiangxi Province, China (Grant No. 20151BAB212012).

Abstract

In this paper, a computational modeling study of stream propagation in the atmospheric-pressure helium plasma in ambient atmosphere (oxygen) is presented. A coupled fluid model between time-dependent plasma dynamics and steady state neutral gas flow is employed to provide a fundamental insight into the evolution of the streamers. The obtained simulation results showing that the sheath forms near the dielectric surface and shields the axial stream propagation. The stream front propagates with axial velocity in a range of 104 m/s–105 m/s. And, the increasing accumulated surface charge should be responsible for reducing the propagation velocity of the streamer front in the axial direction. Besides, when the gas flow rate is 1.1 standard liter per minute (SLM), we find that the concentration of oxygen drastically increases at a larger radial position near a treated surface. Therefore, Penning ionization by helium metastables and oxygen peaks at an off-axis position, corresponding to the ring-shaped emission profile in cylindrical coordinates. In this case, the simulated results show the ring-shaped ground atomic oxygen density profile near the treated surface (z = 0.5 mm) at a large gas flow rate of 1.1 SLM, which is consistent with the observation in a similar experiment.